Can't get my 300 AR to cycle

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fishman
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Can't get my 300 AR to cycle

Post by fishman »

I can't get my suppressed 300blk AR to cycle. 10.5" barrel, carbine gas system, 1/8" gas port, adjustable gas block rifle length buffer tube, rifle buffer and spring. I should've gotten a barrel with a pistol length gas system.

It won't cycle 220 sig ammo or my handloads ( 205 grain cast lead over 9 grains of lil gun) these are already borderline supersonic.

I've tried a carbine spring. I've tried removing 2 of the 5 buffer weights. No luck

It will eject a shell but won't pick up a new one or lock back on an empty mag. Any advice?
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themonk
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Re: Can't get my 300 AR to cycle

Post by themonk »

Need more info:
What suppressor
What gas block
What barrel
Whats the logic on the rifle length buffer system on a carbine gassed gun (or do you mean the vltor A5 system?)
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daviscustom
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Re: Can't get my 300 AR to cycle

Post by daviscustom »

I assume it runs with supers?....bolt locks back and all that?

I think your assessment of choosing the wrong gas system is probably correct.

If this is not a new development with the rifle....if it has never functioned with subs....there are two approaches to fix the problem. You either need more gas, or less mass/resistance in the bolt and buffer and spring. You can experiment with lighter buffer springs/buffers and maybe solve the problem fairly inexpensively.....maybe a reduced weight BCG would solve it, but that is an expensive maybe.

Was the barrel sold in that gas configuration, or was it a custom set-up? If the manufacture will stand behind it, they should either make it run or replace it I would think. It sounds like it really needs pistol gas or a larger gas port. Hopefully someone will chime in if it is a lost cause working with carbine length gas, but I don't see why enlarging the port wouldn't make it work.

Since you are using an adjustable gas block, that gives you wiggle room if you decide to open it up yourself.... in case you go a little big trying to open up the port. If you end up working on the port, just enlarge in small increments (numbered sized drill bits, a few thousandths at a time) test it as you go until it functions then go a size or two bigger for good measure. You probably will end up having to use different settings for subs and supers.

What kind of gas block are you using?
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Re: Can't get my 300 AR to cycle

Post by Fulmen »

Definitively the wrong gas system for subs. A bigger port might solve it, but the risk of bullet shaving increases. Besides, as you're already at tube ID it might help all that much. Plugging the original port and fitting a pistol length tube would probably be the best solution.

Themonk: Using a carbine spring in a rifle tube gives you a weaker main spring. But as as over-travel is controlled by the buffer you have to use rifle length.
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fishman
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Re: Can't get my 300 AR to cycle

Post by fishman »

themonk wrote:Need more info:
What suppressor
What gas block
What barrel
Whats the logic on the rifle length buffer system on a carbine gassed gun (or do you mean the vltor A5 system?)
Form 1 suppressor, the one in my signature.
Seekins precision adjustable gas block (wide open)
I don't remember who's barrel and it doesn't say on it. It was sold as a 10.5" w/ carbine gas system. I didn't mod it.
People mix gas systems and buffer systems all the time. If it wasn't kosher to mix the two then what length buffer tube is supposed to go on a mid length gas system gun? I've never seen a mid length buffer tube or buffer.

I've never shot a super through it, I don't have any and I don't have any bullets to make any. I can't enlarge the port any more, it was already bigger than the ID of a gas tube. I've read that 10.5" barrels with carbine gas systems will cycle subs, but only while suppressed. They supposedly cycle supers fine.

Switching to a pistol gas system barrel will fix the problem but I'd like to keep that as a last resort because my silencer is welded on, it's not an SBR. I guess ill have to try a lighter buffer and or spring and hope.
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themonk
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Re: Can't get my 300 AR to cycle

Post by themonk »

fishman wrote:
themonk wrote: People mix gas systems and buffer systems all the time. If it wasn't kosher to mix the two then what length buffer tube is supposed to go on a mid length gas system gun? I've never seen a mid length buffer tube or buffer.


I get that. I am asking if it was part of a kit and was recommended to you by the barrel maker or if you had a plan going in to use it for a specific benefit or its was just parts laying around.

Any idea what the gas hole size is on the Seekins? May want to ping them tomorrow to get the spec just to see if it is equal or smaller that your 0.125.

I am sure you have checked this but with a gas port that big you don't have a lot of room to be off when putting on the gas block (you normally have wiggle room). May want to double check you a perfectly aligned.
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fishman
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Re: Can't get my 300 AR to cycle

Post by fishman »

themonk wrote:
fishman wrote:
themonk wrote: People mix gas systems and buffer systems all the time. If it wasn't kosher to mix the two then what length buffer tube is supposed to go on a mid length gas system gun? I've never seen a mid length buffer tube or buffer.


