Subsonic Ammo Turning Supersonic

[tulsacrittergetter]

Hey guys. Been a long time since I posted. Hope everyone is doing good.

I have an issue with a couple different types of ammo. I am shooting 300 Blackout subsonic rounds (220 grain) through a 16" barrel with a 7.5" suppressor. The report from the muzzle is very quiet, but I'm still getting a sonic crack when the rounds are fired. I know what subs should sound like. I shoot several suppressed .22LR's, and there isn't a sonic crack, and there shouldn't be.

The same thing happened this morning with some .223 subsonic 60 grain rounds I purchased from Beck Ammunition. I shoot a lot of varmints at night (suppressed .22LR), but I need something more powerful than .22LR for the larger raccoons. So, I thought I would try the subsonic .223's since most of my targets are 50 yards or closer. I just stepped out back and popped off a few of the .223 subs, and they were very quiet, but I heard a sonic crack from both rounds.

What the heck? Under what conditions will a subsonic round turn supersonic, and how can I fix this? Is it the longer barrel? Usually, 300 Blackout subs are shot from 10.5" barrels with suppressors. So, maybe shooting 300 Blackout subs from a suppressed 16" barrel would cause the round to gain some velocity? Also, the .223 sub was shot from a suppressed 20" barrel, 1:9 twist. So, in both cases, a longer than normal barrel was used.

Any information from you guys will help. Thank you.

 

[emapples]

Hey guys. Been a long time since I posted. Hope everyone is doing good.

I have an issue with a couple different types of ammo. I am shooting 300 Blackout subsonic rounds (220 grain) through a 16" barrel with a 7.5" suppressor. The report from the muzzle is very quiet, but I'm still getting a sonic crack when the rounds are fired. I know what subs should sound like. I shoot several suppressed .22LR's, and there isn't a sonic crack, and there shouldn't be.

The same thing happened this morning with some .223 subsonic 60 grain rounds I purchased from Beck Ammunition. I shoot a lot of varmints at night (suppressed .22LR), but I need something more powerful than .22LR for the larger raccoons. So, I thought I would try the subsonic .223's since most of my targets are 50 yards or closer. I just stepped out back and popped off a few of the .223 subs, and they were very quiet, but I heard a sonic crack from both rounds.

What the heck? Under what conditions will a subsonic round turn supersonic, and how can I fix this? Is it the longer barrel? Usually, 300 Blackout subs are shot from 10.5" barrels with suppressors. So, maybe shooting 300 Blackout subs from a suppressed 16" barrel would cause the round to gain some velocity? Also, the .223 sub was shot from a suppressed 20" barrel, 1:9 twist. So, in both cases, a longer than normal barrel was used.

Any information from you guys will help. Thank you.

I am pretty sure longer barrel lengths can increase your muzzle velocity , but the techies will be on soon to confirm

 

[Mad Professor]

1) Have you Chronographed any of the mentioned ammo? Or are you basing everything on your ear and manufacturer claims?
2) I don't see a 60 gr .223 on Beck Ammunition's page. I see 52, 55, and 75gr and they are targeting all of them at 1010.
3) What manufacturer of 300BLK 220? I clocked Remington factory 220s at 1091-1167 with an average of 1126 from a 16" barrel, the same ammo went 869-971fps from a 9" barrel. The ES and SD of both were not what I call acceptable. But I've clocked some reloaded ammo that was just as bad. My reloads (mixed case) using A1680 with a the same bullet were 918-945fps from a 9" and 1095-1120fps from a 16" barrel. With the test of my ammo, I would be increasing the speed a bit on my 9" load and maybe backing off a touch on my 16" load if I was gathering critters with it. Maybe target 1050-1070 fps.


The speed in which they will break the sound barrier will depend on the air density. So primarily air temperature will be the biggest factor.

Different powder burn rates will greatly impact what the effect of barrel length will have on the speed.

Also most bullets for 300 won't have any expansion at subsonic speeds. If you want expansion, you need to be looking at some of the exotics like Maker or similar.

In the .22 world for varmit, you might try one of 2 segmented ammo offerings from CCI. They are pretty devastating on small game. #0064 is 32 grain rated at 1640fps #0074 40 grain rated at 1050fps. I don't see supersonic speeds from the #0064 out of a suppressed pistol. They make a "quiet" version #0970 that is only 710fps, but I'm not sure I would mess with it.

