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Old February 16, 2000, 01:59 AM   #1
headroom
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What is needed to load up subsonic loads in a highpower cartridge like a 308 or '06. I don't imagine you can use regular powder with low charges.
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Old February 16, 2000, 10:12 AM   #2
Art Eatman
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Pistol or shotgun powders; and heavy bullets.

In an '06, I know 20 grains of 2400 will get you around 1,800 ft/sec, which is still supersonic. So, even less powder, and a 220-grain bullet would maybeso work out okay. Probably ought to use a cast-lead bullet...

I have loaded a .32 lead ball (What's that, 00 or 000 Buck?) in front of five grains-weight of some kind of shotgun powder. Good squirrel load.

FWIW, Art
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Old February 16, 2000, 10:43 PM   #3
labgrade
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"don't imagine you can use regular powder with low charges."

You can, it's just not safe low charges with some powders can cause excessive pressures.

Why sub-sonic? Or are you looking for something that's only more pleasant to shoot?

Hornady makes .310" round balls that when loaded with 5 or so grains of Unique or Bullseye makes a nifty "gallery load."

American Rifleman - Oct '87/Shoot Cheap by Roy Dunlap has an excellent article on low-cost, low-velocity loads for several high power rifles. Call 'em up & try to get a copy. Good stuff.

I shoot a Lyman #31141/170gr cast using Unique at about 1500fps. Very accurate in my 30-06 to 100yds (never tested it further), cheap to shoot & recoil is less than a .223 (probably quite a bit less).

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Old February 18, 2000, 01:17 PM   #4
headroom
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The reason subsonic came to mind is that i was thinking the other day of this past summer i sat on the edge of a prairie dog town on a real windy day, and eventually walked pretty much into it with a 22lr and just wondered if you could us a rifle that was not too loud but would still hit a dog hard unlike the 22. The only rifle i have is a 280 right now and i just try to make it as useful as possible.
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Old February 18, 2000, 03:52 PM   #5
saands
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The Lee reloading manual has an interesting section on developing lighter loads. The one thing that seems to be common in all I've read on this is that it is best if you can avoid lots of empty space in a cartridge. This seems to make the .308 a better candidate for sub-sonic than the .30-06, wven though they perform about the same at full power. I'd look at the Lee manual ... and be REALLY careful with the edge of the envelope ... the ice you're walking on there is really thin!
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Old February 19, 2000, 08:27 AM   #6
Cougar
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At a club here in Nothern Ohio they have an informal competition using their high-powered rifles at the club's indoor range. They are using their 6mm Rem TCU(?) match rifles with a cast bullet load that they told me runs around the sub-sonic threshold. Quite the plinker, wouldn't you think?
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Old February 19, 2000, 11:04 AM   #7
Ricciardelli
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"subsonic" doesd not relate to the loudness of the fired cartridge. It relates to the speed of the bullet, and the sound generated when the bullet exceeds the speed of sound.

Example: The old-fashioned "Cherry Bombs"
and "Ash Can" firecrackers did not break the sonic barrier, however, they were loud.

Second example: Even an air-operated pellet pistol makes noise...

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Old February 21, 2000, 07:12 AM   #8
Cougar
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Yes, I know that the sub-sonic/super sonic threshold is actually the speed of sound.

The speed of sound (in air) varies with air density, normally around 1070fps at sea level. I could give you the actual formula for figuring it out for yourself, but why bother? For most of us, that is those of us in the US that live below 5000'msl, it really doesn't matter all that much.

The major reason for 'sub-sonic' ammo is to reduce the sound signature of the bullet as it flies though the air. A super-sonic bullet actually makes a sonic boom, albeit a small one. That is the 'crack' one hears as a supersonic bullet flies by (a separate noise from the bang of firing).

Another reason for sub-sonic ammo is that an object flying through the air at sub sonic speeds has different aerodynamics than one at supersonic speeds. As the speed of an object increases, the shock wave pattern changes. When the object reaches the speed of sound, the shock waves detatch from the object. At this transition point, if the object has some minor imperfections at the rear edge, the force of the shockwave will be uneven, causing the object to deviate slightly in its flight. This transition effect also works in the reverse, like when a supersonic object (a bullet) slows down to the speed of sound.

This last reason is why target ammo for a .22LR is always subsonic. The heel of a .22LR bullet is very hard to make perfectly. A .22 high velocity round is just barely supersonic. As it slows and reaches the critical speed, the bullet will upset its flightpath slightly.

For those of us that are into Physics heavily, F=mv^2. Force = mass x velocity x velocity. The force needed to push the same bullet at a lower velocity is less than a faster one by a whole bunch. This means that we use less powder to make a subsonic round than a supersonic round for the same bullet weight.

Less powder = less noise at firing. Less noise means you can tolerate it better (especially in a confined space like indoors).
For every action there is an equal and opposite reaction. Less powder = Less force. So less powder = less recoil force. Less force (speed) on the bullet means less energy downrange. Less energy downrange means that less energy will be transferred to the backstop. Less energy transferred to the backstop means that at some point, you can stop the bullet with an indoor range type backstop without blowing holes through it! Indoors is neat when the weather gets too nasty to go outside to an outdoor range.
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