ar-10 feed problem


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ss101
March 12, 2011, 04:56 PM
I have a RRA LAR-8, brand new (120 rnds through it so far) and I'm having some pretty significant feed problems. Every 2-4 rounds the weapon will not go all the way back into battery after it ejects the spent casing. It stays open somewhere from 1/16" to 1/4". I can eject the misfed round by charging the weapon and it feeds the next round fine, also, when releasing the bolt from the open position it chambers fine. If I reload the misfed round into the magazine and continue firing the round feeds fine. I have never had any ejection problems.

Another problem which happened in the last 40 rounds or so: every 2-4 rounds the firing pin would strike the primer but not pentrate deep enough to ignite it. There would be a small dimple in the primer but it would not fire. When I reloaded and rechambered the round it fired fine.

I broke down and cleaned the rifle before the 1st shot and after the first 60th round. The only thing that I didnt clean was the extractor because I couldnt get the pin out. I have a feeling that the second problem could be caused by a tight or dirty extractor. Any help here would be great, thanks in advance.

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Mags
March 12, 2011, 05:19 PM
Check and see if you have foreign material in the receiver extension. Also check case dimensions.

I've owned a RRA LAR8 and it was the heaviest POS I have ever owned, but it was accurate. The FAL mag design was a bad idea.

DoubleTapDrew
March 12, 2011, 06:25 PM
Have you tried different ammo? I'd try that, and take apart the BCG and clean/lube it as per the manual. I did have an out of spec mag that caused feeding issues in mine.

rcmodel
March 12, 2011, 06:32 PM
every 2-4 rounds the firing pin would strike the primer but not pentrate deep enough to ignite it.For whatever reason, the bolt is not rotating fully into the locked position.

That prevents the hammer from hitting the firing pin with full force, or hitting it at all.
It also prevents the firing pin from reaching all the way out of the bolt face to the primer because the bolt carrier can't fully encompass the bolt all the way until it it fully locked.

1. Are you shooting reloads?
2. Out of spec surplus ammo?
3. Have you cleaned and oiled the bolt carrier, cam pin, and other moving parts?

BTW: Small dents in the primers are normal, and it happens to all AR-15 based weapons. The dent is caused by the free-floating firing pin bouncing against the primer when the bolt slams shut during feeding.

rc

Robert
March 12, 2011, 06:49 PM
I too wonder if you are shooting reloads. I had the same thing happen to my FAL in the middle of a match. I had seated the bullets just a little too far out which was causing it to not close all the way. Once I had "seated" the bullets with the action they fired fine. But going single shot in the middle of a stage sucks.

I seated the bullets in my next loading a couple thousandths deeper and all was well.

ss101
March 12, 2011, 07:00 PM
I have broken down and lubed the BCG as per the manual, minus the extractor. All ammo is federal American eagle. Used military CLP lube

Mags
March 12, 2011, 08:12 PM
Is it the American Eagle that is designed for the M1A?

ss101
March 12, 2011, 09:03 PM
I think it's just generic .308 win

ss101
March 12, 2011, 09:16 PM
What could cause the bolt to fail to rotate all the way forward?

KvG
March 12, 2011, 11:00 PM
are you holding onto the mag when firing?

ss101
March 12, 2011, 11:22 PM
Also, I'm using a combination of the magazine that came with the gun and surplus L1A1 mags.

ss101
March 13, 2011, 12:18 PM
Sometimes yes, sometimes no but it doesnt seem to affect the problem one way or the other. I had one mil surp L1A1 mag that was out of spec and causing the most awful looking misfeeds. The follower would move up front-first and the bolt would damn near cut right into the casing and bend the round in half when it came forward.

Why would the bolt not move all the way into position? Can the cam pin go in backwards or something? When you move the bolt in the carrier by hand it feels a little tight but not like its binding. Any AR geniuses out there know this one?

ss101
March 13, 2011, 09:47 PM
anybody?

1858
March 14, 2011, 06:57 AM
If I reload the misfed round into the magazine and continue firing the round feeds fine. I have never had any ejection problems.

