Reloading subsonic .308 and .223?

[libertyman777]

What are the problems/situations to keep in mind when loading these rounds subsonic?

Thanks,

Paul

[LouBoyd]

Long range precision subsonics (such as the Whisper series) all have a few things in common.
1. They shoot low drag heavy jacketed bullets (heavy for their caliber)
2. The have faster twist barrels than is required to shoot the same bullets at supersonic velocities.
3. They have small capacity cases so that the required engraving forces can be achieved, yet still have a large expansion ratio in a reasonable length barrel.
4. Fairly fast powder is used to achieve high chamber pressure without much velocity.
5. Barrels are usually quite short. Longer barrels hurt velocity consistancy whch is very important to subsoinc accuracy.

Both the 308 and 223 cartridge are designed to shoot relatively light bullets from relatively long barrels at relatively high velocity. Primarily because of their large case capacity neither but also because of longer twist rates and long barrels typical 308 and 223 rifles aren't very good for subsonic use. Sure, you can push a bullet out the bore at around 1000 fps, but it's very unlikley to give close to the accuracy or range of one of the Whisper series in a purpose built rifle.

What are you trying to accomplish? What performance do you want? If it's just a low recoil plinker then you can load light charges of fast powder with cast lead bullets.

[libertyman777]

Originally Posted by LouBoyd

What are you trying to accomplish? What performance do you want? If it's just a low recoil plinker then you can load light charges of fast powder with cast lead bullets.

Well, I do know that my next can will be .30 caliber and that I'm switching barrels using a Savage action. I will certainly be shooting supersonic with both cartridges. But I'm also looking to experiment with some subsonic reloading for these rounds too.


It would also be nice if I could find a subsonic hunting round for these two as well. I would assume that they would have the same expansion problems that the Whisper has, correct?

My .308 barrel is a done deal right now. It's a 26" tube 1/10 twist. I haven't bought the .223 yet. You say I should go for fast and short? What length? Is 1/8 fast enough? 1/7?

Thanks,

Paul

[mooster1223]

Typical whisper projects have 16" barrels with 1/8 to stabilize the 240SMK.

[LouBoyd]

Originally Posted by libertyman777

Well, I do know that my next can will be .30 caliber and that I'm switching barrels using a Savage action. I will certainly be shooting supersonic with both cartridges. But I'm also looking to experiment with some subsonic reloading for these rounds too.

It would also be nice if I could find a subsonic hunting round for these two as well. I would assume that they would have the same expansion problems that the Whisper has, correct?

My .308 barrel is a done deal right now. It's a 26" tube 1/10 twist. I haven't bought the .223 yet. You say I should go for fast and short? What length? Is 1/8 fast enough? 1/7? =
Thanks,
Paul

No, What I was trying to say is to quit trying to use large volume cases for subsonics. Quit trying to make one barrel perform well at 1000 and 3000 fps. If you do the perfomance of both will be compromised.

My advice would be to have a barrel made for your Savage specifically for subsonic shooting. The most standard and arguably the best performing subsonic is a 30 cal 8" twist barrel chambered in 30-221 (aka 300 Whisper or 300 Fireball). Make it no more than 16" long (to meet US legal requirements for a rifle) . Better would be 10 inch if ballistics is the only consideration . Thread both the 26" 308 and the 30-221 to fit the same 30 cal suppressor. You can then shoot full load 308's with greatly reduced muzzle blast or the 30-221 quietly. That way you won't waste either cartridge's excellent performance.

223 is an excellent high velocity cartridge, but for a subsonic 22 you'll find the 22LR with it's tiny case capacity far more satisfactory.

[libertyman777]

Oh, I understand now. That makes a lot of sense.

You bring up another question to my mind. Why is 10" better? Is it due to length of the tube for burning the powder and then limiting possible velocity?

If so, has anyone tried to backbore a 16" barrel to 10"? If so, do you think a can could still be threaded?

Paul

[LouBoyd]

Originally Posted by libertyman777

You bring up another question to my mind. Why is 10" better? Is it due to length of the tube for burning the powder and then limiting possible velocity?

If so, has anyone tried to backbore a 16" barrel to 10"? If so, do you think a can could still be threaded? Paul

10" is enough barrel to easily accelerate a 240 grain jacketed bullet to 1000 fps using the 30-221 cartridge with reasonable loads. A longer barrel just requires more powder to overcome bore friction. That's not a problem unless the variablity of the bore friction from shot to shot causes variable muzzle velocity and excessive vertical stringing. Variable bore friction isn't the only cause of variable muzzle velocity, but variable muzzle velocity is usually the limiting factor in the useful range of a subsonic firearm. For shooting at typical hunting ranges, say 200 yards, a 16" barrel vs a 10" barrel shouldn't make much difference. Vertical stringing increases with the square of the time of flight and more than the square of the distance to the target.

The only reason not to use a 10" barrel are legal reasons under Federal and state laws. I don't know how a back bored barrel (or a permanantly affixed extension) for use with or without a suppressor would be treated legally.