Burn rate vs barrel length

I have a new 224V with a 30" Bartlein 5R bull barrel, progressive twist to 6.5, reamed for an SMK 90 grain, and I'm curious about burn rate vs barrel length. I've never tuned a load for such a long barrel. The gunsmith, Joe Carlos, developed a load for the rifle using N-140, but as I come up to speed on this new barrel it got me wondering about the relationship of burn rate to barrel length. How do you all think about that relationship when developing a load, and how do you go about trying burn rate variations?

 

A longer barrel gives the powder more time to burn and pressurize before the bullet leaves the barrel. This means you can use more of a slower burning powder and still manage to burn all of it.

 

That is a very long barrel compared to the powder charge. The 224Valkyrie is known for high pressure that kills primer pockets after a couple of loads. With the extra barrel length you can achieve same velocity using a slower burning powders to push a heavy bullet resulting in less wear on your gear.

 

I don't know if small arms are the same but in artillery weapons the aim was to get the charge to be all burnt when the projectile was about two thirds of the way along the barrel.

 

Quick Load provides the pressure and velocity vs barrel length curves, % of powder burned, and a number of other informative outputs which allows you to explore many options in order to narrow down the most likely candidates for testing.

 

There are some gains in tuning to a burn rate but I will offer you some food for thought not related so much to tuniing.

For velocity, typiclly the faster shooting powders in long barrels are the faster powders in short barrels and visa versa. I'm sure there are exceptions to this rule but I would stand behind this statement as a general rule.

Great job on seating the bullet out to take advantage of the case volume. That said, before you start reloading please do yourself a favor and check your case volume. Compare this to standard .223 and other similar sized cases. I mention this becaiuse many are trying to make a 224V into a 22-250 and the case volume barely rivals that of a 223.

Lastly if you are truly worried about tuning a 224v to a given powder you would probably be far ahead to worry about sorting and prepping your brass. With a cartridge meant to compete with 223 in sales you can not expect much out of factory brass. It kind of defeats the purpose to spend a ton of time in load development when you are skipping the primary components.

As stated above by others. I have picked up brass at sboots out of bolt guns that show either excessive pressure or very soft brass. My gut tells me I am seeing overpressure rounds and that the brass is no more nor no less strong/hard than the typical .223 remington. Having a 30" tube will gain some velocity from such a small cartridge hut try to be realistic and shoot more towards the 223 in terms of velocity.

 

Great feedback, thanks. Let's assume full and detailed case prep, including sorting, neck turning, etc., concentricity verification, and everything else I can do to enhance all elements required for precision. You're right to stress that since without controlling those variables it won't be possible to know if powder changes make an actual improvement.

Given that, my assumption is that certain loads of different powders will complete their burn just as the bullet passes what? The gas port in a semi-auto, or the end of the barrel? CharlieNC suggests using QuickLoad software, which looks like an interesting tool.

I assume that it'd be possible to achieve the same muzzle velocities with a very fast-burning powder that completes its burn early, versus a slower-burning powder that completes its burn at the last possible moment. Would it be a correct assumption that the faster-burning powder would be tougher on the rifling (assuming we stay within acceptable pressure) then the slower powder? So it seems that'd be a point in favor of tuning the powder to the barrel. Are there other factors than muzzle velocity, say, bullet stabilization, etc? I'm hoping you all can give me some things to think about as I tune loads to this longer barrel, and appreciate everyone's feedback so far.
Jeff

 

Google Chris Long Optimal Barrel Time; it is a theory concerning barrel harmonics and gives barrel times which should provide best accuracy. Quick Load calculates this barrel time, such that you can evaluate load options on the computer without firing a shot. Some folks do not believe this is a valid approach; myself and many others find it is very close for predicting nodes. I always begin a new load development in this manner to identify a safe starting point in terms of pressure, and to begin testing with fine differences in powder charge since I know I will be in the vicinity of a node.

 

All that matters is accuracy as long as velocity is near top speed. I say that because it is always the powder that makes accuracy. 5 or more powders might make nearly the same speed but one powder will be like magic ! No one knows why but that's the way it works. In your case powders that fill the case to the point of light compression are the ones to use.

 

Jeff -

Howdy !

If you get a chance, take a look @ embscomputerart.com

This is an on- line copy of the users’s manual for the “Powley Computer”.

Homer Powley was a reknowned ballistician, with a gift for making internal ballistics more understandable for shooters w/ questions.

Homer explains some internal ballistics facts through the use of “Expansion Ratio”. That’s just one area he covers in the user’s manual.

It’s a worthwhile read!


With regards,
357Mag