I have a Winchester Model 70 in .270 converted to .25-06 with a 26-inch Hart barrel. Lyman #50 lists the most accurate powder in their 26-in test barrel with a Winchester case as H-1000 with 58.0 gr maximum delivering 3038 fps with a Sierra flat base 117gr spitzer.
I have both Winchester and R-P cases, but I'm shooting a Sierra 117gr SPBT rather than the flat base. I wanted to see if there was any difference between the two cases.
I loaded 5 rounds each with H-1000 but stayed 2.0gr under max at 56.0gr, CCI 200 primers, and seated the bullets 0.02" from the lead with an OAL case-base to ogive of 2.735".
I tested the speed with a Magnetospeed chronograph and reset the position after each shot fired as it jumped about an inch with each recoil, and I alternated the shots with each of the cases.
To my surprise, the 5 R-P cases delivered an average of 3118 fps (ES 44) while the Win cases almost matched the Lyman numbers with an average of 3049 fps (ES 54) (recall this is 2.0gr under the Lyman charge).
I weighed two fired cases of both manufacturers, then filled each of the 4 with water until I produced a meniscus. Weighed again, the volume in the R-P cases averaged 68gr while the Win cases averaged 69 grains (rounded off).
Is it possible that the larger Win case volume produced less pressure to account for the lower velocity?
I suspect the difference in Lyman's 3038 fps in Win cases at 58.0gr vs. my 3049 fps with 56.0gr is more complex, but what might be the effect of my using a boat-tail vs Lyman's use of a flat base?
I have both Winchester and R-P cases, but I'm shooting a Sierra 117gr SPBT rather than the flat base. I wanted to see if there was any difference between the two cases.
I loaded 5 rounds each with H-1000 but stayed 2.0gr under max at 56.0gr, CCI 200 primers, and seated the bullets 0.02" from the lead with an OAL case-base to ogive of 2.735".
I tested the speed with a Magnetospeed chronograph and reset the position after each shot fired as it jumped about an inch with each recoil, and I alternated the shots with each of the cases.
To my surprise, the 5 R-P cases delivered an average of 3118 fps (ES 44) while the Win cases almost matched the Lyman numbers with an average of 3049 fps (ES 54) (recall this is 2.0gr under the Lyman charge).
I weighed two fired cases of both manufacturers, then filled each of the 4 with water until I produced a meniscus. Weighed again, the volume in the R-P cases averaged 68gr while the Win cases averaged 69 grains (rounded off).
Is it possible that the larger Win case volume produced less pressure to account for the lower velocity?
I suspect the difference in Lyman's 3038 fps in Win cases at 58.0gr vs. my 3049 fps with 56.0gr is more complex, but what might be the effect of my using a boat-tail vs Lyman's use of a flat base?