Barrel life for a 17 FB/ Mach 4
- Thread starter obaro
- Start date
Fitch
New member
I've sometimes used the Overbore index here:
http://accurateshooter.wordpress.com/2008/05/05/overbore-cartridges-a-working-definition/
as a basis for doing that sort of estimate.
The formulla the author uses is an approximation of bore area (not counting the area reduction due to lands) divided into the water grain capacity of the brass. For example, for a .17 FireBall, the diameter is .172, the water grain capacity of the brass according to QuickLoad is 20.5g which yields an index value of 882.
It's not anything official or sanctioned by anybody but it seems to make sense that as the index is higher barrel life is shorter. The lowest indexon the chart is the .30BR which is famous for having a very long barrel life - national matches have been won using barrels over 8,000 rounds.
Using estimates of barrel life and the chart in the link I've found over time that the plot of barrel life as a function of this index is surprisingly close to a straight line when I plug the numbers into EXCEL.
with that as background, and the calculated index of the .17 fireBall calculated on the same bases as the chart of ~882 which is about the same as a 6mm Dasher, slightly less than a .30-06. If the index is reliable, and the estimates of 4,000 rounds for a .30-06 are correct (I don't know anybody that's shot out the barrel of a .30-06), I'd go for the low side of that range because it's a .17, so 4,000 rounds, maybe more, maybe a bit less. Probably niticably longer barrel life than a .22-250 index of 1091 (mine was gone in 2,500 rounds) or .17 Remington index of 1140 (which would have a predicted life of around 1500 rounds).
Important Notes:
How the rifle is loaded can have a substantial impact on practical barrel life. I'm finding my .17Remington has it's best accuracy around 3,800 to 3,900 fps and I'm hoping loading it "down" to that MV extend it's life compared to always shooting it at muzzle velocities up around 4,300 to 4,400 with the same bullet.
Acceptable accuracy also affects barrel life. Bench Rest accuracy life will be noticably shorter than hunting accuracy life for the same cartridge both because of acceptable maximum group size being less for a Bench Rest competitor than a hunter.
YMMV
Fitch
http://accurateshooter.wordpress.com/2008/05/05/overbore-cartridges-a-working-definition/
as a basis for doing that sort of estimate.
The formulla the author uses is an approximation of bore area (not counting the area reduction due to lands) divided into the water grain capacity of the brass. For example, for a .17 FireBall, the diameter is .172, the water grain capacity of the brass according to QuickLoad is 20.5g which yields an index value of 882.
It's not anything official or sanctioned by anybody but it seems to make sense that as the index is higher barrel life is shorter. The lowest indexon the chart is the .30BR which is famous for having a very long barrel life - national matches have been won using barrels over 8,000 rounds.
Using estimates of barrel life and the chart in the link I've found over time that the plot of barrel life as a function of this index is surprisingly close to a straight line when I plug the numbers into EXCEL.
with that as background, and the calculated index of the .17 fireBall calculated on the same bases as the chart of ~882 which is about the same as a 6mm Dasher, slightly less than a .30-06. If the index is reliable, and the estimates of 4,000 rounds for a .30-06 are correct (I don't know anybody that's shot out the barrel of a .30-06), I'd go for the low side of that range because it's a .17, so 4,000 rounds, maybe more, maybe a bit less. Probably niticably longer barrel life than a .22-250 index of 1091 (mine was gone in 2,500 rounds) or .17 Remington index of 1140 (which would have a predicted life of around 1500 rounds).
Important Notes:
How the rifle is loaded can have a substantial impact on practical barrel life. I'm finding my .17Remington has it's best accuracy around 3,800 to 3,900 fps and I'm hoping loading it "down" to that MV extend it's life compared to always shooting it at muzzle velocities up around 4,300 to 4,400 with the same bullet.
Acceptable accuracy also affects barrel life. Bench Rest accuracy life will be noticably shorter than hunting accuracy life for the same cartridge both because of acceptable maximum group size being less for a Bench Rest competitor than a hunter.
YMMV
Fitch
Last edited:
