Author Topic: Semi auto PCP pistol (Read 9425 times - 1 votes)
)

rkr · « **Reply #60 on:** January 10, 2025, 01:24:23 PM »

Quote from: JPSAXNC on January 10, 2025, 11:58:12 AM

Finally over the hump, the new hammer spring was the magic pellet. The vent hole in the TP. worked just fine, I'm getting too much return pressure now, it goes auto and then latches. So I'm thinking of plugging the vent hole and drilling it out very small, and then increase the diameter if needed to get the best balance? What do you think?

You could also add vent holes to the hammer tube at the point where hammer has gone back enough

JPSAXNC · « **Reply #61 on:** January 10, 2025, 01:24:36 PM »

I had another thought, I retested the gun at the same pressure 1700psi. And the velocity was lower with the new hammer spring. So I'm pretty sure the hammer is bouncing off the back of the valve. So I'm going to put the real stiff valve return spring back in then retest it.

JPSAXNC · « **Reply #62 on:** January 10, 2025, 01:39:04 PM »

rkr, The hammer is completely vented just before it latches up. I retested the gun at 1700psi. and the velocity was lower with a harder hammer strike. So I'm pretty sure the hammer is bouncing off the back of the valve now. I'm going to put a real stiff valve return spring back in the valve and then retest it.

JPSAXNC · « **Reply #63 on:** January 10, 2025, 04:48:57 PM »

Well, the stiff valve return spring made the valve duration to short to cycle the hammer. So I put the softer valve return spring back in and reduced the diameter of the vent hole in the valve. The hammer didn't get enough air to go back far enough to latch. So it looks like I need to keep the original vent hole in the valve and make a valve return spring that is stiffer than the soft one but not as stiff as the real stiff one. Maybe that will work?

Rob M · « **Reply #64 on:** January 11, 2025, 12:41:21 AM »

is there an oring on the hammer ?? are you sure youre trigger is resetting fast enough to catch the hammer ?

sb327 · « **Reply #65 on:** January 11, 2025, 07:39:09 AM »

Quote from: Rob M on January 11, 2025, 12:41:21 AM

is there an oring on the hammer ?? are you sure youre trigger is resetting fast enough to catch the hammer ?

Along with the above, is there a buffer stop at the back or is it a hard stop? A buffer (rubber) will allow a slightly slower change of direction and as such, allow sear to reset easier in the event of faster (too much) hammer return.

Dave

JPSAXNC · « **Reply #66 on:** January 11, 2025, 09:14:27 AM »

Rob, The hammer has an internal o-ring. Yes, I'm thinking the sear might not react fast enough. David there is no buffer just a hard stop that is only about .050 past the sear. The one (consistent thing) that happens through the various changes I have made is the gun double taps on the first shot, or goes full auto. I'm convinced the sear isn't latching I'll try tweaking the sear spring to make it little stiffer. I'll also see if I can fit in a buffer. Thanks for the replies.

JPSAXNC · « **Reply #67 on:** January 12, 2025, 08:03:01 AM »

I fitted a buffer to the end cap, It didn't make any difference. The problem I see right now is the hammer spring is still to weak, I have some new wire coming tomorrow. In the past I've seen that guns using knock open valves require somewhat stiff hammer springs and valve return springs to be consistent. We will see.

rsterne · « **Reply #68 on:** January 13, 2025, 01:18:03 AM »

Solder and number drills should do the trick....

Bob

JPSAXNC · « **Reply #69 on:** January 14, 2025, 08:02:43 AM »

The new hammer spring wire might come today. I think I know why the hammer didn't latch when it came back far enough to catch the sear. The sear can be pushed down below the latch point buy the force of the hammer if the hammer comes back to fast. So I'm thinking of putting a pin through the frame below the sear to prevent the sear from being pushed down to far.

subscriber · « **Reply #70 on:** January 14, 2025, 05:24:57 PM »

Leave room for a soft plastic tube to slip over the hammer travel limit pin, to reduce the bounce potential of steel on steel, James.

JPSAXNC · « **Reply #71 on:** January 15, 2025, 08:54:16 AM »

I was hoping that the sear would bounce off the pin to get back into it's set position faster. I don't know what's going on in the gun but everything I've done to try to make it work right has had the opposite effect. The only time the gun was showing promise was when the forward breech screw was a little long and pressing on the hammer slightly putting a drag on the hammer right at the valve stem. (Slowing the strike and rebound). My only thought is that the hammer is probably to light at 50 grams?

rsterne · « **Reply #72 on:** January 15, 2025, 12:46:46 PM »

Stronger sear spring?.... I assume you are running a drop sear style trigger?....

Bob

JPSAXNC · « **Reply #73 on:** January 15, 2025, 04:27:49 PM »

Hi Bob, Yes, a drop sear. The sear spring is not a coil spring, I don't know how to describe it. But if you go to JG air gun parts site, and look under Benjamin 422 parts there's a pic of the spring. I did try bending the legs on the spring so the sear was much stiffer, but that didn't solve the issue of the gun double tapping. I just increased the hammer weight from 44 grams to 61 grams, to see if I could slow it down a little but now it triple taps and then locks back. I'm thinking of reducing the size of the bleed hole in the valve to see if that helps?

rsterne · « **Reply #74 on:** January 15, 2025, 05:46:15 PM »

Can you fit an SSG on the hammer spring?.... Set it with enough gap for the hammer to rebound past the sear, and it should take most of the energy out of the spring on rebound to prevent it double firing.... Because it slows the hammer turn around (as it absorbs hammer energy into the spring), it will hopefully give the sear time to pop up.... If you use a very long, light spring, with a bit of preload (vary that until you find what works) it will take even longer for the hammer to slow down and reverse.... The stronger the spring and preload, the quicker it will stop the hammer, and that might not give the sear time to pop up....

Bob

Semi auto PCP pistol