 

[Shadowrider]

So, maybe shooting 300 Blackout subs from a suppressed 16" barrel would cause the round to gain some velocity?

I'd just about bet on it though I have no experience with the caliber or that brand ammo. My competition 9mm loads are loaded with one of the fastest burning powders on the chart. I've tested them in 3.5", 4.5, 5.0, 7.0 and 16" barrels and can see an increase in velocity in every case. I was actually expecting the 16" carbine to drop some. It didn't.


Sent from my iPhone using Tapatalk

 

[dennishoddy]

I'd just about bet on it though I have no experience with the caliber or that brand ammo. My competition 9mm loads are loaded with one of the fastest burning powders on the chart. I've tested them in 3.5", 4.5, 5.0, 7.0 and 16" barrels and can see an increase in velocity in every case. I was actually expecting the 16" carbine to drop some. It didn't.

Burn rates are critical for velocity on barrel lengths as you well know.
There is a reason we use shotgun powders in our pistol loads.

 

[Jwryan84]

Need shorter barrels

 

[tulsacrittergetter]

1) Have you Chronographed any of the mentioned ammo? Or are you basing everything on your ear and manufacturer claims?
2) I don't see a 60 gr .223 on Beck Ammunition's page. I see 52, 55, and 75gr and they are targeting all of them at 1010.
3) What manufacturer of 300BLK 220? I clocked Remington factory 220s at 1091-1167 with an average of 1126 from a 16" barrel, the same ammo went 869-971fps from a 9" barrel. The ES and SD of both were not what I call acceptable. But I've clocked some reloaded ammo that was just as bad. My reloads (mixed case) using A1680 with a the same bullet were 918-945fps from a 9" and 1095-1120fps from a 16" barrel. With the test of my ammo, I would be increasing the speed a bit on my 9" load and maybe backing off a touch on my 16" load if I was gathering critters with it. Maybe target 1050-1070 fps.

Here is the 60 grain .223 subsonic offered by Beck Ammunition: http://beckammunition.com/ammunition/.223-Rem/223-rem-subsonic-60gr-v-max-subsonic-new.html

 

[Mad Professor]

Here is the 60 grain .223 subsonic offered by Beck Ammunition: http://beckammunition.com/ammunition/.223-Rem/223-rem-subsonic-60gr-v-max-subsonic-new.html

You need to chronograph it to make sure you are getting what they advertised. By those specs, it should stay subsonic.

 

[tulsacrittergetter]

I went to a friend's house last night and brought all of my cans. I have a 1.5" OD / 1.350" ID titanium form 1 can, and it was in this can that the .223 and 300 Blackout rounds were going supersonic. I also have a 1.765" OD / 1.480" ID titanium + aluminum form 1 can which obviously has much more volume than the smaller titanium can, and the .223 subs were 100% subsonic through this larger can. Both were shot on a 16" barrel.

I have been using CCI 40-Grain Subsonic Segmented Hollow-Point, which seemed to put down possums and other smaller critters better than the solid point Aguila and other CCI subsonic rounds I am accustomed to using, but they weren't doing so well against larger raccoons. I've had a couple get away from me wounded (which I later found dead). So, I am really wanting to try the .223 subs because I'm dealing with the same velocities but a larger projectile. And, inside 50 yards, there isn't much (if any) bullet drop inside 60-70 yards. Plus, Beck Ammunition sells an expanding hollow-point .223 specifically for this situation.

Until I can afford to get a shorter .223 barrel for my AR, I'll just have to use my larger form 1 can when hunting since I don't have the luxury of using supers when I hunt varmints. I wish I did! I'd just use full-power 300 Blackout 150-grain rounds.

ORRRRRR, I could build a 9mm AR pistol and shoot subsonic hollow points

Of course the real answer is to start reloading like so many people on this forum have suggested that I start doing. Relying on store-bought ammo to achieve what I'm trying to do has proven to be challenging.

Thanks for the replies. I appreciate it.

 

[beastep]

I have seen the Rem 220s go super under a lot of different conditions. And the SD on those is horrible.