23 January 2017
I have been thinking of some variation on the 6/22-250. - Three decades ago, I built a 6mm-.250 on a trued 788 action for the CBA Silhouette Class and then the CBA closed the class. Using R-P .250 Savage brass with necks turned to clean up to uniform thickness, the rifle shot cast bullets well. I have an affectation for any cartridge built from the .250 Savage case. However, today I use the 6mm BR since the case volume is similar and the brass does not need formed. I still have the barrel and might reinstall it to experiment.
Case volume looks good for a 90-100 gr bullet. - It is, you get consistent velocity. I mainly used RCBS 243-95-SP and SAECO 85 grain TCGC bullets, Reloder #7 powder, monotype and Linotype, sized .244, high-speed LBT Blue lube, with good results. The rifle was light and hard to steer from sear release to bullet exit. It is analogous to shooting 200 yards with the .22 LR for ASSRA matches, you can influence the path of the bullet while it is still in the barrel.. That is why I worked velocity up to the 2200/2300 feet per second range to help steer the rifle better.
It is going to need to wait a bit until I sort out these two 243s, though. - I have a .243 Winchester Model 70 Varmint converted to a High-Power Target configuration. My hope was to shoot cast at 200 and 300 yards with jacketed at 600 yards. However, I changed jobs and never again had time to shoot High-Power matches. The rifle showed promise at 200 yards, but the cast did not hold up at an actual 300 yards. Velocity variations caused vertical stringing. I went back to H-4831 and the Sierra 100 grain soft point boattail bullet for all ranges.
Can a person get to 1"- 10 shot groups with a standard 243 - in your opinion? - I think your goal is possible. My first experience was the Ruger #1 in 6 mm Remington that shot well. Several 10-shot groups under an inch with the RCBS bullet.
Discussing 6 mm cast bullets with Mike Mohler at Fairfax, we had several observations. Mike felt he had to work the bore smooth and be very consistent with powder charge. I agree with his observation. We discussed gas checks and their quality, a major stumbling block in 6 mm cast bullets. You can see the height of the shank varying from one side to the other on certain lots of gas checks. Sorting these gas checks, they do not shoot as well. Gas check quality is seldom checked.
Farm boy from Illinois, living in the magical Pacific Northwest