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Discussion Starter #1
Hello everyone! I have a Usc to ump conversion done by Tommy built that I've had for a while. When I first had it converted I had a horrible ftf problem. The bolt would catch on the brass casing and push the bullet above the barrel. It would happen several times a mag (at least 5 or more per magazine). I had sent it back for repair. Now it's mostly fixed. I have put 300 rounds thru it since I got it back and I have had zero ftf during during actual shooting, however when I'm reloading- just the very first round of the mag will ftf. About 1 out if 2-3 mag reloads. After the first round the rest are flawless. I found that If I use the bolt release or the charging handle with anything less than maximum force to close the bolt this will occur. Any opinions?. I'm very ocd about failures. If this was literally anything else I would of sold it already. Out of my 20 guns I own this is the only firearm I do not trust Which frustrates me because its my favorite firearm, my most expensive firearm in total investment and my only firearm that is stamped.

I don't wanna send it back to tommy built again because I don't think it's their fault and I already felt guilty doing it the first time. when you completely modify a weapon beyond it's original design things happen and it can't be blamed on anyone.
 

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I'm sure it has to do with the angle mag. It is a result of how the hooks were opened up on the UMP lower and how the magazine well was widened. I had some similar issues with my conversion, but fixed them by changing ump lowers and opening up the magwell some more especially at the front up to the feed ramp.

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Discussion Starter #3
I'm sure it has to do with the angle mag. It is a result of how the hooks were opened up on the UMP lower and how the magazine well was widened. I had some similar issues with my conversion, but fixed them by changing ump lowers and opening up the magwell some more especially at the front up to the feed ramp.

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How much do you open the mag well? Should the mag body be able to go past the magwell in the upper receiver?. Also tommybuilt correct the lower hooks. There is absolutely zero play between the upper and lower with no gap between the 2. I think that's what fixed most of the issues with the ftf as since now it's just during fresh mag reloads.
 

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That's how much I opened mine up but I'm not sure that much is necessary. If you can wait until tomorrow I can post pictures.

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Discussion Starter #5 (Edited)
That's how much I opened mine up but I'm not sure that much is necessary. If you can wait until tomorrow I can post pictures.

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Great, thank you! I'm going to buy some dummy rounds and do the reloads while I perform the work to see what changes or not.
 

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I'm using US mags for compliance reasons.
The reason I ask is I had FTF issues using US made magazines. Apparently the feed lips were either out of spec or flexed way to easily. I mentioned this to Adam and he took my old ones back and sent me some new ones with metal reinforced feed lips. I haven’t had an issue since, but this was also a few years ago.


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Forgot about 922r (it's dumb) and use the factory mags. Are you using the factory barrel or HDPS barrel? They have different barrel ramp designs.
 

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I'm using US mags for compliance reasons.
That's honestly your biggest issue. The US made mags are just never going to be reliable to the level you want. You are lucky yours work at all. Mine don't work yet my HK mags are flawless.

I would start there before cutting anymore into your receiver.



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Are you being OCD about your reloads? OAL? Bullet seat depth? Factory type crimp? FMJ? Same bullet profile as factory that works?
The ftf can not be simply from the fact that you reload but more so how you reload.

Hello everyone! I have a Usc to ump conversion done by Tommy built that I've had for a while. When I first had it converted I had a horrible ftf problem. The bolt would catch on the brass casing and push the bullet above the barrel. It would happen several times a mag (at least 5 or more per magazine). I had sent it back for repair. Now it's mostly fixed. I have put 300 rounds thru it since I got it back and I have had zero ftf during during actual shooting, however when I'm reloading- just the very first round of the mag will ftf. About 1 out if 2-3 mag reloads. After the first round the rest are flawless. I found that If I use the bolt release or the charging handle with anything less than maximum force to close the bolt this will occur. Any opinions?. I'm very ocd about failures. If this was literally anything else I would of sold it already. Out of my 20 guns I own this is the only firearm I do not trust Which frustrates me because its my favorite firearm, my most expensive firearm in total investment and my only firearm that is stamped.

I don't wanna send it back to tommy built again because I don't think it's their fault and I already felt guilty doing it the first time. when you completely modify a weapon beyond it's original design things happen and it can't be blamed on anyone.
 

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Discussion Starter #12
Are you being OCD about your reloads? OAL? Bullet seat depth? Factory type crimp? FMJ? Same bullet profile as factory that works?
The ftf can not be simply from the fact that you reload but more so how you reload.
I'm talking about reloading the gun with fresh mags. Not reloading ammo.
 

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Discussion Starter #13
That's honestly your biggest issue. The US made mags are just never going to be reliable to the level you want. You are lucky yours work at all. Mine don't work yet my HK mags are flawless.

I would start there before cutting anymore into your receiver.



Sent from my Pixel 3 XL using Tapatalk
That's honestly your biggest issue. The US made mags are just never going to be reliable to the level you want. You are lucky yours work at all. Mine don't work yet my HK mags are flawless.

I would start there before cutting anymore into your receiver.



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So you still have ftfs like this with the US made mags? I cannot find german mags anywhere.
 

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Discussion Starter #14
Forgot about 922r (it's dumb) and use the factory mags. Are you using the factory barrel or HDPS barrel? They have different barrel ramp designs.
I'm using the factory bolt and barrel. The barrel is just cut and threaded.
 

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So you still have ftfs like this with the US made mags? I cannot find german mags anywhere.
My US made mags barely hold in the rounds anymore. They will just pop out haha. Causes all sorts of malfunctions.

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Had these same issues consistently with US mags. Finally ditched them and use nothing but German mags and the issue is gone.
 

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I had same issue with a US. Ditch them and go German. In the last 6 months these mags have jumped over $100. There are several on Gunbroker now.
 

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Sorry, I missed that. My experience with those is what other people are saying use Use German mags only.
Different gun, but I tried ETS plastic 30 and 40 round mags in my three different fa MP5s and they totally failed to feed or would ftf after just one successful round. I loaded them 3-5 less, very lightly lubricated the inside of the mag body and the follower with a dry lube and just could not get them to work. Tried breaking them on my cement garage floor but they are tough! Hard to load, German HK loader would not work with them. Was going to sell or give them away because PTR people like them but I would have hated for them to fall into German MP5 owners hands and for someone to be wanting to depend on them so I lined them up at the range against the 25 yard berm and shot them to death with an MP5 using old HK straight mags in my SD.


I'm talking about reloading the gun with fresh mags. Not reloading ammo.
 

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Great, thank you! I'm going to buy some dummy rounds and do the reloads while I perform the work to see what changes or not.
Here are some pictures of my magwell. As you can see its opened up to the exact size of the UMP lower opening.

The most important area for adjusting angle of the mag is in the front up to the feed ramp. In my case I went slightly past the feed ramp.

PXL_20210115_164804534~2.jpg
PXL_20210115_164552528.jpg
PXL_20210115_164517111.jpg
PXL_20210115_163923886.jpg


View attachment 282960

View attachment 282961
 

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Discussion Starter #20
Here are some pictures of my magwell. As you can see its opened up to the exact size of the UMP lower opening.

The most important area for adjusting angle of the mag is in the front up to the feed ramp. In my case I went slightly past the feed ramp
Awesome thank you! Imma get some german mag first and test it out before I start doing any cutting, if I can find any that aren't 100$ a piece
 
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