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Fast Burning vs Slow Burning Powder Question
sigarmsp226
Member Posts: 2,461 ✭✭✭
In my reloading manuals most of the loads are listed from the ighest FPS to the slowest FPS for each powder type and I see a trend in these numbers. It seems that the further down the list of powders you go the different powders reflect that it takes more powder to acheive the same FPS as the one listed above it...In sain gthis here is my question - If I have a powder that thakes 25Gr to acheive 3000FPS and another powder type that takes 28Gr to acheive 3000 FPS which one of these is burning SLOWER?
My second question is - I have a Steyr SBS 30-06 with a 23.6" barrel and another one that is my sons that is the Mountain Rifle version that has a 21" barrel. The groups in my 23.6" barrel gun has better groups with the load I am using over the shorter barrel. Does this mean I need to use a faster burning powder for the shorter barrel rifle to acheive better accuracy?..... Thanks to all who can help....Mark
My second question is - I have a Steyr SBS 30-06 with a 23.6" barrel and another one that is my sons that is the Mountain Rifle version that has a 21" barrel. The groups in my 23.6" barrel gun has better groups with the load I am using over the shorter barrel. Does this mean I need to use a faster burning powder for the shorter barrel rifle to acheive better accuracy?..... Thanks to all who can help....Mark
Comments
To your second question, no. Or better said, not necessarily. You might get better accuracy with a slightly faster powder, or not. You might equally get better accuracy with a slower powder. Each barrel is a law unto itself, largely. How that barrel vibrates as the bullet passes down the bore affects accuracy greatly. THE best powder and load for that barrel will produce a consistent vibration that is the same place every time at the instant the bullet exits. That's your accuracy load.
Powder "speed" and barrel length are not related. IOW the powder that gives the highest velocity in a 26" barrel will also give the highest velocity in a 18" barrel (all the powder that's going to burn, has burned in the first few inches). The extra length just lets the gas work longer on the bullet.
Group size is a different thing entirely, you have to try different powders, charges, bullet weights, styles, brands etc to find the combo that HIS rifle likes.
If there was one "best" combo, reloading would be boring [:D]
The powder that takes more to achieve the same velocity is the slower one. However it's also, as a rule, capable of reaching higher velocities than the faster powder (more gas generated = more work can be done) and while the peak pressure won't be any higher, the average pressure down the barrel will be higher.
Powder "speed" and barrel length are not related. IOW the powder that gives the highest velocity in a 26" barrel will also give the highest velocity in a 18" barrel (all the powder that's going to burn, has burned in the first few inches). The extra length just lets the gas work longer on the bullet.
Group size is a different thing entirely, you have to try different powders, charges, bullet weights, styles, brands etc to find the combo that HIS rifle likes.
If there was one "best" combo, reloading would be boring [:D]
Agreed on the powder speed question.
I'll disagree with the barrel length statement. A longer barrel allows the more gas of the slower powder to be used. If you use a slower powder in a short barrel you're just pushing usable gas out the end. While all of the powder is ignited within the first couple inches of the case it is not burned, or completely consumed. The hot gases are still expanding as the uber-rapid oxidation is still taking place. If you don't believe that shoot a rifle at night and watch the muzzle flash. Especially with a short barrel and slow powder. That is powder still being 'consumed'.
However, the point tailgunner makes is valid. In that you still have to find the right speed for the bullet/case combo that you are loading for. Too slow of a powder won't give enough initial push and too fast a powder and you can't use enough to push hard enough. Because the pressure in the case works against itself and not to pushing the bullet down the tube.
As for the harmonics of the barrel it's true that you have to find what load is going to work best in your barrel. Unfortunately, all too often I see little short pencil barrels that take a really wringed out load to get them to shoot better. So the shooter can save a pound while walking the mountains. Thicker barrels help enormously with harmonics. You may not get benchrest groups, but I've seen thicker, short barrels reduce group sizes across the board with most loads. What may be barely acceptable in the pencil barrel is usually easily within standards in the barrel that doesn't 'twing off' with the wrong load. I have a Ruger Ultra-lite that goes from sub MOA to 3 MOA if you give it a load it doesn't like.
If your Steyr likes a fast powder then go with it. But if it likes a slower powder it isn't going to hurt much if you go with that either. some gases chasing the bullet as it exits is unavoidable. Not like deer are looking for muzzle-flashes at dusk and dawn anyways.
Muzzle flash is the result of the unburned but flammable gasses produced during the burn. Those gases mix with atmospheric oxygen and re-ignite. It produces nothing but light and noise.
Well, you're the rocket scientist. I know it can be done and according to your calculations it can't.
You know that what can be done?
Sorry about the jab if you took it that way, I get a little frustrated.
Here's what I know. When loading rounds we like, usually, to get them to about the maximum value for velocity AND accuracy. Which usually means we back off from peak pressure. Just like when you were flying you took off at full rich and leaned to 75-50 deg rich of peak when in cruise. Better harmonics on the engine, longer wear life. A shot is like a one time cylinder firing. All carbon based fuels do not burn instantaneously. They have a speed. But they are producing pressure as long as they are in a contained area. Once they leave the contained area then they become the light and noise that you talk about.
My point is that you almost never operate at full max pressure to have that happen. In that difference, lies the ability to have a faster powder in a shorter barrel give you more velocity than it would in the longer barrel that got better velocity with the slower powder.
So, yes, maybe you are right. But in common operation we never operate at that point to make it so.
That sounds reasonable, but seldom works out as described. Unless we talk about extremely short barrel length, the powder that produces the highest volume of gas at the highest safe pressure will impart the highest velocity. Because fast powders have to be used in smaller amounts to keep them from generating too much pressure too early, that also means they can generate less gas volume. There simply isn't as much total "push."
So, in practice, a slower powder will produce higher velocity than a fast one regardless of barrel length. (Assuming it isn't so slow that that case can't hold enough of it, of course.)