40 Cal smooth verses full sizing
Oct 27, 2022 9:18:16 GMT -5
jimbob, ballistic, and 1 more like this
Post by sew on Oct 27, 2022 9:18:16 GMT -5
Though I have been involved in smokeless MLing for 23 years, and with a 40 cal for 20 years, I didn’t get involved in truly modern smokeless MLers until about 4 years ago with a 45 and 1 1/2 years ago with 2 state of the art 40s. I’ve recently learned a lot and will share for new 40 cal users.
Obturation is a greater problem in a 40 than a 45. Consistent, quick obturation is vital for great accuracy. The lighter the bullet and powder load, the more difficult the obturation. I’m interested in hunting out to 300 yards with my ultra-lite rifle (8#) and 300-400 with my heavy rifle (18#). Therefore 200-250g for the lite and 275-300 for the heavy. Velocities of 2600-2800 , respectively, is plenty for me. HIS and smooth forming got good accuracy with regular core 225 and 275 AMs. Hard cores, not so good. Higher pressures would have helped, surely.
How to get faster, more consistent obturation? Here’s what I did. 253 Pittman Hammers (4085), annealed, FULL sized, no wad, 62g H322, DI, WLMRPs. The full sized, softened all copper bullets felt like they obturated instantly. The ES was only 6’/sec across 8 shots (2,730+/-3). The sharpness of the felt recoil is an indicator of the quickness of the obturation. Just compare the instant, violent obturation of a cartridge rifle shooting the same energy as a smokeless MLer! There is a noticeable difference when shooting lighter smokeless MLers with mild loads verses a CF of the same energy level. The felt recoil difference in shooting the full sized soft copper bullet and a smooth sized hard core is pronounced! So, a full sized 253g PH, annealed, with a fast powder (H322,62g), DI (for faster ignition) results in not only extremely fast obturation but also in exceptional accuracy!
I’m not recommending this load at all. The QL predicted pressure of ~ 49K and velocity of mid 2600s might be a bit low due to the very quick obturation combined with DI. The obtained velocity was 60-70’/sec faster than calculated. For 45s, smooth sizing and HIS, QL seems very accurate. DI throws that off a bit. 40 cal, even smooth sizing and HIS is usually a little faster than calculated. Full sizing and DI is really faster. Pressure?
Yesterday in 10-15 mph, gusty winds, shooting JB’s ultralite 40 with a 2-8 Duralyt, I shot a ragged hole with 3 shots @ 100 yards, 3” exactly above the aiming point, at 200 yards (2 shots only) 3/4” between but 2” right (wind) and 3 1/2” high and @280 yards (distance limited) 1” low and nearly 4” right , just over an inch for 2 shots. 8# rifle ready to hunt and loaded, 253g copper and well sub-MOA.
So, lessons learned. Full sizing helps, especially with lighter loads and in 40s. Even though the Pittman Hammers are cast, annealing is still advantageous. DI can only have helped also.
Jimbob’s masterpieces.
Obturation is a greater problem in a 40 than a 45. Consistent, quick obturation is vital for great accuracy. The lighter the bullet and powder load, the more difficult the obturation. I’m interested in hunting out to 300 yards with my ultra-lite rifle (8#) and 300-400 with my heavy rifle (18#). Therefore 200-250g for the lite and 275-300 for the heavy. Velocities of 2600-2800 , respectively, is plenty for me. HIS and smooth forming got good accuracy with regular core 225 and 275 AMs. Hard cores, not so good. Higher pressures would have helped, surely.
How to get faster, more consistent obturation? Here’s what I did. 253 Pittman Hammers (4085), annealed, FULL sized, no wad, 62g H322, DI, WLMRPs. The full sized, softened all copper bullets felt like they obturated instantly. The ES was only 6’/sec across 8 shots (2,730+/-3). The sharpness of the felt recoil is an indicator of the quickness of the obturation. Just compare the instant, violent obturation of a cartridge rifle shooting the same energy as a smokeless MLer! There is a noticeable difference when shooting lighter smokeless MLers with mild loads verses a CF of the same energy level. The felt recoil difference in shooting the full sized soft copper bullet and a smooth sized hard core is pronounced! So, a full sized 253g PH, annealed, with a fast powder (H322,62g), DI (for faster ignition) results in not only extremely fast obturation but also in exceptional accuracy!
I’m not recommending this load at all. The QL predicted pressure of ~ 49K and velocity of mid 2600s might be a bit low due to the very quick obturation combined with DI. The obtained velocity was 60-70’/sec faster than calculated. For 45s, smooth sizing and HIS, QL seems very accurate. DI throws that off a bit. 40 cal, even smooth sizing and HIS is usually a little faster than calculated. Full sizing and DI is really faster. Pressure?
Yesterday in 10-15 mph, gusty winds, shooting JB’s ultralite 40 with a 2-8 Duralyt, I shot a ragged hole with 3 shots @ 100 yards, 3” exactly above the aiming point, at 200 yards (2 shots only) 3/4” between but 2” right (wind) and 3 1/2” high and @280 yards (distance limited) 1” low and nearly 4” right , just over an inch for 2 shots. 8# rifle ready to hunt and loaded, 253g copper and well sub-MOA.
So, lessons learned. Full sizing helps, especially with lighter loads and in 40s. Even though the Pittman Hammers are cast, annealing is still advantageous. DI can only have helped also.
Jimbob’s masterpieces.
