GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: JPSAXNC on November 27, 2024, 12:46:42 PM
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I have an idea for a semi auto pistol. I have a grip frame from a Benji 422 it has a semi auto trigger and sear. I could attach it to a tube. The firing valve and hammer would be a copy of the Crosman 600 valve and hammer. The 600 valve and hammer have a big advantage because the hammer is sealed to a projection on the back of the valve. requiring only a tiny amount of air to cycle the hammer. The hammer and bolt would be connected together with a pin so the hammer would carry the bolt forward and back. The disadvantage is that the pistol would be long because I would need 7" of reservoir from the back of the fill valve to the front of the firing valve. On the plus side, the barrel would be long. Also on the plus side the overall profile would be fairly low, like a 2240 using a jet magazine. The overall length would be about 13". It's all in my head right now but I can see a good possibility it would work. I'm going to order a tube and 7075 aluminum for the valves.
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I ordered the materials we'll see how it goes.
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I’m not familiar with the parts exactly you are using but it sounds interesting and I’ll be watching.
Dave
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The Benjamin 422 is a co2 semi auto pellet pistol, a clever design with a sketchy magazine and feed system. The Crosman 600 is also a semi auto co2 pellet pistol, more mechanically complex than the Benjamin. I think both of these guns could have benefited from the spring loaded rotary magazines we have today. That's what got me thinking about building one.
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I got my materials but I'm recovering from pneumonia. It's to cold for me to go out to the shop for now.
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I made a sketch of where the parts will go it's looking good, almost a lego gun. This coming week it's supposed to be warmer, I'll cut some metal.
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Looking forward to seeing it.... Your projects are always interesting....
Bob
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Following.
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I have started work on the valve and tube. I'll start the hammer and will finish polishing the tube ID. today. So this gun is a combination of the Jet hammer and bolt probe stroke lengths, it will use a Jet magazine. The Crosman 600 style valve will use the Jet style poppet and seat, because it's very easy to open, and the Benjamin 422 grip frame. It's a bit of a challenge to get every thing lined up on paper, so I'm making all of the parts to get a better idea of how they will fit together.
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I have to remake the hammer I made a mistake on it. But other wise I think I have the position of the parts worked out so everything lines up. Still more work to do.
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I have the grip frame attached to the tube, I had to make and braze a lug to the tube like on the 422 tube. I made a stem and poppet for the valve, still have to make a front half for it. I haven't worked out a hammer spring for it yet, the back of the hammer is very close to the end cap and the hammer needs 1.185" of travel.
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James,
To minimize hammer weight loss use a small diameter spring, running in a central channel that is drilled in the middle of the hammer from the rear of the hammer. Small diameter springs are stiffer than large diameter springs, so can be made to take up less space. With a small central channel almost all the way through the hammer, you end up with a mostly external guide for the spring. You can use a central guide acting on the rear spring ID that is short enough not to contact the hammer spring tunnel at full cock.
Of course, I could be talking nonsense about your system, because I have not seen the parts you will be using, or their dimensions.
Images or sketches of your planned system with dimensions will help.
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Hi subscriber, If you google Crosman 600 Schematic you can see the hammer lay out. The only big issue I have is that I needed the hammer to have a stroke length .2 longer than stock. I think I can still squeeze in a hammer spring.
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So, the hammer and spring are pretty much defined. Remaking them to enable a longer hammer stroke might be opening the top and bottom of a can of worms :)
(https://www.jgairguns.biz/images/schematic_images/154/CRS600-677-1.gif)
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Oh yes! But I think I have the can of worms figured out. I'm inching my way along.
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Well I made a mistake. I'm ok at visualizing the big picture but some times miss a small detail in between. I was adjusting the clearance between the sear and hammer, but the hammer was feeling draggy over the sear because it wasn't hardened yet. I had already made the threaded hole for the pin that will attach the hammer and bolt probe together and forgot about the hole for the cocking handle which I hadn't made yet. And went ahead and hardened and polished the hammer so I could get the best feel over the sear, and only after realized I forgot the threaded hole for the cocking handle. I drilled the hole with a carbide bit but could not get a thread to cut even with a chrome clad tap. A carbide 4-40 tap cost $90. so threading is out. I redrilled the hole to 1/8" and will use a dowel pin for a handle. Otherwise it's coming along.
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Would it be possible to drill oversized, then loctite some material in that had been drilled/tapped?
Dave
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Thanks, That's a really good idea.
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I'm over the hump as far as getting the parts to fit. I still have to make a fill valve and end cap for the bottom end. When the bottom end is finished I will start on the breech, I'll make it out of aluminum. So far so good.
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I got a little more work done, I threaded the back of the tube and made a plug for it. I'll make a bumper for the end plug to stop the hammer. I have to wind a hammer spring for it, a small diameter spring won't work because there is no support for it. It just buckles, a larger diameter spring will work. Then make the fill valve.
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I have the fill valve mostly made, hopefully I can complete the lower end by the end of the week.
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I had to remake the fill valve, I made the screw pattern wrong. Still making progress.
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When are we going to see some progress pics. Sounds like you’re getting close!
