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Discussion Starter · #1 ·
Hi guys,

Just got my first, of what I'm sure will be a few, HK guns. I picked up my HK USC from my dealer on Saturday. I think I got a decent deal. I got the USC with the factory top rail, and two mags for $1300.

I had been eyeing the USC for the last few months, and when I saw an aluminum grease gun lower come up on gunbroker, I had to jump. I picked up 8 GG mags too. So far, I have $1750 into the gun. I think I'm doing pretty darn good on this project, and I'll recoup a little bit when i sell the two USC mags I have.

The GG conversion went well. Haven't dont a live first test yet, but it dry checks just fine. I'm confident it is OK, but I'll see this weekend.

I have a Burris FFII sight cowitnessed with the sights, and I cut the FS hood to clear up the FOV. Very nice, but the Burris isn't my favorite optic. I'd like to put one of the Zeiss (to keep it German) reflex sights on it if they will cowitness. Can someone verify that, please? If not, I assume an Aimpoint T1 would work?

Also, I have a question with regards to 922r compliance. I've read and searched on this, but all the info I pulled up is for the UMP conversion. I can't find anything for the GG conversion specifically. My understanding is that it is satisfied simply by using M3 mags, right?
 

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the GG conversion lower, and the mags are all US made as far as I know, so that should give you lots of US made parts.
 

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Discussion Starter · #3 ·
the GG conversion lower, and the mags are all US made as far as I know, so that should give you lots of US made parts.
That's what I was thinking. Not sure if the lower counts though. Could that be considered the trigger housing for 922r? I'd think so. The mags are US made, for sure. Got them new in the wrap, from 1962, made in New York; so that is 3 parts for sure, which is all I need, I think.
 

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Good to see your GG conversion went well, let us know how the live firing works out. I also just picked up a GG conversion and some M3 mags but haven't converted my USC yet. I'll be using the GG receiver and stock plus M3 mags for my US parts count.
 

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Discussion Starter · #6 ·
I have the older aluminum GG lower, not the polymer one with the built in stock. My gun retains the USC stock, which is likely to get cut and welded by tbostic pretty soon. Just have to think on some details for it.

The live fire test went fine, for the most part. My hammer pin walked to the left slightly during the first 30 rds. That was easily solved by peening the right side of the pin. Put another 170 rds or so through it afterwards and it was tip-top. So, functionally, it is OK.

I did have some issues with the M3 mags. I have one M3 mag with a square, rather than rounded notch. It didn't lock into the gun at all. I have another M3 mag which refuses to feed properly. These were NIW M3 mags from 1962. I had to dremel the first mag's notch out to make it lock up. That worked out fine.

The one that doesn't feed is still unsolved. The feed lip geometry is subtly different. It is more narrow at the front in comparison to my other mags. Next time I'm out at a buddy's house, we're going to take some dimensions with his calipers and try to set it straight. Not a big deal though. I have a bunch of other M3 mags that are still in the wrap if needed.
 

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Thanks for the live fire test report. This is good info in case I run into similar problems.
I just checked my M3 mags and they all lock into place fine, these mags are from keepshooting.com.
Cheers, 57
 

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Discussion Starter · #8 ·
You're welcome.

I managed to fix the bad mag with a little bit of force and a pair of pliers. There were also some burrs on the inside of the feed lips, so I hit that with some sandpaper too. I filled it and sent 30 rds down range in quick order with it, and it worked fine. So I don't have to open one of my other mags after all.

You shouldn't have a problem with keepshooting's M3 mags. They are quite good and are superior to original USGI M3 mags. USGI GG mags are like snowflakes due to old school production methods, I would guess. Unfortunately for me, I need USGI mags as I'm in NY, so pre-1994 magazines are the only way for me to have more than 10rds these days. A buddy back in FL has a suppressed Cobray M-10 that takes GG mags. He swears by the keepshooting mags. Oh, to be back down south.

Last bit of advice when you finally jump into your conversion. Keep your cell phone handy and take loads of pics as you go. It'll make it much easier to get everything back together. If your GG lower documentation is anything like mine, it will be just useful enough to get you in trouble. Wasn't difficult to put back together, but I'm mechanically inclined, familiar with a few different gun's actions, and even then.. it was easier for me to just stop looking at the docs and figure out myself. Part #s were mislabeled and straight out wrong, steps were missing. Fun time.
 
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