I have been conducting some test on a new barrel.
Cartridge: 6CM,slightly improved 243 Win)
Bullet: 115 DTAC
All of my past barrels have been straight 4 grove barrels.
The new barrel is a 5 grove with angled lands.
With the 5C barrel I’m finding that the loads developed for the straight 4 grove barrel do not transfer.
The 5C barrel appears to have much less friction,bite on the bullet) and thus yields slower velocities with the same loads.
The results of using a 5C barrel seem to be,velocity and powder charge) about the same as using moly coating.
Initially, on this project my thought was that the canted lands would be easier on the bullet and easier cleaning. However, with 5 lands I thought the forces against the bullet,friction down the barrel) would be about the same. So I thought the same loads would work.
However, my rudimentary tests have proved otherwise. The H1000 load of 49.3 grains with the 115 is 250 fps slower with the 5C barrel. I cannot get enough H1000 into the case to equal the velocity of the 4 grove barrel.
I have moved to slightly faster burning powders,4831SC and N160). I’m trying to stay away from R22 as it is a double based powder. And I cannot get my hands on any N165 currently.
So with H4831SC I can get over 3200 fps from the 115, but with unacceptable accuracy throughout the velocity range of 3050 through 3200. ES’s are large.
H4831SC seems to be inconsistent between 5 shot groups. One group give ¼ MOA with good data from the chronograph and the next gives a close to 1 MOA group with huge ES.
With N160 I do not have a good test as to date.
I’m thinking N165 is a good powder for this cartridge barrel combination.
However, it is very frustrating that I have to change everything, as far powder charges go to make this 5C barrel work.
Does anyone have any experience with this that might help.
Joe
Cartridge: 6CM,slightly improved 243 Win)
Bullet: 115 DTAC
All of my past barrels have been straight 4 grove barrels.
The new barrel is a 5 grove with angled lands.
With the 5C barrel I’m finding that the loads developed for the straight 4 grove barrel do not transfer.
The 5C barrel appears to have much less friction,bite on the bullet) and thus yields slower velocities with the same loads.
The results of using a 5C barrel seem to be,velocity and powder charge) about the same as using moly coating.
Initially, on this project my thought was that the canted lands would be easier on the bullet and easier cleaning. However, with 5 lands I thought the forces against the bullet,friction down the barrel) would be about the same. So I thought the same loads would work.
However, my rudimentary tests have proved otherwise. The H1000 load of 49.3 grains with the 115 is 250 fps slower with the 5C barrel. I cannot get enough H1000 into the case to equal the velocity of the 4 grove barrel.
I have moved to slightly faster burning powders,4831SC and N160). I’m trying to stay away from R22 as it is a double based powder. And I cannot get my hands on any N165 currently.
So with H4831SC I can get over 3200 fps from the 115, but with unacceptable accuracy throughout the velocity range of 3050 through 3200. ES’s are large.
H4831SC seems to be inconsistent between 5 shot groups. One group give ¼ MOA with good data from the chronograph and the next gives a close to 1 MOA group with huge ES.
With N160 I do not have a good test as to date.
I’m thinking N165 is a good powder for this cartridge barrel combination.
However, it is very frustrating that I have to change everything, as far powder charges go to make this 5C barrel work.
Does anyone have any experience with this that might help.
Joe
