help - bolt not locking open on ar15

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dghboy315

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Feb 1, 2003
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rockville, md
my ar15 bolt will not lock open when the gun shoots a mag dry. i tried cleaning it and oiling it w/ no change. it just started happening one day. it has happened w/ 5 different mags over 200 rnds. it happens w/ both new wolf polymer 55gr and federal lake city xm193 55gr. it happens every time. but other than that problem, the gun still shoots great.

the only thing i do notice is that there is a slight burr on the top of the bolt catch inside the gun. could this be the problem? it's a very small scratch.

anyone have any suggestions? thanks
 
Have you got another AR to compare yours too? It may be that the slight burr on the bolt catch is where metal used to be and something has broken off. Also take a look in your lower to see if anything that might have broken off ended up there... small bits of metal in there can bind up the fire control group.

The bolt catch is often a cast part, especially on cheaper parts kits, and they have been known to fail on occasion.

Not being able to look at it, it would be tough to say; but if I was going to bet on it, I'd guess that the bolt catch needs to be replaced since it is happening with a variety of mags/ammo and the gun is still cycling well.
 
dghboy315,

The rifle may be 'short-stroking'. This can be caused by a number of things. To determine if the bolt is cycling far enough to lock-back, perform the following test.

Go to a safe location to shoot. Load one round in the magazine. Aim the rifle in a safe direction, if necessary, utilize a rest or bipod to steady the rifle. With you left hand, apply pressure to the bottom of the bolt catch ( just as you would to manually lock the bolt open ) and fire the rifle. The bolt should lock open, if it cycles fully. If not, the rifle is short-stroking.

If it locks during this test, the problem is realated to the magazine, bolt catch, or bolt. If not check for a loose or damaged carrier key, fouled or obstructed gas tube/port, wrong recoil spring, or a mechanical obstruction preventing the bolt carrier from stroking freely.

I hope this may help you determine the source of your problem.
 
I don't have an AR, so I might not know what I'm talking about, but could it be a problem with the follower(s)? Do your mags have the green followers in them?
 
The bolt should lock open, if it cycles fully. If not, the rifle is short-stroking.
Click to expand...

The problem with this test is that if the bolt catch has broken, the bolt will still not lock. Short-stroking of any kind usually leads to other malfunctions such as failure to eject, failure to feed, stovepipes, failure to extract, etc. It would be extremely rare for a gun to feed and fire 100% while having a short-stroke problem severe enough that it will not lock the bolt back on an empty mag.

However, the test would be good to run. If the bolt does lock open, you have eliminated one possibility, though I would still look something to do with the bolt catch as the source of the problem based on what you've posted.
 
Do the test mentioned. If it is short stroking, you most likely have a gas problem of some sort.

If it is not short stroking, my guess would be that your bolt catch has become obstructed from moving freely for one reason or another... since you stated that it used to work and happens with all different mags.
 
i'm not going to be able to shoot again until the weekend, so i'm going to get another bolt catch this week and then do the test this weekend.

as for mags, this problem happens w/ my labelle 30rnd green follower mags, steel 30rnd mags, and 20rnd mags.

thanks, all
 
How about when charging by hand, the bolt will lock up some times and fail other times? would it be mag related or also the tab?
 
the bolt locks up manually, no problem. it locks up both w/ out a mag and i hold down the bolt catch button and when there is an empty mag in and i manually pull back the bold. and it usu. stays locked open . it only fails when shooting a magazine to empty.

this happens w/ 5 different mags.

weird
 
ammo: new wolf polymer 55gr and federal lake city xm193 55gr
i have shot thousands of rnd of both of these brands w/ out any failures.

mags: 3 labelle 30rnd mags w/ green followers, 2 colt 20 rnd mags, 1 british 30rnd steel mag.
 
Have you tried separating the upper and lower and inserting a magazine into the lower to make sure the follower is engaging the bolt catch?

Don't suppose you have a picture of the catch do you?

Have you been seeing any other malfunctions like those mentioned above?

When you say a small burr is there deformation of the metal or just the usual wear where the bolt wears against the parkerizing of the bolt catch?
 
When was the last time you took your magazines apart and cleaned them? If the follower is coming up a little slow that will cause your problem.
 
When you separate the upper and lower and manually move the bolt catch with your finger, does it feel like it is moving freely? I would check this against another rifle for comparison. If your bolt catch is fine, your rifle is probably every-so-slightly short stroking for some reason. If this is the case it would probably be best to send the upper back to the factory for them to take a look at.

Have you changed the gas system in any way, or changed the length of barrel in front of the gas port?
 
I had this happen on an AR that I built. It would lock up manually, but not at the end of a mag. The catch was out of spec. I replaced the catch and it worked fine after that. Turns out that when you lock it manually, you push it up farther than the mag does.
 
Any chance you changed the stock from an A2 to an A1 without using the shorter A1 screw?
 
i have an adjustable duostock installed, no butt plate screws. also, i have not changed the gas system or barrel prior to the problem.

today, i installed a dpms tactical bolt catch w/ new catch spring and buffer. brownells was out of the std bolt catch. i'm going to test it this weekend and see what happens.
 
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