The Beeman P17 My experience are what most people say, this is a really nice pistol. For under $40 there are probably no better air pistols in this category, single-shot, single-pump pneumatics. The pistol is precise and has a nice trigger. The grip comfortable in the hand. A bit of effort is required to pump it, once you figure it out it becomes fairly easy and natural. Loading pellets is also a bit tricky at first but soon becomes second nature Build quality seems ok, with no obvious flaws on my gun. The gun is mostly plastic, but it's very good quality polymer. I suggest a tear down debur and reseal from the get go. One of my favorite go to plinking guns.,
I bought a clean used one, but quickly found out that the bore was drilled and rifled off center. This caused erratic groups and I chose to re-barreled into a .22, using a Crosman 2240 barrel, I duplicated it to match the original 177 barrel profile. A few layers of aluminum duct tape on the piston top, and she is shooting 22 Hobbys at around 350 FPS. Accurate as heck also.
I did a P17 up as described on 'another airgun blog' when I had access to a machinist at work, with the exception of the adjustable piston stroke. Much stronger pump with the two orings on the piston. Unfortunately, it developed the air-spilling problem where the valve dumps the air as you close the pump. Seems to happen more quickly when the weather is warmer, and you can avoid it by recocking if you don't hear the click of the mechanism before you close it all the way. Tried all the suggested 'repairs', none eliminate the problem. Should just buy another one, but hate to lose the mods made to the internals. So I bought a P3 and an HK40, one in .22 with a replacement barrel from Airguns of Arizona and one in stock 0.177. And the trigger on the P3 - HK40 is a little bit better than on the P17, but the P17 still beats the devil out of any other low cost airgun I've found.
I've also had the dump-upon-closing issue, with 3 out of 4 units.
I finally got bored enough to muck about with the internals, but a simple clean-out was not a solid fix.
When it does leak down upon closing, I dry fire to give the valve a whack, and it USUALLY holds air on the next cocking stroke.
Gonna have to mess around some more, no I haven't looked into recommend fixes.