Best HK-94 to MP5 Conversion?

[Vulture06]

I am interested in converting a HK-94 into a MP5-N. Who does the best work and has the best reputation?

Terry Dyer
Murry Urbach
Ralph Smith at RTDS

[SudS]

If you wanted to add names to that list, include TSC Machine:

http://tscmachine.com/

[UDT]

If you wanted to add names to that list, include TSC Machine:

http://tscmachine.com/

+1 To that.

[Schrambo]

I had Ralph do a MP5SD and a MP5-N for me... Absolutely great!

I also had Mike at TSC "freshen up" and remark a MP5K PDW... Loved his work, too...

[B Wood]

you may want to also consider Jayson at IGF.

He does amazing work as well...without the 2 year backlog.

http://www.investmentgradefirearms.com/

[medic103]

+1 for RDTS! Mine is flawless. I'll be buried with it I love it that much.


D

[SIGNUTZ]

*Terry is not taking any new work/clients. IMHO: Murray and Ralph can be hard to get in touch with at times (and can also take a long... time to finish work). Curtis Higgins of S&H Arms (on the recommended dealer list) is the only one I know of that actually answers his phone and has relatively quick turnaround times and very reasonable prices (e.g. change barrels costs $100). He does top quality work and I have owned several firearms built by him as well as all of the other mentioned gunsmiths. Curtis just finished an H&K53 for me built from a brand new H&K post-gun 53 and new 93 host receiver. Best build I have seen so far for a "true" transferrable 53.

[CThurman]

Mike at TSC Machine. He does factory perfect work including the restamp - not factory "pretty good" work. He is easy to get ahold of and his turnaround times are consistent and reasonable. He is top notch in terms of both craftsmanship and reliability.

I have seen and owned good work from some of the other smiths mentioned as well, but I really have liked Mike for the reasons stated above

[bnhguns]

+1 for S&H Curtis does nice work!

[mekrek]

I can vouch for Curtis Higgins.

[AviatorDave]

I can vouch for Curtis Higgins.

I saw an MP5 that was done by him recently. While the turnaround time was very fast, it looked it. The remarking appeared to have been done with actual metal stamps instead of engraving. The finish wasn't so nice either, it seriously looked like Krylon. He would have been about $300 cheaper than Urbach, but I wasn't at all impressed with the workmanship. I was about to meet him in Tulsa to drop mine off when I saw that one, and heard others have similar experiences.

I will say this - in my experience, Urbach does MP5s in a resonable amount of time because he does so many of them and the work is so straightforward. Mine was done in about 4 weeks. But then he's had a 91 in for a G3K conversion since April 1st. The last time I stopped by was in June, he said "3 or 4 more weeks, I'll call you when it's done."

But everything I've seen from him is absolutely flawless. He had a bucket of a dozen beat to hell DOJ HK94s. He'd already finished 3 of them, they looked as good as mine that was made from a 94 that had only a few hundred rounds through it.

Everything I've ever heard about TSC Machine, Investmentgradefirearms, and RDTS are similar to my experiences with Urbach, but Urbach beat their pricing by several hundred dollars. The main price difference was in the burst pack conversion - the other guys wanted $300+ to install my sear, Urbach charged $150.

[MONEY]

I just had a HK53 built by TSC Machine & all I can say is that it was the best build experience I have ever had period & I have had guns built by all of the top builders besides S&H arms. Everything with the build was 100% perfect & the customer service is better than anyone I have dealt with not to mention they will return your gun when promised & talk to on the phone if you have any questions.

[E Corker]

TSC Machine will do all my work, not only is Mike local for me, but he is personable and very responsive.He did my MP-5/N in about 1 1/2 - 2 weeks. At the time he was using Lauer for the refinish, but I opted to refinish myself. I had him do the Paddle Mag, Remark, Threaded Three Lug Adapter, and the FBI pack in a 3rd Burst Lower fo $1235.00. He returned all of my original parts aswell. I parked it at home and applied a matte black ceramic enamel and baked it in my oven for 4 hours.

http://i16.photobucket.com/albums/b41/ecorker/DSC00371.jpg
http://i16.photobucket.com/albums/b41/ecorker/DSC00454.jpg
http://i16.photobucket.com/albums/b41/ecorker/DSC00450.jpg
http://i16.photobucket.com/albums/b41/ecorker/DSC00452.jpg

[MONEY]

That finish looks very nice! Where did you get the materials from? Was it easy to do?

