Where is the best place to find info for twist rate, bullet weight and velocity? I'm trying to figure out velocities for a 1 in 10 twist 30 caliber barrel and different weight bullets.
Twist, weight, and velocity tables?
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Re: Twist, weight, and velocity tables?
There's no set table to give velocity info as barrels are different and will give different velocities even with the same load.
There are table listing bullet weights for twist but with the 10 twist you can shoot pretty much any .30 bullet.
If you need to know the velocity then getting a chronograph would be your best bet.
There's no set table to give velocity info as barrels are different and will give different velocities even with the same load.
There are table listing bullet weights for twist but with the 10 twist you can shoot pretty much any .30 bullet.
If you need to know the velocity then getting a chronograph would be your best bet.
Re: Twist, weight, and velocity tables?
You can google "Greenhill Formula" and there are plug ins. You measure the length of the bullet you want to load and it will give you the twist rate it will take to stabilize it.
Basically the longer the bullet the faster you gotta spin it to stabilize it. For best accuracy you want to just stabilize it and not overstabilize. For instance if it calls for 13 twist to stabilize you are not gaining anything by getting a 10 twist barrel.
Then there are some bullets like 168 Sierra MKs that when fired from 308 will go unstable after 900. The Marine Corps rifle team shot 168 loads at 1000 for many years and did fine but now that the 175 is in a 308 can get to 1000 and be stable.
If you have one of the Sierra Infinity programs or one of their older black cover reloading books you can check to determine the velocity needed at start to arrive at 1000 yards above Mach 1 but as the Marines found out it is not critical to punch round holes at 1000 as long as the groups remain the same.
You can google "Greenhill Formula" and there are plug ins. You measure the length of the bullet you want to load and it will give you the twist rate it will take to stabilize it.
Basically the longer the bullet the faster you gotta spin it to stabilize it. For best accuracy you want to just stabilize it and not overstabilize. For instance if it calls for 13 twist to stabilize you are not gaining anything by getting a 10 twist barrel.
Then there are some bullets like 168 Sierra MKs that when fired from 308 will go unstable after 900. The Marine Corps rifle team shot 168 loads at 1000 for many years and did fine but now that the 175 is in a 308 can get to 1000 and be stable.
If you have one of the Sierra Infinity programs or one of their older black cover reloading books you can check to determine the velocity needed at start to arrive at 1000 yards above Mach 1 but as the Marines found out it is not critical to punch round holes at 1000 as long as the groups remain the same.
Re: Twist, weight, and velocity tables?
+1 on the chronograph.
However, for a wealth of information you might try buying a reloading manual to give you ideas about how to get the speed you want. Most run about $20.00-$30-00. About ten years ago, Hornady produced a two volume set that the whole second book was tables of drops of all their bullets. They also talk about different barrel lengths helping or hindering velocity. Longer barrels generally give better velocity, up to a point. Too long and not stiff enough, and they sacrifice accuracy.
A barrel with a long throat that you don't seat the bullet into the lands also helps get better velocity. But again sacrificing potential accuracy. But, not always. You just gotta get a good one stick it on and try it. Talk to a gunsmith who's familiar with target shooting and see what he say's as well.
-good luck.
+1 on the chronograph.
However, for a wealth of information you might try buying a reloading manual to give you ideas about how to get the speed you want. Most run about $20.00-$30-00. About ten years ago, Hornady produced a two volume set that the whole second book was tables of drops of all their bullets. They also talk about different barrel lengths helping or hindering velocity. Longer barrels generally give better velocity, up to a point. Too long and not stiff enough, and they sacrifice accuracy.
A barrel with a long throat that you don't seat the bullet into the lands also helps get better velocity. But again sacrificing potential accuracy. But, not always. You just gotta get a good one stick it on and try it. Talk to a gunsmith who's familiar with target shooting and see what he say's as well.
-good luck.
Re: Twist, weight, and velocity tables?
Maybe I'm asking the wrong question. I have a 1 in 10 barrel and chronograph (also the older Hornady and Speer manuals, and Sierra Infinity.) I'm trying to find the velocity range that stabilizes different bullets. In particular 150 SGK and 175 SMK. I may have just looked in the wrong place in the first place. Pretty much for 200 yard matches I don't need to make M118LR, but want to run the 150's around 2750 or so in a 7.62. Then I got curious as to how slow the bullet would stabilize, probably slower than the charge I need to cycle the rifle. When I get home I'll play with the Greenill formulas and probably find out I didn't look in the right place in what I have.
