SAM K12

[marky-d]

I noticed something shooting my SAM K12 tonight, and was wondering if anyone can offer any suggestions. I realize this is a fairly obscure pistol, but I thought the symptoms might point to something common.

Basically what I'm seeing is that if I maintain a fairly consistent rhythm with my shots (say 10-15 seconds between shots), everything seems great. However, if I take a short break and put the gun down for a while (30 seconds or more), the first shot back lacks velocity. It's an audible difference, and if I wait even longer the shots hit noticeably low. This happens whether or not I leave the gun cocked during the break, and velocity returns for subsequent shots after the first.

Is there some sort of intermediate pressure chamber that could be bleeding off air, and is not being replenished from the main cylinder, or something like that? I would have thought that if it was one of the main seals, the cylinder pressure would slowly drain, but shots would stay consistent.

Any ideas?

marky-d

[brent375hh]

That is unusual. I don't have a exploded view of yours, but on most designs, if the plenum has a leak, the regulator piston would open to bleed air from the tank until the plenum pressure overcame the high pressure side of the piston and the regulator spring, just as if it was just shot. That would just result in leaking air but not velocity, until you hit regulator equalization.

If you leave it for an hour, does it lose tank pressure?

Any chance you are shooting in a cold environment, and the striker has a lot of grease?

[marky-d]

I've been thinking along the same lines as you, that's why I'm stumped! The only thing I could think of was maybe some hysteresis in the regulator, where it doesn't adequately 'top off' the pressure until there's sufficient pressure differential.

I haven't tried leaving it with the tank attached, but I may have to test that.

And no, it's not cold -- typically 70s, indoors. I was considering increasing the velocity adjustment to see if that makes it more stable. I'm not sure how it would explain this exact behavior, but maybe I'm somehow on the lower edge of stability....

Thanks for the ideas!

[brent375hh]

Do you have easy access to the regulator? If it's like many, you can take it off, pull the piston out and measure the o-rings and put new ones in. Note: Keep track of how your spring washers orientation is set up. You can also put a smidge of SuperLube grease on them, and just reinstall. That helped me until I got new ones.