I've had a Mod 48/52 in .22 for 7 years now and have generally been very pleased with it. One problem which I've not been able to fix --and admittedly I have been a bit lethargic on this-- is that goes through cheap scopes like mad. I have the best stops and mounts but never got around to buying a quality scope. As a result I've just thrown away my third scope, a Norica, and bought a Walther 3-9 x 40 with an illuminated reticle. Ok, still not top of the line, but an improvement. Then, just as I was wondering if the Mod 48 would soon make mincemeat of the Walther (oh and btw, it goes without saying that I've checked and re-checked all the bindings and screws; nothing was loose), I had a chance to shoot someone's Mod 54. (again in .22) I was truly impressed with the smoothness and pinpoint accuracy (which I've been able to attain only intermittently) and suddenly the prospect of a long-lasting zero started looking aattractive.
My question is, is it worth upgrading from a Mod 48/52 to the 54? I can get a decent trade-in price on the 48 so cost is just about bearable. Will there be a lasting improvement in accuracy due to the recoilless operating system, or should I just concentrate on setting up the 48 correctly?
Also, I chronographed the 48 with Gamo Magnum pointed pellets (weight unspecified)at 680 fps, +- 9 fps. This seems low; is it normal?
It seems from your post that you are hoping to upgrade to the 54 because it will be easier on scopes. The 54 is more of a scope killer than the 48/52.
Jim Maccari hints that scope destruction could come from faulty piston seals that allow a too harsh firing cycle. Maybe have your 48/52 tuned before selling it off for another scope killer. Even with a tune you will need a sturdy scope, but at least you end up with a rifle that should bring in more cash if you decide to sell it.
Without a pellet weight, no one can evaluate your chrony numbers. The 48 will launch a .22 pellet anywhere from 825 to 575 fps depending on the weight. Your 680fps puts you right in the middle of the range.
Depending on the quality of the Gamo pellet, that +- 9fps could be attributed to pellet weight variation. In that case I don't think you have a seal problem. I would expect to see a lot bigger variation in speed if you had bad seals.
Invest in a good scope first. Then consider a tune. Then consider a different gun.
The Pro-Magnum is a 13.7 grs. pellet and the Magnum is a 15.5 grs. pellet. From what you say about pointed, I would assume you're talking about the Magnum, but the Pro-magnum is also slightly pointed.
Anyway, your gun is yielding almost 16 ft-lbs. not bad, but I would check the seals.
Personally, I would go different from what Whiteleather says: I would have the gun tuned, then I would get a really good scope (not necessarily expensive, try the Leapers scopes) and then if results were not up to snuff I would swap the gun.