Hi, new to this forum but thought I'd throw a question out there. When firing my DPMS AR15, it runs smooth as silk. Until about 80/100 rounds in. Then it fails. The pin is still striking the round, enough to leave a dimple, but not enough to set it off. This happens with various ammo from cheap wolf, to spendy federal. Now, the question; would you (a) get a new pin, or (b) get a new hammer spring? I also noticed last time I stripped it down that the bolt doesnt slide smoothly into the carrier but seems to slightly catch around when the ejector enters the carrier. Is that normal?

Thanks. Happy and safe shooting all!

Brody,

First off, welcome to WGO!! Second. How much carbon caking is there on your bolt and BCG? The pin is a free floating pin, as you know so it takes a good whack to get it to make a good primer strike. Too much carbon build up can lead to the pin not able to strike the primer fully.

Do all the parts look fine? The firing pin, where it strikes the primer isn't mushroomed or flattened at all?

Hey, thank you! I keep it very clean. I ran solvent in there and got it sparkling. The pin appears to be in fine working order but I havent had the chance to compare to a new one to check for blunting. No mushrooming tho. Just don't want to spend $ on a part that wont fix the issue so looking for all suggestions.

I would think that the hammer spring being too light, it would happen at round 1, just as much at round 100. Spring fatigue is a possibility though. One thing too.. As an AR owner, it is almost your DUTY to carry a spare LPK and firing pin .

You don't have a lightened hammer do you?

Yeah, I'm learning this. Standard hammer. Looks like I'll just spend $20 and get a titanium pin and see if that helps. Thanks!

My AR gunsmithing book recommends against titanium firing pins unless you're shooting competitively. One of the things I noticed on my AR was that the leade had become caked with crap, which I think contributed to to misfires from light primer strikes. The leade is the part of the chamber that the round seats into. I think what was happening was the round would be stopped from seating all the way down, and then when the pin struck the primer, it pushed the round forward just enough to create a light strike.

I haven't proved this to myself because I haven't been shooting since the last time I had so many misfires. My wife's AR on the other hand fired all of the misfired rounds from mine with no problems. Her rifle had nowhere near as much crap in the leade.

Take a look in your chamber to see what it looks like. I had never specifically scrubbed mine because I never realized it was necessary. My only previous experience with .223 was with Mini-14's, which are blow back operated, so all the crap contained in the exhaust gas was never an issue because it was never in the chamber.

Would utilizing the forward assist help the seating? I've tried that after a misfire with the dimpled round. But maybe because it was already dimpled it still would fail at that point?

Thanks for all the feedback! Great forum.

The same book says that the only time you should ever use the forward assist is when you've done a check for a round in the chamber ("cobra check"). Once you've done the check, you'd use the forward assist to re-seat the round. Any other time the round isn't fully seated there's something else wrong that needs to be fixed (like crap in the leade).

I'll strip it down in the morning and see what I can see. Thanks fr the info. Whats the name ofthe book you are referencing?

Gunsmithing the AR-15 by Patrick Sweeney

His other AR15 books are amazing as well! Volume two is not layed out as well as the first (pictures not on the same pages as the text), but the info is still great. I have not read volume three.

Great. Thanks.

In 30 years of familiarity with all things AR, the first things I always check are ammo, and MAGAZINES.
You mentioned that the problem occurs with varying ammo, so that's good. Now, how many mags do you have, and is it possible the problem may be manifesting itself when you use a particular one? Put a piece of masking tape with a number on each of your mags, and make note of which mag is in when you have the problem.
FTF could easily be the mags feed lips or follower.
Are you shooting 5.56mm or .223?
I don't think it's the firing pin. Either crud accumulation, or mag. Or, when you start getting into the "weird" stuff like bolt bounce. That can cause a lite strike.
The fact to remember is that it works for the better part of three mags before it happens. Are you firing rapid-fire? Is the gun really hot when this happens, or are you shooting at a slower pace? 16" or 20" bbl?

So, my problem with light strikes turned out to be entirely of my own making. When I installed the LPK, I put the hammer spring on upside down. With the help of a friend and one of the guys at my new range, we were able to diagnose & fix the problem right there at the range. After getting the spring in right side up, I was able to run through an entire magazine without a single misfire.

Maybe this'll help you with your problem?

Thanks for the tip. I havent had a chance to really go over it as of yet but will add that to my list of possible issues.