The JSB 25.39gr pellets are definately the way to go in a factory unmolested Marauder. A 40fpe for 40 shot tune would be shooting around 840fps. That is probably the ultimate numbers for a factory setup. The people you read about shooting the 34gr pellets (me) have modified a lot to do so at good speeds and have very reduced shot counts. You definately need to check everything on your gun. Clean the barrel, check all the screws, remove the lawyer spring (look it up on YouTube), and check that the shroud is snug and not loose, because you should easily be able to do half inch groups at 50 yards. There is a little bit of a learning curve but very rewarding. I will tell you this, these airguns are not firearms at all, you can not touch or bang the barrel or you will shoot off. Benjamin has a picture on their website of a guy with his hand resting on top of his barrel shooting, yeah right, he wasn't hitting anything doing that, I assure you. Too many people gloss over telling people this, but it's true. The airguns you can be rougher with cost really big bucks and you will recognize the difference when you see it. Treat the gun right and it is as accurate as anything, but more fun.