M1A jamming problem

Red State · Sep 18, 2011

My M1A has a an occasional problem that causes both a FTE and a FTF.

As the ejecting case is flying out, it is getting caught by the operating rod and slammed up against the bottom of the front scope ring. This causes the spent case to be jammed in between the operating rod and the scope ring, thus preventing the bolt from closing on the new round. This happens about once every 100 rounds.

Has anyone else had this problem?

Maybe my ejector needs to be upgraded?

Or maybe the ARMS #18 scope mount is preventing the case from flying out in the direction that it should, and is causing the case to bounce into the way of the operating rod? Should I cut some material out of the part of the scope mount that is directly above the ejection port?

I hope I don't need a higher scope mount. I love the low line of sight with my current setup. Picture attached in the next post:

Red State · Sep 18, 2011

A good picture of my scope mount and ring is attached to the first post of this thread:

http://www.thehighroad.org/showthread.php?t=527436

M1key · Sep 18, 2011

Since you can't adjust gas, first thing would be to change ammo...

See what that does.

M

Red State · Sep 18, 2011

I have an adjustable gas valve that I bought so I can shoot the Hornady 155gr A-Max.

Would you recommend increasing the speed of the oprod in order to make the ejections more forceful?

This malfunction has happened with a couple of types of ammo.

M1key · Sep 18, 2011

Okay, then try giving it more gas...

I had to fix mine (no way to adjust gas) by taking a bit of the corner off the ARMS base, since I didn't want to change ammo I was shooting.

Good luck

M

4v50 Gary · Sep 18, 2011

M-14s are designed to work with mil-spec ammunition. Underpowered loads can make the extraction more sluggish, giving less time for the ejector to perform its function. Overpowered loads not only peen the receiver, but may work too fast for the extractor and ejector to work reliably. If the gun worked fine with the current ammunition before the scope mount and scope were installed, then if the ammunition is not within milspec (with respects to pressure and velocity), try more mil-spec ammunition. If the ammunition is mil-spec, then the design of the mount may be inherently wrong for the design. This is not surprising for aftermarket items.

The Ruger Mini-14 pounded many scopes including Leupold to pieces. Why? It wasn't designed for a scope. The receiver acted as a tuning fork, transferring unwanted vibrations into the scope. Additionally, the shock of the ejected shell striking the scope mount also transferred a lot of unwelcomed energy to the scope. Continual firing literally pounded any scope including Leupolds until they broke. Ruger engineers responded by re-engineering the Mini-14 to have side ejection (as opposed to top ejection) and included a buffer ring to help dampen the recoil transferred to the receiver when the op-rod slammed back. What's the relevance? As pointed out earlier, aftermarket items may not be properly engineered to ensure that functional reliability is preserved.

I'm hesistant to suggest a hotter load that is beyond mil-spec. It's like shortening the barrel of a semi-automatic (Garand or M-14). If the gas port is moved closer, it will allow gas to work on unlocking the action sooner before the pressure is reduced. To compensate for it, a smaller gas port than normal is drilled to lessen the gas entering into the chamber to act on the op-rod. Shortening the barrel also results in gas pressure dropping sooner too. You want the pressure to be sufficient to function the action fully with spec ammunition (either SAAMI or Mil-spec). So, the port may have to be opened a little more. The exact size is determined by the engineers first on paper and then by trial and error.

I swear I didn't drink anything other than water tonight.

Red State · Sep 19, 2011

M1key, I may do what you did. As you can see in the attached pictures (a view from the side and a view through the magwell), the empty cases are impacting the bottom of the scope mount. I think I can grind the mount to an angle in that area so that it helps to "kick" the cases to the side and away from the gun.

Interestingly, it looks like some of the cases are also hitting the scope turret cap. I didn't plan it this way, but the Buckmaster cap has angled sides that should also help to clear the spent case.

Since I plan on shooting at least two loads regularly (and haven't yet been able to narrow my list past four loads), I am not sure how useful the adjustable gas valve will be to me. Hopefully I can get it tuned so that both of those loads are accurate and RELIABLE.

bryank30 · Sep 19, 2011

I have the SAME problem with my national match M1A and arms scope mount! Its frustrating as hell. I'm always thinking if I had access to an end mill, I would machine some meat off either the front scope ring base or the ARMS 18 mount

Red State · Sep 19, 2011

I hate to admit it, but I think I will just use a bench grinder to modify my mount.

Good idea regarding the bottom of the scope ring. I could shave some of that, too.

LemmyCaution · Sep 19, 2011

Try replacing your extractor, ejector, and related springs with USGI units before grinding expensive gear. This solves most people's problems with bad ejection angles.

TIMC · Sep 19, 2011

it does look like your scope base does stick out too far in the picture.
Here is a pic of mine with the Smith Enterprises M-21 mount.
Just for grins; your gas block didn't slide forward a little on you when you had it apart did it? the reason I ask is I just came across this problem with somone at the range the other day.

madcratebuilder · Sep 19, 2011

This is a documented problem over at M14firingline. The current version of the ARMS #18 has more metal and some are machining this back with a bevel to be more like the early mount.

Some say, and I agree, this is a rifle problem. A usgi extractor and a usgi ejector and ejector spring would be what I would change. I understand that there are two different styles of ejector springs and one preforms better. You might want to check on that.

henschman · Sep 19, 2011

You should try replacing the extractor with a GI extractor. That is a pretty common problem, and it is usually the SAI commercial rifles and their extractors that it happens to. It is definitely a rifle issue... the US military uses the ARMS #18 mount and it works fine for them.

roklok · Sep 19, 2011

Ahhh........I had the same problem with my ARMS 18. Tried everything, handloads of every sort, changing ejector and extractor to USGI, reprofiling tip of ejector, even completely cut out the section of rail above ejection port, leaving only the rail where the rings mount front and rear.

In the end, nothing worked. I would think I had the problem fixed, and then 50-100 rounds in, I would have a jam, just like you described. Finally sold the mount on Ebay. I carry my M1A in grizzly country and it must be reliable, one stoppage every 100 rounds is way too many.

The ARMS 18 is a rock solid, low mount, but...it simply did not work on my M1A. I have not put a scope back on my rifle, but if I was, I would try the Bassett mount.

Red State · Dec 5, 2011

follow up

Well, I loosened the loctite and took the mount off the gun and put it on the bench grinder.

In the attached picture you can see the freshly ground surfaces. Its a bit hard to tell from the angle of the picture, but the cuts are angled at about 45 degrees so that a shell ejecting up gets kicked directly right.

Red State · Dec 5, 2011

In these pictures you can view from directly above and directly below to see just how much material I took off.

As far as mounting the scope rings, my only choices now are the very front and very rear slots - which is fine since those are the only ones I used previously.

The mount has since been refinished and baked at 350 degrees and is now re-mounted.

Time for a range trip for testing.

henschman · Dec 6, 2011

Hmm, let us know how it works.

I'm glad I got mine to work with a new GI extractor and ejector... cutting the rail wouldn't work with my ACOG base, and all the other mounts put it too high to use.

M1A jamming problem

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