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Discussion Starter · #1 ·
Rifle: Bushmaster XM15-E2S 16" Carbine (not M4 model), bought used, very well maintained, 0 malfunctions so far.

Ammo: Federal ballistic-tip 55gr, Remington UMC FMJ 55gr, and Wolf steel-case FMJ 55gr.

As the title says, I hand-cycled 3 different types of rounds (all factory-load 55gr) through my Bushmaster carbine just a few minutes ago. Every round cycled smooth as glass, but I still have some concerns:

1. Primers: Every round I cycled through the rifle has large dimples left in the primers! I have examined the primers of cartridges I have fired in the past and the dimples left in the hand-cycled rounds appear to be almost as large/deep as the dimples left in the fired casings! I asked my roommate for permission to hand-cycle several "new-in-box" rounds of the same type through his very very old DPMS (I think it's a DPMS...) carbine, and there were no dimples left in the primers, even after 3 cycles of the same round using both my Bushmaster magazine as well as his piece of s**t aftermarket magazine!! Is this normal?! Or is my rifle almost firing every round I cycle through it??!! I am seriously freaking out about this!! I disassembled the bolts and examined the firing pins of both my rifle and my roommate's rifle. Nothing seems out of the ordinary, no severe wear on either, no obvious difference. Unfortunately I can't get a good look at the feed ramps/bushings unless I screw the entire barrel off, which I don't want to do without professional assistance.

2. Bullets: Every round I hand-cycled through my rifle now has several gouges on the bullets front to back in a "screw" pattern. Looks to me like the linear motion of the bolt -vs- feed ramps combined with the circular motion of the bolt is causing the "screw" pattern gouges on the bullets. But why are the gouges so deep? Something wrong with the bolt or the feed ramps?

Is this normal?

ALSO, would I benefit by upgrading to TRUE M4-style feed ramps? I've heard so many positive things about the reliability of "true" M4-style feed ramps that I'm very tempted to make the investment regardless of whether I need it or not. After all, this is my current SHTF rifle, so reliability is more important than anything :D


Any, and I mean ANY input on either of my questions is greatly appreciated! If there is a problem, what is the solution? Don't worry, I don't care about cost, I'll replace whatever is necessary. Hopefully there is no problem and all of my concerns are normal, but I'd like to know for sure from people who have real talent and knowledge of the AR platform.

Thanks in advance!
 
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Discussion Starter · #2 ·
Well the firing pin the the AR is a freefloating unit. When the boltcarrier goes home and the bolt locks the pin probably does lightly hit the primer.

Try this. Take your roommates DPMS firing pin and place it into your AR. Cycle some rounds again and see if you get the same problem. If you don't then most likely your firing pin was mauf. out of specs.
 
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Discussion Starter · #3 ·
Well the firing pin the the AR is a freefloating unit. When the boltcarrier goes home and the bolt locks the pin probably does lightly hit the primer.

Try this. Take your roommates DPMS firing pin and place it into your AR. Cycle some rounds again and see if you get the same problem. If you don't then most likely your firing pin was mauf. out of specs.
I'll give that a shot tomorrow. Thanks.
 
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Discussion Starter · #4 ·
If you're getting screw pattern scratches on your brass, you have a fouled or rough chamber. Take a .40 cal bore brush, clean the crap out of it, and then polish the chamber with a cloth of fairly tight fit to your chamber and some lapping compound/jeweler's rouge.

Make sure you clean all the polishing compound out of the chamber before you fire it.
 
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Discussion Starter · #5 ·
Like Jeep says, your firing pin may be too long, out of spec. Dimples are normal in rifles with free float pins, but is usually limited to a slight dimple. All of mine do this.

Could you post pictures on what you are talking about?
 
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Discussion Starter · #6 ·
120mm said:
If you're getting screw pattern scratches on your brass, you have a fouled or rough chamber. Take a .40 cal bore brush, clean the crap out of it, and then polish the chamber with a cloth of fairly tight fit to your chamber and some lapping compound/jeweler's rouge.

Make sure you clean all the polishing compound out of the chamber before you fire it.
The scratches are all on the bullets, not the brass. It's weird. I'll go ahead and do what you said here, I'm sure it will help.
Bidah said:
Could you post pictures on what you are talking about?
I tried several times last night to take pictures of both the primers and bullets but I can't get clear pictures of things that small on my crappy little camera.
 
