Target fps for subsonic hunting loads?

[thresk]

What speed do you hunters load for subs? Working on a 168gr load for hog hunting and am at about 1000fps right now but wondering if I should go higher (minimum speed of sound for me will be 1100fps, so I could add 50fps and gain ~10% more energy?). Want it to be as quiet as possible but don't want to give up any more energy than I have to, I hear a lot about the "trans-sonic zone" and would like to avoid that but don't really know much about it or how far below sos it goes. Might be splitting hairs but want to get this "right". Thanks.

[smustian]

Find the best accuracy load that is less than 1050 and you will be golden.

[tallburnedmidget]

Find the best accuracy load that is less than 1050 and you will be golden.

+1

[bangbangping]

Find the best accuracy load that is less than 1050 and you will be golden.

Yep. And that often can be found around 950 or so. I would suggest a heavier bullet over higher velocity if you're concerned about energy.

[steven11b]

Why 168gr bullet? I dont think there are 168gr .30cal bullets that will expand at sub velocities.

[thresk]

I would suggest a heavier bullet over higher velocity if you're concerned about energy.

Well I'm also concerned about sound, so wanted something in between the superquiet sub-140gr bullets and the louder 200gr+ heavy hitters.

Why 168gr bullet? I dont think there are 168gr .30cal bullets that will expand at sub velocities.

See above, and I was able to swap with a friend for some lehigh bullets - only got 30 of em but they appear to be really good, also pricey so want to get close to the speed I want with a cheapo bullet before testing them.

[Klem]

The supersonic crack builds from 90fps below the speed of sound to its loudest 150fps above the speed of sound. This is why commercial loads aim for around 1,010fps. Below the '90fps below the speed of sound' threshold there is no supersonic sound signature so you may as well load up to as close to that as possible. You won't be able to eliminate the sound of the bullet pushing the air aside while subsonic so again, you may as well load for 1,010fps.

Loading 168gns for subsonic is going to give you problems and comes with risk. Problems with having enough pressure to cycle your AR and risk with the fill capacity dropping below the 80% mark. Below 80% powder fill in a case and you risk SEE (Secondary Explosion Effect) and Flash-Over, basically damaging your gun.

The muzzle pressure (sound) between a 168gn and 220gn is almost the same so you won't save any sound at the firing point. Once the bullet is in flight a subsonic 168gn will sound exactly the same as a 220gn so again, no savings there.

Muzzle Pressure
220gn SMK @1,010fps = 3,650lbs
168gn SMK @1,010fps = 3,555fps

(Reference: Quickload).

If you really want to save sound then going the lightest 30cal bullet and forgoing the pressure needed to cycle the action will give you a noticeable difference. Something high bulk/weight ratio like a Barnes 110TTSX so you have enough shank in contact with the case neck without it being ridiculously short. Using around 6gns of Trail Boss.

Muzzle Pressure
110TTSX @ 1,000fps -= 1,530lbs...So, half the sound at the muzzle than your 168 or 220gn Sierra's.

In summary, going half way between the heaviest weight 30cal bullets and the lightest is not going to help. You don't save on sound. It is unlikely you will have enough pressure to cycle your gun, and you end up having to fill cases below 80% (safe levels) to keep them under 1,100fps.

Here's a sound file of a suppressed Blackout firing 220gn SMK's at a steel gong, 100yds. 12 shots...Four recorded at the firing point The next four recorded at the 100yd mark directly below the steel gong. Finally the sound at the 100yd mark without gong. In other words, the last eight shots are what the target hears 100yds from the firing point. While it sounds loud at the firing point the target is probably going to be more spooked by what your bullets are hitting and the sound of a 30cal bullet pushing through the air. You won't be able to mitigate those two sounds by shooting a lighter bullet or using a suppressor.
http://vocaroo.com/i/s0Uy7B9C8Jam

(the squeaking sound is the gong swinging in the frame. The three lots of four rounds have been spliced together with the software, Audacity. As the speed of sound is faster than the bullet you can hear the firing point a fraction before the steel gong is hit on shots 5-8 which I think is pretty cool).

[dellet]

The biggest factor in a quiet sub sonic load will be powder choice (even if you are not using a suppressor).

Choice of powder will depend first on what you are shooting, hand fed or gas fed. Then on barrel length.

You can get a 168 grain bullet to run quietly and reliable in anything 300 Blackout. It get's more difficult in AR's with a barrel length over 20" and carbine gas to stay sub sonic.

Bullet flight noise will be determined more by bullet shape than anything else. The 168 Lehigh will probably be in the running as one of the loudest.

The trans-sonic zone is basically 950-1350 fps and is more of a worry for bullet stability and accuracy than noise as long as you stay below speed that would cause a crack. 1000 fps is a nice round number to try for.

The more information about what you are shooting you can give, the better answers people can give you.

[thresk]

^^Thank you both for the great info, I should have mentioned this is for a bolt rifle, using W231 powder as it's the fastest I have on hand.

Bullet flight noise will be determined more by bullet shape than anything else. The 168 Lehigh will probably be in the running as one of the loudest.

What other factors besides ballistic coeff. do you need to look at? I just figured the higher the bc, the quieter but idk.

The muzzle pressure (sound) between a 168gn and 220gn is almost the same so you won't save any sound at the firing point.

Hmm didn't know the pressure was so similar, might have to look at some heavier bullets (don't want to go lower as it will need to take down hogs up to 200lb).

[dellet]

^^Thank you both for the great info, I should have mentioned this is for a bolt rifle, using W231 powder as it's the fastest I have on hand.

Bullet flight noise will be determined more by bullet shape than anything else. The 168 Lehigh will probably be in the running as one of the loudest.

What other factors besides ballistic coeff. do you need to look at? I just figured the higher the bc, the quieter but idk.

The muzzle pressure (sound) between a 168gn and 220gn is almost the same so you won't save any sound at the firing point.

Hmm didn't know the pressure was so similar, might have to look at some heavier bullets (don't want to go lower as it will need to take down hogs up to 200lb).

For lack of a better explanation, the shape of the bullet will determine the pitch or tone or the hissing sound the bullet makes as it passes by. Big flat points and big hollow points generally make more noise. That 168 Lehigh has about the biggest hole in the front of any 30 cal bullet I know of.

Here's a good read

http://firearmsid.com/Feature%20Article ... llets2.htm

The flash and bang of firing will likely be better thing to work on than bullet flight noise.