I worked backwards.
Figured I wanted about 500fps remaining at 40 yards using a pellet with a BC of about .0225. Working the charts backwards, that works out to launching the pellet at about 625fps (and if you want 500fps left at 50yards, would lauch at about 660fps).
The mods. to get one up to 625-650 aren't hard to do at home and aren't drastic modifications...can get it done simply. Smoothing the tubes, polishing the moving parts, adjusting the springs a little bit, transfer port seal, and opening the bolt probe's intake port will get you....no valve mods. or excessive spring tinkering needed for that speed. Certainly can get them to shoot faster, but that brings up accuracy.
Want it to shoot 1" or under at max. range (and I'd be happier if they shot inside 3/4"). A +700fps arigun will have the energy to work fine out to 65-75 yards, but unless it can shoot inside that 1" limit, wouldn't be real useful.
This was shot at 50yards...running right at the accuracy limit, and just at the energy limit, so I'd call this the max. range for this rifle.
So far, the rifle that shot that above group, is the "winner"...My qb78 hasn't been able to group quite so well and I'll limit it to 40yards.
After doing the same type of tests with the QB78 mentioned above that was runing 710fps (.22), found that accuracy wasn't good enough to take advantage of the extra power, so i backed that rifle down to 630fps. It's a 40yard gun, so i gave it 40yard power. Doesn't hurt to have more power than you need, but I like to run the QB78 on cartridges, and saving gas/extending shot count made it worth the effort to lower the vel. to it's "ballance point" (where power and accuracy run out at about the same distance).
'Ballance point"...some rifles have way more accuracy than power (traditonal spring-air match rifles fall into that catagory) and many have way more power than accuracy. Best would be for the two factors to kind of balance out, running out of power and accuracy at about the same place...would reduce the temptation to blast away at critters out of range.
That 500fps limit is too high for small birds and little critters....can work with a lot less speed. The SAME basic mods. used to bring the rifle up to 650fps are aslo needed to increase accuracy. Anything you do to make the rifle run more smoothly, less friction, and a smoother flow of gas help it to shoot better..can't shoot good groups unless the rifle is consistant (and consistancy..running off that big tank...is proably why the QB79 shoots a bit better).
