New upper not locking after last round

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Joker80p
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New upper not locking after last round

Post by Joker80p »

I just recieved my 300 upper. I’m shooting remington super sonic 120grain. Cycles fine but doesn’t hold open after the last round. I have it on a dpms lower that I don’t see any marking on the buffer as to what buffer it is. Thinking back I do recall I was having issues with my 5.56 upper as well. It would cycle 5.56 flawless but when I shoot .223 it gives me issues as well. The lower has an a2 stock so from what I see should be a 5 oz buffer? Anyone have any idea
20X11
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Re: New upper not locking after last round

Post by 20X11 »

Barrel length and gas system for the upper please? Are you running a carbine upper on a rifle lower?
Joker80p
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Re: New upper not locking after last round

Post by Joker80p »

16” barrel carbine length gas system. It’s a dpms lower with an a2 stock. The buffer is a rifle buffer
20X11
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Re: New upper not locking after last round

Post by 20X11 »

A. Take the buffer out and weigh it to verify 5 oz.
B. Solve the .223 issue first. There is no reason a .223 shouldn't cycle a properly setup/lubed rifle config.
C. Try different magazines? Feed lips may be dragging on the bcg.
Joker80p
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Re: New upper not locking after last round

Post by Joker80p »

20X11 wrote:A. Take the buffer out and weigh it to verify 5 oz.
B. Solve the .223 issue first. There is no reason a .223 shouldn't cycle a properly setup/lubed rifle config.
C. Try different magazines? Feed lips may be dragging on the bcg.

I pulled the buffer and weighed it but is 5 oz too heavy ?
20X11
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Re: New upper not locking after last round

Post by 20X11 »

Joker80p wrote:
20X11 wrote:A. Take the buffer out and weigh it to verify 5 oz.
B. Solve the .223 issue first. There is no reason a .223 shouldn't cycle a properly setup/lubed rifle config.
C. Try different magazines? Feed lips may be dragging on the bcg.

I pulled the buffer and weighed it but is 5 oz too heavy ?
Lots of folks have had success with similar setups. 5oz rifle buffer in a rifle tube with a rifle spring SHOULD work. The fact that you have issues with .223 loads indicates you have another issue (ie, not enough lube, not enough gas, drag on the bcg, a non-standard rifle spring, etc.)

Edit: Since gas is upper related and you have issues with 2 different uppers, you should focus on the lower.
Joker80p
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Re: New upper not locking after last round

Post by Joker80p »

20X11 wrote:
Joker80p wrote:
20X11 wrote:A. Take the buffer out and weigh it to verify 5 oz.
B. Solve the .223 issue first. There is no reason a .223 shouldn't cycle a properly setup/lubed rifle config.
C. Try different magazines? Feed lips may be dragging on the bcg.

I pulled the buffer and weighed it but is 5 oz too heavy ?
Lots of folks have had success with similar setups. 5oz rifle buffer in a rifle tube with a rifle spring SHOULD work. The fact that you have issues with .223 loads indicates you have another issue (ie, not enough lube, not enough gas, drag on the bcg, a non-standard rifle spring, etc.)

Edit: Since gas is upper related and you have issues with 2 different uppers, you should focus on the lower.
After a few good cleanings and more shooting the 5.56 straightened out I jut wondered if t could be related to the buffer. The 300 upper is brand new only 30 rounds thru it so I’ll clean it up good again and see. You say bolt resistance I did notice that the bolt face has a lot more resistance on the gas rings on this bcg vs the one in my 5.56 which is a lot smother and easier to push in and pull out
Boolit_Head
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Re: New upper not locking after last round

Post by Boolit_Head »

Only 30 rounds? That thing is not even close to breaking in. I always find a new upper needs a wet bolt and a hundred rounds before I even consider if it has a problem or not. Got to shoot the kinks out first, the bolt needs a bit of break in on all the new finishes.
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dellet
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Re: New upper not locking after last round

Post by dellet »

A rifle buffer with carbine gas in 300 Blackout can be a problem. It will depend on the load and the gas port size. Subs will probably be a complete no.

Most people that use a rifle stock use a spacer so they can use a carbine, 3oz buffer, or H2 4.6oz.

Carbine gas and subs will work best with a carbine buffer.
300 Blackout, not just for sub-sonics.
bamashooter
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Location: Alabama

Re: New upper not locking after last round

Post by bamashooter »

Joker80p wrote:
20X11 wrote:
Joker80p wrote:

I pulled the buffer and weighed it but is 5 oz too heavy ?
Lots of folks have had success with similar setups. 5oz rifle buffer in a rifle tube with a rifle spring SHOULD work. The fact that you have issues with .223 loads indicates you have another issue (ie, not enough lube, not enough gas, drag on the bcg, a non-standard rifle spring, etc.)

Edit: Since gas is upper related and you have issues with 2 different uppers, you should focus on the lower.
After a few good cleanings and more shooting the 5.56 straightened out I jut wondered if t could be related to the buffer. The 300 upper is brand new only 30 rounds thru it so I’ll clean it up good again and see. You say bolt resistance I did notice that the bolt face has a lot more resistance on the gas rings on this bcg vs the one in my 5.56 which is a lot smother and easier to push in and pull out
Swap BCGs and see if that clears it up. And run it a bit wet.
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