Barrel Length vs Powder Burn Rate

[Brians356]

Many load data sources specify a 24" test barrel. Suppose I have a range of load data for a cartridge like 260 Rem, all for a 24-inch barrel. If I want to choose a couple of likely powders to test, but for a 20 or 22-inch barrel, should I favor the faster powders in the list?

My goal is (as always) good velocity and accuracy, but also maximum in-barrel powder burn, and minimal recoil and muzzle blast (max efficiency). It seems to me that as the barrel gets shorter, the faster powders would become more favorable than the slower ones - all else being equal (humor me!).

Comments welcome!

 

[mikecr]

~24" I imagine represents the mean in hunting barrel length.
Actual planning in this is where QuickLoad shines.

 

[scpaul]

Usually for a shorter barrel to maintain as much of the velosity and accuracy as possible, I'd try the slightly faster powders first. You have to remember that every barrel/load combination is an individual. Little things like 1/2 gr. of powder or 10 gr. of bullet weight, most anything can make a big differance in certain combinations. I've got 1 rifle that I thought that the barrel was shot out because I bought it used, cheap. When I finally tryed IMR-4350, C/T 150 gr. bullets and Winchester WLMR primers, it was like I'd grabbed the wrong rifle. That load made all the differance in the world. You might ask if someone with a similar weapon can give you some loads to start with. Remember to reduce the loads for trial in your rifle. Ya'll have a good one, Paul

 

[Minesweeper3433]

I focus on slower burning powders in my rifles with longer barrels.

 

[Brians356]

Ok, case in point:

Hodgdon lists no fewer than 21 powders in 260 Rem for 120-grain bullet (24-in barrel). Slowest (H1000) to fastest (SR 4759).

Velocity plateaus at mid-2900 fps between H4831 (2954) and H414 (2968) with 100V (2934) and H4350 (2960) and some others in between.

As powders get faster than H414, velocity drops into 2800s and 2700s all the way up to the second faster powder listed - Benchmark - for which velocity jumps way up to 2935. So Benchmark is an outlier, a velocity spike amid the fastest powders.

Benchmark load density is pretty low (40.0 grains, when a quick survey suggests 308-based cases will hold ~47 grains Benchmark uncompressed) and of all the 21 powders, pressure is highest at 59,500 PSI. So it's giving the 120-gr pill quite a smack in the butt.

I would consider Benchmark a good candidate for a short-barrel 260 Rem with this bullet weight. To be discovered will be how much of that 2900+ velocity it will retain from a 22-inch barrel, but my hunch most if not all the powder would be burned in the bore. If it turned out to be resistant to good accuracy, the point would be moot. The next best and slower candidate is Varget at 2877 fps, but it's a short jump from there to H414 at 2968.

 

[justinp61]

Interesting read, as I have test loads for my 22" bbl Savage mdl 16 260 loaded up with H4350, 123gr Hornady SSTs.

 

[TC260]

I've shot tons of rifle cartridges in specialty pistols, don't over-think burn rates. Buy a can of H4350 and let 'er rip. If the gun doesn't shoot, the powder ain't the problem .

 

[dalej]

Load to cartridge capacity, forget about barrel length. Cartridges that require slow burning powder will perform best with slow powder in long and short barrels. If your barrel is spitting unburned powder it will do with the same in short and long barrels.

 

[Brians356]

I've shot tons of rifle cartridges in specialty pistols, don't over-think burn rates.

The thinking part is half the fun. I ain't letting go.

Once you shot a rifle round in a pistol, I'm sure you lost your innocence then and there.

 

[Brians356]

Cartridges that require slow burning powder will perform best with slow powder in long and short barrels.

So Benchmark is too fast for 260 Rem?

 

[Brians356]

If your barrel is spitting unburned powder it will do with the same in short and long barrels.

I never said I sought to avoid spitting unburned powder, but thanks for the observation FWIW.

Also FWIW, probably all barrels will spit some unburned powder.

 

[savagedasher]

Norma URP VV 550 Winchester760
URP will give you 101 % fill 99.27 % burn and use 12 inches of barrel to get 95% of Velocity. with 2900 FPS. Dirty, temp sensitive. Larry

 

[savagedasher]

Get your self QL and you can play with all the powders and bullet barrel length and never fire a shot.
It is not perfect but the best I have found. Larry

 

[dalej]

Load to cartridge capacity, forget about barrel length. Cartridges that require slow burning powder will perform best with slow powder in long and short barrels. If your barrel is spitting unburned powder it will do so with all barrel lengths.

 

[savagedasher]

Load to cartridge capacity, forget about barrel length. Cartridges that require slow burning powder will perform best with slow powder in long and short barrels. If your barrel is spitting unburned powder it will do so with all barrel lengths.

Dale if that was the case their would only be one powder for all guns. Larry

 

[4xforfun]

Load to cartridge capacity, forget about barrel length. Cartridges that require slow burning powder will perform best with slow powder in long and short barrels. If your barrel is spitting unburned powder it will do so with all barrel lengths.

Dale if that was the case their would only be one powder for all guns. Larry

I am not a balistition, but I remember reading an article in PS a few years ago. The topic was BBL length vs powder. The jist of the article was this.....the best powder for any given cartridge-bullet combo will always be the correct powder no matter how much you cut off of the bbl.

 

[Brians356]

I am not a balistition, but I remember reading an article in PS a few years ago. The topic was BBL length vs powder. The jist of the article was this.....the best powder for any given cartridge-bullet combo will always be the correct powder no matter how much you cut off of the bbl.

That may well be true - but it depends on how you define "the best powder". Even if it is only purely accuracy that counts (as one might assume from it being written in Precision Shooting) I would still question it.

 

[dcali]

Not everything printed in PS was correct. At all. That doesn't sound even close to making sense to me. You would have to ignore the volume of the bore for that to be true, and that's just not sensible. The bore volume is bigger than the chamber volume, and it matters. Even the most basic internal ballistics calculation rely on knowing the barrel length.

 

[KevinThomas]

No one has actually said the term yet, but we're talking about expansion ratio here. And yes, cartridges that have low expansion ratios generally favor slower burning powders. Very high expansion ratios, on the other hand, call for very fast powders. There's just two ways to change expansion ratio; the first is case size, or increasing the combustion chamber. The second, is changing the barrel length. There's some very definite limits on the second option.

Changing the case size is the more common approach, since you can achieve the biggest difference without making the gun either unwieldy, or so short that you're turning it into a flame thrower. Generally speaking, the larger capacity cases benefit more from slow burning powders than smaller cases, regardless of the barrel length. To a point, anyway. Over the past few years I've seen a good many shooters who want very short, compact rifles, but insist on the most powerful cartridges. These are often the same guys who then moan about muzzle blast or getting less velocity than they think they should be. Don't have an answer for them, other than to simply point out expansion ratio as the ultimate "cause and effect" demonstration.

 

[1shot]

I agree with several posters as they have very valid points, but Minesweeper3433 hits the nail on the head. I compete with a 6.5mm GWI and am starting my work-up on a 284 Shehane for those so nice sun-shiny days. I also shot the 6.5x284 in between the two cartridges. To keep apples to apples you have to look at the overbore of the cartridge, the length of the barrel and certainly last but not least the bore diameter versus the thickness of the jackets and what the jackets are made from. All of these have a bearing on the type of performance you were looking for. I hope I brought some clarity as opposed to more confusion to your problem, but none-the-less, a very good question,
I hope this helped,
Lloyd