Wasn't my idea to size .22s down to .20...credit to @Motorhead for the concept
Recently revisited the idea that I originally investigated here: https://www.airgunnation.com/threads/20-jsb-exact-jumbo-heavies-resized-from-22.1094891/
But this recent adventure was with the .22/25.4grain Monster Redesigns.
So, yes, a .20/25.4.
Evident in the photo, they get pretty long. Rifle test bed was the Ghost, which has a standard Lothar rifling twist rate of 1:17.7, at least in this case. Which prompted all kinds of internet deep dives on length versus twist rate. Ie, can a 1:17.7 stabilize something so long? Berger has a pretty cool calculator. Kolbe is also a data source. But ultimately, seems there has been very little (read NONE) actual research producing viable data on projectile length versus rifling twist rate for pellets. And that dearth of usuable/trustable data might even extended to airguns as a whole (slugs too).
The fastest I could get them was 870fps, but the shot cycle was pretty miserable, and the gun was working hard to produce that. The barrel is 18 or maybe 19 inches long, and while the transfer port is optimal for a .20, this is simply trying to squeeze a whole lot of air through a relatively tiny hole, pushing on the base of a relatively small diameter projectile, that also has a very large bearing surface (read friction) to overcome, without a long barrel to aid in most efficient use of the air. Ultimately 850fps was the happy point for tuning. And 25.4grain at 850fps is just a smidge over 40fpe. Not too shabby.
Related tidbit that was interesting for me...the exact same settings that would push these .22 Monster RDs to 960fps as a .22, would only do 870fps with them as .20s. So, 52fpe, versus about 42fpe. While not completely apples to apples (the .22 barrel was 23inches long) pretty apparent it's easier to make power in larger calibers.
So, at 850fps the gun was REALLY quiet. Every little drop of air was going into propelling that big .20/25.4grain abomination.
The big question: how'd they shoot?
Well, 5 shots into 3/8" at 30 yards. And it put 8 into 1.5" at 60 yards on a windy day. But at 100 yards everything fell apart. 5-6 inch groups at 100 yards. So.....very useable as a hunting option for 60 yards and less, but something bad happens between 60 and 100yards.
As for the stabilization....I was expecting keyholes and other signs of no-goodness. But all the holes are nice clean round holes, even at 100 yards.
While not the type of long range accuracy I'm looking for, a fun experiment anyway.
Recently revisited the idea that I originally investigated here: https://www.airgunnation.com/threads/20-jsb-exact-jumbo-heavies-resized-from-22.1094891/
But this recent adventure was with the .22/25.4grain Monster Redesigns.
So, yes, a .20/25.4.
Evident in the photo, they get pretty long. Rifle test bed was the Ghost, which has a standard Lothar rifling twist rate of 1:17.7, at least in this case. Which prompted all kinds of internet deep dives on length versus twist rate. Ie, can a 1:17.7 stabilize something so long? Berger has a pretty cool calculator. Kolbe is also a data source. But ultimately, seems there has been very little (read NONE) actual research producing viable data on projectile length versus rifling twist rate for pellets. And that dearth of usuable/trustable data might even extended to airguns as a whole (slugs too).
The fastest I could get them was 870fps, but the shot cycle was pretty miserable, and the gun was working hard to produce that. The barrel is 18 or maybe 19 inches long, and while the transfer port is optimal for a .20, this is simply trying to squeeze a whole lot of air through a relatively tiny hole, pushing on the base of a relatively small diameter projectile, that also has a very large bearing surface (read friction) to overcome, without a long barrel to aid in most efficient use of the air. Ultimately 850fps was the happy point for tuning. And 25.4grain at 850fps is just a smidge over 40fpe. Not too shabby.
Related tidbit that was interesting for me...the exact same settings that would push these .22 Monster RDs to 960fps as a .22, would only do 870fps with them as .20s. So, 52fpe, versus about 42fpe. While not completely apples to apples (the .22 barrel was 23inches long) pretty apparent it's easier to make power in larger calibers.
So, at 850fps the gun was REALLY quiet. Every little drop of air was going into propelling that big .20/25.4grain abomination.
The big question: how'd they shoot?
Well, 5 shots into 3/8" at 30 yards. And it put 8 into 1.5" at 60 yards on a windy day. But at 100 yards everything fell apart. 5-6 inch groups at 100 yards. So.....very useable as a hunting option for 60 yards and less, but something bad happens between 60 and 100yards.
As for the stabilization....I was expecting keyholes and other signs of no-goodness. But all the holes are nice clean round holes, even at 100 yards.
While not the type of long range accuracy I'm looking for, a fun experiment anyway.
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