Maybe I'm asking the wrong question. I have a 1 in 10 barrel and chronograph (also the older Hornady and Speer manuals, and Sierra Infinity.) I'm trying to find the velocity range that stabilizes different bullets. In particular 150 SGK and 175 SMK. I may have just looked in the wrong place in the first place. Pretty much for 200 yard matches I don't need to make M118LR, but want to run the 150's around 2750 or so in a 7.62. Then I got curious as to how slow the bullet would stabilize, probably slower than the charge I need to cycle the rifle. When I get home I'll play with the Greenill formulas and probably find out I didn't look in the right place in what I have.
Re: Twist, weight, and velocity tables?
In your 10 twist those bullets can be shot subsonic down to 1000fps but when you say cycle the rifle I am assuming you have a semi auto. You Won't want them that slow. They will stabilize fine at 2750fps but you will need to work up the load.
In your 10 twist those bullets can be shot subsonic down to 1000fps but when you say cycle the rifle I am assuming you have a semi auto. You Won't want them that slow. They will stabilize fine at 2750fps but you will need to work up the load.
Re: Twist, weight, and velocity tables?
Do not go below minium published charge weights as you are asking for a catastrophic failure due to anomaly in propellant ignition.
Do not go below minium published charge weights as you are asking for a catastrophic failure due to anomaly in propellant ignition.
Re: Twist, weight, and velocity tables?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hummer</div><div class="ubbcode-body">Do not go below minium published charge weights as you are asking for a catastrophic failure due to anomaly in propellant ignition. </div></div>
What this means is that if there is too little powder in the casing when the primer fires it doesn't light the powder and then have it burn at it's designed rate, it flashes over the entire charge all at once and can blow stuff up. Don't load low, you probably won't start getting pressure signs, it'll just go BOOM!
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hummer</div><div class="ubbcode-body">Do not go below minium published charge weights as you are asking for a catastrophic failure due to anomaly in propellant ignition. </div></div>
What this means is that if there is too little powder in the casing when the primer fires it doesn't light the powder and then have it burn at it's designed rate, it flashes over the entire charge all at once and can blow stuff up. Don't load low, you probably won't start getting pressure signs, it'll just go BOOM!
Re: Twist, weight, and velocity tables?
I wasn't looking for subsonic. Just reduced recoil and wear on an old .308 Garand. Issued ammo was M118LR, no reason to push that hard. If I'm going farther than 200 yards it's either 600 with the AR or farther with .30-06 This weekend I'll be testing .308 for 2750 fps with the 150 SGK's, RL15 loads from 42 to 44.8 grains.
I wasn't looking for subsonic. Just reduced recoil and wear on an old .308 Garand. Issued ammo was M118LR, no reason to push that hard. If I'm going farther than 200 yards it's either 600 with the AR or farther with .30-06 This weekend I'll be testing .308 for 2750 fps with the 150 SGK's, RL15 loads from 42 to 44.8 grains.
Re: Twist, weight, and velocity tables?
The Greenhill Formula is well suited to things like Flat based, round nose (or flat nose) bullets. Things commonly shot at the turn of the 20th century. For long, pointy bullets with boat tails you want to use the Miller Stability formula. The Greenhill Formula may say it's stable when it really isn't.
It sounds like the answer to your question is this:
With that 1:10 twist rifle you can properly load (aka, right powder and case prep) for loads below 1000fps and still have stability with 150gr FMJBT's
The Greenhill Formula is well suited to things like Flat based, round nose (or flat nose) bullets. Things commonly shot at the turn of the 20th century. For long, pointy bullets with boat tails you want to use the Miller Stability formula. The Greenhill Formula may say it's stable when it really isn't.
It sounds like the answer to your question is this:
With that 1:10 twist rifle you can properly load (aka, right powder and case prep) for loads below 1000fps and still have stability with 150gr FMJBT's
Re: Twist, weight, and velocity tables?
I think that does what I asked about. I just have to figure out the variables for the bullets.
I think that does what I asked about. I just have to figure out the variables for the bullets.
