Thanks for the info. You are right about the big bonus with the SSG being the huge reduction in noise, especially at a little lower levels. What were your fill levels and air usage? And pictures of final product and gun would be nice.
Here is a link to the valve screw shear test and below that is what I had in a Word doc on valve screw replacement and breech screw replacement for the disco.http://www.gatewaytoairguns.org/GTA/index.php?topic=72672.0Valve mod The jig is made from a piece of 1" x 1.5" x 2" aluminum.... A block of steel would be better for production work.... I drilled a 3/4" hole 1.5" deep and then ran a 5/8" mill down along the bottom side and removed 0.015" to form a shallow groove (ie the hole is slightly "pear" shaped).... This forms a "V" block so that when the valve is inserted it only touches at two points.... On the opposite side is a 3/8" SHSS with the end ground flat so that it won't damage the valve when snugged up.... There are two holes drilled in the top beside the setscrew.... The front one is a #21 drill (the correct size for tapping a 10-32 thread) and the rear one is a #11 drill (just clears a 10-32 tap).... There are two brass pins, the smaller one has the end machined to 0.128" which just fits in the 8-32 tapped hole in the Disco valve.... The larger one has the end machined to nicely fit in a #21 drilled hole.... To use the jig, you slide the rear valve half in until one of the screw holes lines up with the front hole and then slide the small pin down until it locates in the 8-32 thread hole.... Then you snug up the 3/8" setscrew to hold the valve in place and pull out the pin.... If you were doing a bunch, you would set the block up in the mill, aligning the hole with the head.... but I just used a hand drill and drilled by eye, using the hole in the block to guide a #21 drill to clear out the threads in the valve.... I used a normal drill, very carefully, to just remove the threads, making sure the point didn't dig in as there isn't much meat between the bottom of the hole and the inside of the valve.... I then changed to a drill ground flat on the end to make the hole full depth with no danger of cutting through.... This operation could also have been done with a 5/32" end mill provided you stopped at the correct depth.... I loosened the setscrew, removed the valve, and the threads were evenly removed, so I turned it around and replaced it in the jig and slid it in until the newly drilled hole lined up with the rear hole in the jig.... I slid in the larger pin to locate the valve and snugged up the setscrew again....Using a 10-32 plug tap, with the hole as a guide, I tapped the hole until the tip of the tap just touched the bottom (about 3 threads).... I then changed to a bottoming tap, and got nearly 6 threads total.... I repeated this for all three holes and then ran a countersink into the top of each hole in the valve just to provide a slight relief because the thread on the screws stops a few thou from the head.... I had to shorten the 1/4" long low-profile 10-32 screws to 3/16", properly finished the ends, checked the thread in a nut (rather than risk galling the aluminum valve), and then installed them to make sure they went all the way down and that the head was seated on the flat on the valve.... Everything worked perfectly, so it was time to install it in my 9mm and give it a try.... The screws I am using are rated at 180,000 psi tensile strength, which means 108,000 psi in shear.... That will give me a 4.4:1 safety margin at 3000 psi, making the screws no longer the weak link in the Disco.... The OD of the head on the screw is a few thou smaller than the holes in the Disco tube, but the head still seats well enough to spread the load and the transfer port still lines up as good as they ever do.... Breech screw fix I usually just end up replacing the breech screws with 6x32 button head screws... I learned with my disco which has the same tiny #4 screw that they are just way to easy to strip.... so I picked up a handful of the 6x32 button heads in stainless.... simple matter to retap the hole on the tube, don't even need to drill a fresh hole just start our tap in the hole that's there... its big enough it will recut perfect threads. You then need to hit the breech hole with a #27 drill bit and then turn the head of the screw down a touch and/or open the couterbore of the hole up a bit..... I usualy turn the screw head down to about .214 and then use a 7/32 (.2188) bit that I ground the face flat (or a 7/32 end mill if you have one lol) to counterbore the hole.... never strip a breech screw again and holds MUCH nicer...... combine that with clamping the breech for assembly/disassembly and life is a lot easier
I thinned out my poppit, and took some material off corner in valve, breech, tried a bigger tport (think I put the stock one back later), made hole in gauge block bigger and drilled and tapped valve for 10-32 high tensile screws so comfortable filling past 2K. Those things got me a few more shots from stock, but the increases from the SSG dwarfed them. I was just thinking that, since the SSG is improving efficiency, maybe time to increase tport for power. I am open to suggestions...that is why I started this thread, as disco is my first PCP and I'm flying by the seat of my pants. There are so many things that can affect other things that is hard to know what combination will work best.
Time to start one. I have been working on an SSG for my .22 disco. When I first got it I was disappointed with the 14 or so usable shots. In the past I have tried with my diy PA and some porting of valve, thinning poppit, and different tport sizes to try to get over 20 shots with jsb 15.9 at 800-850fps. I am a rookie at this and nobody up in my area that I know doing this stuff so flying by the seat of my pants.This is just what I want for hunting small game. I have come close to it. I had drilled out my endcap long ago and threaded so I could change springs on the fly so Bob's first SSG was easy to adapt to. I tried Bob's first SSG 3inch and used my existing .040" thick springs in varying lengths but power dropped was first in mid 600fps. I made a new longer one and a couple of springs and even welded a 3/8 nut to the back of my endcap to be able to use the longer ssg before coil bind. I got back to 750fps and got a ton more shots. I am waiting on order for 10" long .312 springs n .037, .041. .047 and .055 for testing.
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