Effects of powder burn rate on muzzle blast

[mikecr]

Blast is simply uncorking pressure. The more pressure, the more blast. The closer you are to the muzzle, the more blast.
Shorter barrels both increase the magnitude of blast and your proximity to it.

Not true at all.
A 6PPC at competitive pressure (which is way higher than viable in hunting capacity cartridges), produces exceptionally low muzzle pressures(below 6Kpsi). This, with it's common ~21-22" barrel.
A 6BR loaded 20Kpsi lower in peak(than a competitive 6PPC) would need a barrel around 28" to drop muzzle pressure so low.

Also, when barrels are too short, muzzle pressure can go through the roof. In fact, if not adjusted for, it can greatly exceed the primary pressure peak. Somewhat similar to an excessively under loaded cartridge.
A Pressure Trace example:

This is a sample, with explanation at: https://www.shootingsoftware.com/pressure.htm

 

[Rdlningcltchdmpr]

Hey guys! I was looking for information how different rifle powders have an effect on muzzle blast. I can find no real answers or calculators on the subject. I know, I must be real bored and can't afford a costly DB meter. What I was wondering is which powder would have more muzzle blast? 38.0 grains of IMR4198 or 38.0 grains of the slower IMR4895? Rifle would be a 308Win. with an 18inch barrel. Would the muzzle velocity come into play as far as muzzle blast also or is it more a matter of powder charge or both? I would appreciate any opinions or data on the matter. Stay safe and have a great 4th!

Fun ! I had a 600 mohawk 18" - 308 win. Max load of blc-2 powder with 125 balistic tips. Fireball- huge! Wicked muzzle blast! Must try , accurate yes. Fun!

 

[amtx2019]

Very cool Rdlningcltchd!! I had one to in 6mm. was a great gun and cool to shoot after dark!!

 

[amtx2019]

Very interesting info Mikecr. I would have to hire a translator!! Looks like it does everything.

 

[Hohn]

Not true at all.
A 6PPC at competitive pressure (which is way higher than viable in hunting capacity cartridges), produces exceptionally low muzzle pressures(below 6Kpsi). This, with it's common ~21-22" barrel.
A 6BR loaded 20Kpsi lower in peak(than a competitive 6PPC) would need a barrel around 28" to drop muzzle pressure so low.

Also, when barrels are too short, muzzle pressure can go through the roof. In fact, if not adjusted for, it can greatly exceed the primary pressure peak. Somewhat similar to an excessively under loaded cartridge.
A Pressure Trace example:
View attachment 1188085
This is a sample, with explanation at: https://www.shootingsoftware.com/pressure.htm

Not true at all? So you're saying it is NEVER the case that shorter barrels increase magnitude or muzzle blast and your exposure to it? That shorter barrels never increase pressure? That they don't place you closer to the blast?


If you say so.

 

[Oso]

I started hunting with the 300BO when it first came around Oso. I think it is a great round for 150 yards and under. I have taken a substantial number of deer and hogs with it. I still consider building a 300BO bolt rifle but I have so much 308 stuff it makes sense to stay with it. With a load of 36 grains of IMR4198 and a 125 grain Nosler BT I am getting about 2700 fps at the muzzle. Not as quiet as the 300 but very mild blast and recoil.

I built an 300BO on CZ 527 with 18" barrel. With approx. 18.5gr of H110 I am getting 2400 fps with 125gr bullet.

 

[amtx2019]

I am very tempted to build another one Oso. My pet load was 19.5 grains of H110 with the Barnes black tip. real killer load. Your getting some good velocity with that 125.

 

[Oso]

I am very tempted to build another one Oso. My pet load was 19.5 grains of H110 with the Barnes black tip. real killer load. Your getting some good velocity with that 125.

110GR Barnes TAC-TX is devastating...it is my go to hunting bullet. I had to move to head shots to avoid ruining good meat.

 

[dellet]

The first thing that needs to be defined is “Muzzle Blast”. It can mean a few different things and they are mitigated differently through burn rate. They also can have different effects.

Are you talking muzzle pressure that will have a direct influence on recoil?

Or the volume of the report?

At a very basic level, faster powders will have less muzzle pressure, which may or may not be perceived (heard) blast. Loud Shot is a perfect example, it's a reasonably fast powder but also noisy.

If you have access to Quickload, what you start to see is a Higher peak pressure (faster powder) results in lower muzzle pressure. This is also why faster powders also start giving gas guns cycling issues.

Normally to achieve a certain velocity, a faster powder will use less total powder, and burn more of that charge. So if you have a 30 grain load burning 90% and a 40 grain load that burns 80% you have twice the unburned powder exiting the barrel. In that example you have added 5 grains of weight that will calculate into effective recoil, in addition to the likely higher muzzle pressure.

Smokeless powder burns more effectively under pressure, the higher the pressure the better the burn, the faster the bullet accelerates, the sharper the recoil, but the shorter the duration, and faster the dissipation.

Noise mitigation is a completely different problem. I use N120, 1680, Shooters World Blackout, CFE BLK, 5744 as examples because I have done a lot of testing with them. Depending on whose chart you use, they will change positions with each other. All have a noticeable difference in report volume and to my ear N120 is noticeably quieter. To my knowledge there is no way to see that difference on paper. You have to try.

A lot of good discussion came out in this thread. I used the same weight powder charge of 5744 and 2400 and a 325 grain bullet in a sub 9 pound 45/70. Some of my thinking changed doing this.

http://forum.accurateshooter.com/th...how-do-you-predict-or-measure-effect.3942898/

One other thing I am certain of, is that for every thing I know for certain when it comes to loading, there is an exception.

 

[mikecr]

Not true at all? So you're saying it is NEVER the case that

I didn't say never, or always, and I qualified my contentions with examples.
If my offense here is boxed-in to 'at all', then I'll concede a wrong implication on my part.

Your declarations: "The more pressure, the more blast.", and "Shorter barrels both increase the magnitude of blast and your proximity to it.", may be truthful in some context (like regarding sound).
But I don't know. All I can see, as written, is that these declarations do not pass all tests.
These things are not so cut & dry

 

[yotehater]

I feel like the thin profile barrels don't block or reflect as much of the blast either. Not like a recessed crown bull barrel will.

mikecr, I'm having trouble understanding that 80,000+ psi spike after the bullet has left the muzzle. Why don't copper crushers see that? It might be some kind of barrel harmonics misdiagnosed by the pressure software. That kind of pressure would surely blow the primers and enlarge the pockets. If it's really happening. Interesting, I need more data on that.

 

[amtx2019]

I was under the impression as the bullet traveled down the barrel, pressure dropped behind it.

 

[mikecr]

The pressure does drop with barrel travel. From ~55Kpsi down to ~10Kpsi for example. Then shorten the barrel and it might only drop to 20Kpsi at the muzzle (or worse). Look at the pressure drop I pictured earlier, considering the reality that the barrel was too short.
Now add an unburned slug of powder to bullet mass, with a poorly designed cartridge (like a 30-06), to an excessively short barrel, and muzzle pressure can go up even more. In fact, in that case pressure would be higher the entire length of bore, -because the powder slug IS adding to projectile mass.

The premise behind shorter-fatter, lower body angle, higher shoulder angle cartridges is to keep most powder burning in the chamber.
Newer cartridges and most wildcats do this. Gibb's front ignition did it best.