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Discussion Starter · #1 ·
Looking for subsonic ammo that will stabilize in my fnscar17.
Purchased 168 gr amax subsonic from. Beck ammo. Supposed to stabilize in a 1 to 12 barrel. First 2 shots round next 3 keyholed. Anybody had any luck?
Have a silencerco specwar suppresser want to try it in.
 

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Have only shot factory subsonic .308 in my remington sps tactical 1:10 twist. Wouldn't go there in the scar unless you find a quality hand load to get it just right.
 

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No gas shut-off...maybe a bad idea.


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I have two boxes of Corbon subsonic .308 and I have yet to become brave enough to use it with a suppressor due to all the bad things that you hear about subsonic .308. I may just shoot it unsuppressed just to use it up without having any potential problems like a baffle strike.
 

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Guys, need an education here. I just ordered two boxes of the above from Buds. Why the caution? I have ZERO experience with subsonic. Will this not cycle in the SCAR? What else should I know? My 700 is also set up. Should I leave it for that rifle?
 

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I've heard the same thing as others have mentioned, main problem being key-holing. I'm going to stick to shooting subsonics in 5.7 and 300 blackout once I get my MPW.
 

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Save it for the 700, same reason I bought one. Don't risk your 8-900 suppressor. The SCAR barrel is not made for subsonics.
Guys, need an education here. I just ordered two boxes of the above from Buds. Why the caution? I have ZERO experience with subsonic. Will this not cycle in the SCAR? What else should I know? My 700 is also set up. Should I leave it for that rifle?
 

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Discussion Starter · #10 ·
Yes I definitely don't want to tear up my suppresser. That's why I shot it unsuppressed at paper to see if I got any keyholing.
I sure was hoping to shoot subsonic out of it. I guess from what others are saying I might be out of luck. Well maybe some one might Come up with the right subsonic load.
Thanks for the response.
 

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I would be shocked if you would get a baffle strike due to unstabilized ammo.

Keyholing is caused by uneven aerodynamic pressure on the nose of the bullet being greater than the stabilizing gyroscopic force. But you have to put that into perspective. In order to go from straight in the barrel to tilted - 2-3 degrees to get a 0.300 projectile to be 0.340 in diameter (I recall reading that 223 cans are about 0.040 oversized in the bore), you'd need about 2 degrees of rotation to touch the baffles.

2 degrees from muzzle to the end of the can, maybe 12"? At 1000 fps, that's 2000 degrees per second, 33 revolutions per second? 2,000 RPM? And your angular acceleration would have to be 4000 degrees per second squared. I don't buy it. I don't think stabilization has an impact on baffle strikes.

Now, if you get big sloppy bullets that dont have the CG concentric with the bore, you will get a big lateral jump coming out the muzzle. I'd believe that could cause a baffle strike. But if that is the case, twist rate won't fix it. If anything, twist rate would make it worse.
 

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I've seen some guys with slower twist barrels have success with the Hornady 180 grain round nose bullets. The round nose has more bearing surface than conventional match bullets so it was able to stabilize a bit better to prevent keyholes. They make a 110 grain and 150 grain round nose as well that may be easier to stabilize at lower velocities with the 1:12 twist barrel.

I haven't tried to load any yet, but if this became your primary load with the Scar you could always buy the largest size gas control screw to see if you could get the action to cycle, and then open it up more if needed. This is definitely a fun project I would pursue if I had more time.

Definitely shoot any new reloads without a can first to look for keyholes. While not real likely I have read of some guys trashing their can from unstabilized bullets.
 

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Sorry for repeating parts of a post I made in MAMS thread but the only logical reason to want to run subsonic is to aid a suppressor in quieting the rifle... subsonic and suppressors go hand in hand...

I love my .300Blk AR because AAC designed both subsonic and supersonic .300 Blk to run interchangeably in it, but...

Realize that with subsonic .300 Blackout/Whisper you are shooting a roughly 220 grain projectile at roughly 1050 fps... so close in ballistics to a .45 handgun that you can interchange the ballistics charts. With an SBR you are doing it with 10+ inch barrel so you will gain a ton of accuracy with the SBR over a .45 handgun, but the hitting and killing power is still within 10% or so of a .45 handgun. That is important for ethical hunting considerations because too often people confuse the .300 Blk SUPERsonic ballistics with .300 Blk SUBsonic ballistics where the supers slightly outperform 7.62x39 verses the subs equaling a .45 handgun. If you wouldn't hunt it with a .45 handgun, don't hunt it with subsonic .300 Blk.

