Few questions on subsonic rifle ammo

[Skribs]

I just have a couple of questions on subsonic rifle ammo (specifically talking about rounds designed to be subsonic in a normally high-velocity platform, like subsonic 5.56 or 7.62 ammo):

1) In an UNSUPPRESSED rifle, is there any difference in noise? Not just the dB volume, but also in the way the noise is perceived.

2) Subsonic ammo typically has significantly lower energy than a normal cartridge. Does this affect cycling at all in gas systems? Does this affect the felt recoil?

3) To my understanding, subsonic ammo would create a wound profile more similar to a pistol round, in that the majority of the trauma is caused by the crush cavity instead of the stretch cavity and/or fragmentation. Is there anything special about how subsonic rifle ammo causes tissue damage, or is the basic design just to have it yaw and crush along the way?

 

[pseudonymity]

For #1, I would say yes, but as the bullets are larger and larger, the difference is harder to discern since the muzzle blast tends to be louder. For instance, the Hi Point carbine in .45 has a pretty distinctive sound - louder than a .22lr for instance, but nowhere near the muzzle blast of the same round from a pistol. The difference in a .22lr with a long barrel is really pretty easy to hear IMO - while the muzzle blast from a .22lr at 1050 fps and 1250 fps is not much different, the HV round has a very definite "crack" to it that the standard velocity round does not.

 

[Telekinesis]

In an unsuppressed rifle you may have a small difference in noise, (and the sonic crack) but it would be negligible. Think about the difference in 115gr 9mm (supersonic) versus shooting 147gr (mostly subsonic) ammo from a pistol, both sound roughly the same.

Depending on your rifle, subs may or may not affect cycling. For example some .300 blackout rifles will not cycle reliably while shooting subs unsuppressed (suppressor adds back pressure that helps the gas system). but if you have an adjustable gas system like a FAL (or an AR-15 with a switchblok) you can just tune it to the lower pressure.

I don't have any first had experience, but my suspicion is that you're right about the terminal performance of subs. It depends on your specific round, but from what I can see you're getting something close to .45ACP when it comes to terminal performance. You're limited to about 1000-1050fps to keep it subsonic so that means velocity can't really help you get the rifle-like temporary cavity. Something else to consider woud be that some rifle rounds may not expand very well when fired at low velocities.

 

[Cee Zee]

If you're talking rimfire ammo then yes there is a big difference in the noise level. You don't get the sonic boom from the bullet breaking the speed of sound. With larger rounds it's hard to tell since most calibers are either sub-sonic or super-sonic. For example you rarely see a super sonic .45 round or a sub-sonic 30.06 round. I don't think I've ever seen either. AFAIK the main caliber that varies between super and sub sonic is the .22LR. And there you will see a big difference in noise level. With bigger rounds the sonic boom would have to be there but the powder going off is so much louder that you likely wouldn't notice the difference.

As far as feeding a semi-auto goes, again if you're talking a .22 there is a difference although many semi-auto .22's will cycle with most ammo that is not real far below the speed of sound. If you drop down to 800 fps (as some rounds do like the CCI "Quiet" rounds) or even lower to the speed of the Aquila Colibri ammo then almost certainly you will not see a .22 cycle.

I don't know what other rounds you're talking about that might be either sub or super sonic so I can't comment on that. I could easily be missing something or just overlooking something. That's what happens to us old folks.

I do see what people here are saying about other rounds that might be either sub or super sonic but I have no experience with the details you're looking for. I can only talk about rimfire ammo.

 

[Skribs]

To be clear, I'm talking about the "tactical" subsonic ammo, like 100gr + 5.56 rounds or the 220 gr .300 Blackout. Where you're talking a difference between say a 125 gr bullet at well over 2000 FPS vs. a 220 gr bullet at 1000. In addition to the lack of sonic boom, I think there is less powder in these (could be wrong, though) so I have to ask about the sound.

Edited my OP for clarification.

 

[mtrmn]

When I load up subs for mine they do have less muzzle blast than full-house loads. A 55gr FMJ sub drops about 11" at 100 yds compared to a full house load. The full power .223 loads through my YHM 7.62 Titanium sound maybe a tad louder than a normal un-suppressed 22LR that's supersonic. The subs sound about like a Daisy BB gun.

I have not and will not fire any subs with bullets that weigh 100 gr or more through any of my 223's. I do not want to risk baffle strikes due to the bullets not being stabilized in my 1/9 twist barrels.

Subs will not cycle any of my ARs. I don't know, but I think you have to have a gun especially set up for use with subs for it to be reliable.

In order for a sub to be a sub, you must decrease the powder (and use a different type) until the velocity is somewhere close to 1050 fps. There are very few bullets that will mushroom or even deform when fired into water at this velocity. Some companies claim to have bullets that will, but I haven't spent the coin to try any. I have no need for hunting or anything else with sub loads, only experimentation. They are very underpowered with rainbow trajectories, and I pretty much quit hunting several years ago. If it were legal for me to hunt suppressed, I would still use full power loads.

The supersonic crack is very loud-much louder than I thought it would be. I had a trusted friend fire my 308 AR while I stood about 10 yds to the side of the 100 yd targets. I was behind a large tree. The sound of the bullet passing by was just about as loud as the sound I hear when standing next to the shooter. Like someone shot a 22LR. The sound came from the direction of the closest point where the bullet passed my position. I did not hear a single sound from the direction of the shooter. Any and all sound from the shooter's position (a 308 AR cycling and the tiny amount of muzzle blast left over from the suppressor, if any) was drowned out by the bullet noise.

I now know why deer etc react so strangely if you shoot at them and miss. All they heard was a crack right above their back or under their belly that sounds like a 22LR. Unless you hit something near them, there's no visual confirmation of what made that noise. They don't know which way to run, and many times just stand there freaked out, or run toward the shooter getting away from the bullet's impact behind them.

 

[the count]

You better know what you are doing when creating sub sonic rifle ammo. It's a fun way to blow up your gun if you use the wrong powder/charge combination. I recently made a batch of subsonic rounds in 223 using Trail Boss. It made my AR15 into a single shot rifle. Just not enough power to cycle a semi auto. In a bolt action, no problemo.

 

[Skribs]

I was planning on buying it rather than making it.

 

[mtrmn]

Again, unless you have a dedicated setup, sub ammo WILL NOT cycle an AR.

In 22LR, I have no trouble at all with cycling sub ammo through semi's.