I get that. I am asking if it was part of a kit and was recommended to you by the barrel maker or if you had a plan going in to use it for a specific benefit or its was just parts laying around.

Any idea what the gas hole size is on the Seekins? May want to ping them tomorrow to get the spec just to see if it is equal or smaller that your 0.125.

I am sure you have checked this but with a gas port that big you don't have a lot of room to be off when putting on the gas block (you normally have wiggle room). May want to double check you a perfectly aligned.
My only AR lower already had a rifle buffer tube. I obviously didn't have the option of a rifle length gas system on my 10.5" barrel so they had to be mismatched.

I don't know the gas block port size, I can't get it off to measure. I should email/call them. I have checked the alignment.
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daviscustom
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Re: Can't get my 300 AR to cycle

Post by daviscustom »

I have seen problems with seekins gas blocks not having enough adjustment to calm an severely overgassed rifle but I don't recall seeing this issue. If you have a standard gas block laying around you could try it and see if the seekins is restricting flow.

DUH! on the port size :mrgreen: ....wasn't thinking about it being at the tube id size already.

I believe mine is a 10.5-11" Ballistic Advantage...don't have a 30 cal can to test it with yet. It cycles both supers and subs...but it is pistol length gas.
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Re: Can't get my 300 AR to cycle

Post by Fulmen »

Without changing the gas system your options are limited. First make sure everything moves with as little friction as possible. You might consider cutting the spring a bit, removing weights from the buffer should help some as well. A lightweight BCG is another possibility. But I would try loading with a slower powder first, more powder means more gas.
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fishman
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Re: Can't get my 300 AR to cycle

Post by fishman »

I called seekins, the port is .16" plenty big enough. I can't try another gas block without cutting this one off or cutting the silencer off.

I tried removing all 5 weights from my buffer and put a carbine spring in, no luck.

I have some h4198, ill try that
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fishman
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Re: Can't get my 300 AR to cycle

Post by fishman »

fishman wrote:I have some h4198, ill try that
11.5 grains. Nope.

I have some heavier bullets on order, maybe that'll do it.
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John A.
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Re: Can't get my 300 AR to cycle

Post by John A. »

Here's an inexpensive and easy option. I installed both on my blackout. Works well. I now can use really fast burning pistol powders, which make for a lot more quiet subsonic.

http://www.davidtubb.com/tubb-springs/a ... -stainless

http://www.tacticallink.com/Taccom-Ultr ... -AR15.html

If the above doesn't fix it, you may also want to consider lightening your bolt. You can drill or mill material in the rear of the carrier that doesn't affect anything.

Those are your last resorts to changing the physical location of your gas port/diameter/barrel.

I don't know of anything else to try other than the above. Changing bullets is probably not going to do anything to help. You won't see a meaningful difference in pressure between 208 gr and 240 gr with all else being the same. I'm sorry, but that's not going to be much help at all.
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Dellet
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Re: Can't get my 300 AR to cycle

Post by Dellet »

First post here, have a bit of a history on 300blktalk.

I enjoy stepping outside the norm with the cartridge, your build interests me as these barrels are showing up more and more. By the book it won't work, I think it might with the right powder.

The two most likely to work and a third you might have, Accurate LT-30, 4227, and Hodgdons new
CFE BLK. Those three produce a huge amount of gas at low pressures. I think LT-30 and CFE are the most likely. Both of those have allowed me to run very light bullets (sub 150) in carbine gassed systems without a suppressor. 4227 I use for 125's in an 8" barrel.

You might just be able to make it go without any more alterations than you already have.

Accurate has load data for LT-30, Hodgdon for CFE. It might take some fooling around, but I think it might go.
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fishman
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Re: Can't get my 300 AR to cycle

Post by fishman »

Image

My bolt carrier went on a diet. I cleaned out my bolt carrier really well. Heavier bullets. 11 grains of imr 4198 (barely supersonic). Still carbine spring. Still no weights in the buffer.

No dice.

A 10.5", pistol gas, barrel is on its way. Time to cut some welds :(
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fishman
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Re: Can't get my 300 AR to cycle

Post by fishman »

Image

It works :)

Pistol gas system barrel did the trick.

All the weights are back in the buffer, regular rifle spring. 8.2 grains of lil gun under a 225 grain hornady match hpbt. Now it's time to adjust the gas block.

I'm confident that barrel would've worked with supers, maybe with subs and a slower powder.

Hopefully this thread saves someone from making the same mistake.
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