Desperately seeking subsonic cycling - new guy.

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Westerly
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Re: Desperately seeking subsonic cycling - new guy.

Post by Westerly »

I reduced the 220 Grain SMK, 8.7 grain AA #9 loads to 2.090” OAL. That only increased the velocity with no remedy in cycling the action (worse actually, didn’t even eject most of the rounds). When I can eventually obtain some A1680, I’m beginning to doubt that it will be the magic fairy dust that will allow this thing to function with subsonics. I also wonder how big a factor the presence of a proper silencer at the muzzle allows cycling. Does it provide back-pressure to push it over the top?

It’s beginning to look like I’m in for quite a frustrating journey (throwing parts at this thing). I’m not concerned about the lower handling 5.56, the gun is dedicated to 300 BLK, so I'm happy to make semi-perminant changes. What do I need to make this a carbine length gas system cycle subsonics and yet not beat itself to death with full power loads? Perhaps I’m asking for too much.
The true soldier fights not because he hates what is in front of him,
but because he loves what is behind him.
” G. K. Chesterton
tfbit
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Re: Desperately seeking subsonic cycling - new guy.

Post by tfbit »

Just wait for some A1680 to show up. It's the right powder. If you ever make it up to Eugene, PM me and I'll sell you a pound.
No matter what you read on the intarweb CCI450s and CCI41s ARE NOT BALLISTICALLY IDENTICAL with H110! I'm also not a intarweb lawyer so I don't argue with anyone who is.
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farm use
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Re: Desperately seeking subsonic cycling - new guy.

Post by farm use »

Westerly wrote:I reduced the 220 Grain SMK, 8.7 grain AA #9 loads to 2.090” OAL. That only increased the velocity with no remedy in cycling the action (worse actually, didn’t even eject most of the rounds). When I can eventually obtain some A1680, I’m beginning to doubt that it will be the magic fairy dust that will allow this thing to function with subsonics. I also wonder how big a factor the presence of a proper silencer at the muzzle allows cycling. Does it provide back-pressure to push it over the top?

It’s beginning to look like I’m in for quite a frustrating journey (throwing parts at this thing). I’m not concerned about the lower handling 5.56, the gun is dedicated to 300 BLK, so I'm happy to make semi-perminant changes. What do I need to make this a carbine length gas system cycle subsonics and yet not beat itself to death with full power loads? Perhaps I’m asking for too much.
Dont give up on it! It will work, If you cant find A1680 right now, try to find some RL 7. It is close to A1680 and will work. Good luck!!
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Hog+
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Re: Desperately seeking subsonic cycling - new guy.

Post by Hog+ »

When you were working with the 223 sub rounds did you notice that timing is everything with the AR? If the 1680 works and #7 works then the powders between, on the burn rate scale, might well work (I know 2015 BR will work, I use it in my 6.5 Grendel loads). But if 4227 will not work then 1680 is the bottom of the scale not the middle. There are 7 powders on my scale between #7 and 1680, with 2015 being below #7.
Ed
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AJMD429
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Re: Desperately seeking subsonic cycling - new guy.

Post by AJMD429 »

darr3239 wrote: Suggested subsonic load:
• R-P 300 AAC BLACKOUT brass
• Remington 7.5 primers
• 11.2 grains of A1680 powder (Adjust powder charge down as needed. Factory ammo is 1010 fps for 16" barrel)
• Case length is 1.368 +0.000 -0.020
• Sierra 220 MK loaded to 2.120 OAL (this length is optimal for reliable feeding from USGI magazines)
• Chamber pressure 21,100 psi.

Generally, reliable functioning with subsonic 300 BLK is only achieved with a suppressor. You need a .30 cal. one.
My 16" S&W 300 Blk upper functioned fairly well with 125 gr factory Remington supersonics, and most-of-the-time with 220 gr factory Remingtons without a suppressor, so I got my hopes up that I could load up something to work well without much effort.

Unfortunately, even using A1680 powder at 11 grains, AND with a suppressor (Mystic, so it is .357 instead of .308), the weapon fails to cycle at all, even when I replaced the factory gas block with an adjustable one and set it 'wide-open'. My CMMG upper, also 16", cycles just fine with that suppressor.

I'm still trying to sort all this out, and that is why I posted my request for a "Tutorial on Gas Systems". . . . .

. . . . . but I didn't get much in the way of answers. . . . . :|
bani
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Re: Desperately seeking subsonic cycling - new guy.

Post by bani »

my 16" PSA barrel, carbine length gas, cycles 220gr with a1680 fine with or without suppressor.

have you tried PNW subsonic ammo? i've found that works a lot better than remington.
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Re: Desperately seeking subsonic cycling - new guy.

Post by Westerly »

Hog+ wrote:When you were working with the 223 sub rounds did you notice that timing is everything with the AR? If the 1680 works and #7 works then the powders between, on the burn rate scale, might well work (I know 2015 BR will work, I use it in my 6.5 Grendel loads). But if 4227 will not work then 1680 is the bottom of the scale not the middle. There are 7 powders on my scale between #7 and 1680, with 2015 being below #7.
Ed
Right! I usually run straight to the burn rate chart and forgot to on this load. Now I see why Lil' Gun is popular with this round (being right next to A1680 on the chart). I also see why the IMR-4227 would be a better "do-fer" than the AA #9. I've got less than half lb. of the 4227 and about 4 lbs. of the #9, thus the futile effort.
AJMD429 wrote:
darr3239 wrote: Unfortunately, even using A1680 powder at 11 grains, AND with a suppressor (Mystic, so it is .357 instead of .308), the weapon fails to cycle at all, even when I replaced the factory gas block with an adjustable one and set it 'wide-open'. My CMMG upper, also 16", cycles just fine with that suppressor.[/i]. . . . . :|[/b]
What a drag! Maybe I should refrain from throwing good money after bad and come up with plan "B". I don't mind the challenge and it's kinda fun to tinker...as long as hope remains. I guess S&W didn't expect anybody to actually use the subsonic qualities of the 300 BLK cartridge. I have a whole bunch of S&W pistols and an M&P15 Sport (also an entry level AR), which my wife and I use for IDPA and 3-gun. I'm becoming disillusioned with their products.

I should have read these recent posts prior to putting another order in at Midway (a few minutes ago....DOH!)
The true soldier fights not because he hates what is in front of him,
but because he loves what is behind him.
” G. K. Chesterton
tfbit
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Re: Desperately seeking subsonic cycling - new guy.

Post by tfbit »

There's a reason that most of the people not having problems with 220 gr subs in their carbine gas 300 Blackout ARs are using A1680. Although I can understand your frustration, not being able to get your hands on any right now, you wouldn't fill your diesel trucks tank with regular and then start replacing parts till it worked. Position on a burn rate chart also has little to do with how well a powder will work in an application. H4198 is way closer to A1680 than No. 9 is but it gave me little joy when I tried it for subs.
No matter what you read on the intarweb CCI450s and CCI41s ARE NOT BALLISTICALLY IDENTICAL with H110! I'm also not a intarweb lawyer so I don't argue with anyone who is.
bani
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Re: Desperately seeking subsonic cycling - new guy.

Post by bani »

midsouth shooters has 5744 powder in stock, which is a suitable substitute for 1680.
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Re: Desperately seeking subsonic cycling - new guy.

Post by Legionaire »

^^^ 5744 works great in my 16" carbine length gas gun suppressed or unsuppressed as does 1680 of course.
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