Do you have access to go/no-go gauges or some way to measure the headspace of the chamber? It's possible that your chamber is right at the limit of minimum headspace and the AE ammunition has some variation in case head to shoulder dimension which is common. This could explain why some rounds chamber easily and others don't. The fact that you can chamber the round on the second attempt makes me wonder if the shoulder is being bumped back slightly as the bolt tries to close. You mention that the bolt is 1/16" to 1/4" from closing but it could be bouncing back slightly to that position.

madcratebuilder
March 14, 2011, 09:49 AM
You mention that the bolt is 1/16" to 1/4" from closing but it could be bouncing back slightly to that position.

Possibly this. I assume the bolt stays back after the last round is fired. I don't know what buffer RRA uses but I would try a heavier one. Use lots of oil on the BCG, these big rifles like to run wet, particularly when new. Get some LC surplus 7.62 and see if it feeds OK.

Z-Michigan
March 14, 2011, 11:12 AM
Headspace is a possibility, however I would also try some different type FAL mags. I understand that rifle is intended to use both metric and inch mags, but FAL mags were made by dozens of countries and dimensions can vary a bit. In my experience an FAL is usually OK with this variability, but the LAR-8 is trying to make FAL mags work with a completely different operating system, and it may be more finicky.

Get some like-new metric FAL mags (try Palmetto State Armory, Whatacountry, or DSA) to try. While you're at it I would try a different brand of new production .308 ammo.

Z-Michigan
March 14, 2011, 11:15 AM
Can the cam pin go in backwards or something? When you move the bolt in the carrier by hand it feels a little tight but not like its binding. Any AR geniuses out there know this one?

1) On a .223 AR made to military specs, the cam pin cannot go in backwards. It won't fit.

2) On some cheaper .223 ARs (OA, DPMS, etc.) a machining step is simplified and the cam pin can go in backwards.

3) I have no idea if the cam pin will go in backwards in your LAR-8, which is a different and proprietary design.

4) There is supposed to be a significant level of friction between bolt and carrier, caused by the gas rings being tight in the bolt's gas chamber. That is normal. If you extend the bolt, it should support the weight of the carrier. However, it should not feel like it's actually binding. If it requires more than modest hand pressure to make the bolt move in the carrier, something is out of spec.

Miketrance
April 3, 2011, 01:05 PM
I have broken down and lubed the BCG as per the manual, minus the extractor. All ammo is federal American eagle. Used military CLP lube
I just bought a LAR-8. I shot it and had the exact problem you describe. I was also using federal american eagle ammo. I bought two boxes one of remmington pro match 168 gr BTHP, and the second of the american eagle. I ran the box of match and didn't have a single malfunction. EVERY round of the american eagle malfunctioned. Perhaps the American eagle is a bit long. It seemed to snag in the Mag and it wouldn't feed unless I pulled the charging handle after every shot. The spent cartridge ejected fine but it wouldn't feed a new one. I'm going to pull it apart today and clean and lube it but I think I'll stay away from the American eagle.

Welding Rod
April 3, 2011, 02:21 PM
Miketrance beat me to it, but I was about to sugget changing ammo. It sounds to me like the ammo is too weak and you are short stroking and running out of steam before going back into battery.

isc
April 4, 2011, 01:04 AM
I went with the DPMS rifle instead of the RRA, even though I initially wanted to be able to use FAL mags. When I researched, I read that they had to remove one of the bolt's locking lugs to get it to feed with an FAL mag and that they had some issues working those bugs out. Since the Army was fielding the new M110 I decided to go with the design closer to the one we were using in combat.

If you ended up with a riflw that has issues, I'd look first and foremost to the factory where it was made and see about getting it repaired under warranty or if it was recalled.

madcratebuilder
April 4, 2011, 06:33 AM
I have broken down and lubed the BCG as per the manual, minus the extractor.

Remove the extractor, clean and lube. Look for any burrs. Sometimes you can get a build up of brass shaving around the extractor that stops it from completely seating over the lip of the case. This can stop the bolt from rotating completely in to position.

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