Author Topic: XS60C PCP Repeater project (Read 455383 times))

stalwart · « **Reply #780 on:** January 29, 2015, 03:55:37 AM »

Cutting the square hole in the steel tube, for that insert, big enough to allow it to rest on aluminum again, and cutting a relief for it in the trigger housing will let it drop out of the way.

If a safety isn't going to be used, and the fore and aft adjustment of the trigger group, for properly setting the safety's relationship with the sear, isn't used...that hole can be made just long enough, and positioned so the trigger housing is positively indexed to the rear. This will allow max stroke of the striker.

RHytonen · « **Reply #781 on:** January 29, 2015, 12:47:37 PM »

Watching with great interest!
I've been thinking along these lines, with the addition of a longer barrel.

Had either of you considered the Cothran valve for this project?

-Rod

rsterne · « **Reply #782 on:** January 29, 2015, 01:03:45 PM »

I've never seen the Cothran valve, but it seems like a good product.... I am confident we can achieve what we want without a problem, at signfcantly lower cost than a Cothran setup....

I now understand about setting the front trigger mounting lug down into the tube to increase hammer travel.... now pondering the other details to increase the hammer travel as much as reasonably possible....

Bob

rsterne · « **Reply #783 on:** January 29, 2015, 05:25:49 PM »

I spent the morning measuring and working on the valve and hammer.... Eric machines the back of the valve to fit inside the backing block to shorten the assembly, and because of the short MRod poppet, I did the same thing with the hammer.... I machined the front of the block for a #016 O-ring....

The stub on the valve is a slide fit into the block, and will be glued or soldered to it to seal it so that the air can't leak below the O-ring on firing.... The nose of the hammer was turned down smaller, so that it won't hit the block and can drive the stem of the poppet below flush.... Here is why....

With the valve and block assembled, the MRod poppet just protrudes behind the block, which is moved forward over 0.20".... The nose on the hammer currently is stock length, and when the flange on the hammer hits the back of the block, the valve will be open 0.25", which is more than we need.... I will likely shorten the nose on the hammer about 1/16" to gain a bit more hammer travel as we don't need 1/4" of lift.... Here are the parts slid together....

The hammer, in this position, is about 7/16" further forward than where it used to stop when it hit the back of the block in it's original location.... This, of course means that the cocking pin would hit the front of the slot in the breech, so I then lengthened that as below....

When the hammer face hits the back of the block (in its new location), the cocking pin would also hit the cocking flange on the bolt, so I ended the slot in the same location as the back of that flange with the bolt fully forward and the handle down.... There is no more travel possible for the cocking pin, I was able to get everything there was....

Bob

stalwart · « **Reply #784 on:** January 29, 2015, 11:16:07 PM »

Lookin' good!

Rod, the Cothran is best suited for either big bore, or a target rifle (very light striker, short stroke... for minimum lock time). It's just not cost effective in the .30 Grizzly. As Bob indicated... there are no real benefits. The one pictured earlier is going into a single shot MRod barreled .25, set up to take bigger bore liners on demand. In .25, it will be very easy to cock!

rsterne · « **Reply #785 on:** January 30, 2015, 12:00:07 AM »

I spent half the afternoon building a new backing block for the valve to accept two 1/4"-28 screws in the sides, got it all finished, and decided I didn't like it.... There wasn't enough room, IMO, between the O-ring and the side of the screw head, plus it didn't give me a good way to mount the stock.... So, I decided to use the original block, solder it onto the valve so that I could hang onto it, and drilled and tapped two more holes to 5mm x 0.8mm (the same as the current valve and block threads), plus spot faced all three holes.... I had some HoloKrome 5mm low profile SHCSs, which were perfect for the job.... The head is a fraction larger and thicker than a 10-32 low profile screw, but they are still far enough from the O-ring groove.... An alternate method would be to make a new block, using three 10-32 SHCSs with a full thickness head.... The head would then just protrude from the receiver, whereas these are just below flush.... Both are thicker than the tube, however, which is where all the load is taken anyway....

The nice thing about this arrangement is that I can use the original valve mounting hole to accept the pan head stock mounting screw.... Since the front of the stock has been cut off to allow for the tank, it had to be replaced, and this will do a nice job.... This setup has over a 3:1 safety margin in the tube, and the screws are over 4:1 in shear, at 3000 psi, so it's built to laugh at a regulator failure....

