S&T PPSH-41 weirdness.

[Siggi]

I'm hoping somebody here might have a clue what's going on with mine.

It's brand new but I had it modded by the shop. High-speed motor and gears, decent piston and piston-head and I fitted a G&G green bucking. I also tightened the hop-up dial, which was loose and causing problems.

Here's the weirdness; with the stock spring (which looks janky as hell) it puts 0.2g BBs out with next to zero hop-up at 330fps. Which is pretty poor. With an M120 spring it drops to 220fps. With the stock spring from my G&G MG-42 it does even less. My son's brand new one is doing 350fps (zero hop), absolutely stock.

Looking into the hop with the nozzle forward it seems to be connecting ok and I feel no air coming out the feed-hole. It puffs air nicely out of the muzzle into the palm of my hand. I've read around and there doesn't seem to be an issue of the barrel being too short as 400fps has been reported with an M120 spring. Which leaves me at a loss to understand what's going on. I did consider the possibility the stock spring is an M150 monster but that wouldn't account for somebody else's doing 400fps with an M120.

Any ideas would be much appreciated. TIA.

 

[matjfowler]

I would try to see how much resistance the new bucking is putting on the BB by pushing one past it down the barrel - maybe it is tight and sucking the power. I've had 100fps drained by an interfering bucking.

 

[n1ckh]

You mention high speed gears & motor. This could possibly be the problem, if you've got a high torque motor then try that

High speed motors aren't generally used to pull monster springs along with high speed gears. With so few combined teeth on the all the gears, your not pulling the piston back that far so not getting much air coming out

As I said, try a torque motor & see what happens (sounds like you do cqb with a high speed setup)