AR-15 bolt release jamming

[TonyDedo]

I bought a bunch of Colt 20 round AR-15 mags last night from Collectors for the Appleseed shoot this weekend. I went to test them out at the range, and I had one reaccuring problem.

After loading a fresh mag, sometimes when I pushed the bolt release, the bolt wouldn't close all the way. It would get stuck somewhere around halfway closed, with the round halfway into the chamber.

It didn't happen all the time (maybe 1/4), and it was easily solved by pulling and dropping the charging handle, but I can see how it might be a pain at a shoot like this. Is there an easy fix, or do I need to replace the springs and/or followers?

 

[icyclefar]

I find that will occur when magazines are fully loaded. Try 19 rounds in the 20's, and see if the problem goes away. Most that I talk to use the minus one approach for all AR mags.

 

[bpm990d]

Make sure the bolt is lubed properly.


B

 

[LoginName]

Is the problem with all the mags or just a few?

Could be the springs or the feed lips on the mag body are bent/damaged/cracked. If they're pre-ban USGI 20 rounders they could easily be 25 - 30 years old or more, so they've seen some use.

Remove the floorplate and give the springs and interior of the mag body a good cleaning and lite wipe down with lubricant.

Note... if you haven't done it before, it's a bit tricky removing and reinstalling the follower and spring.

Are you loading them with a full 20 rounds?

Try underloading them to 18 rounds and see if that corrects the problem.

 

[TonyDedo]

Underloading - Brilliant! This is why I love you guys! I'll be sure to try that this weekend.

As for lubing the interior, what should I use? I thought lubing the mags will make them dirty and sticky.

 

[bpm990d]

http://www.mobil1.com/USA-English/MotorOil/Oils/Mobil_1_0W-30.aspx

 

[JonJ]

Just curious as to why why you used the charging handle and not the forward assist.

 

[LoginName]

Underloading - Brilliant! This is why I love you guys! I'll be sure to try that this weekend.

As for lubing the interior, what should I use? I thought lubing the mags will make them dirty and sticky.

Just a lite wipe down with CLP should be fine.

Unless you're in a combat situation or roll around in the dirt a lot with your mags, I wouldn't be concerned about it.

 

[96cbr900rr]

I have a similar problem with my AR-15, and in this condition the bolt and carrier are too far to the rear for the forward assist to engage the grooves in the carrier.

 

[bpm990d]

I have a similar problem with my AR-15, and in this condition the bolt and carrier are too far to the rear for the forward assist to engage the grooves in the carrier.

If the BCG is dirty or improperly lubed it can cause this problem. It slows down the velocity of the BCG so that there is not enough energy to strip off a round. If everything is clean and you are still having that problem, try a new buffer spring.

B

 

[TonyDedo]

Just curious as to why why you used the charging handle and not the forward assist.

I don't think my rifle has a forward assist.

 

[96cbr900rr]

If the BCG is dirty or improperly lubed it can cause this problem. It slows down the velocity of the BCG so that there is not enough energy to strip off a round. If everything is clean and you are still having that problem, try a new buffer spring.

Not to get off Livinlawatertown's problem, but with my particular issue it goes deeper than that as the problem will occur without a magazine inserted as well. I have also tried swapping out the BCG and the buffer, and buffer spring to no avail. also lube seems to have no impact as well, whether using a light coating or having it dripping in oil it still hangs the same.

 

[bpm990d]

I have a similar problem with my AR-15

but with my particular issue it goes deeper as the problem will occur without a magazine inserted as well

Sounds like a completely different problem.

B

 

[96cbr900rr]

Similar as in the location of the bolt hanging within the upper. I in no way meant that the cause is the same...

Perhaps I should have said: I have an issue in my AR-15 that in no way shape or form has the same cause as the previously described issue, as it will occur without a magazine inserted, but when it does fail, the BCG will be in the same situation, hung up half-way closed with a round half in the chamber.

I was not addressing the causation of the bolt hang initially, but was responding to the question posed as to why the forward assist is not used in this situation.