[AviatorDave]

I just had a HK53 built by TSC Machine & all I can say is that it was the best build experience I have ever had period & I have had guns built by all of the top builders besides S&H arms. Everything with the build was 100% perfect & the customer service is better than anyone I have dealt with not to mention they will return your gun when promised & talk to on the phone if you have any questions.

Money- what did that run you? I've got two 53 kits, I'm trying to decide if I want to do them both myself, or have one done by one of the more experienced pros and I'll copy it for the second. I have all the equipment I need to do it myelf except I can't remark it because I don't have an engraver.

My Urbach MP5-N conversion was "only" $900 including paddle mag release installation, replacing the barrel, remark, refinish, and sear into burst pack. It seems like a 53 build would involve the exact same amount of work, except for not needing the burst pack as it's already done. I'm thinking he would charge me about $750 based on what my MP5 cost.

[AviatorDave]

TSC Machine will do all my work, not only is Mike local for me, but he is personable and very responsive.He did my MP-5/N in about 1 1/2 - 2 weeks. At the time he was using Lauer for the refinish, but I opted to refinish myself. I had him do the Paddle Mag, Remark, Threaded Three Lug Adapter, and the FBI pack in a 3rd Burst Lower fo $1235.00. He returned all of my original parts aswell. I parked it at home and applied a matte black ceramic enamel and baked it in my oven for 4 hours.



Wow, you did an outstanding job on the refinish. So you can just park the entire thing, barrel, trunnion, triple frame and all? Just remove all the loose parts? Do the welds take the parkerizing as well?

I was just looking at a Summit Racing catalog tonight - they have powder coat kits that are very affordable now, thought I might try it on one of my heavily used shooters.

[SudS]

My Urbach MP5-N conversion was "only" $900 including paddle mag release installation, replacing the barrel, remark, refinish, and sear into burst pack. It seems like a 53 build would involve the exact same amount of work, except for not needing the burst pack as it's already done. I'm thinking he would charge me about $750 based on what my MP5 cost.

If you are using a 53 kit, the job includes replacing the cocking tube...that's one of the biggest reasons for getting a 53 kit in the first place (plus an original barrel is nice too). Otherwise, the smith has to cut into the receiver of the gun to form the cocking notch (or use the RDTS method of moving the cocking mechanism forward).

[MONEY]

Money- what did that run you? I've got two 53 kits, I'm trying to decide if I want to do them both myself, or have one done by one of the more experienced pros and I'll copy it for the second. I have all the equipment I need to do it myelf except I can't remark it because I don't have an engraver.

My Urbach MP5-N conversion was "only" $900 including paddle mag release installation, replacing the barrel, remark, refinish, and sear into burst pack. It seems like a 53 build would involve the exact same amount of work, except for not needing the burst pack as it's already done. I'm thinking he would charge me about $750 based on what my MP5 cost.

I believe the build was $1250.00 but since I bought some other parts from TSC I am not 100% shure. All I can say is that I am a perfectionist when it comes to my HK builds & Mike & Tammy @ TSC have been the only builders that have built a factory perfect gun with first class service.

[SudS]

TSC Machine is $1,200 for the 53 conversion.

[xtphp1]

TSC Machine is who gets my business. 2 MP5, and a 21E so far. I researched for 3 years on my 21 before I sent it to anyone to get totaly rebuilt. I picked TSC, and can't be happier.



I will say this - in my experience, Urbach does MP5s in a resonable amount of time because he does so many of them and the work is so straightforward. Mine was done in about 4 weeks. But then he's had a 91 in for a G3K conversion since April 1st. The last time I stopped by was in June, he said "3 or 4 more weeks, I'll call you when it's done."


You've got to be kidding. Urbach is known world wide to take the longest time to return any work. A simple search on the internet will show volumes of complaints and his inability to get in contact with him. I used him once. Never again. Yes he does beautiful work, but I know personally people who have waited years to get stuff back from him. Only a fool would send anything to Urbach if you want it back in your lifetime. You better send a case of beer with your gun.

