5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

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BlogSarge
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5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by BlogSarge »

I built a 5” AR pistol in 300blk. Not sure why. But no reason why not, so I went ahead.

I chrono’d two supersonic loads; Barnes 100 Black Tip and Maker 85gr Overwatch.

Both loads functioned flawlessly both with and without can. Both grouped decently both with and without a can. Neither load’s brass seemed to show signs of over pressure, although a few had dings on the case mouth. Ejection was at about 5 o’clock, where I normally see anywhere from 2 to 4 o’clock with my other ARs.

But, with both loads, the suppressed velocity was about 900 fps slower than unsuppressed. Typically in longer barrels I see Either no significant change, or more commonly a slight increase.

110 BlackTip- Suppressed 1002. Unsuppressed 1901

85gr Maker-. Suppressed 1180. Unsuppressed 2144



BLK???

Is the extra back pressure opening the action before the bullet exits, causing slower speeds? Anybody have thoughts?
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dellet
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Re: 5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by dellet »

I would suspect chronograph error. What type was it?

If point of impact did not change significantly I would really question chronograph. At 50 yards I would expect around an inch low or more. At 100 more like 2-3 " low.
300 Blackout, not just for sub-sonics.
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bangbangping
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Re: 5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by bangbangping »

dellet wrote: Sat Apr 04, 2020 7:36 pm I would suspect chronograph error.
This. Unless it's a .22 suppressor and the bullet has to force its way out. :lol:

I just can't imagine a suppressor slowing a bullet down at all, much less 900 fps.
BlogSarge
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Re: 5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by BlogSarge »

It is a Caldwell G2.

I wondered about it being the problem. I did suppressed, unsuppressed and suppressed again with the same results. And, I zipped 20 or 25 rounds through it out of our new department guns, which are integrally suppressed and seemed to get correct fps based on a prior run of a few other of the new guns.

I think I’ll have to set it up again and shoot some more. I can’t think of any other reason.
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Re: 5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by BlogSarge »

bangbangping wrote: Sat Apr 04, 2020 8:01 pm
dellet wrote: Sat Apr 04, 2020 7:36 pm I would suspect chronograph error.
This. Unless it's a .22 suppressor and the bullet has to force its way out. :lol:

I just can't imagine a suppressor slowing a bullet down at all, much less 900 fps.
I had to stop and think about this. I built a 350 Legend upper and blissfully threaded a 22 cal muzzle brake on it. It did n’t group too well! But the can is a 762-SDN-6, so it should be good with the blackout!
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plant.one
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Re: 5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by plant.one »

BlogSarge wrote: Sat Apr 04, 2020 10:53 pm
I built a 350 Legend upper and blissfully threaded a 22 cal muzzle brake on it. It did n’t group too well!
oppsie! lol i bet that was.. interesting :shock: :mrgreen: :mrgreen:
Reloading info shared is based on experiences w/ my guns. Be safe and work up your loads from published data. Web data may not be accurate/safe.
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BlogSarge
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Re: 5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by BlogSarge »

Yup. I was getting two or three pieces of the bullet hitting the target. Ruined the barrel, of course. So I built a 350 SBR and have a GSL Technology can coming specifically for it.

By the way, I still have brass, lol!
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Re: 5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by noname »

Maybe the short barrel (5 inch) has something to do with the 900 fps issue. Do not take it as gospel but from what I have learned a 9 inch barrel is the shortest to get optimal, "consistent" results in 300 BO. I have one suppressor that the manufacturer said never use it with a can less than 9 inches.
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dellet
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Re: 5” AR Pistol- Dramatic FPS Decrease w/ Suppressor

Post by dellet »

noname wrote: Wed Apr 08, 2020 8:44 pm Maybe the short barrel (5 inch) has something to do with the 900 fps issue. Do not take it as gospel but from what I have learned a 9 inch barrel is the shortest to get optimal, "consistent" results in 300 BO. I have one suppressor that the manufacturer said never use it with a can less than 9 inches.
The suppressor should not rob velocity in a barrel that short it should add.

You would have to define optimal and consistent. 1900 fps with a 150 grain bullet or 2200 fps for a 110 grain bullet from a 7 1/2” barrel may not be optimal but it is adequate. That would be no different than saying a 9” barrel is not optimal compared to a 16” or a 16” to 20”.

As for consistent, MOA on demand should be considered consistent and is quite easily done with a sub 9” barrel.

If a suppressor can not handle the muzzle pressure of an 8” barrel shooting supers, it should be considered sub par when compared to almost anything on the market without aluminum baffles or blast chamber.
300 Blackout, not just for sub-sonics.
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Re: 6” AR Pistol- Dramatic FPS Decrease w/ Suppressor..... Not Anymore

Post by BlogSarge »

I set up the chronograph again today to see what results I would get with the suppressor on.

The 110 gr Black Tip yielded 1968 Fps and the 85 Maker gave 2222fps. Unsuppressed speeds were 1901 and 2144, so these suppressed results today are right where they were expected to be.

I don’t know what happened the other day, must have been chrono gremlins. Certainly wasn’t operator error....... :roll:
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