OT: WHAT DETERMINES MUZZLE BLAST?

[Bogie35]

Hey folks. This is probably a real rookie question, but what causes the intensity of muzzle blast? I know the barrel length affects it, since that's where most of the gases escape. But what else? Is it chamber pressure? Powder quantity?

I would like to attempt to quantify muzzle blast for comparison of cartridges. For instance, if I take a 45 Colt and a 44 Mag, which one will be louder? And to what extent?

Thanks,
bogie

[preventec47]

A couple of things I have gathered is that the shorter the barrel
and the higher the bore pressures, the louder the blast.
It could also be that the larger the amount of powder the louder.
Also possibly the larger the bore size all other things equal
maybe louder also.

One observation that I have not been able to reconcile are the
huge booms I hear from hundreds of yards away when
at the rifle range. These sound like bombs from B-52s
and they are the muzzle loader guys shooting over
at another range. Almost like thunder actually. These
seem much louder than the booms from magnum pistols
from the much closer pistol range.

What I am saying is the muzzle loader pressures are
real low.... a lot like shotguns I guess. I dont get
to hear any shotguns at the gun range for comparison
so I dont know about those but they area also very
low pressure.

[Old Savage]

Pressure at the muzzle when the bullet exits the barrel. I think the Oehler 43 can tell what it is.

[Cliff]

You might try to get your hands on a copy of "Hatcher's Notebook". He has a lot of data about this stuff. Back when high velocity smokeless loads were introduced the military did a lot of experiments on ways to reduce the noise (aka) muzzle blast. The Germans developed their M98Gewar (29") barrel with the 154 +- bullet in an effort to reduce muzzle blast, it did work, but made and unwieldy rifle for trench and inclose fighting. Mainly the gases are exiting the bore at hyper sonic velocities and creating sonic booms is the short answer. Some of it is preception, short barrels closer to the ears, long barrels seems to reduce the noise somewhat. I will go for now and be quiet. Good Day and ATB

[Marc]

OS has it. Muzzle pressure. Longer barrels reduce muzzle pressure and blast. Smaller powder charges reduce muzzle pressure too.

[Buck Elliott]

Yup. Old Savage has the answer. Whatever the powder, the charge, the bullet -- it's gas pressure at the muzzle that we detect as "Muzzle Blast..." Add to that the velocity of the escaping ejecta ( bullet & gasses) and you get the distinct "signature" of the fired round. Hyper-velocity loads will have the super-sonic "crack" added to the report.

YMMV

[KWK]

Shorter barrels mean higher gas pressures when the bullet exits. Higher pressures should result in stronger sound waves. The shorter barrel delivers a double whammy: the higher pressures are released closer to your ears, and sound energy decays with the square of distance traveled.

The volume of the gases surely affect the blast as well. A muzzle loader uses a great deal of low pressure gases, and mingled with these gases are lots of tiny solids which when they fly from the muzzle also displace air.

The bore seems to determine the frequency content, with smaller bores having more of a crack.

I've never seen a complete explanation of the physics behind muzzle blast.

[Bogie35]

I got to thinking about this when I was at the range the other day. I heard a rifle at the 500 yard range adjacent to the 250 yard range I was shooting on. It was probably a couple hundred yards away from me. It made a HUGE boom! And you could hear the sound carrying off into the distance for a few seconds after each shot. Turns out, it was a guy with a 50 BMG.

The sounds of my 35 Remington and the 270 Win and 30-06 next to me could not even be compared to the boom of that 50 BMG. It would be like comparing a firecracker to a 12 gauge.

bogie

[Bogie35]

Here's a super cool photo example of muzzle blast:

MUZZLE BLAST.jpg

The impression it makes on the water is shocking!

bogie

[Doc Hudson]

I'm not going to argue with the other guys, I'm not enough of a mathematician, ballistician or physicist to make a reasonable argument. All I can do is offer my opinion based on my own observations. you can decide if those opinions agree or oppose those of O.S. and the others.

It is my opinion that muzzle-blast is effected by barrel length, cartridge pressure, and powder burn rate.

large charges of slow burning powder produce more muzzle-flash than comparable charges of fast burning powder. And the shorter the barrel the bigger the fireball. It is my opinion that the large fireball is caused by powder burning beyond the bore. Using the same 19.2 grain charge or @in 296 and a Sierra 125 gr. JHP in a 20" carbine, a 4" revolver and a 2 1/8" revolver produce vastly different muzzle-blast/flash effects. In the carbine, the fireball of the flash is relatively small and the blast is not obnoxious. In a 4" revolver the flash is pronounced, producing a fireball perhaps as much a three feet in lengtj and a foot in diameter. The blast is much more pronounced as well. In a 2 1/8" M-640 both muzzle-flash and muzzle-blast are truly horrendous. The flash is like turning on a high wattage strobe light with a fireball appearing to be a couple of feet in diameter and five or six feet long. The muzzle-blast, to a person as much as six feet to one side of the shot, feels like being slapped in the face. The sound level is truly deafening.

Why? It is my opinion that the blast and flash increase with the shorter barrels due to the fact that the shorter barrels permit a larger volume of unburned powder granules to be expelled from the muzzle before ignition. The combustion of these expelled granules contribute to the flash and blast.

You can test this by shooting a heavy charge of slow-burning smokeless powder or blackpowder over either fresh snow or a clean white sheet. Use different barrrel lengths and you should notice a substantial difference in the amount of ejecta that exits the barrel and falls o the ground in the shorter barreled arms.

Like I said, I'm not arguing with anyone, just stating my opinions and we all know what opinions are worth.

[KWK]

The amount of powder burned must count. I've wondered if the muzzle pressure determines the peak pressure of the wave but the amount of gases (powder) determines the length of the pressure pulse (and thus perhaps the wavelength or frequency).

Pressure traces show little increase in the rate of chamber pressure decay once the bullet exits, so there must be some supersonic choking of the flow.

Again, I don't understand it all; I'd like to read an explanation of the process.

[Old Ironsights]

That picture of the Mo reminded me of the time we rolled a new butter bar on an exercise.

He just wouldn't listen when we told him that he was standing too far forward of the gun line. When we lit off the gun (M110, 8" SP, long tube with brake) he rolled about half way to the outer aiming stake.

Kinda funny actually.

[piller]

OI, what is it about Butterbars that makes them do such dumb things? We had one who would use his .45 to set his compass on to steady it. He constantly got lost and led us where we were not supposed to be. We had a good F.O. assigned us who always knew where we were.

Wish I could have been on the Bridge of the Mighty Mo when those 16 inchers went off. I envy the crew who got to see it from up there. Amazing power and sub-MOA accuracy at 25 miles. WOW!

[milton]

Pressure ,time and volume of gas.