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chucko · July 1, 1999, 01:54 AM

I know that the deceleration back down through the sonic barrier has quite an effect on a little 22LR bullet. The resulting shock wave causes the bullet to start wobbling.

Though the forces involved during acceleration and decelleration are the same, the effect is not as bad when accelerating up through the sonic barrier because bullet has just left the barrel and still has much of its original energy and rotation to help it to re-stabilize.

With 22LR, it is important to know at what range your bullet goes sub-sonic, because this is the maximum range that you will be able to get tight groups. Some shooters opt to shoot sub-sonic or near sub-sonic ammo in order to get around this problem. With near sub-sonic ammo the bullets decelleration down through the sonic barrier happens soon after it has left the barrel and it is still able to re-stabilize itself due to its retained rotation and energy. If you notice, match grade 22LR ammo is not a hot load. It usually hovers right around the sonic barrier.

I would ASSUME that at least part of this principal is aplicable to larger bullets, though probably to a lesser extent.

Though I can think of no way to measure it, I can see how the rotational rate of a bullet would also be critical in calculating its maximum effective/reliable range. If a bullet of "L" Lenght, "D" Diameter, and "W" Weight, needs to rotate a minimum of "R" RPMs in order to maintain its stability, the distance at which its rotation fell below that level would be its maximum effective/reliable range.

Intresting side note:
To test the formula shown above, I pulled the bullets from a Portugese NATO 7.62x51mm, and a UMC .308win. The Portugese appeared to have a longer bullet than the UMC before I pulled them. I discovered that both we identical in length ( about 1127 thousanths). The UMC is seated much deeper in the brass. 425 thousanths for the UMC and 365 thousanths for the Portugese. I don't have a scale to weigh them right now.

Chuck

[This message has been edited by chucko (edited July 02, 1999).]

July 1, 1999, 01:54 AM	#11
chucko Senior Member Join Date: May 20, 1999 Posts: 151	I know that the deceleration back down through the sonic barrier has quite an effect on a little 22LR bullet. The resulting shock wave causes the bullet to start wobbling. Though the forces involved during acceleration and decelleration are the same, the effect is not as bad when accelerating up through the sonic barrier because bullet has just left the barrel and still has much of its original energy and rotation to help it to re-stabilize. With 22LR, it is important to know at what range your bullet goes sub-sonic, because this is the maximum range that you will be able to get tight groups. Some shooters opt to shoot sub-sonic or near sub-sonic ammo in order to get around this problem. With near sub-sonic ammo the bullets decelleration down through the sonic barrier happens soon after it has left the barrel and it is still able to re-stabilize itself due to its retained rotation and energy. If you notice, match grade 22LR ammo is not a hot load. It usually hovers right around the sonic barrier. I would ASSUME that at least part of this principal is aplicable to larger bullets, though probably to a lesser extent. Though I can think of no way to measure it, I can see how the rotational rate of a bullet would also be critical in calculating its maximum effective/reliable range. If a bullet of "L" Lenght, "D" Diameter, and "W" Weight, needs to rotate a minimum of "R" RPMs in order to maintain its stability, the distance at which its rotation fell below that level would be its maximum effective/reliable range. Intresting side note: To test the formula shown above, I pulled the bullets from a Portugese NATO 7.62x51mm, and a UMC .308win. The Portugese appeared to have a longer bullet than the UMC before I pulled them. I discovered that both we identical in length ( about 1127 thousanths). The UMC is seated much deeper in the brass. 425 thousanths for the UMC and 365 thousanths for the Portugese. I don't have a scale to weigh them right now. Chuck [This message has been edited by chucko (edited July 02, 1999).]