AR 15 bolt catch problem

[TonyAngel]

The muzzle is 12:00. If I interpret what you are saying correctly, then it is kicking the brass behind you. It sounds like the ammo is maybe a bit weak, you're running too heavy a buffer or you have a gas leak or misaligned gas block or a combination of all three.

Still, I'd try factory ammo. If that doesn't do it, then get rid of the bad lever. Or do it the other way around.

If you're new to reloading, you really can't go by what is published in a manual. The only way to know what your ammo is doing is to chronograph it. Although there are some exceptions, loading ammo to a few grains under a published max doesn't even come close to factory M193 or the like. This is why loading manuals tell you to use the data as a reference only. Your start low, and work your way up watching for pressure signs.

 

[Taurus 617 CCW]

Do you have a standard buffer or a "hydraulic buffer" installed?

http://www.midwayusa.com/product/38...e-hydraulic-recoil-buffer-ar-15-carbine-3-1-4

If you have a standard buffer then I would start going through the process of finding a gas leak. One place that is often overlooked is the interface between the gas key and the top of the bolt carrier. It can be very minor. If that checks out, I would suspect that the gas hole in the barrel is involved. It may be misaligned to the gas block or undersized. I have seen both.

 

[awgrizzly]

Is the AR brand new or bought second hand? The speed of the powder burn rate is as or maybe more important than power of the load. If powder burns too fast the ooomph (pressure peak) is lost by the time the bullet passes the gas hole. If not the MAD you may consider how well the bolt carrier was lubed, some need to be run wet. Otherwise probably the gas system, like:

Loose gas key or misaligned gas tube. If new it's a manufacture flaw. If used there should be signs of wear in movement of barrel or gas block.

Check gas key for tightness and look at mouth on key for damage or wear on one side. You can move bolt carrier without the bolt in and out to feel if it makes contact with the gas tube. A problem with alignment can indicate a bent tube, a misaligned gas block, or loose barrel nut.

Pull the hand guard and check the gas block. Look for signs that it has moved and/or gas leakage between it and the barrel. Try to eyeball the center of where the gas tube enters the gas block to see if it seems to align along the center of the barrel back to where it enters the upper receiver (you may not be able to detect a problem this way but it may be obvious... worth a look). If the gas block is held in place by set screws check to see if the set screws are tight. Look for signs of movement.

Check where the gas tube passes through the depression or hole in the barrel nut... if it looks wedged to one side it isn't aligning with the gas key... you should have damage at the key and end of tube. This would be a fabrication problem if the gun is new, but if old this usually is a problem with non-pinned gas blocks moving or a barrel nut turning, often due to vertical grips or bi-pods attached to bottom of hand guard... and then there's Bubba.

 

[Tex4426]

Stadard buffer..shooting in the morning...ill start with the bad lvr

 

[Tex4426]

The brass lands at 4 oclock from the muzzle...if i old my right hand straight out at 90 degrees. I would be pointing at most the brass..a few would be 10 degrees farther or 100 degrees

 

[madcratebuilder]

To do any meaningful troubleshooting on this AR you really need to #1 remove the BAD lever and #2 shoot with some M193.

The failure to lock on the last round could be the hand loads, the BAD lever, or the combination of both. I would check this before chasing gas system bugs.

Using the brass ejection pattern to diagnose problems is a good aid but it's not a hard and fast rule. There are too many variables that effect ejection patterns.

 

[Tex4426]

Un fortunantly i went shooting and grabed the wrong tool to remove the lever..out of the 10 time i fired the last shot the bolt held open on one..so ill have to try again this week...i went to the local gun shop and picked up some ammo got a box of hornady superperformance match 75g bthp because i wanted to try some heavier bullets....so far the gun shoots terrific just want to get this bolt catch issue takin care of

 

[Tex4426]

Also i dont usually buy factory ammo so who makes m193 and y should i use that to test?

 

[kwelz]

M193 is the standard .mil training round. It is pretty much the standard when it comes to 55 grain AR ammo. It won't be under or over powered. As for who makes it there are a number of companies. Federal being one.

http://www.ammunitiontogo.com/advan...193&osCsid=dit1h4cb0ugf4vafk8ljlbpt94&x=0&y=0

 

[hentown]

4 o'clock is just about perfect. Probably nothing wrong with that Predator Pursuit upper, assuming that it was assembled @ RRA. Probably the B.A.D. lever. I use a variety of mags in my various ARS, inclucing Thermolds, G.I. mags of different manufacture, and P'mags. I've never had the bolt fail to lock back after the last round, and I've shot everything from mild to pretty stiff loads.

