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CMMG 22lr upper, light strikes...

4.4K views 10 replies 0 participants last post by  John A.  
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#1 ·
A little back story. The upper works 100% on my Aero lower with Geissle SSA-E trigger.

I bought a LW15 polymer lower that I mentioned in another thread, and into that upper I put a DPMS trigger group that I had worked on my Bill Springfield. The trigger group has maybe 300 round fired with it before I took it out of the Aero upper and replaced it with the Geissle trigger. Nothing wring with it, I just had the money for a better trigger and went with it.

First time out with the new set-up was last night at an indoor range. I was shooting federal bulk pack ammo, and most of these(90%) went off without trouble. The rounds that went off do appear to have shallower than normal primer strikes.

What can be done?
 
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#2 ·
I don't have any advice, but did have a question. I apologize for getting off topic but how do you like the LW15 lower so far? How is the quality? I was just looking at one of those and for the money was thinking why not give it a try.
 
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#5 ·
I'm pretty sure the geiselle triggers are all flat faced.

If the bolt and fire controls are clean (especially around the firing pin), I don't have a reccomendation besides take it back out.
Yes, but he said that his Geiselle trigger worked just fine. He is having the issues with the DPMS trigger group. And if I remember correctly, many of the DPMS hammers are notched. I could be wrong though.
 
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#6 ·
I bought a LW15 polymer lower

into that upper I put a DPMS trigger group that I had worked on my Bill Springfield.

I took it out of the Aero upper and replaced it with the Geissle trigger.
I didn't read that it was the DPMS trigger he was having problems with.

If it is the DPMS fire controls he's having problems with, verify the hammer spring legs are on top of the disconnect/trigger retaining pin instead of resting under it on the floor of the lower.
 
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#8 ·
Just got home from work.

The hammer is DPMS and is not notched. The spring legs are sitting on top of the trigger pin.

One thing, I didn't clean the bolt after the last outing, but I only fired about 100 rounds. This outing I shot maybe 50 rounds more.
 
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#9 ·
It wouldn't hurt to take the bolt down and clean it out good.

The CMMG's are based on the Atchisson/Ceiner design and if the firing pin channel the bolt goes through gets funked up, it could ignition problems. It's happened to mine before, though I usually shoot mine suppressed, which adds to the fouling in the gun.

You could also check the firing pin for burrs and things while it's out. It's not going to hurt to check everything while you have it apart.

Another thing, you can check to make sure the bolt is closing all the way too. If there is any grit between the bolt and chamber section of the parts, that may be allowing the bullet to chamber although not fully closing, which could cause the firing pin to not get a good hit on the rimfire.

Just a few things to check. Hope it helps.
 
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#10 ·
I had the same issue...and then my friend the same issue after he built his dedicated upper as well. Both mine and his have lighter competition triggers.

So here is the big reveal:

The problem with both of them was the feed ramp. The feed ramp goes all the way up to the chamber and does not allow the rim of the cartridge to sit flush with breach. Go ahead an check yours with a dummy cartridge **NOT A LIVE ROUND**.

I figured it out by looking at the CMMG conversion kit (the bullet looking thing with the ramp attached) that I originally used and it did not have that problem. Anyway, I've put some pics up on my blog what I had to do to fix it.

woodhousellc[dot]com/?s=cmmg (sorry can't post links yet)

A little round file, some polishing and dummy cartridge should allow you to fix it right up. Reducing the strike surface of the firing pin also helps a little, but it does not solve the root cause.

-TriggerMeister