AR Hiccups

[carinab]

So my new rifle has the hiccups....

It'll feed a few rounds, then not strip the next one and the bolt will close on an empty chamber. New mags so it's not a mag spring issue. I was running 55gr Wolf and when running someone else's hand loads (which were hotter), the malf changed. The bolt would lock back and a tap on the mag would result in it's dropping closed. Although it would cycle 20-25 rounds before coughing with the hotter loads where it would only cycle 2-3 with the Wolf.

Undergassed? Out of spec magwell or mag catch? Both?

[Dan Sierpina]

More information on the rifle itself would be good. Barrel length, gas system length, adjustable gas system, is the bolt carrier standard weight, type of stock, is the buffer lightened? All of these can contribute to the malfunctions, and help diagnose the problem.

Oh yes, what kind of mags?

By the way, it sounds like it's short stroking. Try lubing the bolt and carrier really well, to start. Check to see if the gas block may have moved forward.

Edited July 28, 2010 by Dan Sierpina

[Outsydlooknin75]

Check your buffer, if its a heavy, try going lighter.

[carinab]

The rifle...in .556

Magpul 20 round mags and DSG 30 round mags...but it malfed with my buddie's tried and true mags too...

I'm thinking it's two issues. Wolf is anemic but with the hotter hand loads, if I put stress on the mag (tugged or twisted), the bolt would lock open despite there being rounds left in the mag.

[carinab]

So much to learn.....

[BritinUSA]

Is this a new rifle ? Did you smother the bolt with slide glide ? Someone was shooting a new AR at the last open day at the local range and having the exact same issues. It was a very tight rifle (custom built) and all tolerances were tight. I got him to put some Slide Glide Lite all over the bolt and after that it worked like a champ.

[Graham Smith]

You might want to look at the mag catch and the mag seating. If the mags are not seating all the way, you can get problems like this.

[Merlin Orr]

Sounds like two separate problems. Lube and Mags.

I would suggest you never ever use a heavy lube... may work for a little while but does not last nearly as long and fills up with gunk.

Use Mobil One and keep the bolt lubed with special attention to the gas rings. Use a little bottle where you can squirt the oil directly into the two side by side holes in the bolt carrier over the rings.

Wetter is Better. Most AR problems are to little lube.....

I think Dan is on the money... Sounds like short stroking to me.

Try using P Mags and the torsional twist problems should go away.

Edit.. Just saw you were using P mags. IMO they are the best and If it won't run with them it is not a mag problem. Have your gunsmith recut the feed ramps.

Edited July 28, 2010 by Merlin Orr

[Dan Sierpina]

Take the upper off the lower reciever, check that the bolt catch snaps back down onto the lower( No mag in lower). With an empty mag in the lower, does the bolt catch engage the follower in the center of the magazine. Try it with a couple of pieces of empty brass, is the bolt catch near the rim of the brass? Does it lift off the reciever with the brass in the magazine? (It shouldn't on this one)

Remove the bolt carrier from the upper. Is the gas tube centered in the groove in the top of the reciever? Slowly inserting the bolt carrier should not have a "bump" where the gas tube enters the carrier key.

Again, check to see if the gas block has slid forward from the shoulder on the barrel. Does it look canted to one side?

As Merlin noted, lots of wet lube, no sticky stuff. Oil the gas rings.

[Beretta Lover]

could be a rifle length (long) buffer spring in a carbine stock

you might need the proper (short) carbine buffer spring

[Bryan 45]

My brother in law had a factory Colt that had feed issues once. Colt customer service diagnosed it over the phone. The mag catch was either screwed too tight or too loose. I don't remember which. Try backing the mag catch off one turn. If that makes it worse, tighten it up 2 turns.

[smokshwn]

+1 on shortstroking

Check the gas block to make sure it is installed straight and square over the gas port and is tight. If the block twists or is isntalled out of alignment it not only cuts off a little gas but there is also more resistance as the gas tube is now twisted in the bolt carrier. If it is adjustable open up the gas.

Lube......a good oil, mobil 1, miltec, fp10, slip2000 etc. use it generously.

let us know what you find out.

[Dan Sierpina]

Make only one change at a time. That way you'll find out exactly the problem and solution.

I'd start with the simple one....lot's of lube.

[George]

Sounds like the wimpy Wollf stuff has it short-stroking. Agreed on light lube like motor oil and using plenty of it. Check gas rings to make sure end gaps are not aligned (the ring gaps need to be spaced 120 degrees apart on assembly).