 

[toejamm]

Receiver Extension

I had the same problem when I installed a new receiver extension tube and stock kit on one of my AR's. I installed it on two others to be sure it wasn't my rifle. Same problem, bolt would not hold fully open on the last round.

Problem was that the receiver extention tube was fabricated one or two turns too deep, and the spring didn't have enough room to compress fully and the carrier would not cycle far enough away from the receiver to lock the bolt. I couldn't back off the tubea turn or two because the detent would pop out.

ATI sent me another tube which was longer and problem solved.

Potential solution - Back off the receiver extension tube one turn or two if possible. All you need is the wrench which is inexpensive (8 to 12 bucks).

The castle nut may be staked, so you may have to drill it out before loosening the nut.

Good luck.

 

[Tex4426]

I built tbe lower myself..i use loctite ...i didnt stake it down for this reason right here in case i have to take it off

 

[toejamm]

Tex4426

Even if you did use locktite, you could try and back off the receiver extension tube.
Of course it is your call, but your problem seems very similar to the one I had.

Two quick questions:
1) What make tube, spring and buffer did you use in your build?
2) Could you try another tube that you or someone else has lying around? even an old A2 stock?

Good Luck.

 

[Tex4426]

To be honest idk what brand..i dont remember what the package said..i would assume ATI or UTG since it was only like 30 bucks..ive been considering buying a new one if i find that is the problem

 

[mastiffhound]

I had the same problem, it was the CAA Countdown mag. I switched to my Colt, Magpul, Tapco, and Bushmaster mags. The problem disapeared. What brand of mags are you useing? When in doubt check the mag. Same problem came up with my buddy's AKM. He switched from the cheapo surplus mags to New Tapco mags, his problem went away. Pick up some Colt or other aluminum GI mags. They are the standard. Just between my Magpul and Tapco their is a diference in the mag followers.

 

[Tex4426]

Magpul pmags is my primary mag

 

[Tex4426]

Right now i believe its the bad lever or rrciever tube

 

[toejamm]

Tex4426

Since my episode, I've purchased two Vltor Emod stock kits for two other of my AR's.

If you find that it is indeed, the receiver extension tube, I highly recommend the Vltor products. A bit higher priced than others, but worth it IMO.

I hope it works out for you.

 

[Tex4426]

i ordered a new buffer tube from midway...its a DSA and had all 5 star reviews so we will give it a shot...i had no choice to order because i messed mine up taking it out...for whatever reason i used red locktite and messed up the threads because the sling plate sliped and basically flattened the thread...only at midway can i go to buy a buffer tube and spend 200 bucks

 

[AK103K]

$25 for the stock, and $175 in shipping?

 

[Tex4426]

no.no no...went on their to get 1 item bought 7 items

 

[DBR]

One other thing to look at: on several brand name lower parts kits I have had an issue with Pmags interfering with the bolt hold open movement.

Put the empty Pmag in the bare lower (no upper) and look at the rear of the mag where the bolt hold open is. The Pmag has more material on the spine of the mag than a milspec mag and I have had this interfere with the bolt hold open movement.

My solution was to remove the bolt hold open and remove enough material that it didn't interfere but you can also relieve the area on the Pmag that causes the problem.

 

[awgrizzly]

There are a lot of things that can cause this problem. The significant part to me is that the bolt carrier will lock open OK when the carrier is pulled back with the charging handle. That indicates that the carrier may not be traveling far enough to the rear when fired. However, something others here might answer for me, if that is the case would the carrier be able to catch the rear of the cartridge upon closing. Not far enough back to lock open yet far enough to load the next cartridge... the difference must be minimal.

In the end the OP will figure out the problem, but to me it's an interesting exercise in diagnosing a malfunction, a worthy learning process.

 

[Tex4426]

I will check and make sure the mag isnt interferring when i get home later...didnt even thunk of that

 

[Desolo]

What LPK did you use?

Ive heard that DPMS/CMMG Bolt catch's sometimes have trouble with magazines other then USGI types due to being a tad shorter... They work fine when done by hand but the rifle wont click it when cycling with certain magazines, and Id imagine that any added weight on the bolt catch may make this worse....

Just a thought!