[kendeepdiver]

RALH SMITH AT RDTS HAS DONE 2 K GUN'S FOR ME. I LOVE TO SHOW THEM OFF. THE BEST FINISH I HAVE SEEN. THEY SHOOT EVEN BETTER.

[mp5a3]

Mine is a Billistics (RR) I've heard they're pretty good..

[Novagator]

Another for TSC machine. you cannot tell the gun from a factory gun, plus Mike and Tammy provide the best customer service too.

[hk_mtbr]

My MP5 is an S&H conversion and it runs like a top.

My $0.02

[AviatorDave]

TSC Machine is who gets my business. 2 MP5, and a 21E so far. I researched for 3 years on my 21 before I sent it to anyone to get totaly rebuilt. I picked TSC, and can't be happier.



You've got to be kidding. Urbach is known world wide to take the longest time to return any work. A simple search on the internet will show volumes of complaints and his inability to get in contact with him. I used him once. Never again. Yes he does beautiful work, but I know personally people who have waited years to get stuff back from him. Only a fool would send anything to Urbach if you want it back in your lifetime. You better send a case of beer with your gun.

Nope, not kidding. My MP5-N was done in 3 weeks, my 91 has been there for 8 months. Maybe I need to stop by with a case of Bud Light next time.

[mp5a3]

Nope, not kidding. My MP5-N was done in 3 weeks, my 91 has been there for 8 months. Maybe I need to stop by with a case of Bud Light next time.


No no my friend, never Bud Light. Bring some Microbrew or a good Belgian beer, If someone brought me BL I'd take longer :-)

[AviatorDave]

No no my friend, never Bud Light. Bring some Microbrew or a good Belgian beer, If someone brought me BL I'd take longer :-)

It's not my favorite, but every time I go by, that's what he offers me - his fridge is full of it so I figure that is his favorite.

[CZ-75]

OK, guys... I'm going to chime in here. I'm not going to comment on who is better than whom, but I WILL opine on which conversion type is better than the other as it relates to the barrel.

HK barrels are pressed into the trunion, then held into place with a barrel pin that is 5mm thick which goes through the trunion and through a groove in the barrel.

Conversion Type 1 (Pull out the old barrel and push in a new one):
Most smiths who use this method will rotate the "new" barrel 1/3 turn so that the 3-lug is alligned properly and once inserted, they can ream a new channel in the barrel, which also goes through the existing holes in the trunion. This reaming process can inadvertantly enlarge the holes in the trunion. This is the same procedure that HK uses when they rebarrel an MP5. Therefore, they make barrel pins which are .05 .10 and .15 oversized to use when they do a rebarrel.

Conversion type 2 (leave the HK94 barrel in place cut it down to MP5 length):
If done properly, the barrel is cut down and then threaded. A 3-lug adapter is then permanently added in such a way to make it virtually invisible to anything other than an x-ray machine.

I had a conversion done using the first method, and I had a catastophic failure. An over-sized pin was not used. The constant force of firing and bolt carrier movement caused my barrel pin to shear, and the barrel walked forward enough to allow the bolt carrier to start slamming into the trunion.

If I had to do it all over again, knowing the difference in conversion types, I would have opted for a smith that performs the second type of conversion.

Messing with removing and then inserting a barrel on a host weapon that you already know works.... It ads an unnecessary variable to the equation.

So I suggest talking to the smiths with good reputation to see which method they employ and make your decision accordingly.

[jjrphs]

HK barrels are pressed into the trunion, then held into place with a barrel pin that is 5mm thick which goes through the trunion and through a groove in the barrel.

Conversion Type 1 (Pull out the old barrel and push in a new one):
Most smiths who use this method will rotate the "new" barrel 1/3 turn so that the 3-lug is alligned properly and once inserted, they can ream a new channel in the barrel, which also goes through the existing holes in the trunion. This reaming process can inadvertantly enlarge the holes in the trunion. This is the same procedure that HK uses when they rebarrel an MP5. Therefore, they make barrel pins which are .05 .10 and .15 oversized to use when they do a rebarrel.