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Discussion Starter · #7 ·
You should snag a Go-No-Go gauge and see if it passes. Alternately rather than just taking the FP, try the whole BCG from your roomies rifle and see what comes from that. Regardless, point down range and away from anything you don't want destroyed, I think you have a very serious issue here.

As for the feed ramps.. yeah they help, but more for select fire weapons. Now I will admit that in my unscientific observations, my AR's with the M4 Feed Ramps function more reliably than the one upper I have without (a bushy XM15ES-2). I haven't done any "serious" testing to prove or disprove this for my weapons. Though if I remember the next time I go out, I'll take the Bushy upper with me and give it a couple of tests mags and see if anything is different.

If you're asking if you should run out and get an upper with them.. well that's your money man.. I can't give you a real good reason to or not to. Maybe Pat will pipe in on this one. I'm far more concerned about the primer strikes.
 
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Discussion Starter · #8 ·
The scratches are all on the bullets, not the brass. It's weird. I'll go ahead and do what you said here, I'm sure it will help.I tried several times last night to take pictures of both the primers and bullets but I can't get clear pictures of things that small on my crappy little camera.
Compare your bullets to the rifling. It's "possible" that you have a bad chamber. Also make sure that the bullets aren't being set back.

Good news: If it's a bad chamber, a Ned Christiansen's chamber reamer can fix you up, pronto, for pretty cheap.
 
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Discussion Starter · #9 ·
Interesting timing, I was just reading an article (this one) and toward the bottom it talks about the free-floating firing pins on the AR. It says that a damaged or protruding pin can cause a round to fire when the bolt closes:

Q. I chambered a round in my AR and then unloaded it later. The primer has a small dent in it, apparently from the firing pin. Should I be worried about this? Won't that cause a slam-fire? Should I switch to a Titanium firing pin?

A gas-operated semiautomatic operates on gas bled from the barrel. This gas is channeled to the bolt operator, which blows the bolt open and ejects the spent shell casing. A heavy spring then returns to bolt carrier to the closed and locked position on the next round. In the case of weapons with free floated firing pins (SKS, AR-15, etc.), the inertia of the firing pin carries it forward and it strikes the primer as the bolt closes. (The "slam"). Generally this will dimple the primer and leave a small indent. This isn't anything to worry about as primers for centerfire .223 and 5.56mm are pretty "hard" and aren't likely to be set off by this impact.
Early M-16s had a problem with slamfiring because of the firing pin design. Eventually Colt redesigned the pin to be lighter and therefore carry less energy into the primer. Slam-fires are pretty rare in modern ARs provided they are well maintained but they can be caused by a broken or protruding firing pin, foreign matter on the bolt face that is carried into the primer, foreign matter in the firing pin assembly that prevents it from retracting sufficiently, overly soft or poorly seated primers, or other malfunctions. As for titanium firing pins, they are probably not worth the headache. Indeed they are lighter and may reduce the already small chance of slamfires, but titanium also does not handle impacts well and can be brittle. A broken or cracked titanium firing pin is a lot more likely to cause a slamfire than a regular pin.
It should be noted, however, that repeated chambering of the same round increases the likelyhood of a slamfire, or of a hangfire (slow to ignite) or misfire (failure to ignite) due to damage to the round's primer. If you chamber and clear your rifle on a regular basis, make sure you change out the top round so that you don't rechamber the same round more than once or twice.
Finally,
always point your rifle in a safe direction when chambering live ammo. As with any machine, there is always the possibility that something will go wrong and the round will fire. If you are chambering your home-defense gun, ride the charging handle and use the forward assist to lock the bolt forward, always keeping the muzzle pointed in a safe direction.

Firing pin redesigns.
Colt eventually adopted the No. 2 design.
Maybe you have an excessively heavy firing pin?

Sorry, I'm about as new to AR rifles as can be. I was just reading up and noticed the coincidence because I had just learned about the free-floating pins.
 
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Discussion Starter · #13 ·
Personally, I'd clean the chamber really well with a brush as someone else has already advised, take the bolt apart and clean/ inspect the firing pin and if it kept doing it, take it to my (good) local gunsmith for inspection.
 
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Discussion Starter · #15 ·
quit hand cycling live ammo ;)
all you are going to do is create worries and problems with bullet setback along with the possibilities of a ND/AD :(
 
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Discussion Starter · #16 ·
I was having the same problem. Took (2) 10/20 round Pro Mags my rifle (600) rounds of mixed Wolf Steel Case and Rem from Wally World and needle nose pliers to the shooting bench.

