Reaming holes in lower

[darkest2000]

I've never had an instance where I need to ream the holes for the parts to fit. they may be a bit tight occasionally but nothing a drop of CLP and gentle tapping from a mallet won't fix. The anodizing is very important to have because the trigger pins can become enlarged (oval) over time from use if the hardened anodized finish isn't there.

I really doubt they took into account the thickness of the finish.

And yeah they've been making the AR for what, 50 years now? I'm pretty sure they've got that part figured out. Besides, Anodizing is a surface altering treatment, it doesn't change the dimension like sprayed on finishes do.

[Curley Red]

Thanks for the info everyone, I just wanted to make sure of what I wasn't sure of. I feel it is better to ask before doing.

[Nathan Krynn]

Well, at my company (LockMart), the hole diameter was after finishing. Pretty much standard in aerospace. On the AR15, the coating is a hard finish and you want it in the holes.

We do have to account for finishing. Our anodize is .8-1.2 thou and yes it needs to be accounted for.

Good example is the back of the FCG where the rear lug of the upper fits in. Anodizing can take the lower from loose to too tight to fit except with a hammer. After all with both sides it is up to 2.4 thou in that area that determines upper fit.

[Calplinker]

Lower

I'd like to enlarge the hinge pin hole on my POF lower, I wouldn't have to use their hinge pin and sleeve set up on the DPMS upper. But my assumption is that doing so would remove the "hard coat" anodizing and expose the softer alloy beneath. Is that accurate? If accurate for the relatively little used hinge pin isn't it worse for the trigger and hammer pin holes?

The Mega lower on my first AR build didn't line up 100% with the PWS upper. Only way to get the pivot (hinge) pin in was to whack it with a mallet. Ugh.

Basically, I was in the same situation as you and considered reaming out the hole.

Then, I had an idea and instead decided to buy an extra hinge pin and just remove metal from the shaft of the pin and leave the lower alone. I used a stationary disk sander to do it quickly and just turned it by hand wearing gloves. You could also just use a file or sandpaper and do it by hand.

Of course this removed the black finish from the pin, but once I got it to fit nice and snug without having to be tapped in, I just hit it with back to black or one of those pen things I had laying around.

This approach made more sense to me as I was worried about buggering up my lower. Pins are something like $2. I messed one up by accidentally taking off metal from the head when my hand slipped. No worries. I just tossed it out and picked up another pin.