Dave
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Getting close to finishing the tube and valves. Today I hope to have the hammer spring and guide made and see if the valves hold air and the hammer cycles. Maybe some pics this week.
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The tube holds air and fires. The hammer won't cycle yet because there is no back pressure with the open transfer port. The hammer spring was a nightmare, I tried winding a big diameter spring so the tube id. would be the guide but no luck. I used a small diameter spring, only one coil from not being able to cock it. The hammer needs 1.2" of travel, but there is only enough space for the spring guide to be .548 long. I had to place the spring guide in the back of the spring so that just as the spring is starting to kink the guide keys it into it. The trigger pull is a creepy 3-5 lbs. hard to tell exactly. The trigger is very simple, a transfer bar connects the trigger to a vertical lever that moves back to drop the sear. I'll have to lay out a breech for it, I have a barrel.
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I have block for the breech started, and see an issue. I used three screws to hold the valves equally spaced. The two upper screws interfere with the breech block, I'll machine a slot to clear them. I've managed to build myself into a number of boxes, so far I've been able to find a way out.
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James,
That sounds like an exciting way to make things. Since I learned to use CAD, I prefer to use that to ensure nothing clashes in a complex design. Of course, I do lots of designs without ever making parts, so you are way ahead.
I prefer using a manual mill and lathe to CNC, so perhaps there is hope for me yet.
Merry Christmas
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Yep, the fun never ends. The breech block is about 4.4" long I was going to use a 6" long 1/16" diameter drill to make a pilot hole through the breech. It broke about 2" in. Today I get to see if I can remove it some how. I already have another bad idea to see if I can get to it. LOL
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Ouch!
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Yep, the fun never ends. The breech block is about 4.4" long I was going to use a 6" long 1/16" diameter drill to make a pilot hole through the breech. It broke about 2" in. Today I get to see if I can remove it some how. I already have another bad idea to see if I can get to it. LOL
Ouch. I've broken a drill in a similar way. The breech is made out of aluminum? Maybe you can dissolve the steel bit using warm alum solution?
Depending on where the drill broke, your choices are pretty limited. I've never had luck with extractors. Could try carbide, but if that breaks, good luck. Another more expensive option is EDM.
I have a different question. Why such a small hole over such a long distance? Small drills wander. Second, you are in gun drill territory, a simple twist drill is really hard to drill a long straight hole. Your L/D ratio (length/diameter of drill) is 4.4/(1/16) which is 70.4! Twist drills have a tough time with L/D greater than 10. Yes, it can be done, but 70? You need a gun drill, or it's equivalent. Or you possess some mad machining skills, in which case, I'm in awe.
https://unisig.com/information-and-resources/what-is-deep-hole-drilling/what-is-gun-drilling/
https://www.cnccookbook.com/gun-drilling-bta-drilling/
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The tip of the broken drill was about 2" deep and about 1" of drill was stuck in the aluminum block. I first tried drilling it out with a carbide drill, but the carbide couldn't t cut it. So I picked up the part from the opposite end and drilled down to the broken drill hoping to push it back out, but it wouldn't budge. So I tried using a length of straight 1/16" music wire as a drift tapping the the broken drill from both ends, finally it looked like it moved about .001, I could feel a slight edge with a pick. So I set it back up and went back in with the carbide drill and was able to push it out . So I finished the bolt probe hole on the mill, and then put it in the four jaw chuck on the lathe to bore the hole for the barrel. The critical part will be to get the depth of the magazine slot right so it's in line with the barrel and the bolt probe.
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I think you should buy a lottery ticket with that save!
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I got the magazine slot cut, the depth is right and it's a nice snug fit. Now I'll have to drill screw holes in the tube to mount it. I'm going to use a spare barrel I already had made for my Jet pistol. There's still more work to do.
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The breech is finished, not too much left to do. The overall length is 12.5" the weight is 26.6 oz. I still have to make the bolt probe and do some deburring and finish polishing the inside of the tube. Last I'll have to modify the grip frame to clear the bottom screw on the firing valve, the mod won't be visible from the out side. I have a magazine ordered for it, but it won't come till next Friday. I'll take some pics this week.
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JAMES PICS
(https://live.staticflickr.com/65535/54238609534_8ab8a599e2_z.jpg) (https://flic.kr/p/2qCT3Yf)image0 (1) (https://flic.kr/p/2qCT3Yf) by murphyrobert9 (https://www.flickr.com/photos/56743574@N07/), on Flickr
(https://live.staticflickr.com/65535/54237477122_117a9386ef_o.jpg) (https://flic.kr/p/2qCMfkU)image1 (https://flic.kr/p/2qCMfkU) by murphyrobert9 (https://www.flickr.com/photos/56743574@N07/), on Flickr
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cool project james.. I didnt gather all the details , but looks like a solid design . My concern is the trigger, unless its set up for semi auto , you will have full auto all the time.
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Thanks for the pics, Rob,
The bolt and hammer combination makes it clearer how the semi-auto works: A projectile is fed from the mag into the barrel past the TP, directly before the hammer smacks the valve stem.