If the bolt latch is catching the bolt with snappier ammo and the mag is not empty, check the bolt latch to see if it's return spring is too light letting it engage by flopping while the bolt is cycling. The spring on the bolt catch should prevent the latch from catching the bolt carrier unless the mag is empty and follower is lifting the bolt latch into engagement.

[Junior]

Sounds like two separate issues? Do you have a pair of calipers? If so measure the wall between your mag well and your bolt catch it should be 0.093"... if it's too far back (less than .093") you can get the rifle to fail to hold the bolt open... also sounds like there is definitely a gas issue. How are your cases looking? Are the heads of the casings still in tact or is there any marring?

[Les Snyder]

Is the bolt carrier key tight?

[twodownzero]

Lots of lube really shouldn't be necessary to get an AR to run. When I was in the Army, we shot ours basically dry most of the time, and they didn't act up all that often.

[George]

Lots of lube really shouldn't be necessary to get an AR to run. When I was in the Army, we shot ours basically dry most of the time, and they didn't act up all that often.

I agree for purposes of tactical usage, but competition specific AR-15's are quite a different animal.

A military grade AR pattern firearm (especially the new M4 with short gas system) using military ammo has plenty of gas pulse to get the job done (way too much in fact) and running bone dry is very doable, even preferable in some situations (dusty, sandy and frigid). The heavy buffer and full power spring snap the bolt back in place with authority after the hefty gas pulse slams the bolt carrier fully to it's rear stop, good function juju all that l)

In a race rifle where lightened bolt carriers and adjustable gas blocks are used to minimize sight recovery time, minimizing friction with ultra slick lubrication schemas is a very good idea. Add wimpy ammo to the mix and you have real bolt-stopper going there. A race rifle wants to function reliably but also wants to minimize reciprocating mass movement of the rifle by the bolt carrier so a careful compromise has to be made.

But in general, a box stock A2 or M4 config rifle in good mechanical condition oughta' function just fine dry with snappy ammo (read 55gr shjt that moves downrange better'n 3000 fps in a 16"er here)

[twodownzero]

I'm not saying that lube isn't a good idea. Of course it is. An AR should run with a minimum of lube, though.

Competition-specific stuff is all fine and dandy, but there are no alibis in our sport and I'd rather have something that runs 100% than chase that last bit of performance at the expense of reliability.

[George]

I'm not saying that lube isn't a good idea. Of course it is. An AR should run with a minimum of lube, though.

Competition-specific stuff is all fine and dandy, but there are no alibis in our sport and I'd rather have something that runs 100% than chase that last bit of performance at the expense of reliability.

This sport is pretty much gun racing. Depends on whether your interests are in Formula One (Open) or Stock/Modified (Limited/Tactical) style racing as to how far you may feel the need to tweak the gear for course

A front line competition dedicated firearm with every good tweak available can be a very, very reliable one too IF you have it sorted out well and know/respect the maintenance schedule that is required for that specific vehicle.

But, if I ever needed a mad moment rifle, you can bet it would be the stocker A2 carbine with the conservatively set JP trigger that I would be grabbin' outa' the safe, end of story.

[dsmw5142]

Check the land surfaces of the bolt, lugs and mating races on the upper receiver for nicks, gouges, burrs or rough surfaces. If there are any remove/smooth them with a fine stone or file.

Check the gas seal between your gas tube and carrier key by removing the bolt from the carrier. Remove the charging handle and slide the carrier in to the weapon feeling for any drag where the key comes in contact with the gas tube. You may need to very gently bend the gas tube to the point that you feel little or no drag.

Check your upper buttstock bolt. I have seen some upper buttstock bolts made that did not have holes drilled through them. These will definitely cause a short cycling problem since the air in the buffer tube has no place to escape. This will prevent the bolt from cycling fully to the rear, in effect turning the buffer tube into a pneumatic piston, compressing the air and not letting it out.

If it's a gas leak issue, I would look very carefully at your carrier key. Not only are they a source of binding, but a bad key to tube fit is a common source of excessive gas leakage.

Check that your magazine lips aren't colliding with your bolt carrier or pinching the portion of the bolt that rides between them.

Edited August 1, 2010 by dsmw5142

[carinab]

Thanks!!! Lots of good suggestions! Which I happily passed on the mfg since they will be getting the rifle back to work on. Eventually I may be savvy enough to fix this sort of thing on my own....but in the meantime, I'll drive 'em and let the mechanics fuss under the hood - as it were! I'll let you know what they figure out.