..a 48 in .177 shooting Crosman Premier Lights? I shot a 15 shot string thru my crono yesterday with a new box of CPLs and the gun averaged 905fps with a high of 917fps and a low of 897fps(seems pretty consistant to me). I saw at starightshooters.com they tested the same gun and pellet at over 1000fps. the gun has about 1200 rounds thru it, I bought it new from natchez in 2006. Accuracy is good, I can shoot 1" groups with most pellets at 25 yards and iron sights so Im very happy. I was just concerned that Im shooting lower than tested velocities and thought maybe a seal was going bad.
That's under 15fpe, I suspect a seal or spring issue. That gun should be powerful enough that CPL's are too light (i.e. go fast enough to be unstable).
you may have a breach lock up situation. when you move the cocking lever forward what are you feeling? there should be some resistance when the lever is
about 1-2" from closing. if it closes with no resistance it may need to be adjusted. there is a turnbuckle for that adjustment.
springs can be had pretty cheap. the breach seal can be replaced. it is a cheap part. the piston seal is a little more work to replace but not an expensive part. maybe its just time to re-build the gun. spring and seals.
Could be a leaking breech seal? check that first because its the easiest to fix also. Then check for a broken main spring or ripped piston seal. A good tune will fix all as well.
When I look at the breech, I cant see anything in there but what looks like gunk and dirt. How hard is it to disassemble and clean the breach and replace the seal if needed? the gun has never been taken apart since I bought it new and it shoots very accurately.
but you do need a spring compressor. that spring is strong and will launch itself accross the room. will be difficult to get it back together as well without the compressor. they can be made with some enginuity.
once that trigger block/end plug is out its a piece of cake after that ut you should follow someones instructions. i don't have a link but i am sure someone here does.
a new breech seal and piston seal might liven it up (after a new break in period) actually 900 fps is not bad really. its in the velocity range that
gives good accuracy. if you go up to rated velocity of 1000 fps it is not
going to shoot as accurately. get beyond 950 and it will deteriorate. it does not matter how fast it shoots if you can't hit the kill zone. the diablo shaped pellet likes 900 fps as long as its constistant.
your side lever should be adjusted so it creates the lockup between the breach seal and the barrell. when you close the lever there should be a slight increase in resistance at about 1 1/2 to 2" before closing, like you are compressing the seal slightly. if the rod bends and contacts the reciever it is
probably adjusted for too much lockup. second i would replace the breach seal.
i found that easiest to do with the sliding compression chamber removed from the gun. since it is apart i would fit a new piston seal anyway. i would put a thin coat of JM heavy tar on the spring (assuming the spring is not broken) and the guide is good. polish the spring ends and molly them. put a very thin coat of molly on the side of the piston seal and just back of there. on the flair at the end of the piston put a thin coat of molly. put some thin coat of clear tar (jm) on the sliding comepression chamber (this will not change velocity but will make smoother cocking).
its kind of hard not to do it all once it is apart but check that lockup first.