Shortest 300 blk barrel

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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dellet
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Re: Shortest 300 blk barrel

Post by dellet »

I would say yes, but can't stand behind it. Partly its computer generated numbers, partly there are too many variables. In can show you how I base the thought and I think it's solid

I looked at what I thought was your can. Rated for 308 18" barrels and longer. With that one load that I just pulled at random it would be around 11,000, you're in the same ballpark.

Most manufacturers will say 8" is fine for Blackout supers. That 125 SST load is 12,000.

Some loads for 300 WM in 22" barrels average around 13-14,000. At 20" pressure goes up about 2000. That can give you an idea.

Just remember it will also shoot hotter, can will heat up faster. I just wouldn't be doing a bunch of mag dumps.

Hope that helps some. I just haven't used anything less than 5" and only helped with that project. So far he hasn't blown up his can.
300 Blackout, not just for sub-sonics.
PNW17
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Re: Shortest 300 blk barrel

Post by PNW17 »

dellet wrote: Fri Apr 19, 2019 10:00 pm I would say yes, but can't stand behind it. Partly its computer generated numbers, partly there are too many variables. In can show you how I base the thought and I think it's solid

I looked at what I thought was your can. Rated for 308 18" barrels and longer. With that one load that I just pulled at random it would be around 11,000, you're in the same ballpark.

Most manufacturers will say 8" is fine for Blackout supers. That 125 SST load is 12,000.

Some loads for 300 WM in 22" barrels average around 13-14,000. At 20" pressure goes up about 2000. That can give you an idea.

Just remember it will also shoot hotter, can will heat up faster. I just wouldn't be doing a bunch of mag dumps.

Hope that helps some. I just haven't used anything less than 5" and only helped with that project. So far he hasn't blown up his can.
Appreciate the insight. No mag dumps for me. That would be unbecoming of a gentleman.
2manyToys
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Re: Shortest 300 blk barrel

Post by 2manyToys »

When I talked to Liberty about the first generation Mystic-X, before the 300WM rating, they said to keep chamber pressures under 40,000 psi IIRC, but I didn't get a muzzle pressure number from them. Obviously there's a big difference between chamber and muzzle pressure.
PNW17
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Re: Shortest 300 blk barrel

Post by PNW17 »

If this carbon and copper crud doesn't slow down after break in I am probably going to make this into a gas piston design built from scratch to accommodate the short length.
PNW17
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Re: Shortest 300 blk barrel

Post by PNW17 »

My bolt doesn’t close without being slammed in. The same bolt works fine with all my other AR’s and closes by itself. I tried lapping it and that didn’t improve it. Any suggestions on how to improve? My default is just to buy a new lightweight bolt but I’m not there yet.
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dellet
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Re: Shortest 300 blk barrel

Post by dellet »

PNW17 wrote: Tue Apr 23, 2019 10:04 pm My bolt doesn’t close without being slammed in. The same bolt works fine with all my other AR’s and closes by itself. I tried lapping it and that didn’t improve it. Any suggestions on how to improve? My default is just to buy a new lightweight bolt but I’m not there yet.
Sounds like something in the upper.

Does that happen without a round in the chamber?

I would make sure it's not binding on the gas tube, probably by removing it and the charging handle.

Was the bolt tight when you were lapping that into the extension?
300 Blackout, not just for sub-sonics.
PNW17
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Re: Shortest 300 blk barrel

Post by PNW17 »

dellet wrote: Wed Apr 24, 2019 4:40 pm
PNW17 wrote: Tue Apr 23, 2019 10:04 pm My bolt doesn’t close without being slammed in. The same bolt works fine with all my other AR’s and closes by itself. I tried lapping it and that didn’t improve it. Any suggestions on how to improve? My default is just to buy a new lightweight bolt but I’m not there yet.
Sounds like something in the upper.

Does that happen without a round in the chamber?

I would make sure it's not binding on the gas tube, probably by removing it and the charging handle.

Was the bolt tight when you were lapping that into the extension?
Yes it happens or at least I noticed it without a round in. I need to disassemble and check the gas tube but I’m pretty sure it’s the bolt lugs slightly interfering with the barrel lugs. I threw lapping compound on the bolt and cycled it a hundred times. Didn’t seem to help. I have a new lighter bolt on the way so we’ll see if that one fits better.
PNW17
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Re: Shortest 300 blk barrel

Post by PNW17 »

PNW17 wrote: Sat Apr 20, 2019 6:36 pm If this carbon and copper crud doesn't slow down after break in I am probably going to make this into a gas piston design built from scratch to accommodate the short length.
Ordered the steel to build an ultra short gas piston system so will document that here as well.
PNW17
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Re: Shortest 300 blk barrel

Post by PNW17 »

Fixed the bolt that was tight. It was the gas tube the needed to be bent slightly up. Got the short gas piston gas block roughed out and squared.

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PNW17
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Re: Shortest 300 blk barrel

Post by PNW17 »

Got the short adapter for the can that cuts the length down a bit more. The alternate piston gas block is on the mill now being bored out.

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