Is that correct, James? If so, variable friction in feeding could affect the valve strike. I guess you need to make it feed smoothly, or ensure there is a little more hammer strike than required.
Mentally, this arrangement reminds of an open bolt SMG. If the mechanism that pushes the bolt back, short strokes, just short of latching the sear, it will go full-auto.
For normal semi-auto operation, the sear will need a disconnector, that allows one shot per trigger pull. Trigger release will need to reset the disconnector. Without such a disconnector, you will have full-auto.
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Thanks for posting the pics Rob. The grip frame is from a Benjamin 422 pistol it's a semi auto so that is covered, contingent on the hammer going back far enough to latch up. I tried to adjust the hammer strike on the valve stem and the bolt probe seating to be simultaneous. So that the mass of the hammer and probe would hold the breech closed for an instant. It's not going to be a power house if it works, I'm hoping for 12fpe. The reservoir is about 51cc's. subscriber, open bolt smg was the basics for the idea.
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James,
So the thrust of air on the probe is what will cycle the action, just like a blowback PB? In your instance, the inertia of the bolt equals roughly twice that of the combined mass of the probe and hammer, because the parts are moving forward as the firing cycle starts. This assumes that the valve opens before the probe runs out of stoke. Else, the 2X value become 1 x, which is probably plenty for a low powered airgun shooting a light pellet (compared to a PB).
As long as the probe is still sealing the breech it would not matter too much if it moves before the pellet has left the muzzle. Yes, the expansion volume would increase slightly as the pellet travels down the barrel. I am sure that Bob could calculate the effect on air efficiency, but I doubt it matters very much.
What you don't want is the hammer re-cocking violently, because that may be hard on the parts, and cause sharp recoil. The latter may be fun, as the pellet will be gone from the barrel, so it will not be hold sensitive like a spring piston airgun. It may affect the amount of time taken to settle for the next shot, compared to a Leshiy 2, for example; shooting at equivalent power.
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Hi subscriber, There's a 1/16" diameter hole drilled through the valve along side the stem hole that will feed air into the o-ring sealed hammer to cycle the action. Surprisingly The push back on the probe is very small. When I was fiddling with the Velox pistol I removed the spring that pushes the bolt forward to see how much push back there was on the probe, and at 11 fpe. in .22 the probe didn't jump back. But the probe is attached to the hammer and another part. So there was a lot of mass for the probe to move, but still at 11fpe. and the probe being the same diameter as the pellet. I expected the probe to jump back but it moved only slightly. I wonder about the hammer recoil to, I'll find out in a couple of days.
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Thanks for the detail, James
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the hammer recoil with a 1/16th hole will be violent.. My last semi auto ball shooter didnt even have a dedicated hammer bleed hole , it easily cocked the heaviest hammer spring i had.. ( i just oversized the stem hole a few thou, and that was enough) its actually quite amazing how reliable this simple design is , barring any pellet and mag jams. Its part of the reason crosman 600s are soo relaible
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Hi Rob, If the 1/16" hole is to big, I'll press a plug into it and drill a smaller hole. Yeah, with the o-ring sealed hammer It might a bit much. Another issue might be Hammer lock up, there's only about 1/16" from the sear latch to where the hammer bottoms out. If the bounce is to violent it might be to fast for the sear to catch the hammer.
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it will probably be fine assuming the sear has enough spring to return in rapid fashion.
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it will probably be fine assuming the sear has enough spring to return in rapid fashion.
I agree. You don’t want a very big window there because it will be too rough on the sear.
Dave
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I assembled the pistol, charged it to 1500psi. and tried it a couple of times. The velocity was very low and the hammer bounced and didn't go back far enough to latch. The hammer has good force going forward. I had put in a super heavy valve return spring, that seemed the likely problem. Because I recharged it and it hadn't used hardly any air. I put in a lighter spring and will test it again tomorrow.
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The lighter valve return spring didn't make any difference, low velocity and a little bouncing same as before. So I suspected the hammer was compressing air so I removed the o-ring sealing the hammer. Recharged to the same pressure and got a long full auto burst, but still no lockup. So the hammer was definitely compressing air. Now the dilemma, The id. of the hammer is very close to the od. of the back of the valve. So the hammer is still probably compressing air because the velocity is still very low. So I can turn down the back of the valve a little to help vent the hammer but how much of a reduction would be to much. The back of the valve is .495 od. and the id. of the hammer is .498-.499. What's your best guess?
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Put a bleed screw in the back of the hammer to tune the leakage?....
Bob
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That's a good idea Bob, but the hammer is to hard to drill and tap. I took the gun apart again and saw an issue with the valve stem, I left it to long, so the low velocity could have been due to the pellet blocking the transfer port, because the hammer carries the probe and if the hammer doesn't go far enough forward neither does the probe. I tweaked the clearance on the valve body a bit and will try again tomorrow.
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Anneal the (back of the) hammer?.... Use a small torch, heat the center to dull cherry and let it cool slowly....
Bob
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Very cool and excellent work!!
