Thank you Jim. I think I understand. I didn't realize that the start pressure of the 177 was that much higher. I figured with the smaller surface area that it might be higher. I didn't realize it was that much higher.I'm not sure I understand, "recoil displacement (travel) is actually greater". Are you talking about the travel of the 22 pellet?I think what I'm understanding here is kind of what I suspected for a long time. That was the 177 R1s sharper shot cycle is from trying to stuff a lot of air though a small hole rapidly.I know increasing the transfer port size will likely decrease velocity but do you think the size increase might soften the shot cycle of the 177 R1 by reducing some restriction??Thanks for replying. I love learning new stuff.Be wellRon
Quote from: Bayman on June 03, 2022, 06:34:10 PMThank you Jim. I think I understand. I didn't realize that the start pressure of the 177 was that much higher. I figured with the smaller surface area that it might be higher. I didn't realize it was that much higher.I'm not sure I understand, "recoil displacement (travel) is actually greater". Are you talking about the travel of the 22 pellet?I think what I'm understanding here is kind of what I suspected for a long time. That was the 177 R1s sharper shot cycle is from trying to stuff a lot of air though a small hole rapidly.I know increasing the transfer port size will likely decrease velocity but do you think the size increase might soften the shot cycle of the 177 R1 by reducing some restriction??Thanks for replying. I love learning new stuff.Be wellRonHi Ron,A friend and I measured the start pressures for a range of pellets, and the .22" was circa 66% that of the .177", which is no great surprise, as that's the CSA ratio reciprocal of the two calibres.If a .22" pellet starts to move 78% into the compression stroke, the .177" will typically hang on in the breech until nearer 85% into the stroke. That means between those two points, cylinder pressure with .22" is slightly lower at any given piston position, so the piston travels further, so the rifle recoil displacement associated with the compression stroke is a little further.I'm not sure that opening up the transfer port would be helpful, and it could make matters worse. The issue is that there is too much kinetic energy in too much air at piston bounce for .177", and energy that does not make it to the less efficient pellet powers piston bounce. I think I'd be looking at reducing the energy the spring makes available to the piston, or reducing the swept volume, or a bit of each. In either case, I'd be sacrificing a little muzzle energy to obtain a much nicer recoil cycle.Another option would be to fit a lower rate (softer) spring with more preload. This will slow recoil acceleration a little, but give higher force to slow, and limit, piston bounce. Best wishes,Jim
I wonder if the relationship between start pressures and pellet tail area are linear? -YPS again, great topic and discussion!
Most of my .177 pellets seem to have really flared skirts. More so than my .22 pellets. -Y
Quote from: Yogi on June 04, 2022, 11:43:53 PMMost of my .177 pellets seem to have really flared skirts. More so than my .22 pellets. -YYogi is the before or after they have been shot? Just trying to digest all this great info.
I decided to install a new 20 caliber barrel on my R1.
Ron,Assuming that the R1 is the HW80, it has 81mm of available stroke. Bearing in mind that the pellet gains most energy while it and the piston are travelling in the same direction, the .177" JSB will have ~12mm of potential piston travel left after it starts to move, the FTT nearer 7.5mm so, all other things being equal and in the absence of dieseling, the JSB should give higher muzzle energy.Dieseling creates a pressure spike that gets the FTT moving earlier in the stroke, so it can equal and sometimes exceed the muzzle energy of the JSB. Having said which, I have always found FTT to give the better accuracy in my HW77 and HW95s, so that's the pellet I set the rifles up for. I'd say your drop in muzzle energy is almost certainly the new seal, which should sort itself out as the rifle gets some use.
What are your velocities with the 20cal pellet's?
That's just a tic slower then I thought, the ave I see with a 13.5gn is around 750 to 760fps, and 800 to 820fps with a 11.42gn FTT, 740fps is usually what I see with a shock rifle in .22cal with a 14.66gn FTT, IMO, your piston seal must be a tic tight! JMO