Light Primer Strikes With Bushmaster Xm15

[RifleShooter]

Let me preface this by saying that this is the first time I have used an AR-type rifle, so I have very little idea what is actually going on behind the scenes, so to speak. I have learned quite a bit about the AR system in general in the past month, but now apparently it is time to delve a little deeper.

I just got my brand spanky new(to me) Bushmaster XM15, which had about 200 rounds through it before I got my hands on it. I know the trigger group has either had work done or has been replaced, because the trigger pull has a miniscule first stage, and a clean break that is way too light to be stock. The first time I dry fired the gun, I wasn't sure that I had done everything correctly, because the hammer striking the firing pin was so soft, it felt as if something must be broken. However, not knowing the rifle at all, I decided to give it a try.

The first time out, the only ammo I had was some surplus stuff from the UAE. Out of 60 rounds, 4 did not go 'bang' the first time. That of course included the first round I tried, which scared me to death. 3 of 4 fired on the second try, the 4th took 3 tries. At the time I blamed it on the obviously inferior ammo. (I had one round that had a chunk out of the case up near the case mouth!)

The second time, which was today, that I got to shoot the rifle, I had some of the same cheap ammo, along with some American Eagle and two flavors of Wolf. Okay, so not match ammo, but I'm trying to learn enough to play in 3 gun matches without reloading .223 in addition to the 9mm I already load. Anyway, out of another 60 rounds, including 15 of the cheap UAE stuff, I only had one failure to fire, and that was on one of the Wolf rounds.

When I ejected the Wolf cartridge, I found a very small dimple in the primer, not nearly deep enough to set off the primer. Checking the spent casings, I did not find any that looked like they had light strikes. I loaded up the Wolf round again, and it fired just fine.

So, I'm now thinking that somehow the hammer strike is too light in the gun. What can I check? I'm definitely new to the AR platform, but I'm going to be digging in and stripping it all down to learn how things work. I know that in some guns, a light trigger pull equates to a light hammer strike. Is that the case with the AR? I just need a direction, or a place to start looking.

Thanks! You guys rock!

Arnie

Edited September 11, 2006 by RifleShooter

[shred]

FWIW, the 'tiny dimple' on an AR round is only a symptom of the round feeding into the chamber. The AR-design firing pin hits the primer very lightly on chambering a round.

[mike_pinto]

It doesn't sound like a huge problem yet, but in my limited experience, I have seen this with a crude bend in the hammer spring to try to lighten the trigger pull. It sounds alot like it was replaced with a RRA 2 stage trigger. I think I might contact RRA to get a two stage trigger spring replacement kit and try that out. Alot of folks hear from a friend that if you bend the hammer spring it will lighten the pull (Which your assumption would be correct, light trigger, light strike) The only problem is that you can bend it too much. I shoot with the stock RRA 2 stage match trigger and it works fine for 3-gun. It has a 4.5 lb take up and breaks crisp at 2 lbs for the second stage. You may want to order a new firing pin as well just to cover all the bases.

I am sure someone will recommend a new JP trigger kit, which no one can deny is the best, but I believe in starting cheap and spending more in the long run!!

Mike

[Dan Sierpina]

I've also seen people put the hammer spring on backwards to lighten spring tension, it unwinds the spring instead of tightening it on cocking. Similar results, occasional light strikes, and sometimes the pins would walk becase the spring legs didn't contact the pins tightly enough to retain them. And, as Mike mentioned bent spring legs. The legs should be straight, no bends.

[chp5]

You have several options. If this is a "garage-engineered" trigger job, you may want to get a smith to check it out. Messed up trigger jobs often lead to doubling or worse down the road.

You could also get the spring kit Mike mentioned. If you're running light springs, you can also cut off the "tail" of the hammer. This lightens the hammer and makes it more reliable with light springs. Look at the JP lightened hammer on their web sight and make your hammer look the same.

[mike_pinto]

chp5,

I believe he is running a 2 stage trigger, if he takes off the backside of the hammer, the sear will have nothing to engage.. I would take it to a smith if the springs don't work right.

Dan said what i accidentally left out about the springs in backwards. A buddy of mine had the light strikes when another friend installed his JP with the springs in backwards. It was light, but useless.

Mike

[chp5]

chp5,

I believe he is running a 2 stage trigger, if he takes off the backside of the hammer, the sear will have nothing to engage.. I would take it to a smith if the springs don't work right.

Dan said what i accidentally left out about the springs in backwards. A buddy of mine had the light strikes when another friend installed his JP with the springs in backwards. It was light, but useless.

Mike

Good catch.

[cking]

Even the JP spring kits sometimes fail to light surplus ammo. ie hard primers. Put a factory spring on hammer and problem will probably disappear.