My new Timney trigger & CMMG Sierra .22lr upper

[Microgunner]

They don't like each other and didn't want to play well together.

First off, I installed the Timney #667S 3# trigger into my S&W M&P-15T lower.

It couldn't have been much easier.

The only "difficult" part was getting the second set screws into the holes around the hammer spring. Got it done with the help of my brother. Three hands are needed.'

The trigger is nothing short of amazing in improved function over the stock trigger parts. Crisp clean break with about .0625" over travel. Fell in love instantly.

Decided to mount the CMMG Sierra .22lr upper and warm it up in the back yard.

It would only fire one round or less out of three with very faint firing pin marks on the brass.

Took the rifle back inside and studied it awhile.

Decided that the new Timney hammer just wasn't striking the firing pin hard enough to reliably ignite the cartridges. CMMG upper worked great with the stock, much harder hitting hammer.

Decided to sharpen the very blunt firing pin, so, a little at a time I thinned the firing pin chisel point.

With each little bit I sharpened reliability improved slightly.

I thinned the firing pin as far as I dared but the trigger/upper combo was still woefully unreliable.

The CMMG firing pin return spring is very short and very stiff so I decided this was where I'd modify next.

Cut half a loop off the spring, was more reliable.

Cut another half loop off spring, was more reliable yet.

Cut another half loop off for a total of about 1.5 loops and the rifle was absolutely reliable running Remington golden bullets and CCI Mini Mags through the CMMG upper like shit through a goose.

Stretched out the spiring to keep the firing pin from protruding and possibly causing a slam fire, reassembled for what seemed the 30th time, test fired, all good.

Put it away, will clean it next week.

Haven't tried the Timney with the 5.56 upper yet.

Too loud for the back yard.

[imschur]

Good post. I need to see if mine behaves the same

[Hunter87]

That's exactly the same issue I was having cut my spring down too and now it's working fine.