I have a DPMS lower and sometimes it will not hit the primer hard enough.Is it my rifle or hard primers in cheap ammo

PecosKid -

Most probably it's a weak spring. They're cheap enough; try another. Another cause possibly could be too-short (out-of-spec) firing pin, again a cheap thing to swap out. [You should always have a spare firing pin as part of your field repair parts in your buttstock anyway.]

Does your DPMS rife perhaps have a match trigger and low-inertia (low-mass, fast) hammer? This could also be/contribute to the problem.

Less likely but worth considering: your firing pin could be undergoing some resistance during its travel (binding) in bolt/carrier assembly. Try swapping out a whole complete bolt+carrier assy from another known-good AR.

Please DON'T associate hard (military) primers with 'cheap ammo'. Have you noticed that when you chamber a round in an AR (nd then eject it without firing) that there is a slight primer indentation? THIS IS ABSOLUTELY NORMAL AND WITHIN SPEC!! In fact if you DO NOT see any indentation, you DO have a problem.

[This is even mentioned in the military M16 tech manuals, avaiable at every gunshow and online at [url]http://old.ar15.com/books[/url] ]

I think most commercial mfgd 223/5.56 ammo today has hard/military primers - I'd bet due to popularity of AR15s. Home reloaders for .223 bolt guns may use different primers however, and that could lead to trouble. Military rifle ammo *intentionally* has hard primers; in fact if you mistakenly use soft pistol or rifle primers (say, w/reloads) there is some chance that you could have an accidental discharge upon chambering a round. [Yet another great reason to always keep your barrel pointing in a safe direction, esp while charging/cycling rifle.]

So make sure you have a good hammer spring and a standard mass AR15 hammer.

Bill Wiese
San Mateo, CA

Thanks Bwise,for taking the time

There are gauges to check firing pin protrusion.

I also would check the headspace with your current setup, just to be sure it's not excessive.  If you're swapping another carrier & bolt in, you want to check headspace anyway.

The first thing to check is whether the arms of the hammer spring are lying ON TOP OF THE TRIGGER PIN. If the arms are under the trigger pin, it can soften the hammer blow.  [:D]

Good Points Bill,
I would probably clean where the firing pin goes first with a pipe cleaner or something similar. Quite a bit of exhaust gas is funnelled thru there, and there could be a speck of something there hindering the firing pin from going forward with some bravdo.

2nd point - Yep, been their done that. The if you're reloading for an AR15 type gun make sure you use the hard military-style primers. Initially, I couldn't figure why I was getting slam-fires upon closing the bolt by releasing the bolt catch from my reloads, but later I found out about the AR firing pins and military primers. Scarced the $hit out of me.

Get a Wolff extra power hammer spring.