Watching :D
Jesse
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I might be making some progress. Today I realized that the hammer was not vented in the tube so it was compressing air on the valve and in the tube. Also I discovered that the hammer was not going fully forward, when the breech was attached. I'm going to open the clearance holes in the breech for the screws one size. And ink the pin and the slot the pin rides in to see where it's rubbing if that is the problem.
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dont vent , its likely not the issue.. if anything add bigger hammer spring
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Hi Rob, There was a number of things I had to adjust. I just tried the gun again at 1700psi. The velocity was 520fps. but the hammer did not go back far enough to latch. I'm pretty sure the hammer spring is to stiff for the hammer to latch. The problem is that when the hammer is cocked, there is only about .540 clearance between the back of the hammer and the end cap. And I have to fit a spring into that space that can then send the hammer forward 1.2". I'm going to wind a spring with a bigger diameter so it won't be as stiff, and see what happens.
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good to hear velocity is sorted out.
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The velocity. I assumed that the barrel I grabbed was .22, it took 4 weeks to notice it wasn't.
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I'm trying to get everything to move as smoothly as possible. The bolt probe was a little off center and rubbing on one side of the breech. I bored the holes for the barrel and probe in two separate operations. So I made a mandrel to go in the barrel bore, and using a small boring bar trued up the bolt probe hole. It feels like I need to make the o-ring groove in the breech of the barrel a little deeper, The probe goes in a little tight . I want just a little contact. I'm winding a hammer spring, I made three but there a little weak. I'll try one more.
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Sounds like you are on the right track, James
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One more attempt to wind a spring today, 8 coils per inch was still to weak I'll try 6 coils. Another issue is the finish on the hammer and in the tube, both are turned on the lathe to polish. The hammer would slide more smoothly if one surface was polished linearly. The bleed hole I made in the valve for the hammer had to be positioned so that it came out in the transfer port, the valve throat is to small to make the hole in line with the throat. The problem with that is the transfer port is smaller than the valve throat so there's a big pressure drop in the transfer port so the hammer doesn't get enough push back from the air. Yes, I could drill out the valve stem hole larger to get the air in line that way but I would rather not because when there's free play on the valve stem the valve does not open and close exactly the same every time and hammer energy is lost due to the free play.
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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?
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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
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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.
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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.
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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?
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is there an oring on the hammer ?? are you sure youre trigger is resetting fast enough to catch the hammer ?
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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
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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.
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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.
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Solder and number drills should do the trick....
Bob
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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.
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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.
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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?
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Stronger sear spring?.... I assume you are running a drop sear style trigger?....
Bob
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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?
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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
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An SSG won't work. There is no lock up for the bolt probe, which is fixed to the hammer by the pin so they both move together. In order to keep the breech of the barrel closed when the gun fires the hammer needs to be held firmly against the valve stem as long as possible. The lock up for the breech is the combined mass of the hammer and bolt probe and the stiffness of the hammer spring. PS. There is also no room for an SSG.
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I saw something interesting. My valve stem was changing the distance it stuck out of the back of the valve. The valve stem is about 3 times longer than a typical stem, having about 3 times the mass. I had been super gluing the poppet on to the stem, it works fine for a short stem. But with the long stem when the valve slams shut, the mass of the stem over comes the super glue and the stem creeps back out of the poppet. I'll make a new stem and try to thread the poppet on.
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I made a new valve stem, and plugged the 1/16" vent hole in the valve. The diameter of the new valve stem is .122 I increased the stem hole in the valve to .126 but I'm not getting enough air to cycle the hammer back. I had made a bronze sleeve to go inside the hammer to make it heavier, tomorrow I will cut an o-ring groove in the front of the hammer to try to capture more of the air.
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The basic system works. I discovered a problem with the sear and transfer bar, years ago I had made a custom sear for the grip frame and it turns out the sear won't drop far enough the disengage the transfer bar. So some times the shock of the hammer hitting the end cap would jar the transfer bar to disengage and some times not. I have a plan to try to fix it.
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The sear is working right now. I sleeved the oversize valve stem hole, and I'm trying to unplug the original air bleed hole I made in the valve. Going oversize on the valve stem hole didn't work out, it was to big.
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It's below freezing in my shed so progress has been slow everything is to cold to touch, but things are coming along. I'll be able to do some testing in a couple of days.
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Finally, the hammer is cycling perfectly. The next test will be with the magazine in place.
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Congrats, James!
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Thanks subscriber. The design is super simple, the only drawback is that the gun has to remain cocked when a magazine is in place. Now I'll have to work on the tuning to get a good balance between velocity and blowback force. It's very tame at 1700psi. but I don't know things will work at higher pressure?
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I just tried it with the magazine in place. It works perfect, but the velocity was about 20fps. lower due to having to push the pellets out of the magazine. The Jet mag spring is stronger than it needs to be. I can increase the velocity even at low pressure, but I'll have to see how that affects the blow back force.
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I wonder how much noise comes out of the breech, compared to the muzzle? Probably mostly mechanical.
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Noise, that reminds me I was going to do a tissue test. Right now I have a land slide of other work to do that I put off to get the pistol working.
