Anyone ever think pellet size, fit, depth of rifling engraved in pellet, weight, all cause pellets to hit at different POI? Well, of course we have. What about spin drift?
I mean, spin drift at 1000 yards can be what, 8-12" with a centerfire? This must also show up in pellets/slugs. Especially since the only calculator that spits out anything near correct figures for all 3 (Sub, Super, & Hypersonic) twist rates is The Kolbe calculator. It highly disagrees with Air Force's 1:14 barrel twist. Yet, the factory barrel can shoot anywhere from 60-120 grain within 50 yards (expect wobble/keyholing when too heavy, too far); but I also see it does shoot 86-91/92 grain factory recommend slugs with exceptional accuracy (calculator be dammed) somehow, sub sonically, with a fairly high grade of accuracy.
Back to my problem with the 1:18 twist .25 Sumatra. Exceptional accuracy from muzzle through 150 yards and beyond. I haven't tested past 200. The QUESTION, is why are my 50 grain .253 slugs hitting 4 mils to the right at 200 yards when all three are within 1" @ 32 yards. Just using hold over, not clicking, rifle, scope perfectly centered, not canted. The same pellets 25.43, 33.95 are dead on out at 150 yards with hold over.
When I try a 50 grain .253" Starrett micrometers calibrated correctly, TP# 7 or 8, darn slug hits 4 mils to the right out at 200 yards.
Anyone care to guess or explain what's occurring here? I plan on ordering some .251, .252, .253 OD slugs in 40 through as heavy as I can find in .25. I'd guess around 60-70 grains. The Sumatra wasn't designed for single loading but it has a fairly long breech chamber do a slug could be designed.
Edit: January 21, 2020.
I never tested my twist rate on some airguns. Just assumed that they were all 1:16. Boy was I wrong. Way off on Air Force barrel. I’d thought TJ uses 1:14 so Air Force must be. Darn thing isn’t even 1:16, it’s supposedly 1:17.7 so 1:18. SLOW for any heavy RBT .22 slug.
I found the shortest 28.5 grain RBT Griffin slug did best, and best isn’t anywhere near my desires or knowing what optimal could do.
So just wanted to clarify.
I mean, spin drift at 1000 yards can be what, 8-12" with a centerfire? This must also show up in pellets/slugs. Especially since the only calculator that spits out anything near correct figures for all 3 (Sub, Super, & Hypersonic) twist rates is The Kolbe calculator. It highly disagrees with Air Force's 1:14 barrel twist. Yet, the factory barrel can shoot anywhere from 60-120 grain within 50 yards (expect wobble/keyholing when too heavy, too far); but I also see it does shoot 86-91/92 grain factory recommend slugs with exceptional accuracy (calculator be dammed) somehow, sub sonically, with a fairly high grade of accuracy.
Back to my problem with the 1:18 twist .25 Sumatra. Exceptional accuracy from muzzle through 150 yards and beyond. I haven't tested past 200. The QUESTION, is why are my 50 grain .253 slugs hitting 4 mils to the right at 200 yards when all three are within 1" @ 32 yards. Just using hold over, not clicking, rifle, scope perfectly centered, not canted. The same pellets 25.43, 33.95 are dead on out at 150 yards with hold over.
When I try a 50 grain .253" Starrett micrometers calibrated correctly, TP# 7 or 8, darn slug hits 4 mils to the right out at 200 yards.
Anyone care to guess or explain what's occurring here? I plan on ordering some .251, .252, .253 OD slugs in 40 through as heavy as I can find in .25. I'd guess around 60-70 grains. The Sumatra wasn't designed for single loading but it has a fairly long breech chamber do a slug could be designed.
Edit: January 21, 2020.
I never tested my twist rate on some airguns. Just assumed that they were all 1:16. Boy was I wrong. Way off on Air Force barrel. I’d thought TJ uses 1:14 so Air Force must be. Darn thing isn’t even 1:16, it’s supposedly 1:17.7 so 1:18. SLOW for any heavy RBT .22 slug.
I found the shortest 28.5 grain RBT Griffin slug did best, and best isn’t anywhere near my desires or knowing what optimal could do.
So just wanted to clarify.
