Thread: Myth? - shorter barrel = use faster powder?

Originally Posted by Shearer

If you are genuinely interested in an answer, as he said, do your own research. Are you incapable? Do you expect someone else to do it for you?

What the hell was GRT ????? (now I now)

Things I have found when reloading for short barrel rifles (14-17 inch 308s and 7mm08s mainly) is the following:

• Higher pressure loads burn powder efficiently
• Heavier bullets typically help increase powder burn (Maybe due to increased barrel time)
• Heavier bullets also reduce effective velocity loss (fps/inch) from barrel chop (provided they aren't so big they cut into case capacity)
• Typically the fastest shooting powders dont really change too much regardless of barrel length (ie 16 to 24)
• Quickload or GRT is super useful for reloading especially when experimenting ie 225 eld ms in a 16.5 inch 308 bErgara at excessive COALs and to test theory's that can then be confirmed by actually doing them (following safe reloading practices of course)

My experience has been that the “use fast burning powders for a short barrel” isn’t really a thing. Certain powders in certain configurations just tend to give better velocities then others and is completely subject to a much larger range of considerations. I think burn rate is more associated to cartridge size and projectile weight with barrel length not really being a consideration. At the end of the day some just go better then others in different setups. Just gotta look at others results and go try. Classic example I have with the fast powder short barrel argument is my 260. It has a 19” barrel and gets the best velocity using Rel 26 which is marketed as a magnum powder due to being right up there for slow burning. Had the guy tell me I was wasting my time when I went to buy the stuff for a 260 as “all the powder will be burning outside the barrel and it will be shit”, boy was he wrong and I enjoyed passing on that it went awesome hahaha.

I put some numbers through GRT for entertainment:

6.5x55 SE with 129gr Interlocks, 20" vs 29" barrel.

Max Loads (same charge, barrel length doesn't change the load)
20" 29"
2206H 2732 2983
2208 2713 2953
2209 2760 3041
2213SC 2738 3011
2217 2808 3105 (over 100% fill)

Optimal Barrel Time (Node 6.5 for 20" and 4.5 for 29")
20" 29"
2206H 2661 2938
2208 2620 2888
2209 2665 2968
2213SC 2640 2937
2217 2717 3023 (over 100% fill)

So if velocity is your sole criteria it looks like the barrel length is irrelevant. However for accuracy you would have to test it.

It all depends if you want muzzle blast or velocity. Shorter barrels burn faster powders more efficiently than slower powders but the shorter barrel precludes getting optimum velocity. Long barrels give top velocities with slower powders within safe pressure limits. Bear in mind that all NZ game can be reliably killed with 150 grain bullet at 2500 feet per second, short barrels are easier to carry, and I don't know of any game animals that can read a ballistics chart!

Originally Posted by Stocky

Things I have found when reloading for short barrel rifles (14-17 inch 308s and 7mm08s mainly) is the following:

• Higher pressure loads burn powder efficiently
• Heavier bullets typically help increase powder burn (Maybe due to increased barrel time)
• Heavier bullets also reduce effective velocity loss (fps/inch) from barrel chop (provided they aren't so big they cut into case capacity)
• Typically the fastest shooting powders dont really change too much regardless of barrel length (ie 16 to 24)
• Quickload or GRT is super useful for reloading especially when experimenting ie 225 eld ms in a 16.5 inch 308 bErgara at excessive COALs and to test theory's that can then be confirmed by actually doing them (following safe reloading practices of course)

Originally Posted by stagstalker

Certain powders in certain configurations just tend to give better velocities then others and is completely subject to a much larger range of considerations. .

Yes it's not so 'black and white' as I initially thought....lots of considerations = grey area...

Originally Posted by Magnetite

I put some numbers through GRT for entertainment:

6.5x55 SE with 129gr Interlocks, 20" vs 29" barrel.