I had a conversion done using the first method, and I had a catastophic failure. An over-sized pin was not used. The constant force of firing and bolt carrier movement caused my barrel pin to shear, and the barrel walked forward enough to allow the bolt carrier to start slamming into the trunion.

If I had to do it all over again, knowing the difference in conversion types, I would have opted for a smith that performs the second type of conversion.

Messing with removing and then inserting a barrel on a host weapon that you already know works.... It ads an unnecessary variable to the equation.

So I suggest talking to the smiths with good reputation to see which method they employ and make your decision accordingly.

Conversion Type 1a: Pop (or drill) the pin, then with the appropriate size bar and 3# sledge........"knock" the old bbl out. Reinstall new bbl by 1st turning down the chamber stub so that it's a "slip fit" into the trunion.......makes proper positioning and head-spacing much easier don't ya know. Drill and hammer in a new pin and yer done!

Performed (even on rifle caliber) by more than a few lazy "basement" HK smiths lacking both the proper tools and the knowledge of their own limitations.

[E Corker]

Thanks, it really wasn't hard or expensive.Just a little practice and patience.

I used Brownell's Manganese Phosphate Park Solution, and I'll have to find the paint, to tell you what it was exactly. Each metal takes the park differently, sheet metal reciever was lighter in color than the barrell and and so forth.There is a blackener that can be done for a totally uniform park job, but as HK weapons are also painted ,the mismatched colors don't matter. I had spoke with Mike about the finishing when I dropped the gun off, and he gave me the basics on what to get, so i did some research and got some stuff and did some practice runs on junk till I figured it out. The hole process is real simple. Mike gave me a barrel and chamber plug to keep the solution out.He is REAL helpful. A-1 in my book

Ed

[MONEY]

OK, guys... I'm going to chime in here. I'm not going to comment on who is better than whom, but I WILL opine on which conversion type is better than the other as it relates to the barrel.

HK barrels are pressed into the trunion, then held into place with a barrel pin that is 5mm thick which goes through the trunion and through a groove in the barrel.

Conversion Type 1 (Pull out the old barrel and push in a new one):
Most smiths who use this method will rotate the "new" barrel 1/3 turn so that the 3-lug is alligned properly and once inserted, they can ream a new channel in the barrel, which also goes through the existing holes in the trunion. This reaming process can inadvertantly enlarge the holes in the trunion. This is the same procedure that HK uses when they rebarrel an MP5. Therefore, they make barrel pins which are .05 .10 and .15 oversized to use when they do a rebarrel.

Conversion type 2 (leave the HK94 barrel in place cut it down to MP5 length):
If done properly, the barrel is cut down and then threaded. A 3-lug adapter is then permanently added in such a way to make it virtually invisible to anything other than an x-ray machine.

I had a conversion done using the first method, and I had a catastophic failure. An over-sized pin was not used. The constant force of firing and bolt carrier movement caused my barrel pin to shear, and the barrel walked forward enough to allow the bolt carrier to start slamming into the trunion.

If I had to do it all over again, knowing the difference in conversion types, I would have opted for a smith that performs the second type of conversion.

Messing with removing and then inserting a barrel on a host weapon that you already know works.... It ads an unnecessary variable to the equation.

So I suggest talking to the smiths with good reputation to see which method they employ and make your decision accordingly.

I totally agree with what you are saying but a good HK Smith should be able to do version 1 if they know what they are doing but the truth is alot of them do not. All I know is that I will never again use ANY HK smith that does not return phone calls , does not check their emails , has a bad rap about returning a build way past the promised time or takes over 1 year to finish my build because I might be dead by then. I understand these smiths probably get a bunch of people who just want to talk all day or waste their time but if the smith can not talk to you after they have your weapon then they are not worth it in my opinion.

[CZ-75]

Money,

My type 1 conversion was done by a smith that is widely regarded as one of the best. He's one of the few that almost everyone highly recommends.

I sent it back after researching the problem enough to tell the smith that my barrel was too far forward. It was returned saying that the new F carrier was OK, disregarding my claim that the barrel was too far forward.

I sent it right back, and reiterated the problem. He fixed it free of charge, and apologised for his mistake, but the fact remains that if I had chosen a smith who does type 2 conversions, I never would have had the problem to begin with... at least not that problem.

