Gas Pressure at Muzzle .308 / .30-06

[Para Bellum]

Hi Folks,

I'd like to know, which hunting rifle would be the least damaging to my ears and to my dog's ears. As far as I understand, 6dB in sound pressure mean DOUBLE the noise, so what seems little, can be a lot. I have found this data here:

.223, 55GR. Commercial load 18 _" barrel 155.5dB
.243 in 22" barrel 155.9dB
.30-30 in 20" barrel 156.0dB
7mm Magnum in 20" barrel 157.5dB
.308 in 24" barrel 156.2dB
.30-06 in 24" barrel 158.5dB
.30-06 in 18 _" barrel 163.2dB
.375 — 18" barrel with muzzle brake 170 dB

I assume that the gas pressure at the muzzle ist one of the major factors. And this we should be able to determine. So, I'd like to compare the .308 with the .30-06 with 150gr and 180gr bullets in barrels of 58cm (22.8") and 60cm (23,6") lenght.

What would be the gas pressure at the muzzle with an average load for
.308 with 150gr in barrels with 58cm (22.8") length,
.308 with 180gr in barrels with 58cm (22.8") length,
.308 with 150gr in barrels with 60cm (23,6") length,
.308 with 180gr in barrels with 60cm (23,6") length,
.30-06 with 150gr in barrels with 58cm (22.8") length,
.30-06 with 180gr in barrels with 58cm (22.8") length,
.30-06 with 150gr in barrels with 60cm (23,6") length,
.30-06 with 180gr in barrels with 60cm (23,6") length?

Or does anyone have and idea or better data with which we could figure out, which serious hunting caliber from 270 to 300WM would be the least ear-damaging with wich bullet weight choice?

Thanks and have a good Sunday,
PB

 

[Crosshair]

There is not enough data to give you anything useful. The muzzle pressure can vary wildly depending on the powder used and the charge weight.

Best option is to just buy a muzzle can if that is an option.

 

[Bart B.]

Check the stuff in this web site:

http://www.frfrogspad.com/intballi.htm

It's got some reasonable info on that. Other intersting stuff, too.

I know that port pressure (about an inch behind the muzzle) in M1 Garands is about 10,000 psi for the .30-06 round. When their barrels are chambered for the 7.62 NATO round, it's enough less that the port has to be several thousandths bigger to get the same cycling reliability. Not surprising as there's about 13% less powder in the NATO round so pushing out the same bullets means lower port pressure; muzzle velocity, too.

 

[Para Bellum]

Thanx Folks.

So, just a simple question: What causes more sound pressure and gas pressure at the muzzle with a given caliber and barrel length, say 30-06 and 58cm (22,8"): A heavy bullet (180grs) and slow powder or a light bullet (154grs) and fast powder?

 

[Art Eatman]

Granted that my memory could be off, but IIRC the Garand was designed for a pressure at the gas port of 2,000 psi.

Para Bellum, the heavy-bullet, slow-burn deal would have a higher pressure at the muzzle--which is why folks use the adjustable dealie on Garands. The faster-burn powder burns to completion sooner, at a shorter distance.

As near as I can tell in an '06, going from 22" to 26", and using H414 or IMR 4064 instead of 4895 gives an additional 200 to 300 ft/sec advantage. (That's mostly based on scope settings and trajectory at my 500 yard range.)

 

[Para Bellum]

as always: Thanks Art!

 

[mete]

The trick is to burn all the powder within the barrel !! Burning outside the barrel makes for a bigger boom !
The best combination of bullet weight/burning rate to do this if you're a handloader. I'm sure the "reduced recoil" factory loads have low muzzle blast.

 

[Bart B.]

Art claims:

As near as I can tell in an '06, going from 22" to 26", and using H414 or IMR 4064 instead of 4895 gives an additional 200 to 300 ft/sec advantage. (That's mostly based on scope settings and trajectory at my 500 yard range.)

I don't believe that. No way. While 4 extra inches on the barrel will usually gain 100 fps, using either of those powders won't get an other hundred or more fps in velocity. Not with two barrels with the same bore dimensions, bullet, case, primer and neck tension and peak pressure, one 22 inches using 4895 and the other 26 inches using H414 and IMR4064.

Your tools used to measure the differences and come up with your claim, are broken; or way out of adjustment. If you used two different barrels, one has a tighter bore than the other; the typical cause of such wide differences in velocity between two barrels of different length. Which one do you think it is?