My A-5 (LPK, CO2, Palmers stab, polished internals) shoots hot with the PSI I have to use to get it to recock.  I have to turn the FVA all the way in to get it below 300 FPS.  After polishing the internals, I had to bump the PSI from 375 to about 425 to get it to recock consistently.  I expected the opposite.  The rear bolt slides much easier with the polished internals so it baffles me why I had to jack up the PSI.  Would a softer rear spring lower the velocity and make it easier for the rear bolt to come far enough back to catch the sear?

Co2 with the Palmers regulator.  The reg set at 375 PSI before polishing the internals.  Had to set it to 425 PSI after the polish to get enough blowback to get it to recock.  At 375 and 425, I have to turn the FVA most of the way in to get the velocity below 300.  That happens even though my paint rolls right through the barrel.  With tight fitting paint, I think I would get even a higher velocity.  I basically get too much air going out and not enough blowback.  I am thinking the rear spring is too strong - hits the valve too hard producing high velocity and too strong for full bolt return to cocking position.

You may have overpolished, to the point where you have a leak around the hammer o-ring, resulting in additional air required for recocking.

Can you hear anything like a leak when pressurized?

Your fix may be just a fatter o-ring for the hammer.  Or new receiver halves.

Would that have anything to do with the high velocity, hard to recock problem?  If the reg gets the pressure where it should be, what would the type gas matter?  I am new to paintball so I in the learning stages.  I love to tinker and I am facinated with the gun, upgrading and learning what everything does.  I plan to go to HPA in the future but can't get it refilled anywhere close to home.   I am looking into my own filling setup.

I feel like my polishing job was on the lite side.  I used brillo pads and polished only a few minutes.  From reading some of the polishing info, it seemed it went quicker for me than typical.  I don't hear any leaking.  Does most of the blowback force come while the hammer is inside the powertube or does it continue after it exits?  With the high velocity problem, what do you think about a softer rear spring?

Softer rear springs generally make it harder for the gun to recock.  Softer rear spring = less force pushing on the valve = less air coming from the valve to recock.

Softer rear springs is a common way to increase efficiency by reducing the amount of air used for blowback.  In your case, you might been a stronger rear spring, but that would also increase your velocity, so that's no good.

Hmm.  Interesting problem.  I shall ponder - hopefully somebody smart will come by in the meantime.

Some pics of the 2 valves provided by JackRock showed me what I was looking for.  I am new (1 month) to paintball so I haven't figured out all the terms, which was causing some misunderstanding.  I was interested in the part of the shaft of the valve plunger that sticks out the back of the valve body and is struck by the hammer.  The one that came in my gun was tapered so, as it was pushed in by the hammer, the gap between the hole and the shaft got bigger and allowed more blowback air to send the hammer back to recock.  My LPK valve plunger shaft looks like the pic and is thicker and untapered.  There is noticably less gap in the plunger hole in the back of my LPK valve over my stock valve when the plunger shaft is pushed in.  After verifying the plunger shaft was correct, I disassembled the valve, cleaned and oiled everything and put it back in.  My first dry shot (PSI about 425) went pop-pop-pop and then it recocked.  My second shot recocked as it should.  Every shot after that recocked correctly.  I dropped the pressure on my Palmers to about 400 and every shot recocked correctly.  I kept dropping the PSI until I was down to about 350 and it was still recocking correctly.  I plan to visit the local PB park today to set the velocity.  Now that the gun is recocking correctly without having to jack up the PSI, I hope to get my velocity right without having to use all the FVA.  I am glad I had this trouble because I went from knowing nothing about the gun to having a pretty good beginners knowledge of the gun and how it all works.  This hobby is a blast.