Dedicated 22 LR upper: light strikes

[TitoR]

Ok here is the build parts:

CMMG barrel w/ collar

CMMG conversion bolt

Aero Precision stripped upper

ALG 12" hand guard & brake

BCM GF Charging handle

Election port cover and forward assist kits from brownells

Put the upper together and went to the range to test. I was not able to get ignition on any bullet. There is the faintest of marks on the bullet rim, so the firing pin is not striking it with force, or the bullet is moving forward when struck. I checked the firing pin and it moves freely and it works perfectly in another upper with the conversion bolt using the chamber adapter.

Any ideas on what may be causing this?

In the meantime, the upper is coming apart to see how the collar is interfacing with the barrel and bolt.

Tito

[Shooter115]

I'm thinking for one reason or another your bolt is sitting back too far in the upper and the hammer is barely hitting the firing pin. Leading me to believe something is out of spec, incorrectly assembled or it's failing to go fully into battery.

I won't be home till later tonight, but if you need me to mic some parts for you let me know. I have basically the same upper you do and with a little work on the feed ramps it runs like a Swiss watch.

[TitoR]

I just completed taking apart the upper. What I found was that the feed ramp was extending all the way to the barrel chamber.

This is causing the bullet rim to sit on the ramp instead of the flat of the barrel chamber. When struck by the firing pin the rim gives, instead of been pinched against the barrel chamber.

Filed a radius at the end of the ramp following the contour of the bullet rim to clear the bullet rim.

Tomorrow I'll go to the range to test an will post the results.

Tito

[Shooter115]

When I put mine together I had to do quite a bit of work on the feed ramp / chamber mouth to get it running right. The edges were so sharp that it was shaving the bullets as they were feeding. Results were poor function and accuracy. Once I cleaned up the feed ramp and broke the sharp edge on the chamber mouth she runs like a dream with even the cheapest bulk ammo.

[TitoR]

Ok, the filing worked. I had good ignition, although still had some failures to ignite. I'll file a bit more, break the edge of the chamber mouth and polish the chamber.

The other thing i noticed was that a few times the bolt was held open with still one round in the magazine. I am using the better mag adapter with S&W magazines. I am planning to soften/polish some of the edges of the bolt hold open actuator of the adapter before i go out to test again. Any other suggestions on what may be causing the premature bolt hold?

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[Shooter115]

Never had a problem with either CMMG or Black Dog mags.

[Dwight Stearns]

Sometimes the extractor drags a little bit on the sides of the extractor cut-out. A little light polish on the sides of the extractor and the cut-out does wonders.