Ejecting/cycling issue with LR-308

[George_cle]

18" Proof Research .308 barrel with rifle-length gas. Ballistic Advantage upper/lower, Sharps BCG, carbine buffer tube with JP Silent Capture buffer , Seekins Select adjustable gas block. About 50 rounds through the build right now.

I dialed the gas down from fully open to the point where it wouldn't lock back. I then settled at a spot that locked the BCG back reliably. Throughout the whole adjustment range, it would either eject brass just a foot or so, or the spent case would remain floating on top of the magazine.

I've had experience with overgassing in .308s where the case either didn't strip because the BCG moved too fast, or because it bounced so hard on the shell deflector that it ended back back above the magazine. I don't see how this could be a gassing issue, since I seem to have dialed the gas down to the right spot. I don't know if the buffer would make that much of a difference if I have the gas dialed right.

I'm at a loss here.

 

[Ernest 5.56]

Where was the ejection with the gas block fully open?

 

[George_cle]

The Sharps XPB BCG has double ejectors, and upon pressing on them, the spring tension seems normal. It has a double ejector spring and the donut.

Where was the ejection with the gas block fully open?

Stated in original post. It was the same throughout the range of dialing the gas down from fully open to more balanced.

 

[George_cle]

The Sharps XPB BCG has double ejectors, and upon pressing on them, the spring tension seems normal. It has an extractor spring with the black rubber insert in addition to a donut.

 

[nagantguy]

Brass floating on top of the mag, brass turned backwards but not ejected, and the ever feared death jam-spent case stuck about next round trying to chamber .I had horrors with these 3 FTJ issues with my first 308 franken Rifle . Playing with different buffers and springs got it running 100% . I started off addressing the issue with AGB as DPMS and most other big bore ARs are notorious for being over gased. Issue persisted and spring and buffer were the fix . Been close to 4 years now so I’d have to do some digging to find exactly what I had and what I ended up with- whatever was everyone’s favorite here back then as this issue you are experiencing is what brought me to the Hide . And I bought the two or three most recommended springs and buffers.

 

[George_cle]

Trying a regular .308 spring and buffer is going to be my next step. Until I see how it works, I just can't pin it on the buffer, since I regulated the gas. Buffer changes usually work when the system is overgassed. But it's still one of the few things that could possibly be affecting this.

 

[tjtoolson]

Do you have the spring kit for the jp? I have a proof carbon 18”, aero agb, and jp scs and I adjusted the buffer spring weight and gas to get it right. I am running a jp full mass bolt. I am running suppressed.

I started with the mid weight spring, adjusted gas but it still wasn’t ejecting optimally. Changed the spring weight to heavier and now it’s running like a top.

 

[hlee]

Sounds like a bad extractor. Brass slips off of the extractor claw prematurely causing weak ejection.

 

[padom]

Trying a regular .308 spring and buffer is going to be my next step. Until I see how it works, I just can't pin it on the buffer, since I regulated the gas. Buffer changes usually work when the system is overgassed. But it's still one of the few things that could possibly be affecting this.

I've never had a JP SCS with any of the springs cause the issues your having and I've built getting upwards of 50 large frame gassers over the years with JP SCS and JP and RCA BCG's...

Have you confirmed your gas block and gas hole are properly aligned? What size gas port?

I actually had a guy on here with a Proof CF barrel with too small a gas port and opening it up fixed his issues....

 

[George_cle]

I've never had a JP SCS with any of the springs cause the issues your having and I've built getting upwards of 50 large frame gassers over the years with JP SCS and JP and RCA BCG's...

Have you confirmed your gas block and gas hole are properly aligned? What size gas port?

I actually had a guy on here with a Proof CF barrel with too small a gas port and opening it up fixed his issues....

Gas block is aligned. I didn't measure the gas port. It's getting enough gas, because I dialed gas down until it stopped locking back, and then back up until it locked back reliably.

 

[George_cle]

Do you have the spring kit for the jp? I have a proof carbon 18”, aero agb, and jp scs and I adjusted the buffer spring weight and gas to get it right. I am running a jp full mass bolt. I am running suppressed.

I started with the mid weight spring, adjusted gas but it still wasn’t ejecting optimally. Changed the spring weight to heavier and now it’s running like a top.

I don't have the spring kit. I'm wondering if changing that will help, since I have regulated the gas. If I hadn't done that, I would definitely be leaning toward a buffer system imbalance. Unless I'm missing something.

 

[tjtoolson]

Ya with the gas block being adjustable and you’ve played with it I think it’s an extractor issue of some kind.

 

[Runnineh]

I had the same issues with my build. My first issue was I had the wrong size buffer tube. I don't know the exact measurements but the ar10/lr308 tube is longer. Second was my buffer was too light, so I picked up a heavy buffer and stronger spring. (Heavybuffers.com) Third was my bolt. The extractor tips were a bit too long (dpms) and the extractor was weak, so I replaced with a kak dual ejector. Not one single change fixed my issue, but all 3 did. Hope this helps, I fought my rig for a long time thinking it was my agb or ammo.

 

[lash]

Not saying this is your issue since you seem to have played with and checked your extractor, but I had an extractor claw break just a the claw part itself somewhat broken.

 

[George_cle]

I had the same issues with my build. My first issue was I had the wrong size buffer tube. I don't know the exact measurements but the ar10/lr308 tube is longer. Second was my buffer was too light, so I picked up a heavy buffer and stronger spring. (Heavybuffers.com) Third was my bolt. The extractor tips were a bit too long (dpms) and the extractor was weak, so I replaced with a kak dual ejector. Not one single change fixed my issue, but all 3 did. Hope this helps, I fought my rig for a long time thinking it was my agb or ammo.

Here is a slo-mo video of what it's doing:

https://photos.app.goo.gl/1g2yvSrNULnNT5fu9

 

[padom]

Here is a slo-mo video of what it's doing:

https://photos.app.goo.gl/1g2yvSrNULnNT5fu9

Swap BCG and see if that corrects the issue. It looks like it's not properly ejecting

 

[Runnineh]

I would try the heavy buffer and spring to slow it down. Like I said that's exactly what mine was doing.

 

[mtrmn]

There is a possibility that the BCG is still too fast when it gets enough gas to operate. The adjustable gas may not be the ultimate solution in every case. Some guns are just too overly sensitive to find the sweet spot with gas adjustment alone. Adding weight can widen that window. JMO

ETA: I slowed the video down to 1/4 speed and watched it repeatedly. It appears the extractor may be at fault but it's still too hard to tell if the bolt ran off and left the empty shell too soon. Like stated above, swap the BCG to see if it changes things.

 

[Precision Underground]

Looks to me like the extractor is holding onto the case for too long or else the carrier is moving too fast. Locking back is only part of getting the carrier speed right. There has to be time for the extractor to let go before the carrier bottoms out. Make sure there’s not a burr on the extractor that’s hanging onto the case. Chamber a piece of brass and pull the handle back and see if it ejects out easily or if it tries to bounce back in.

 

[tucaz]

definitely need to check the extractor and its spring but regardless, you need to up your buffer set up. 308 carbine buffer set ups are a joke

i’ve had good luck with slash’s HSS 6.5 oz ar15 buffer, sprinco red carbine springs and a vltor a5 tube.

 

[bigjake83]

(1) You're using a Sharp's BCG when the only Bolt Proof states to us is a JP.

(2) You need to slow your BCG down so add a tungsten weight to your JP SCS.

(3) Reevaluate your gas adjustments after adding buffer weight, you want it to lock back and eject between 3-4 O'clock.

(4) If you're using a Buffer Retainer Pin with your SCS , Don't!