i have a very old s&w terrier in 38s&w has some cylinder slop but when triggers pulled it gets tighter can this be fixed? less cylinder shake?

More info needed. If it is tight when the trigger is pulled (ie if you pull the trigger all the way through and hold it after the hammer drops) this is the only time it really has to be tight. A little wiggle when the trigger and hammer are at rest is inconsequential. Usually "cylinder shake" refers to the end shake phenomenon (cylinder moves front to back affecting head space and cylinder gap.) This can be repaired with shims on the extractor rod (they go inside the disassembled cylinder) or by stretching the yoke where the extractor goes through. Neither of these problems is a job for an amateur to fix, but you have to ask yourself how bad they really are... I can't tell from your question. BTW, which of the several variants of Terrier do you have? This will affect parts availability if they are needed. They have been made since the '30s and for some of us "very old" means different things!

Froggie

yeah was refering to when at rest the cyl moves side to side some but when fully pulled trigger its tight

Well, the bottom line is, when the trigger is pulled and the round is fired, that is the only time the cylinder being tight really matters. The slop you are feeling when the gun is not in battery doesn't really make much difference unless it is so extreme the cylinder can jump time, otherwise, the cylinder being properly locked at the moment of ignition is what is needed. I have a pre-War Terrier that is so loose on the cylinder lock it sometimes comes unlocked and rotates freely when it is not in battery, but it still locks up on the next available chamber regardless. I consider this the hairy extreme of what I will accept, and until I tighten that up enough to eliminate the skip, it isn't a SHTF gun, but something to "play with." JMHO, YMMV

Froggie