The Firing Line Forums - View Single Post - A little confused, questions about barrel length and velocity

Kimio · February 14, 2013, 08:18 AM

Okay, so I'm a little confused here.

For the longest time, I was told that typically the longer the barrel the greater the velocity and amount of spin is imparted on the bullet. This of course varies from round to round due to bullet load and twist rate, but the general idea has remained the same, depending on the round, you will need x twist rate and x amount of barrel length in order to stablize the round for extended distances.

So lets take the .308 for example, I was under the impression the ideal length for san an FAL or an M1A would be at least 18" in length (17" and some change if you want to get specific) since you get the better part of both worlds, you have enough length to stablize the round for longer distances (300yd maybe?) while not having the barrel so long that it becomes cumbersome (I'm not humping the rifle up a mountain so it's not as big of a concern for me)

shorter barrels will cause a loss in velocity and therefore a loss in accuracy, at least in the case of the .308 cartridge.

Now I'm being told that the loss in velocity is neglible and that shorter barrels can actually increase over all accuracy due to changes in the barrels harmonics and rigidity (I though this was affected more by if the barrel is free floated and also depended on the type of materials used in its manufacturing)

So which is it? I keep getting mixed responses, part of the reason I'm asking is because I'm debating on building a 16" FAL PARA, the rifle probably will not be shot out any farther than 300yd 400yd if I'm feeling lucky, and while I'm not expecting to get 1MOA our of it I am hoping to at least get MOM (Minute of Man) out of the rifle with the shorter length barrel (I like the handiness the carbine version of the rifle)

Clarifications please?

February 14, 2013, 08:18 AM	#1
Kimio Senior Member Join Date: January 2, 2011 Location: Arizona Posts: 1,171	A little confused, questions about barrel length and velocity Okay, so I'm a little confused here. For the longest time, I was told that typically the longer the barrel the greater the velocity and amount of spin is imparted on the bullet. This of course varies from round to round due to bullet load and twist rate, but the general idea has remained the same, depending on the round, you will need x twist rate and x amount of barrel length in order to stablize the round for extended distances. So lets take the .308 for example, I was under the impression the ideal length for san an FAL or an M1A would be at least 18" in length (17" and some change if you want to get specific) since you get the better part of both worlds, you have enough length to stablize the round for longer distances (300yd maybe?) while not having the barrel so long that it becomes cumbersome (I'm not humping the rifle up a mountain so it's not as big of a concern for me) shorter barrels will cause a loss in velocity and therefore a loss in accuracy, at least in the case of the .308 cartridge. Now I'm being told that the loss in velocity is neglible and that shorter barrels can actually increase over all accuracy due to changes in the barrels harmonics and rigidity (I though this was affected more by if the barrel is free floated and also depended on the type of materials used in its manufacturing) So which is it? I keep getting mixed responses, part of the reason I'm asking is because I'm debating on building a 16" FAL PARA, the rifle probably will not be shot out any farther than 300yd 400yd if I'm feeling lucky, and while I'm not expecting to get 1MOA our of it I am hoping to at least get MOM (Minute of Man) out of the rifle with the shorter length barrel (I like the handiness the carbine version of the rifle) Clarifications please?