Max Loads (same charge, barrel length doesn't change the load)
20" 29"
2206H 2732 2983
2208 2713 2953
2209 2760 3041
2213SC 2738 3011
2217 2808 3105 (over 100% fill)

Optimal Barrel Time (Node 6.5 for 20" and 4.5 for 29")
20" 29"
2206H 2661 2938
2208 2620 2888
2209 2665 2968
2213SC 2640 2937
2217 2717 3023 (over 100% fill)

So if velocity is your sole criteria it looks like the barrel length is irrelevant. However for accuracy you would have to test it.

Yeah it's interesting. I've never used this type of program before .... really helpful.

Originally Posted by gundoc

Shorter barrels burn faster powders more efficiently than slower powders

Not correct according to that GRT ballistics program. Slower powders in 20" barrels were faster than faster powders.

Originally Posted by Hermitage

Not correct according to that GRT ballistics program. Slower powders in 20" barrels were faster than faster powders.

I think he is correct. The muzzle blast increases with slower powders meaning more wasted energy even though the velocity is higher.

I used 2208 in a 16" 308 with a 165gr gameking. From what I was told I needed to use a faster powder but had much more luck with 2208 which is slower

Side note, GRT, where do we give our money? Sounds like a program thatd tickle my pickle

Originally Posted by stagstalker

My experience has been that the “use fast burning powders for a short barrel” isn’t really a thing. Certain powders in certain configurations just tend to give better velocities then others and is completely subject to a much larger range of considerations. I think burn rate is more associated to cartridge size and projectile weight with barrel length not really being a consideration. At the end of the day some just go better then others in different setups. Just gotta look at others results and go try. Classic example I have with the fast powder short barrel argument is my 260. It has a 19” barrel and gets the best velocity using Rel 26 which is marketed as a magnum powder due to being right up there for slow burning. Had the guy tell me I was wasting my time when I went to buy the stuff for a 260 as “all the powder will be burning outside the barrel and it will be shit”, boy was he wrong and I enjoyed passing on that it went awesome hahaha.

Yeh I think the level of overbore seems to be a huge factor that and obviously physical case capacity for the some Bulkier powders. Like H1000 in the likes of the 243, 7mm Mag, and 300 Win one doesnt quite fit when talking case capacity. But I could be wrong thats just something i seem to have noticed.

Originally Posted by Magnetite

I think he is correct. The muzzle blast increases with slower powders meaning more wasted energy even though the velocity is higher.

I was defining 'efficiency' as the highest velocity. Wasted energy is not ultimately 'wasted' if it produces higher velocity in my definition.

I think it's a bit different to what is described. You are trying to get to max safe pressure, and maintain that pressure in order to achieve the most force and thus acceleration on the projectile. As the powder burns, the projectile starts moving.

This means powder is changing from solid to gas as the projectile is going down the barrel.

Heavier projectile means slower acceleration. That means that the area for the gas to expand into is increasing slower than with a faster moving projectile. Do you are balancing the rate of press increase from expanding gas, with the rate of increase of the area ,(barrel and chamber) is increasing.

Shorter barrel means there is less time for the expanding gas to push the projectile. Theoretically, a faster burning powder means that max safe pressure is reached sooner, so that the projectile experiences that force for max duration. The flip side is, that the powder stops turning to an increasing volume of gas sooner. That means that pressure will drop earlier due to expanding area.

I think the theoretical best is max safe pressure instantaneously, which then expands at the exact rate to maintain that pressure as the area increases due to the projectile moving down the barrel.

You also want all combustion to be complete before projectile leaves the barrel so you dont get an obnoxious muzzle flash, and waste energy (inefficient use of powder)

Well I've just done load development for my 17" barreled model 7 latte'o'8
44gn of 2209 was my starting load and was good for 2460fps
44gn of 2208 was max load well over book max and gave 2706fps
Not sure which is faster burning but the 2208 was definitely way better velocity per gn of powder in my short barreled rifle.