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ChrisJM981

Troubleshooting A5 Other FTF

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I went to sight in my other yesterday and it did not go as planned. With a 10 rd P-Mag the first round chambered, fired and ejected. When loading the next round it failed to chamber, bending the bullet to the 11 o'clock position and being pinned by the bolt (see attached). This happened with almost every follow-up shot, even with different mags and different amounts if rounds loaded in the mags. I'd have to drop the mag out to clear the jammed round. Any help in where I should start troubleshooting would be most appreciated. 

Setup:

Spike's billet upper, Ballistic Advantage 11.3" carbine gas Hanson barrel, Spike's lower, Spike's phosphate BCG, VLTOR RE-A5 with H2 buffer & Geissele Super 42 spring. 

 

20210820_192348.jpg

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Short stroking.  Load one round in the magazine, and fire it.  If the bolt locks to the rear, and holds open, then your rifle is not short stroking. 

If it is short stroking, look for a problem with the gas system such as a gas leak or misaligned gas block.  Short stroking can also cause unwanted hair growth on the barrel! :)

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a defensive rifle course i took a few months back, 2 people had similar issues with their "others". instructors took advantage of the situation to remind all of us about lubing our rifles. and once they lubed those 2 "others" nothing bad happened.......possibly a little dry?

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Bolt locked to rear with a single round in the mag. I might have enough of a carbon ring to check the gas port. I only fired 20 rounds or so since it was mangling them. 

i had applied Slip 2000 EWL to the entire bolt and rails before heading to the range. 

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14 minutes ago, silverado427 said:

I would try a different mag.  Have you fired this rifle before. ?

Why the H 2 buffer and super 42 buffer spring.  

 

OP said he tried several mags.  I also question the need for the heavy buffer and spring but if those were causing the issue, it would be short stroking, yet he said the bolt locked back with a single round?  I don't get it @High Exposure ?

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OK. Picture is upside down - I thought you had a charging handle impingement there at first…. That’s very confusing…..
VpLbcgA.jpg

Much better… 

A bolt over base malfunction is typically caused by an under-gassed gun or a bad magazine.

If those were both cleared as possible causes, then I would check to see if you have M4 feed ramps cut into your receiver AND barrel extension so there is nothing to get caught up on during the feeding portion of the firing cycle. If the upper receiver is cut, the barrel extension has to have the cuts as well. If there are no cuts at all, or cuts only on the barrel extension, that should not be an issue.

If that has been ruled out, it could be the A5 length receiver extension with a carbine gas system, a heavy spring, a heavier buffer, and short barrel doing weird shit to the dwell time. The system has to be pressurized long enough for the BCG and Mag to do their jobs of stripping and feeding.

I would attempt to put a standard action spring and buffer in and see what happens. If no change, swap the upper onto a lower with a standard carbine length receiver extension and see if that solves the issue. If not, I would put a standard upper (14.5” barrel with carbine  or middle the gas system) on your lower with the A5 and see if you have issues. Try to isolate the problem to upper or lower half and go from there.

Let is know what you find, I am curious.

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It appears to me that the timing is screwed up.  (A)Try a lighter BCG, (B) snip off a coil or two from the buffer spring, (C) use a lighter buffer. 

The dwell time, the amount of time the gasses push BCG back and the next round is stripped off and chambered is out of whack.  Although pressure is higher in short gas systems, the amount of time the pressure is applied is shorter, so all the moving parts need to be light enough to get pushed back into the extension all the way.

Just for kicks, double check the gas system and make sure there are no leaks.  Look for carbon build up.  Along those lines, it's also possible the gas block is misaligned, restricting full pressure to the rest of the system.

EDIT:  You can try to diagnose short stroking by loading a single round.  If the bolt does not hold open, the BCG is not traveling far enough back to get caught in the catch.

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Likely undergassed due to the short dwell distance between the gas port and end of barrel. Easiest way to try less mass in the recoil system is to pop open the h2 buffer and remove some of the weights. Don't need to buy anything, and it's reversible if it is standard construction. 

But you may need to remove more mass and resistance than that.  I run a stretch 16 barrel with a rilfe length stock. It has a small gas port and not a lot of dwell time. I'm running full gas, lightened BCG, lightened buffer ( empty rifle buffer), and a 10% reduced power buffer spring.  Now it runs like a top even in the cold. 

At the a5 length, I'd mess with the buffer, then if that's not enough, go look for a lgihtened BCG. BRownelss nitrided house brand one is $169.99 and in stock right now. 

 

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21 hours ago, silverado427 said:

I would try a different mag.  Have you fired this rifle before. ?

Why the H 2 buffer and super 42 buffer spring.  

 

Tried 2 colt mags and a Magpul P-mag. This was the first time I fired it. 

H2 buffer is recommended for short barreled firearms using the A5 buffer system. 

Super 42 rifle length was for reliability. I tried a Springco spring with the same results. 

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20 minutes ago, ChrisJM981 said:

Tried 2 colt mags and a Magpul P-mag. This was the first time I fired it. 

H2 buffer is recommended for short barreled firearms using the A5 buffer system. 

Super 42 rifle length was for reliability. I tried a Springco spring with the same results. 

If it's recommended I guess it works then. Problem solved. 

I've seen more people bitching about how to fix problems with an A5 setup who refuse to listen to reason because the a5 system "fixes" a problem they never had with bolt bounce. The whole a5 system is managing a problem that is not worth the effort, ESPECIALLY for people not shooting full auto. It makes troubleshooting stuff like this a pain in the ass. 