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I did a tissue test, it blows a square of toilet tissue about 4" high. I put my hand over the breech and I could feel a small puff of air. The barrel is .22 and 9" long with a 14.3 grain pellet @ 550 fps. and the sealing diameter of the probe moves back about .150 to clear the breech seal.
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PS. The tissue and hand test were done with no mag in place. So I can say there is no sound from the breech. At least not at this pressure, 1700psi.
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The light at the end of the tunnel just got brighter. The hammer jumped the sear @2000psi. because the rebound was to hard. I reduced the id. of the vent hole in the valve and made a new bumper from UHMW which absorbs shock better than the PVC I was using. Now the gun is still getting enough air to cycle the hammer @ 1700psi. and it's working fine @ 2000psi. My goal is to charge the gun to 2600psi. So things are looking good at this point, BUT I have the valve duration dialed way back. I want to increase the valve duration now, but I think doing so will increase the blow back force on the hammer. I'll see what happens.
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Very tricky getting things balanced on a "simple" action. Glad you persevered to get to the "light", James.
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Another test @ 2600psi. Still with the valve duration dialed way down. The gun still functions right. The tissue test showed increased blowby from the breech, and the velocity went from 550fps. to 650fps. I don't know what to think about the velocity increase, because at the higher pressure the valve duration should have been even less? I had made a new valve stem a while back so I could thread the poppet on. I made it out of o-1 rod and hardened it, but it had a small warp and would stick in a certain position. It will wear in eventually, but could be causing issues for now?
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It does not take much air to lift a tissue, so perhaps one should not be too concerned about it. If the tissue was being shredded at the breech that would concern me.
If the velocity is consistent, does that mean the valve sticking and hesitating is consistent? is it possible to rotated the valve 90 or 180 degrees and to see if the shooting behavior changes? I would assume the valve is free to rotate a bit until it finds the most relaxed position; depending on friction coupling to the return spring.
If the valve stem is slightly bent from quenching, ,ight you be able to see where the high spot/s are rubbing? Could you polish those locations, both to reduce friction, and to remove 0.0001" material....
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good job James.. when u make a vid on your phone , send it and ILL post it here.
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Hi subscriber, I took the valve apart and polished the stem, it moves freely now. Yes the blowby is still only a small puff. At 2600 psi. I can feel the hammer thump the bumper on the end cap, so I'm thinking of reducing the vent hole size a bit more. @ Rob, Thanks Rob.
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Great!
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Here's a 26 shot string, fill pressure 2600psi. end pressure 1500psi. 14.3 cphp's 633 619 627 622 619 619 623 623 622 614 617 615 615 622 627 610 620 612 609 614 609 x 607 601 606 594. I'm guessing things are breaking in, or something has shifted? The velocity was higher before, I'll have to look inside. One thing that might have helped the velocity was if the transfer port was about 1/8" further forward so the breech would stay closed longer.
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James,
You really want to pellet to have left the muzzle, before the breech seal cracks open. If the breech opens anytime after the pellet has left the barrel, the velocity of the pellet cannot be affected. If the breech opens before the pellet leaves, the air blast from the breech would be louder and might do more to a tissue that you place over the breech.
That said, if the breech seal cracks while the pellet has an inch of travel left, the velocity should not be too badly affected. If the pellet has half a barrel length to travel when the breech starts to open, then a more significant velocity loss is expected.
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Here's a 26 shot string, fill pressure 2600psi. end pressure 1500psi. 14.3 cphp's 633 619 627 622 619 619 623 623 622 614 617 615 615 622 627 610 620 612 609 614 609 x 607 601 606 594. I'm guessing things are breaking in, or something has shifted? The velocity was higher before, I'll have to look inside. One thing that might have helped the velocity was if the transfer port was about 1/8" further forward so the breech would stay closed longer.
Thats amazing !
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Very even velocity for so many shots.
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Yes, not a bad string. But it's a mix of high and low velocities, something is not repeating consistently. BTW the reservoir capacity is 50cc's
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better than a velox with same capacity
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Yep! Here's some progress, 26 shots 671 667 675 669 669 667 662 658 659 654 653 650 647 645 638 634 632 630 628 618 623 624 613 x 606 599. The efficiency is better than this because I have a leak somewhere. A nice declining string, I will try to tune it to a flat string but I don't know how that will go because the blow back design ties everything together. So dialing back the valve duration to flatten the string will also reduce the amount of blowback and will affect the hammers ability to latch back. We will see.
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youd have to feed the main tank regged air with a secondary tank making it ugly.. Id keep it as is
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Yeah, it's weird. If it was a standard knock open valve, making the string flat would be easy. But this valve doesn't respond the same way. The first 5 shots look regulated and then it goes back to a descending string. I'll fiddle with it a bit more.
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Thinking about it, I have kind of a monster hammer spring wound from .043 music wire with an id. of .408 and od. of .5 and 5 coils per inch. I used my (washer/metering lip) on the poppet trick but the gun didn't even notice, the first 5 shots were still the same velocity as without the washer. I might need a bigger washer/metering lip diameter. This hammer spring is like putting a Stormrider hammer spring into a Crosman 2240 or a Jet pistol.
