Hello Guys,

Long time reader, first time poster.  I bought a Bushmaster XM15 ES A2M4 last month (used) and was able to fire it for the first time yesterday.  I had some Winchester .223 ammo from Walmart and I just recently bought 500 rounds of Federal XM193 5.56, which from what I've read from here, is the one of the best rounds to fire.  Well wanting to save the best for last, I fired all of the Winchester ammo first, about 120 rounds.  It fired flawlessly without a single problem.  I then loaded up about 20 rounds of the XM193.  After shooting about 10 rounds, the magazine would not feed the next round into the chamber.  The bolt would ride over the top of the next round and put a crease in the brass.  At first I thought it was the magazine, so I tried a couple of others.  The same thing happened, except after only about 5 rounds.   Needless to say, I was pretty pissed.

One thing I noticed was that the brass was not clean and shiney like the Winchester brass.  It actually felt a little sticky and looked dirty.  I tried to clean it, but it didn't help.  Has anyone else had problems like this?  Before I took the Bushy out, I did field strip it, cleaned and lubed it.  Would it help if I lightly lubed the brass with some gun oil before loading up the mags?  I'm stumped.   I would hate to think that I wasted my money on ammo that is so highly regarded on this forum.  Thanks for any help/suggestions.

Don't even consider lubing the brass.  That will cause more problems than it solves.

Brouhaha nailed all of the valid points that's for sure.


What kind of Mags are they?

Are you running the rifle dry? Wet? Dirty?

I'd look at the Gas Key.  You shouldn't be getting Short strokes with HOTTER ammo unless there was a problem like the Gas Key.

Ring alignment shouldn't make a shit bit of difference.

Brouhaha: +1

Is the barrel chambered for 5.56?  Could be someone replaced the barrel before you got it.

You're getting good advice in this thread, I'm not able to help in that area.

If ultimately you are unhappy with the ammo, you haven't wasted money completely.  I'm sure me or someone on here will be happy to pay you are fair price for the unused portion.  That's how I can help.

Note that XM193 is most likely hotter than the Wincheter stuff you bought at Walmart.

Quoted: It sounds like either your mags aren't feeding properly or you're getting short strokes. Make sure your mags are clean.

Alternatively, if the bolt carrier group is cycling faster than the magazine can elevate the next round, you can get malfunctions like this.   For example, if the bolt is smashing the "top" side of the next round with the case head under the bolt, it can be due to the bolt returning before the rear of the case is elevated by the mag.

You can rule out short-stroking by firing with one round in the magazine. If the bolt locks back each time, then the gun is not short-stroking.

The fix for too high bolt velocity compared to the magazine feed rate is to (in order of cheapest to most expensive): make sure your mags are in good shape and have new, strong, springs; replace the buffer with a heavier one; replace the bolt carrier with a heavier one; or decrease the gas pressure.

-z

Quoted: One thing I noticed was that the brass was not clean and shiney like the Winchester brass.  It actually felt a little sticky and looked dirty.

Q. What is with this goo and the dings on my Lake City Rounds?

A friend and I had a similar problem and it apprears to be related to a higher action cycle speed do to the hotter XM193 round.  Our rifles functioned perfectly with less intense loads, but would not lock the bolt back after the last round and occasionally not feed just as you have experienced.

I was able to isolate the problem to soft magazine springs.  The fix was a Wolff magazine spring.  It provides greater tension on the follower-I could feel the difference compared to my older springs.  This completely solved the problem for me.  My buddy changed mag springs and also added a heavier action (recoil) spring to solve the problem in his rifle.   I have heard of using a heavier buffer as a cure too.  IIRC Wolff is at gunsprings.com.  The are pricy, but to me it is a cheap investment in reliability.

If its a short stroking problem it is MOST likely TOO much pressure from the gas tube.  Theres a BIG ARTICLE on it ill see if I can find it later and post a link.  The 5.56 is infact hotter and therefore builds more pressure causing the bolt to to go back but still while the case is expanding in the chamber.  A rifle team buddy of mine had the same problem with his new DPMS AR.  He tried my buffer spring my lower my bolt and even tried to tighten his gas block cause he thought it was a lack of pressure problem.  He read the article on short stroking and loosened the gas block to allow a bleed off of pressure and found it fixed the problem.  

Thanks guys for all of the positive feedback.  I can't tell you how much I appreciate it.  After reading each of your replies, I think the concensus is the magazines/springs.  I don't believe it is short stroking because the bolt would lock back every time after the last round was fired (even with the XM193).  Zak-Smith and 03Springfield described exactly what I experienced.  I used the factory Bushmaster 20 round mag as well as some 30 round mags made by Adventure Line Manufacture Co.  I've never heard of the latter magazines, but they came with the gun.  I'll check into replacing the springs or even junking these and getting some reputable magazines.  Hopefully this will solve the problem.    If not, MrMurphy mentioned loosening the gas block.  Hopefully it won't come to this, but in the event that it does, how do you do this?  Thanks again, guys.

Quoted: Thanks guys for all of the positive feedback.  I can't tell you how much I appreciate it.  After reading each of your replies, I think the concensus is the magazines/springs.  I don't believe it is short stroking because the bolt would lock back every time after the last round was fired (even with the XM193).  Zak-Smith and 03Springfield described exactly what I experienced.  I used the factory Bushmaster 20 round mag as well as some 30 round mags made by Adventure Line Manufacture Co.  I've never heard of the latter magazines, but they came with the gun.  I'll check into replacing the springs or even junking these and getting some reputable magazines.  Hopefully this will solve the problem.    If not, MrMurphy mentioned loosening the gas block.  Hopefully it won't come to this, but in the event that it does, how do you do this?  Thanks again, guys.

If too high BCG velocity is the problem and new mag springs don't help, try a heavier recoil buffer.

-z