AR-15 carbine just started to short stroke

[Float Pilot]

This Bushmaster carbine has worked for years. I was shooting it this summer with the old 11.5 inch barrel and suddenly it started to not pick up the next round in the magazine.
So I changed mags,
I went through all 15 of them and it would not pick up the next round.
But it would extract and eject 99% of the time.

Next I cleaned the heck out of it. Still no dice.

Checked the gas key and it is fine,

Then I changed the upper to a 16 inch barrel and it continues to do the same thing.

I wonder if the buffer springs do weird things after 15 years or so...???

Anyway I just changed the buffer and spring, but I can't get out to shoot today. I have another carrier to try as well...

Verrrwwweee interesting......

 

[ants]

Lubricate it? I know it sounds dumb, but it's the most common thing.

Disassemble the bolt, inspect everything (especially gas rings), reassemble with new rings if necessary. If it hasn't been cleaned and lubed in 15 years the gas rings might be frozen in hard black crud.

Check the gas tubes on both uppers. Make sure they are free, make sure they are properly pinned at the front, make sure they engage the gas key properly.

Make sure your ammo is good.

 

[Yosemite**Sam]

I'll second the lube it. Clean the area of the bolt carrier where the gas rings engage. Often that area gets carboned up. With the bolt carrier removed from the rifle take the bolt and plunge it in and out of the bolt carrier (don't get too excited now) to see if the rings are dragging. If it's dry inside the bolt may be dragging and not unlocking properly. Lube it up!

 

[Evil Monkey]

If it's short stroking after working perfectly for a long time then the problem can't be the buffer spring. Springs only get weaker over time. I think the gas rings on the bolt are wearing out and may need replacing. It can also be a gas key issue, being loose and such. Or it just needs lube like others have said.

 

[Float Pilot]

If it hasn't been cleaned and lubed in 15 years the gas rings might be frozen in hard black crud.

I clean very rifle in the house on a quarterly basis when they are not fired.
Every rifle which has been fired gets cleaned and lubed within 24 hours.

This rifle has been shot and cleaned over that 15 year time period. The rifle's bolt and carrier are now slick with light winter oil .
During the summer / fall malfunctions they were slick with Mil-Tech oil.

The bolt carrier and buffer spring move very smoothly and there is no binding or gritty feeling.

The ammo used is stock M193 55 grain FMJ and M855 green tip ball.

The carrier does not have any carbon build up and is nice mirror shiney down in the area where the rear of the bolt and the gas rings live.

While the gas rings look nice, they may in fact be finally worn down enough to let a bunch of gas blow by. Since I totally cleaned it every 60 rounds, it may have been difficult to see any odd carbon build up after those short shooting sessions, back when it was a patrol car trunk gun being shot every other month.

I will check the gas tubes on both uppers to make sure they both did not suddenly do something weird..

The gas key is solid and I properly staked it 15 years ago since Bushmaster did not.

The weird thing is that this happned all of the sudden and did not slowly build up to a total malfunction.

 

[jerkface11]

Could something be wrong with the trigger group causing the hammer to drag on the carrier?

 

[taliv]

that is curious

if you knew enough to properly stake the gas key 15 years ago, i assume you also know not to stick pipe cleaners in the gas tube, as an obstruction in the tube is what i would suspect. (edit: and in any event, it's unlikely that wouldn't be the problem on both uppers)

check around the gas block for black stuff to see if there's excessive leakage. (edit: again, obviously not the problem unless it's happening on both uppers)

check your gas rings by fully extending the bolt in the carrier and standing it up on the bolt. if the weight of the carrier overcomes the friction of the bolt rings and slides down, then you need new rings.

you using the same BCG with both uppers you mentioned?

 

[coyotehitman]

2 uppers with 2 different BCG's or 2 uppers with the same BCG?

1st, I would check to make sure the gaps in the gas rings are 180 opposite each other.

2nd, Swap out the rings.

 

[Float Pilot]

Same bolt and bolt carrier for both uppers. I changed the uppers just to see if it made any difference.

This carrier is a sporter style that came with the gun back in the late 1980s. Gee I guess its really darn near 20 years...

Well anyway I have another military style carrier arouind here some place and I will try that. It is a little heavier and the carrier drags on the hammer instead of the firing pin.

The ring gaps are 120 degrees apart.. But they do no offer much resistance while engaging the interior walls of the bolt carrier... So I will order another set.
They are not all that easy to find up here.

 

[Maelstrom]

Might be a slightly weaker batch of ammo.

 

[taliv]

float, sounds like rings are your problem. bravocompany sells a good bolt upgrade kit/parts.

 

[J. Jay]

Spend $22 and replace the worn parts on your bolt. You been shooting wolf ammo?
http://www.commandsurplus.com/product_info.php?products_id=71261&cPath=7184

 

[Float Pilot]

You been shooting wolf ammo?

Nope, I don't let it on the property.

 

[Al Thompson]

I'm betting buffer spring.

 

[RyanM]

The gas key is solid and I properly staked it 15 years ago since Bushmaster did not.

I was going to say, Bushmaster is notorious for crappy staking, and keys that shoot loose after a couple thousand rounds. Sounds like it's the rings, if there isn't a fair amount of resistance when moving the bolt in and out.

But, have you taken the buffer out and checked everything? Maybe something ended up in the tube somehow, or the buffer fell apart.

 

[J. Jay]

My old bushy did that too. One day just started short stroking randomly. Rebuilding the bolt fixed it.

 

[Al Thompson]

OK, if it does it on two different uppers, I'm even more certain it's the buffer and probably the spring.

not pick up the next round in the magazine.


Classic spring failure - esp. as it's firing and extracting properly.

 

[Timradcliffe345]

Sell it - Get a Colt

 

[Float Pilot]

Who sells AR bolt parts without ripping you off for shipping? This internet shopping stuff is still kinda new to me. I my past life, our parts came from the lowest bidder by the truck load.

 

[RyanM]

http://www.operationparts.com has relatively low shipping via USPS.

Very rare nowadays. I just got a package right now (ordered from elsewhere), that I paid $15 S&H. It says 20 cents on it!

 

[Al Thompson]

Rifle working yet?

 

[Brian Williams]

Float, did you check with Wild West Guns, they might have some AR parts, do a search on the net or go to TFL and look for Wildalaska

 

[Jeremy2171]

Quick check fot the bolt rings...

Take complete carrier assy out and fully extend the bolt from the carrier. Then stand the carrier up on the face of the bolt...the carrier should stay "up" supported by the tesion of the bolt rings. If the carrier "drops" replace the rings.

 

[rob_s]

Jeremy's test is a good one. It's worth doing every time you clean the gun.

 

[Float Pilot]

I ordered two sets of gas rings on November 28th. One set is supposed to be the spiral type one piece. I want to see how well that works.

HOWEVER, eight days later nothing has arrived yet. Glad I paid extra for the fast shipping.

Of course I asked for replacements for the faulty Warne Rings (for the 6.8 AR)a few days before that and nothing has shown up yet either....