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The spring obviously plays the most important role in this balance but don’t dismiss hammer weight. Hammer weight will change the dynamics quite a bit in the cycling of the action.
Dave
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Hi David, Yes, I'm thinking that the hammer weight could be the problem. I have tried stiffer and lighter valve return springs, stiffer and lighter hammer springs in various combinations. The gun will shoot faster or slower strings, but the strings are always descending. The only thing I can think of is that the hammer weight over comes any combination I try. The valve poppet and seat the stem travel length and all the porting were copied from a Hatsan Jet pistol. The Jet hammer weights about 20 grams the hammer I'm using weights about 60 grams. I'm thinking of lightening the hammer? I have run out of other things to try.
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Its always gonna be a decending string , because the mechanisms are intertwined..
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Hi Rob, I made a new hammer that's 30 grams instead of 61 grams it will be finished up today, we'll see if there's any difference. it's worth the experiment anyway.
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I finished the lighter hammer but have a problem. I bored out the hammer to lighten it and pressed a peek liner to get the id. I needed. But the force of the air blows out the liner. I tried drilling a hole in the side of the hammer to pin the liner in, but the hammer is to hard even for a carbide drill. I'm going to try supergluing the liner in today.
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The lighter hammer works, but it still shot a declining string. So I put a very large metering ring on the poppet head, essentially doubling the diameter of the poppet. Fired a new string, it was identical to the last string. There is no way you can double the diameter of the poppet and not see a change in the shot string, unless the poppet is not seeing the airflow directly. I think I know what the problem is I'll work on it to day.
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James, your tenacity is impressive. I hope you reach your goals. Even if you do not, what you have seems useful already.
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Hi subscriber, My firing valve was made in two pieces, the front half is just a support for the valve return spring. To let air in I had drilled 8 3/32" holes around the perimeter of the valve face. But there wasn't enough air coming in to let the poppet respond to the air flow. So I milled out the holes and just left the spring support on two narrow arms, so now enough air is coming in. Still it's shooting a declining string. It's really strange, the design is really no different than the Hatsan Velox and it was a piece of cake to get a flat string. I will experiment again with different springs now that the poppet is responding to the airflow. I have a couple more things to try, then I'll wrap it up and finish raking leaves in the yard.
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Perhaps you could add a pressure regulator? Or would that be cheating?
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I just realized that I copied all of the geometry from a gun that was designed to be charged to 3600 psi. I think it can take that much pressure. The tube is chromoly .875 od. by .743 id. the valves are 7075 aluminum. Each valve is held in place by 3 hardened 8-32 screws. If you think 3600 psi. would be dangerous please let me know. TIA
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Can't answer the danger question without full dimensions of each part, along with material used and heat treatment/state. The air tank contains the most energy at pressure due to its internal volume, so doing some basic calculations for that is highly recommended.
The valve body OD, or tube ID area x the pressure is trying to shear the three screws. This calculation is just as important. Dividing the thrust into 3 for each screw assumes that they bear the load evenly. That depends on how accurately they are placed. Else one or two screws could carry the bulk of the load.
These videos might provide food for thought:
https://www.youtube.com/watch?v=RZ9BJbaPlFY
https://www.youtube.com/watch?v=XIX_Jkqlkjs
https://www.youtube.com/watch?v=a5wX90En61w
https://www.youtube.com/watch?v=xvSx74F0M4U
https://www.youtube.com/watch?v=a5wX90En61w
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Thanks that's helpful. I'm going to stick with a 2600psi fill pressure. I realized all the changes I made to the valve such as valve return springs and metering lips are only affecting the valve duration, I'm thinking changing the valve dwell might flatten the string, I'll try that next.
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I increased the sealing area of the poppet to shorten the dwell, that made a big difference in the right direction. More to come.
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I can shoot a very uniform declining string, each shot a bit slower than the last. To me this shows that the overall mechanical consistency of the gun is good. But if I try to tune the valve for a flat string, the velocities are fairly close but erratic, Here's an example. 584 592 596 603 610 605 608 599 602 605 600 597 599 588 601 603 583 586 572 585 595 590 591 593 591 587. My valve stem might be to short and letting the hammer hit the back of the valve. I'm making a longer stem to if it makes a difference.
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safety factor at 3600 should be 4.7 to 1 for the tube itself .. as for the 3 screws , were assuming 90.000psi for hardened screws so the factor is in a similar range .. I messed up somewhere for the screws , I'll try again. ( I'm getting 6.98 to 1 for the screws ... this assumes only the thread is in sheer plane .elastic deformity of the holes will happen first most likely.. something to check after numerous cycles.
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I'm charging the gun to 3000psi., no issues so far. I have made some progress trying to flatten the shot string. Making changes to the valve didn't help because the hammer was hitting the valve preventing the valve from self regulating. Since the bolt probe is fixed to the hammer, I wanted the hammer travel to be such that the pellet would be far enough forward that it didn't block the transfer port. I had to make the valve stem longer to get more unrestricted valve action. I have no idea where the pellet is when the hammer strikes the valve now, but the velocity is up because the valve is opening further.
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James, your tenacity is impressive.