Granted, my issue was one in a thousand, but why introduce that risk when there is no need to do so?

I will not disclose which smith did it. He made it right, and stood behind his work, so I will do nothing to discredit him... but I will recommend a type 2 conversion over a type 1 conversion so long as the type 2 smith has a good reputation.

[AviatorDave]

Conversion Type 1a: Pop (or drill) the pin, then with the appropriate size bar and 3# sledge........"knock" the old bbl out. Reinstall new bbl by 1st turning down the chamber stub so that it's a "slip fit" into the trunion.......makes proper positioning and head-spacing much easier don't ya know. Drill and hammer in a new pin and yer done!

Performed (even on rifle caliber) by more than a few lazy "basement" HK smiths lacking both the proper tools and the knowledge of their own limitations.

Pound the barrel out instead of using a $100 press? Make the barrel a slip fit? Oh HELL no! I would never rely on just the barrel pin to hold it in place. Only half the diameter of the pin even contacts the barrel, it would eventually get sloppy.

[AviatorDave]

OK, guys... I'm going to chime in here. I'm not going to comment on who is better than whom, but I WILL opine on which conversion type is better than the other as it relates to the barrel.

HK barrels are pressed into the trunion, then held into place with a barrel pin that is 5mm thick which goes through the trunion and through a groove in the barrel.

Conversion Type 1 (Pull out the old barrel and push in a new one):
Most smiths who use this method will rotate the "new" barrel 1/3 turn so that the 3-lug is alligned properly and once inserted, they can ream a new channel in the barrel, which also goes through the existing holes in the trunion. This reaming process can inadvertantly enlarge the holes in the trunion. This is the same procedure that HK uses when they rebarrel an MP5. Therefore, they make barrel pins which are .05 .10 and .15 oversized to use when they do a rebarrel.

Conversion type 2 (leave the HK94 barrel in place cut it down to MP5 length):
If done properly, the barrel is cut down and then threaded. A 3-lug adapter is then permanently added in such a way to make it virtually invisible to anything other than an x-ray machine.

I had a conversion done using the first method, and I had a catastophic failure. An over-sized pin was not used. The constant force of firing and bolt carrier movement caused my barrel pin to shear, and the barrel walked forward enough to allow the bolt carrier to start slamming into the trunion.

If I had to do it all over again, knowing the difference in conversion types, I would have opted for a smith that performs the second type of conversion.

Messing with removing and then inserting a barrel on a host weapon that you already know works.... It ads an unnecessary variable to the equation.

So I suggest talking to the smiths with good reputation to see which method they employ and make your decision accordingly.

Did you mean .005", .010" and .015" oversize, or are those .05, .1, and .15 dimensions in millimeters?

[MONEY]

Money,

My type 1 conversion was done by a smith that is widely regarded as one of the best. He's one of the few that almost everyone highly recommends.

I sent it back after researching the problem enough to tell the smith that my barrel was too far forward. It was returned saying that the new F carrier was OK, disregarding my claim that the barrel was too far forward.

I sent it right back, and reiterated the problem. He fixed it free of charge, and apologised for his mistake, but the fact remains that if I had chosen a smith who does type 2 conversions, I never would have had the problem to begin with... at least not that problem.

Granted, my issue was one in a thousand, but why introduce that risk when there is no need to do so?

I will not disclose which smith did it. He made it right, and stood behind his work, so I will do nothing to discredit him... but I will recommend a type 2 conversion over a type 1 conversion so long as the type 2 smith has a good reputation.

I had a simular problem with one of the so called top HK smiths as well. PM SENT

[repins05]

Money,

My type 1 conversion was done by a smith that is widely regarded as one of the best. He's one of the few that almost everyone highly recommends.

I sent it back after researching the problem enough to tell the smith that my barrel was too far forward. It was returned saying that the new F carrier was OK, disregarding my claim that the barrel was too far forward.

I sent it right back, and reiterated the problem. He fixed it free of charge, and apologised for his mistake, but the fact remains that if I had chosen a smith who does type 2 conversions, I never would have had the problem to begin with... at least not that problem.

Granted, my issue was one in a thousand, but why introduce that risk when there is no need to do so?

