I made a rigid piston and made it long enough to reduce headspace as much as possible. I did a few other mods and ended up at 700 fps @ 10 pumps. 5 pumps were 550 fps. This was with a 7.9 CPHP pellet. BTW, this is a Chinese rifle so don't be surprised if this thread is moved.
maybe I can cut a piece of thick plastic and glue it to the pump head to fill the gap between pump head and valve?
Quote from: nzjott on May 21, 2018, 04:04:17 AMmaybe I can cut a piece of thick plastic and glue it to the pump head to fill the gap between pump head and valve? Yes, that will help.
How about a few small countersunk wood screws to hold it to the piston?Also - it appears the piece of plastic does not go all the way to the edge of the piston. Any empty space robs you of power. Can you take a disc of plastic and sand it on a drill until it is perfectly round and only a few thousandths under the size of the tube i.d.?
You're welcome. That looks good. Can you feel the piston touch the valve at the end of the stroke cycle? You should feel a slight resistance when the pump arm is about 1/2" to 3/4" from closing.BTW, These rifles are $50 here in the USA.
I think there maybe still is 0.5mm gap in between.
Quote from: nzjott on May 25, 2018, 01:05:33 PMI think there maybe still is 0.5mm gap in between. That piece of black plastic looks pretty good. How about putting a piece of aluminum between it and the piston? Maybe cut it out of a beverage can? Or a piece of plastic from a bottle? The piston and valve face really need to touch lightly at the end of the stroke.I also unscrewed the valve slightly to close the gap on one of my experiments.
I got one of these from Walmart maybe a year ago. Found it didn't shoot real well. That was until I happened to try the RWS Meisterkugeln rifle pellets. They make pellets with this name for pistols too, which are lighter. Have not tried those. But the rifle ones are the best in my Umarex. I have a Chinese 3x9 red/green illuminated reticle scope on it, which luckily works well. Haven't tried it farther than 10 yards yet. Not a gun that will be handed down to future generations. Hard trigger. Very loud when pumping. Lots of o'rings to oil, and needs oiling often. I Like the looks of the NPG. Doesn't look "assault weaponey", but I like the looks. I had to order these to mount a decent scope on mine, as the toy scope it came with literally fell apart:ie=UTF8&psc=1[/url]