The Firing Line Forums - View Single Post - The Anatomy of L.R. shooting. So...err...what is it?

Bart B. · October 10, 2012, 07:56 PM

James asks.....

Barrel length: when is long too long?
If you get a 30 inch one, then you can go to Great Britian and shoot their fullbore matches with the .308 Win. That's what it takes for 147 to 155 grain bullets to remain supersonic through 1000 yards. 26 inch is good for lighter bullets from 175 to 200 grains in a .308 Win. 32 inch barrels is about the limit for 155's. One can get a .308 Win. barrel 3 inches longer then set it back 3 inches after 3000 rounds and have a virtual new barrel for much lower cost.

Match barrel or standard, fluted or straight?
A match grade barrel will shoot more accurate and therefore reflect more precisely how well you're doing. Standard barrels used oft times make it hard to tell if the barrel put that shot way out there or you did. But one needs to decide if the added expense is worth it for a match barrel based on their own shooting skills.

Straight; no flutes; fluting does nothing for accuracy and if done wrong, it ruins the accuracy of the barrel.

What effect does twist rate have, and so which is ideal or which should i avoid?
Depends on the bullet. They need to be spun fast enough to keep them point on and stable until they reach the target. If you use a .308 Win. cartridge and want a proven twist for different bullet weights, 155's use a 1:13 twist, 175's and 180's use a 1:12 twist, 200's and 190's use a 1:11 twist. For 220 grain ones, use a 1:10 twist 240 and 250 grain bullets need a 1:8 twist in a .308 Win.

I imagine the tighter the helix, the more stable the bullet, but presumably that also reduces muzzle velocity
Fast twists don't reduce muzzle velocity any measureable amount. The angle of the rifling to the bullet going from a 1:13 twist to a 1:10 twist is small. And the bullets move very slow starting into the rifling. After an inch of travel, they're well engraved by the rifling and how fast they move doesn't matter. A 22 caliber 1:8 twist presents the same rifling angle to the bullet as a 30 caliber 1:11 twist.

Spinning bullet too fast for what they need oft times causes problems. All bullets are unbalanced to some tiny amount. The faster they spin, the more centrfugal force is set up and they'll jump off the bore axis as the exit.

What about the bullet? I know that a higher BC is better, but… Long and heavy or light and short?High BC's help, but at the expense of more recoil 'cause they're typically heavier. The more recoil there is while the bullet goes down the barrel the harder the rifle is to shoot accurately. Many folks quit shooting long, heavy high BC 190 and 200 grain boattail bullets from their .308's at long range 'cause 155's recoil less; and with a 30 inch barrel, the 155's will shoot just fine.

HP or FMJ?
Hollow point; they're more accurate as their heel (body to boattail or base junction) is more perfectly round.

BT or not?
BT's are better past 300 yards. At shorter ranges, there's no significant difference for most folks.

October 10, 2012, 07:56 PM	#10
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	James asks..... Barrel length: when is long too long? If you get a 30 inch one, then you can go to Great Britian and shoot their fullbore matches with the .308 Win. That's what it takes for 147 to 155 grain bullets to remain supersonic through 1000 yards. 26 inch is good for lighter bullets from 175 to 200 grains in a .308 Win. 32 inch barrels is about the limit for 155's. One can get a .308 Win. barrel 3 inches longer then set it back 3 inches after 3000 rounds and have a virtual new barrel for much lower cost. Match barrel or standard, fluted or straight? A match grade barrel will shoot more accurate and therefore reflect more precisely how well you're doing. Standard barrels used oft times make it hard to tell if the barrel put that shot way out there or you did. But one needs to decide if the added expense is worth it for a match barrel based on their own shooting skills. Straight; no flutes; fluting does nothing for accuracy and if done wrong, it ruins the accuracy of the barrel. What effect does twist rate have, and so which is ideal or which should i avoid? Depends on the bullet. They need to be spun fast enough to keep them point on and stable until they reach the target. If you use a .308 Win. cartridge and want a proven twist for different bullet weights, 155's use a 1:13 twist, 175's and 180's use a 1:12 twist, 200's and 190's use a 1:11 twist. For 220 grain ones, use a 1:10 twist 240 and 250 grain bullets need a 1:8 twist in a .308 Win. I imagine the tighter the helix, the more stable the bullet, but presumably that also reduces muzzle velocity Fast twists don't reduce muzzle velocity any measureable amount. The angle of the rifling to the bullet going from a 1:13 twist to a 1:10 twist is small. And the bullets move very slow starting into the rifling. After an inch of travel, they're well engraved by the rifling and how fast they move doesn't matter. A 22 caliber 1:8 twist presents the same rifling angle to the bullet as a 30 caliber 1:11 twist. Spinning bullet too fast for what they need oft times causes problems. All bullets are unbalanced to some tiny amount. The faster they spin, the more centrfugal force is set up and they'll jump off the bore axis as the exit. What about the bullet? I know that a higher BC is better, but… Long and heavy or light and short?High BC's help, but at the expense of more recoil 'cause they're typically heavier. The more recoil there is while the bullet goes down the barrel the harder the rifle is to shoot accurately. Many folks quit shooting long, heavy high BC 190 and 200 grain boattail bullets from their .308's at long range 'cause 155's recoil less; and with a 30 inch barrel, the 155's will shoot just fine. HP or FMJ? Hollow point; they're more accurate as their heel (body to boattail or base junction) is more perfectly round. BT or not? BT's are better past 300 yards. At shorter ranges, there's no significant difference for most folks.