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Hi subscriber, It's just that at the end of the day the valve is a simple knock open valve, regardless of how many systems are tied together. I built myself into a box with the distance the hammer and probe had to travel. But I have way out, I'll have sorted in a couple of days.
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CORRECTION !!WARNING !!! the safety factor on the screws at 3600 psi is 2-1 .. I knew I screwed up somewhere , and now I figured it out.. at 3000 psi its still 2.3 which isn't too bad.. upgrading to 10-32 makes a huge difference
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Thanks Rob, I'm filing to 3000psi. now. I will keep an eye on it for creeping. Like you mentioned before, the aluminum screw holes will probably show some elongation. So far there's no change.
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Getting closer. I wanted 21 shots enough for 3 magazines @ 12fpe. start pressure 3000psi. end pressure 1800psi. .22 cphp's 638 631 632 633 636 628 641 651 637 634 628 633 630 638 626 616 627 621 626 624 625. There's a lot of pressure still left in the gun, it seems to me that I should be able to get more shots. It could be that the hammer is still hitting the valve when the pressure drops far enough. I will mark the face of the hammer with red crayon and see if it leaves a mark on the valve?
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Here's a shot string 24 shots 608 626 632 635 626 641 636 641 630 625 635 639 640 634 630 635 619 623 632 629 629 626 626 624. I'm taking a break from tuning the string, I have a set of sights from a CP1M pistol I'm mounting on this pistol. It's fun to shoot and very quite with the magazine in place, a lot of sound comes from the open breech with no mag. in place.
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I've put about 800-900 shots through this pistol, most have been singled loaded. Shooting though the seven shot magazines, the velocity of the shots increases as the shot count in the magazines decreases. The amount of spring tension on star wheel has a very noticeable effect on velocity because of the drag it puts on the bolt probe. Here's an example fastest shot through the magazine, 646 fastest shot single load, 668.
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A lot of factors!
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Yes, I wonder if some complaints blamed on supposed faulty regulators is due to star wheel drag?
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I have an idea that might over come the star wheel drag. I'll try a heavier hammer with more momentum, it might not make a difference though because when the gun is cocked the tip of the bolt probe is almost touching the back of the pellet skirt. So the hammer doesn't get a chance to build up any speed, but the added weight might help.?
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A heavier hammer didn't make any difference. I removed the star wheel from the magazine so I could check the magazine aliment in the pistol. The shots with and without the magazine were very close. I noticed the star wheel spring was wound from heavier wire than it needs to be, I'll see if i can wind a lighter spring.
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The stock magazine spring was wound from .023 wire, I wound a new spring from .012 wire. It made a noticeable difference, The spring tension at the 7th hole is the same as the 1st hole, barely any tension at all. But there is still a difference in velocity. The bolt probe has a little free play in the breech, so even the lightest pressure from the star wheel can push the tip of the probe downwards, I think causing it to clip the front side of the magazine. I'll make a tighter fitting bolt probe and see if there's a difference.
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Still working on magazine issues. I had to lower the magazine slot on the breech to try and get better alignment. For automatic cycling the alignment has to be as perfect as possible, any amount of drag slows the system and affects velocity. I'll see if it's better today.
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Made some progress with the magazines. But a weird thing happened the first two shots were normal, the third and fourth shots were louder and there was no reading on the chronograph. I took the magazine out and the pellet was still in the firing position in the magazine. Since the hammer and probe are pinned together it's impossible for the hammer to move far enough forward to strike the valve stem, without also cambering a pellet. The only thing I can think of is that when the gun fired the pellet went backwards, back into the magazine. I don't believe that, but it's the only thing I can think of, it happened 4 times. I'll take the pistol apart latter today.
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It sounds as though the magazine didn’t advance until it was pulled from the gun. I’m not sure how much visibility you have of how it’s indexed while it’s in the gun so this may obviously not be the case…?
Dave
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Thanks, that makes sense with the much weaker mag spring that I put in the mag. My brain tends to make mountains out of mole hills.
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Basically the open bolt design has been a success. I have to make a new sear for it though. The factory sear was a crudely stamped part that was lobsided so the hammer only contacted one outside edge. I had made a new sear for it, but it got damaged because I was fiddling with the sear spring tension and set it to light by mistake so the hammer was chipping away at it because it wasn't coming back up fast enough. I'm really pleased with the overall performance it's better than I expected.
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James, it has been a fun education to watch you refine this pistol.
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I’ve enjoyed your adventure as well. Thanks for taking us along.
Dave
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Thanks subscriber, It's an interesting design. Someone with some engineering knowledge and a drawing program could refine the design. I've built myself into and out of so many boxes I've lost count. It wouldn't be an exaggeration to say I've probably had the gun together and apart a 100 times. LOL. I don't see any reason that it wouldn't work in a larger caliber either, the little bit of air that escapes from the breech, could be eliminated by using a shorter barrel so all of the air could escape with the pellet. I don't know what effect that might have on velocity though, because I don't know if the pellet is actually gaining any speed in the 9" barrel. 680 fps. is the highest velocity I've gotten with the .22 CPHP's @3000psi. That's pretty low considering the bleed hole for the hammer is only .033 and the puff out of the breech blows a square of toilet tissue about 8" high. I almost have the new sear finished. Then I will try to refine the length of the bolt probe, in relation to the transfer port. It isn't easy because I can't see how far the hammer moves the valve stem and the hammer is carrying the bolt probe. Anyway it's still fun.
