Hi Geylag,
Glad I've said something of interest..at last!

I've not done a great deal of testing with .22 air but have done some & found in general very good batch's of .22 tend to be rather more common "off the shelf" than .177

I know that altering average velocity just 20/30fps from one test to another has little or no affect on group size if all other things are equal.Over & above that other variables come into play, but it's fair to say from my own experience, at 50m indoors it is possible for a 30ftlb .22 air rifle to consitantly produce 10 shot groups of sub 1" with the correct batch of pellet. Shooting any further than that well lets say do I think sub 1" groups consistantly possible at 100ydsErrrrrrrrrrrrm NO! On occasions perhaps! People do win the lottery!

I have done a fair amount with .177 sporting pcp's & Ft.guns. I once tested a BSA Hornet std rifle indoors at 45yds from a test rig with a batch of Webley Lazerdome, it consistantly shot 10 shots in a group o/d of sub 10mm using a mylar overlay, now I call that impressive! but it was average to rubbish with FTT, Lazerpell, Crossman to name a few, nothing wrong with the other makes just not as good as in this rifle, another Hornet would have produced differing results no doubt! & I might add, I believe this performance to be considered exceptional, not the norm at this range! Don't forget I'm not talking C-C

My FWB P70 converted from 10m to 11.5ftlb, would shoot 10mm dia 10 shot groups at the same range with some batch's of JSB, & Lazerdome,

My steyr LG100 was a "nightmare" it was hopeless even at 6yd with most stuff except RWS Superdome of all things, a pellet that only ever proved to be average in all my other tests, but still very good. Some pellets were that bad I was getting 2 or 3 shots keyhole at 10m, I converted it to shoot FT at 11.5ftlb problem went away, I couldn't be bothered to try & find out why probaly not put together right! never liked the gun anyway!

The test rig used would not, nor was designed, to test break barrel guns, so I don't have any information to share on that.I have no reason to believe a good quality well tuned BB would not shoot as well as a quality PCP.
I did do a little testing using the same method Eley & Anschutz use. ie clamp the barrell, but I've never been convinced by this method, it seems too crude to me, but thats just my opinion!

I did alot of rimfire tests too with Anshutz, Walther, Krico, Diana plus a few sporting rifles & you would not believe how poor some of even the best quality ammo grouped, like 7 out of 10 seperate holes at 50m ouch!!