Ballistic gelatin vs twist rate

[trickytune]

Cant find much info on this but someone must have tested. Lets assume a .223 with the exact same projectile, velocity etc fired through a 1:12" twist vs a 1:8" twist I would like to see results in gelatin. My thoughts are the faster twist would help expansion over the slower twist. This may then affect penetration. Is this why some people have little expansion with some projectiles and others have good expansion? Sectional density is calculated on a bullet before it hits the target but once expansion starts it will obviously change. So a harder projectile that expands less but has lower initial sd will likely penetrate deeper than the bullet with greater sd that expands more easily. Obviously this requires you to match the bullet to the target.

 

[elkaholic]

Cant find much info on this but someone must have tested. Lets assume a .223 with the exact same projectile, velocity etc fired through a 1:12" twist vs a 1:8" twist I would like to see results in gelatin. My thoughts are the faster twist would help expansion over the slower twist. This may then affect penetration. Is this why some people have little expansion with some projectiles and others have good expansion? Sectional density is calculated on a bullet before it hits the target but once expansion starts it will obviously change. So a harder projectile that expands less but has lower initial sd will likely penetrate deeper than the bullet with greater sd that expands more easily. Obviously this requires you to match the bullet to the target.

I agree with you 100%. In fact, there was an article published many years ago by the U.S. military stating just that. They used the M1 carbine with a 16 twist vs the M1 Garand with a 10 twist firing a 110 grain bullet. The bullets were fired into gelatin at equal velocities and the results were VERY different. The 10 twist created a much larger wound channel. I have had people dispute that with me over the years, but my experience backs this up. It only makes sense that a bullet with FAR more rotational velocity (several thousand RPM) would be more apt to expand and/or come apart.......Rich

 

[FearNoWind]

The bullets were fired into gelatin at equal velocities and the results were VERY different.

I can't imagine how you'd compare those two rifles or why anyone would find the resulting data useful. There's more to it than just twist rate, and matching velocity and caliber would not provide meaningful data by themselves.
A better test would have been to produce two identical rifles with different twist rates - which was the standard military testing method during my tour of duty. Did you check the veracity of the article?

 

[trickytune]

I am hoping to test this at the range some time. Using the same ammo from different twist rates. Most of the information I find is about home defence which is of no interest to me. Just working out a good formula for hunting bullet selection for my own use.

 

[elkaholic]

I can't imagine how you'd compare those two rifles or why anyone would find the resulting data useful. There's more to it than just twist rate, and matching velocity and caliber would not provide meaningful data by themselves.
A better test would have been to produce two identical rifles with different twist rates - which was the standard military testing method during my tour of duty. Did you check the veracity of the article?

They fired the same bullets at the same velocity into the same media with the only variable being twist. Why does that not make sense? Sure it would be even better if the barrels were as identical as possible, but that doesn't, by any means, mean it had no merit......rich

 

[FearNoWind]

They fired the same bullets at the same velocity into the same media with the only variable being twist. Why does that not make sense? Sure it would be even better if the barrels were as identical as possible, but that doesn't, by any means, mean it had no merit......rich

They fired the same bullets at the same velocity into the same media with the only variable being twist. Why does that not make sense? Sure it would be even better if the barrels were as identical as possible, but that doesn't, by any means, mean it had no merit......rich

Well, Rich, I spent a good part of my life investigating processes and analysing data. I wasn't questioning your input and I do apologize if you misunderstood the basis of my question. Maybe my professional experience got in the way.
I simply wanted to know the source of the information. You can find "official" test data all over the place but without knowing all the elements connected with the test and who actually did the testing and under what conditions it's unwise (IMO) to just swallow the data and repeat it.
For example, the M1 Carbine was manufactured with barrels having at least two different twist rates (1:16, 1:20) I won't assume they checked the twist rate of the barrel used in the testing. They may have just picked up a rifle, read the "general" technical manuals, and accepted that what they read there applied to the rifle they held in their hands. The technical bullet dimension for the 30 Carbine is 7.62 mm while the tech. data for the Garand is 7.8. Both fall within the .308 bullet category. My question to the testing authority would be which bullet was chosen, what was the target distance (velocity diminishes rapidly over distance) what were the comparative barrel lengths (the more time the bullet remains in the barrel the more effective the twist rate will be over a given distance) what was the twist decay rate over the distance fired, etc.

 

[elkaholic]

Well, Rich, I spent a good part of my life investigating processes and analysing data. I wasn't questioning your input and I do apologize if you misunderstood the basis of my question. Maybe my professional experience got in the way.
I simply wanted to know the source of the information. You can find "official" test data all over the place but without knowing all the elements connected with the test and who actually did the testing and under what conditions it's unwise (IMO) to just swallow the data and repeat it.
For example, the M1 Carbine was manufactured with barrels having at least two different twist rates (1:16, 1:20) I won't assume they checked the twist rate of the barrel used in the testing. They may have just picked up a rifle, read the "general" technical manuals, and accepted that what they read there applied to the rifle they held in their hands. The technical bullet dimension for the 30 Carbine is 7.62 mm while the tech. data for the Garand is 7.8. Both fall within the .308 bullet category. My question to the testing authority would be which bullet was chosen, what was the target distance (velocity diminishes rapidly over distance) what were the comparative barrel lengths (the more time the bullet remains in the barrel the more effective the twist rate will be over a given distance) what was the twist decay rate over the distance fired, etc.

I read this YEARS ago and was impressed by the pics of the wound channels being so significant. At the time, I was too young to know that I should have written down all the references to be prepared for an arguement today