 

[LoginName]

Similar as in the location of the bolt hanging within the upper. I in no way meant that the cause is the same...

Perhaps I should have said: I have an issue in my AR-15 that in no way shape or form has the same cause as the previously described issue, as it will occur without a magazine inserted, but when it does fail, the BCG will be in the same situation, hung up half-way closed with a round half in the chamber.

I was not addressing the causation of the bolt hang initially, but was responding to the question posed as to why the forward assist is not used in this situation.

Does the bolt carrier slide freely on it's own (no pressure from the buffer spring)?

Is the firing pin retaining pin properly installed so that it's not dragging inside the upper receiver?

Try it with the charging handle and bolt removed.

One possibility is that when the upper was built, it was clamped down too tight in the receiver block and the walls of the upper were compressed a bit (that's why the better receiver blocks have an insert for the upper so that doesn't happen).

 

[cdkayak]

To the OP,
I've had a similar issue since I changed uppers on my AR15 SR. I went from a Bushmaster DCM upper to a RRA NM upper. I haven't found the exact cause yet, but the failure sounds similar. On mine it seems the bolt/carrier rides just a hair lower in the RRA upper sometimes causing it to drag or hang up on the rear edge of the mag. When I use a mag with a single round plastic follower I've seen evidence of the bolt lugs scraping along the follower. This drag slows the bolt enough to cause a failure to feed. This occurs with both USGI & new mags. I'm swapping the carrier for the next trip to the range.

96cbr,
One other thing to check in addition to what LoginName suggested is the alignment of the gas tube & key. Make sure they're lined up properly.

 

[bpm990d]

Try this article out. It may be of some help.

It could be a variety of problems and without seeing it, may be hard to diagnose.

B

 

[cdkayak]

Thanks for posting that article, it gives me something else to look for.

CD

 

[96cbr900rr]

Livinlawatertown, If you feel that I am dragging this too far off topic for you, please let me know and I will spin it off into another thread.

Does the bolt carrier slide freely on it's own (no pressure from the buffer spring)?

Is the firing pin retaining pin properly installed so that it's not dragging inside the upper receiver?

Try it with the charging handle and bolt removed.

One possibility is that when the upper was built, it was clamped down too tight in the receiver block and the walls of the upper were compressed a bit (that's why the better receiver blocks have an insert for the upper so that doesn't happen).

The BCG does slide freely with the upper off the lower, also without the charging handle, and with a completely different bolt carrier. The firing pin retaining pin does not drag in the upper as well....
Since we're getting into this we might as well get the entire picture set correctly....

The gun is a mid 80's production Large-hole Colt AR15 Sporter II with the original large-hole A1 upper, no forward assist, 20" barrel, and an A1 stock with original buffer and spring. In this configuration it functions fine, no issues.
A while back I picked up a complete small hole 16" Hbar A3 upper w/ B BCG and charging handle along with a 4 position stock with buffer and spring and an offset pivot pin at a Springfield show. All parts were NIB.
After installing the collapsible stock and 16in upper, it would more often than not have the bolt hang up half way through it's return travel to chamber a round after firing. This occurs with or without a magazine inserted into the rifle. This occurs regardless of the amount of lube (oil) on the receiver and BCG. This also occurs with the original A1 stock and buffer/spring installed. This also occurs with the BCG from the 20" upper installed. I took advantage of one of my buddies and borrowed his BCG from his Bushmaster, while I was not able to do an extended test, from the 30 rounds it fired properly I would say it functions properly, usually the most trouble free round count I'll get is 5 or less....

With the collapsible stock installed and the 20" upper installed the bolt would still hang in the same manner, but at a reduced frequency. reinstalling the original stock corrects the issue when using the 20" upper.

So, I can hazard a guess that something about the buffer extension tube and/or the spring for the collapsible stock is causing an issue, but I'm at a loss as to whats wrong with the 16" upper as the problem occurs in both stock configurations. The only thing I haven't done is put the upper on another lower, as it is a pre-ban configuration, and everyone else I know has post-ban rifles.