If it's the mag, you have basically have one choice. When the bcg/buffer bottom out, the shock is causing a bullet to pop up out of the feed lips. Odds are if the feed lips are this messed up, your bolt over base failure will not involve just one round and will look like a double feed. Odds are that this will be limited to specific mags. This is probably not your problem. 

If it's not the mag, you have two choices. 

1) the whole BCG/buffer combo isn't getting enough oomf and the bolt isn't clearing the mag and it is dragging the bullet halfway out of the mag from friction with the side of the bullet rather than things pushing on the case rim from behind. This will seldom look like a double feed. 

2) The whole BCG/buffer combo  is getting WAY too much gas and returning to battery REALLY fast before most in spec magazines can pop a bullet up to the top. In the free world this is a bit easier to troubleshoot because you try it with a full 30 round mag and that slows down the mag and generally causes a failure to feed with the bolt slamming home on an empty chamber. This usually doesn't look like a double feed, but due to the vigrous movement can sometimes make your mag do weird things. It also is more likely to really bend the crap out of the bullet caught by the bolt. 

You are running a full weight m-16 style bolt. 

With a +15% spring rate spring. 

With a H2 buffer. 

With a carbine length gas system (7.5") 

With an 11.3" barrel. 

So you have a ton of port pressure, but you have a whopping 4" of barrel for dwell time (~4ms), and an unknown size gas port. 

You know what has issues with too little dwell time and reliability? rifle length gas systems on a 16" barrels. That have a similar 4"/4ms of dwell time. That's why you don't see people with 18" barrel and rifle length gas and 6" of barrel for dwell time beefing everything up. That's why the stretch 16 barrel cuts it back to an intermediate length gas system, and those who want to sell a reliable gun with a standard gas system either use a mid length on 16, or a rifle length on a 17.X" barrel with some math done on the gas port. 

Here's a nice article on the subject 

 

Your heavy BCG buffer set up delays unlocking, which reduces battering, but without enough dwell time, you won't impart enough momentum to cycle it correctly. 

If you swapped the super 42 spring for a sprinco green or red, you really didn't do anything. 

Having a heavy buffer and heavy BCG in theory makes it take longer to unlock. You don't have the time to wait before running out of gas is my guess. To keep it from battering things, I'd decrease the mass of your BCG/buffer stack and not dick with reduced power springs until last resort. 

 

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21 minutes ago, raz-0 said:

If it's recommended I guess it works then. Problem solved. 

I've seen more people bitching about how to fix problems with an A5 setup who refuse to listen to reason because the a5 system "fixes" a problem they never had with bolt bounce. The whole a5 system is managing a problem that is not worth the effort, ESPECIALLY for people not shooting full auto. It makes troubleshooting stuff like this a pain in the ass. 

If it's the mag, you have basically have one choice. When the bcg/buffer bottom out, the shock is causing a bullet to pop up out of the feed lips. Odds are if the feed lips are this messed up, your bolt over base failure will not involve just one round and will look like a double feed. Odds are that this will be limited to specific mags. This is probably not your problem. 

If it's not the mag, you have two choices. 

1) the whole BCG/buffer combo isn't getting enough oomf and the bolt isn't clearing the mag and it is dragging the bullet halfway out of the mag from friction with the side of the bullet rather than things pushing on the case rim from behind. This will seldom look like a double feed. 

2) The whole BCG/buffer combo  is getting WAY too much gas and returning to battery REALLY fast before most in spec magazines can pop a bullet up to the top. In the free world this is a bit easier to troubleshoot because you try it with a full 30 round mag and that slows down the mag and generally causes a failure to feed with the bolt slamming home on an empty chamber. This usually doesn't look like a double feed, but due to the vigrous movement can sometimes make your mag do weird things. It also is more likely to really bend the crap out of the bullet caught by the bolt. 

You are running a full weight m-16 style bolt. 

With a +15% spring rate spring. 

With a H2 buffer. 

With a carbine length gas system (7.5") 

With an 11.3" barrel. 

So you have a ton of port pressure, but you have a whopping 4" of barrel for dwell time (~4ms), and an unknown size gas port. 

You know what has issues with too little dwell time and reliability? rifle length gas systems on a 16" barrels. That have a similar 4"/4ms of dwell time. That's why you don't see people with 18" barrel and rifle length gas and 6" of barrel for dwell time beefing everything up. That's why the stretch 16 barrel cuts it back to an intermediate length gas system, and those who want to sell a reliable gun with a standard gas system either use a mid length on 16, or a rifle length on a 17.X" barrel with some math done on the gas port. 

Here's a nice article on the subject 

 

Your heavy BCG buffer set up delays unlocking, which reduces battering, but without enough dwell time, you won't impart enough momentum to cycle it correctly. 

If you swapped the super 42 spring for a sprinco green or red, you really didn't do anything. 

Having a heavy buffer and heavy BCG in theory makes it take longer to unlock. You don't have the time to wait before running out of gas is my guess. To keep it from battering things, I'd decrease the mass of your BCG/buffer stack and not dick with reduced power springs until last resort. 

 

After I get the round out the bullet is probably bent 20-25 degrees to the side, and the case has a good sized dent in it where the bolt hit the case. I would've taken more pictures but my camera phone crapped out. 

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