I will not disclose which smith did it. He made it right, and stood behind his work, so I will do nothing to discredit him... but I will recommend a type 2 conversion over a type 1 conversion so long as the type 2 smith has a good reputation.

Could you discuss how you are able to tell that the barrel is to far forward? Also the consequences from a barrel placed to far forward after shooting it? Thanks.

[CZ-75]

Aviator... Those are mm measurements.

Here is a link to the thread:
http://hkpro.com/forum/showthread.php?t=51320&highlight=serious+problem

I did not notice the problem until I broke a bolt carrier. It was a welded up 94 carrier (no idea who did the work), so I dismissed the breakage as poor heat treating after the weld, and bought a new bolt carrier.

Then, the new carrier started to crack in the same place.

In a properly assembled MP5 (or any roller locked HK), as the bolt carrier moves into battery, the bolt makes contact with the breach, then the bolt carrier continues to move forward under pressure from the recoil spring. This causes the rollers to extend out and make contact with the recesses in the trunion, and the gun is then "locked" into battery. The carrier is stopped from moving forward as the rollers lock into place before the bolt carrier makes contact with the trunion.

If the barrel is too far forward (mine was at least 1mm too far forward), the bolt carrier will contact the trunion before the bolt can make contact with the breech, or at least before the rollers can extend out far enough to lock into place and stop the carrier before making contact with the trunion

The indicator that I missed was the fact that the bolt would move ever so slightly when the gun was in battery. I could actually wiggle the bolt fore and aft with my finger, but didn't notice that until after the second carrier started to crack.

This past April, I went over to the Indiana HKPRO MP5 school, and was able to compare my MP5 to a few of Tom's Post Samples. By this time, I had spoken with enough smiths (Curtis Higgins nailed the diagnosis over the phone in less than 5 minutes). Comparing my gun to Tom's, it was clear that my barrel was too far forward. On Tom's guns, where the barrel seats into the trunion, the place where the barrel widens to fit in the trunion was perfectly alligned with the edge of the trunion. On mine, you could see 1-2mm of the wide part of the barrel was forward of the edge of the trunion.

This confirmed the problem. I spoke to the smith, and told him I'd send the existing bolt group that was cracking along with a brand new F group with the gun.

All the smith did was drop in the F group carrier, and saw what he thought was enough clearance between the carrier and the trunion. He was wrong, and disregarded my claim that the barrel was too far forward, and shipped it back. Maybe he just wasn't listening when I was explaining the problem over the phone. I called him when the gun arrived and asked "so it's normal that the bolt should move a little bit when in battery?" And he said no. I explained the issue again, and he said to send it back again. This time he figured it out and fixed it. He said the barrel pin had sheared. I'll take his word for it, but it is possible that the barrel was not pressed in far enough to begin with (which is what I really suspect).

The strange thing about this problem, is that unless you notice the bolt moving, I never would have figured it out by checking the bolt gap the way I did.

My problem could have been identified sooner if I had been checking the bolt gap using a different method. I would always start with the a feeler 0.02" gage, which is the high end. It would go in with a lot of drag, which meant the gap was in spec, but at the high end. What I didn't realize, is the when the bolt moved aft, the gap narrowed to 0.008.

Once I figured out that the bolt was not really locked, I knew it was a serious issue

Since the barrel has been reinstalled the problem has gone away.

Like I said, this is probably a rare problem, but why introduce another variable into the conversion that may increase the odds of having a problem? I will never have another type 1 conversion performed on any of my guns.

[jjrphs]

He said the barrel pin had sheared. I'll take his word for it, but it is possible that the barrel was not pressed in far enough to begin with (which is what I really suspect).


When the bbl pin shears, you gotta ask yourself how is enough force overtaking the 10-20k pounds static frictional force between the bbl/trunion to break the hardened bbl pin and allow the bbl to slip forward in the trunion?

The short answer is it shouldn't.......unless there is something very definitely wrong such as a dramatic lessening of the static frictional force between the bbl/trunion.

It sounds as though your new bbl was undersized relative to your trunion as shipped......something which should've been plainly evident to your smith and caught

----OR----

Your smith performed a "Conversion Type 1a" on your MP5 where the chamber end of the bbl was turned down a few thousandths......making the insertion of the bbl into the trunion and subsequent adjustments a "hand fit" proposition and much, much easier. It's lazy, sloppy HK work......but this wouldn't be the 1st time its happened.