Had several FTF issues, double feeding, last round popping out

After every occurrence I tweaked the feed lips on the magazines till it the problems were gone 100%. Problem solved, it was the magazine feed lips all along.

Taken from Wiki:

"An additional point of concern in the design is the inertial firing pin, a lightweight firing pin rides in a channel inside the bolt unrestrained, when the bolt locks forward during loading, the firing pin typically rides forward and impacts the chambered round's primer. In military specification ammunition and quality civilian ammunition, this is not normally enough to fire the round and only leaves a small "ding" on the primer, with more sensitive primers or improperly seated primers, this can cause a slamfire during loading."
 
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Discussion Starter · #17 ·
I'm using a titanium firing pin and still get little dimples. I have polished my feed ramps, though, and don't seem to have any accuracy problems. I'd think that deep scratches on the bullets would affect accuracy.

You don't have to take the barrel off to look at the feed ramps. Just take the upper off of the lower.

If the previous owner shot much lacquered Wolf ammo through it, I'd think that the chamber's fouled and could use a good scrubbing. A rough chamber would exacerbate the dimpling of the primer.
 
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Discussion Starter · #18 ·
Like I said 2 posts up.........QUIT hand cycling live ammo !

This was taken from the Ammo Oracle

Q. I chambered a round in my AR and then unloaded it later. The primer has a small dent in it, apparently from the firing pin. Should I be worried about this? Won't that cause a slam-fire? Should I switch to a Titanium firing pin?
A gas-operated semiautomatic operates on gas bled from the barrel. This gas is channeled to the bolt operator, which blows the bolt open and ejects the spent shell casing. A heavy spring then returns to bolt carrier to the closed and locked position on the next round. In the case of weapons with free floated firing pins (SKS, AR-15, etc.), the inertia of the firing pin carries it forward and it strikes the primer as the bolt closes. (The "slam"). Generally this will dimple the primer and leave a small indent. This isn't anything to worry about as primers for centerfire .223 and 5.56mm are pretty "hard" and aren't likely to be set off by this impact.
Early M-16s had a problem with slamfiring because of the firing pin design. Eventually Colt redesigned the pin to be lighter and therefore carry less energy into the primer.
Slam-fires are pretty rare in modern ARs provided they are well maintained but they can be caused by a broken or protruding firing pin, foreign matter on the bolt face that is carried into the primer, foreign matter in the firing pin assembly that prevents it from retracting sufficiently, overly soft or poorly seated primers, or other malfunctions.
As for titanium firing pins, they are probably not worth the headache. Indeed they are lighter and may reduce the already small chance of slamfires, but titanium also does not handle impacts well and can be brittle. A broken or cracked titanium firing pin is a lot more likely to cause a slamfire than a regular pin.
It should be noted, however, that repeated chambering of the same round increases the likelyhood of a slamfire, or of a hangfire (slow to ignite) or misfire (failure to ignite) due to damage to the round's primer. If you chamber and clear your rifle on a regular basis, make sure you change out the top round so that you don't rechamber the same round more than once or twice.
Finally, always point your rifle in a safe direction when chambering live ammo. As with any machine, there is always the possibility that something will go wrong and the round will fire. If you are chambering your home-defense gun, ride the charging handle and use the forward assist to lock the bolt forward, always keeping the muzzle pointed in a safe direction.
 
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Discussion Starter · #19 ·
I was having the same problem. Took (2) 10/20 round Pro Mags my rifle (600) rounds of mixed Wolf Steel Case and Rem from Wally World and needle nose pliers to the shooting bench.

Had several FTF issues, double feeding, last round popping out

After every occurrence I tweaked the feed lips on the magazines till it the problems were gone 100%. Problem solved, it was the magazine feed lips all along.
On mixing Wolf and brass, it is generally considered a bad idea to shoot Wolf and THEN brass. The steel cases do not expand like brass, which allows residue to build up in the chamber, which the follow-on brass cartridges expand into the crud, and possibly not extract.

Just a tip.
 
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Discussion Starter · #20 ·
I would like to add....When I was in Iraq, I reused the same round that I chambered over and over and over again and had no problem.

The only way I did not reuse that same round is if I lost it when i cleared my weapon at the game or i shot up some ammo when I was in sector.

I would say I’ve used the same round 10 times to load. There was a dimple in the primer, I really did not care though. I always pointed in safe direction (clearing barrel) to clear my weapon.
 
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