 

[TonyDedo]

To follow up on this thread, I underloaded my mags all weekend (shot about 400 rounds in total) and didn't have a single problem chambering a round. Turns out we never had to load more than 13 rounds per mag, so I would have underloaded them anyway.

 

[icyclefar]

Kind of makes you wonder why good ole U.S. Govt issue mags have a tendency to go unreliable on you when you load them to their stated capacity ............

 

[Joe R.]

1) My personal opinion of the 20 rd magazines is very low. Most of the older ones for sale have seen better days and won't function well enough to trust my life on. I have 2 I borrowed for high power shooting and found them wanting. I eventually figured out that my prone position isn't that low and I could get by with the 30 rounders instead.

2) Properly made 30 rd mags with good springs and followers should function with the full load. You underload the mags to allow a mag to seat easier on a closed bolt. If most of the time your loading on an open bolt, it's not that big of a deal. You go thru the mags and find the ones that don't work. Stay with US GI spec ( Okay Industries, Adventure Line, etc. ) mags and you'll be fine.

3) Pick up a good MILITARY manual on the M-16/ AR-15 and read it till the ink comes off of the pages!

Joe R.

 

[LoginName]

Livinlawatertown, If you feel that I am dragging this too far off topic for you, please let me know and I will spin it off into another thread.





The BCG does slide freely with the upper off the lower, also without the charging handle, and with a completely different bolt carrier. The firing pin retaining pin does not drag in the upper as well....
Since we're getting into this we might as well get the entire picture set correctly....

The gun is a mid 80's production Large-hole Colt AR15 Sporter II with the original large-hole A1 upper, no forward assist, 20" barrel, and an A1 stock with original buffer and spring. In this configuration it functions fine, no issues.
A while back I picked up a complete small hole 16" Hbar A3 upper w/ B BCG and charging handle along with a 4 position stock with buffer and spring and an offset pivot pin at a Springfield show. All parts were NIB.
After installing the collapsible stock and 16in upper, it would more often than not have the bolt hang up half way through it's return travel to chamber a round after firing. This occurs with or without a magazine inserted into the rifle. This occurs regardless of the amount of lube (oil) on the receiver and BCG. This also occurs with the original A1 stock and buffer/spring installed. This also occurs with the BCG from the 20" upper installed. I took advantage of one of my buddies and borrowed his BCG from his Bushmaster, while I was not able to do an extended test, from the 30 rounds it fired properly I would say it functions properly, usually the most trouble free round count I'll get is 5 or less....

With the collapsible stock installed and the 20" upper installed the bolt would still hang in the same manner, but at a reduced frequency. reinstalling the original stock corrects the issue when using the 20" upper.

So, I can hazard a guess that something about the buffer extension tube and/or the spring for the collapsible stock is causing an issue, but I'm at a loss as to whats wrong with the 16" upper as the problem occurs in both stock configurations. The only thing I haven't done is put the upper on another lower, as it is a pre-ban configuration, and everyone else I know has post-ban rifles.

Even though the parts are NIB... is the buffer spring and buffer the correct ones for a collapsible stock?

 

[ReplicaX]

Buffer and Springs can cause alot of issues. If your BCG travels freely, check your Buffer Assembly. It might not even be the Spring or Buffer, the newer collapsible stock's tube might be the issue. Make sure its not hanging or binding up in the tube.

A lightly lubed BCG is all you need in an AR/M16/M4. Alot of malfunctions I corrected in the Military at the Armory were Buffer/Stock related or the rifle completely dirty.

I've never had "good" 20 or 30rd Mags have feeding issues at full capacity and military mags are beat up far worse than Civilian. If I did have issues it was either Operator error , the Rifle, or a worn Mag Spring.

 

[Nickle]

Kind of makes you wonder why good ole U.S. Govt issue mags have a tendency to go unreliable on you when you load them to their stated capacity ............

We went to the green followers several years back.

Put a green follower in a 20 round mag, and it usually will hold only 18 rounds.

And, the source of loading the mags a few rounds short is from the troops themselves.