CZ-75 I think you need to let all here know which smith did the work. There is no disparagment in indicating who did the work and subsequently fixed the problem........but you do a disservice to all here who in future will have HK work performed and weren't given information to make up their own mind and possibly avert the same type of cost and headache you've gone thru.

[repins05]

Aviator... Those are mm measurements.

Here is a link to the thread:
http://hkpro.com/forum/showthread.php?t=51320&highlight=serious+problem

I did not notice the problem until I broke a bolt carrier. It was a welded up 94 carrier (no idea who did the work), so I dismissed the breakage as poor heat treating after the weld, and bought a new bolt carrier.

Then, the new carrier started to crack in the same place.

In a properly assembled MP5 (or any roller locked HK), as the bolt carrier moves into battery, the bolt makes contact with the breach, then the bolt carrier continues to move forward under pressure from the recoil spring. This causes the rollers to extend out and make contact with the recesses in the trunion, and the gun is then "locked" into battery. The carrier is stopped from moving forward as the rollers lock into place before the bolt carrier makes contact with the trunion.

If the barrel is too far forward (mine was at least 1mm too far forward), the bolt carrier will contact the trunion before the bolt can make contact with the breech, or at least before the rollers can extend out far enough to lock into place and stop the carrier before making contact with the trunion

The indicator that I missed was the fact that the bolt would move ever so slightly when the gun was in battery. I could actually wiggle the bolt fore and aft with my finger, but didn't notice that until after the second carrier started to crack.

This past April, I went over to the Indiana HKPRO MP5 school, and was able to compare my MP5 to a few of Tom's Post Samples. By this time, I had spoken with enough smiths (Curtis Higgins nailed the diagnosis over the phone in less than 5 minutes). Comparing my gun to Tom's, it was clear that my barrel was too far forward. On Tom's guns, where the barrel seats into the trunion, the place where the barrel widens to fit in the trunion was perfectly alligned with the edge of the trunion. On mine, you could see 1-2mm of the wide part of the barrel was forward of the edge of the trunion.

This confirmed the problem. I spoke to the smith, and told him I'd send the existing bolt group that was cracking along with a brand new F group with the gun.

All the smith did was drop in the F group carrier, and saw what he thought was enough clearance between the carrier and the trunion. He was wrong, and disregarded my claim that the barrel was too far forward, and shipped it back. Maybe he just wasn't listening when I was explaining the problem over the phone. I called him when the gun arrived and asked "so it's normal that the bolt should move a little bit when in battery?" And he said no. I explained the issue again, and he said to send it back again. This time he figured it out and fixed it. He said the barrel pin had sheared. I'll take his word for it, but it is possible that the barrel was not pressed in far enough to begin with (which is what I really suspect).

The strange thing about this problem, is that unless you notice the bolt moving, I never would have figured it out by checking the bolt gap the way I did.

My problem could have been identified sooner if I had been checking the bolt gap using a different method. I would always start with the a feeler 0.02" gage, which is the high end. It would go in with a lot of drag, which meant the gap was in spec, but at the high end. What I didn't realize, is the when the bolt moved aft, the gap narrowed to 0.008.

Once I figured out that the bolt was not really locked, I knew it was a serious issue

Since the barrel has been reinstalled the problem has gone away.

Like I said, this is probably a rare problem, but why introduce another variable into the conversion that may increase the odds of having a problem? I will never have another type 1 conversion performed on any of my guns.

Sorry for the problems you experienced. Thank you for the detailed diagnosis.

[CZ-75]

I will tell you that the next time I need work done, it will go to Mike at TSC

[deezgunz]

+10000000000000% for Mike and Tammy at TSC. He's done a MP5, MP5k, 33k, 53 for me...all flawless. His service after the sale is amazing as well. A phone call (I'm local) got me face to face time with Mike and he got my pack/host problems straight. He even used his own ammo!
http://i12.tinypic.com/7y7dsmv.jpg

[silent45]

Had Mike at TSC do a MP5-N for me. Quick, professional, awesome work. Easy to reach and will let you know what is going on through the process. BTW he and Tammy are great people too...