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Friday, March 4, 2011

Subsonics ...

I'm getting ready to join the suppressor crowd, and I've been playing around with some numbers. Obviously, .22 subsonic is loaded pretty generically, as are centerfire pistol calibers. To get the most of centerfire rifle boolits, you need to handload.

The speed of sound is your limiting factor in handloading (we'll assume your suppressor is capable of handling the gas involved). The product of the speed of the projectile and the weight of the projectile give you the energy possible, hence the heavier boolits used (generally) in subsonic ammo.

Handloading subsonic ammo is, I've heard, a tedious process, because the accuracy you need to use exceeds all but the most expensive powder measures. The velocities you want are tedious to come by as well. The speed of sound fluctuates with environmental factors (METT to you arty men out there!), but the biggest factor is temperature. By my quick, down-'n-dirty calculations, you can use hotter subsonic loads in hot weather (because the speed of sound increases with temperature). A change of 100° F results in a change of about 110 f/s in the speed of sound. With a projo weight of 250 grains, that equals 6.7 ft/lb of energy difference between 0° and 100° (at 0% humidity).

So to figure out a single load, you need to determine what the lowest general temperature you're going to be shooting at, develop your load based on that temperature to ensure you don't go supersonic.

From here, you can get as anal as you want, loading your subsonics to fit increments of 10° or what ever your OCD will allow!

This piece is based on nominally scientific stuff, so if I've made an glaring errors, feel free to correct me.


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