Now comes the problem of .308 subsonic in our Scar 17's... you need to load at least a 220 grain projectile and run it as close to the relative speed of sound (usually 1050 to 1080 fps depending on your altitude, barometric pressure, humidity and most importantly temperature where hotter you can run faster and colder you must run slower to keep the bullet from cracking a sonic boom). If you can't get a heavy enough bullet to run the right speed, you are going to have LESS terminal ballistics than a .45 handgun or a .300 Blk. Then there is the issue of stabilizing that big heavy projectile so that it does not rip the baffles out of your suppressor... AAC (a subsidiary of Remington based here in Lawrenceville GA) put years of research and development into developing and SAAMI certification of the .300 Blk to run in the AR platform. To my limited knowledge, no one has even begun such a lengthy process to develop and certify subsonic loads for the Scar 17. And considering the drastic reduction in terms or range and terminal ballistics, I don't expect anyone with the resources to accomplish the task ever will. The Scar 17 was designed to reach out accurately much farther than the AR platform and deliver hitting power far in excess of any intermediate "assault" rifle cartridge because that is what battle rifles are intended to do. Subsonic .308 would completely neuter a Scar.

With that said, check out the FNX-45 Tactical if you haven't already. Instead of the .300 Blk SBR on my list, I think I would rather have the FNX-45 Tactical instead to do essentially the same job...

FNH USA - Distinct Advantage :: FNX?-45 Tactical
 

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I would be shocked if you would get a baffle strike due to unstabilized ammo.

Keyholing is caused by uneven aerodynamic pressure on the nose of the bullet being greater than the stabilizing gyroscopic force. But you have to put that into perspective. In order to go from straight in the barrel to tilted - 2-3 degrees to get a 0.300 projectile to be 0.340 in diameter (I recall reading that 223 cans are about 0.040 oversized in the bore), you'd need about 2 degrees of rotation to touch the baffles.

2 degrees from muzzle to the end of the can, maybe 12"? At 1000 fps, that's 2000 degrees per second, 33 revolutions per second? 2,000 RPM? And your angular acceleration would have to be 4000 degrees per second squared. I don't buy it. I don't think stabilization has an impact on baffle strikes.

Now, if you get big sloppy bullets that dont have the CG concentric with the bore, you will get a big lateral jump coming out the muzzle. I'd believe that could cause a baffle strike. But if that is the case, twist rate won't fix it. If anything, twist rate would make it worse.
I will defer to your obvious knowledge of ballistics with one notation... there is no SAAMI standard I am aware of for .308 subsonic. That makes it a Wildcat round subject to infinite variety of who ever is loading or reloading the cartridges. And since it is not a common thing to do, there are probably few well researched and proven reliable loading charts and tables. As such an infinite number of variable outcomes could be produced from a particular combination of empty case volume, projectile selection, powder type, brand, batch and amount and even the type and brand of primer used. I consider .308 subsonic to be experimental in general and specifically experimental in a Scar 17. I have neither the laboratory equipment nor resources to develop subsonic .308 that I could count on to work reliably in a suppressed Scar without causing some type of damage or raising the rate of expected malfunctions.

It is a cheaper and far more predictably reliable alternative for me to buy a .300 Blackout/Whisper AR and/or an FNX-45 Tactical for maximum suppressed range fun.
 
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Let's not run away here and assume I know more than I do ....

My only comment is that I find it hard to believe there is any destabilizing force acting on a bullet such that it will begin to pitch/yaw at33 revolutions per second coming out the muzzle.

1. Hard for me to believe does not mean I am right. I like to think it does, but I've been wrong before, and I will again.
2. I agree with you, there may or may not be good load data out there. To get good consistency, you want the powder to nearly fill the case, so the pressure spikes quickly,a nd the adiabatic shock wave ignites all the powder early, giving it a chance to burn. If you get a low volume fill, as I assume you would using a 308 loaded to subsonic loads, the powder does not ignite as well, and a lot of it goes out the barrel, and back into the gas system. Exactly the reason the 300BLK will run subsonic, while the 762x39 does not do it well is because the 300BLK case is smaller, so it is a higher fill level.
 

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yea, still not confident running the subsonic .308 through my AAC SR-7, why risk it, especially with my 300 blk rifle on its way, will be plenty of subsonic quiet firing once the MPW is in hand
 

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I am sooo disappointed I shouldn't shoot my subsonic ammo, and this thread helped find the technical dialogue to put the search whether "To shoot, or not to shoot" the sub ammo question out of my 17s. Thanks for that.
 
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