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James, with what you know, you would be in a good position to design and make another semi-auto pistol. I could be wrong, but a pellet probe that pushes the pellet deeper into the breech before the hammer strikes the valve stem my be useful, so the breech stays sealed longer on the return stroke. More efficient to loose 1/8 to 1/4" of effective barrel length from the rear, than lopping off more than that from the front. This has to do with the relative velocity and travel distance of the probe/hammer VS the pellet.
The snag is that your total hammer travel seems limited, because the probe needs to take a bit of a run at the mag to push the pellet out and still have energy left to produce a good hammer strike. Anyway, that is just what I think I have picked up from your journey.
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I got the pistol back together, the new sear works fine and the trigger is a little nicer. I noticed when I was fitting the sear that the lever that engages the sear was pushing up on the sear as the lever moved back causing the trigger break to feel stiff I fixed that. Also the hammer rests a little further back on the new sear so I had to make a new bumper for the hammer to get the timing right between the hammer bounce and the sear reset.
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I spoke to soon about everything working again. It's not a bumper problem, I've tried different bumper lengths and I'm still getting double taps. I had to make a new lever for the sear, to get the sear height right and made the slot in the lever to deep. The sear and lever work the way they should, but I think the sear is pushing the transfer bar down a little further so the transfer bar has to travel a little further to reset the lever. I'll see if I can sort it out?
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It's working now. I started a 2" shorter barrel for it so I could if and what the difference in velocity is like.
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I have an issue with my bolt pattern. Three equally spaced screws, one on the bottom and two near the top allow the valve to tip slightly under pressure. Would one on the bottom and two centered on the side, keep the valve straight? TIA
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James,
I would need to see a picture or sketch to answer you bolt tipping question. Generally, to reducing axial tipping, you would want to reduce slack at the front and rear of a bolt, rather than just one ring of screws.
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Hi Subscriber, It's the firing valve that tips. The firing valve is long because of the projection on the back of the valve that the hammer rides on. The clearance between the diameter of the projection and the ID. of the hole in the hammer is small. So any misaliment will cause the hammer to drag on the projection. Since the valve is held by two screws near the top and one screw on the bottom, and the screw pattern is close to the back edge of the valve. The valve wants to pivot under pressure like a seesaw. The screw hole spacing is 60 degrees so I drilled and tapped for two more screws opposite the top two screws near the bottom, so now 4 screws are holding the valve and the valve should remain straight. I'll find out today.
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Adding stabilizing screws to the valve sounds like the smart thing to do.
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Valve is centered now, the hammer moves smoothly along the projection. After that I noticed quite a bit of drag from the new sear, I've about got that dialed out.
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I worked on the sear to where I could use a little less sear spring tension, But then I had to increase the distance to the bumper to get the sear to latch. So new plan, The vent hole in the valve for the hammer was .033 I made a new insert with a .026 hole to see if I can slow the hammer down a little as it moves back.
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James, you define patience and tenacity.
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I had finished the shorter barrel, it was 2.1" shorter. The velocity dropped by 10 fps. per inch. So the longer barrel was still using the air. I didn't know if it was. I reduced the hammer vent hole in the valve from .033 to .026 and got a surprise, not only did the hammer still cycle, the velocity increased about 40fps. I didn't imagine that the air loss to the hammer was that high!
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Here's a string 50cc reservoir 3000psi fill .22 14.3 grain CPHP's 679 672 678 676 672 673 669 672 668 672 668 665 667 660 662 658 660 654 654 650 652 651 645 643 640. 26 shots. This is Viper territory with a 1300psi. lower fill pressure.
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JPSAXNC,
I just finished reading about your exploits for this build, Very outstanding job,
FWIW, I read that you were having problems with the hammer spring etc.
I have been converting all my AG to the FLAT WIRE spring, full power in a very limited space, a 24#, 5" long FWS will go coil bound in 1.50" when fully compressed.
These springs come in numerous pound ratings and several different OD diameter,
mist all come with .250" I/S hole diameter, there are recoil spring for the PB semi auto pistols, see info here:
https://www.ebay.com/sch/i.html?_nkw=flat+wire+recoil+springs+&_sacat=0&_from=R40&_trksid=p2505460.m570.l1313
HTH,
Tia,
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Thanks Don, Yeah the problem was a long spring in a small space. The set length of my spring is 2 1/4" it has 12 coils of .043 music wire the id. is .406 the od. is .5, I wound it at
5 coils per inch this gave enough power. At the same dimensions and six coils per inch, it was to weak.
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Well shooting it is kind of disappointing, The long barrel plus the recoil is throwing the shots high. The sights I have on it are maxed out, I have an old red dot I could try.
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Different fix, I just made a new blade for the front site about .1 taller, now it's perfect.