Bob

rsterne · « **Reply #786 on:** January 30, 2015, 03:27:42 PM »

More progress this morning.... After much careful measuring (measure ~~twice~~ 10 times, ~~cut~~ drill once! ), I drilled the holes in the receiver to allow access to the valve screws.... While they are not really structural (the load is taken on the walls of the tube inside), if you get them in the wrong place it will look horrible.... I first centered the breech on the forward valve screw hole, and drilled it and the port hole, directly above it, out to 1/4".... The hole in the top of the valve is only 7/32", but I plan on making the barrel port 3/16" x 1/4", so this seemed like a good way to transition from round to oblong, where the air passes through the wall of the receiver between the tube and the barrel.... I then carefully measured the distance between the two bottom bolt holes (on the valve and the block), which ended up being 0.520" (I would suggest stalwart machine the parts to make this exactly 1/2"), moved the cross-slide holding the breech that far back, and drilled out and milled the lower hole for the valve screw.... I double checked that for position, turned the breech 90* in the vice (it had an end stop to index it back in the same fore-and-aft location), measured down to where the center of the tube will be, and drilled a 5/16" hole through both sides of the receiver.... Using a size "Q" drill, which is a perfect fit on the heads of the Metric screws, I enlarged the hole, crossed my fingers, and took the breech out of the milling vice.... When I tried the valve inside, centered by the tube, it fit perfectly....

You will notice that the bottom screw hole broke through into the original rear block screw location, but that doesn't matter, because only the hole for the screw head will be drilled through the steel tube inside.... The screw heads will be a bit deeper once tightened against the flats on the valve, but will still catch in the receiver to locate everything.... Notice the location of the new stock mounting screw.... I'm getting pretty close to being able to drill and slot the tube.... WOO HOO !!!

Bob

cwlongshot · « **Reply #787 on:** January 30, 2015, 03:40:25 PM »

GREAT STUFF BOB!!

Thanks for posting... I am trying to absorb!!

CW

rsterne · « **Reply #788 on:** January 30, 2015, 09:07:12 PM »

It took me all afternoon to drill and slot the tube and modify the trigger housing to fit.... Here is the bottom of the tube, with the valve installed....

You will note that the part of the slot where the front trigger mount goes is shorter and wider than the slot in the receiver.... It is wider to allow the "T" nut to drop down out of the way of the hammer, which will allow the hammer to move the extra distance we have made possible by moving the block forward and modding the nose of the hammer.... The slot is shorter to index the trigger to the fully aft position, to maximize the hammer travel.... Here is the top of the tube....

The cocking slot is longer at the front to allow for the extra hammer travel as well.... When cocking the gun, you will feel the bolt engage the hammer much further forward and have a longer cocking stroke.... You can see the massive port in the valve.... I used a small ball shaped Dremel burr to smooth and fair the top of the port to the 1/4" hole in the tube to minimize turbulence at that point.... Below is the modified trigger housing and "T" nut....

The wider notch in the tube means that the ears on the "T" nut only catch on the sides of the receiver slot, so it projects below the bottom of the receiver.... I therefore had to remove the same amount of material (1/16") from the middle portion of the pad where the front screw goes through the trigger housing to allow clearance for the nut.... When I tested the clearance for the hammer, I found that the center portion of the "T" nut still interfered with the hammer, so I had to file a shallow, curved notch in it to insure clearance for the hammer.... When the trigger is bolted into place, the upper surface of the nut is now about 0.010" below the ID of the tube, so the hammer no longer hits it.... The trigger screw is JUST flush with the top of the nut, and therefore clear of the hammer as well.... but with production tolerances between parts, that is not guaranteed, so the length of that screw must be checked to make sure it won't hit the hammer....

I put everything together briefly and tried cocking the gun, and it cocks smoothly, with a much longer cocking action than previously.... The sear on these triggers has to rotate a long way aft of it's cocked position to cock, nearly 1/4", and that resetting of the sear occurs when the bolt handle is just 1mm (less than 1/16") from the back of the bolt slot.... I have achieved the maximum hammer travel without lengthening the bolt slot....

Bob

Kailua · « **Reply #789 on:** January 30, 2015, 09:58:43 PM »

I know the thought of increasing the hammer stroke was brought up way back in this thread. I also don't want to clutter it up with useless posts like this one. But I just have to say I am always impressed by your solutions to any problem that comes up. Thanks for taking the time to show us the progress to this one and any others that you have done.

stalwart · « **Reply #790 on:** January 30, 2015, 10:27:02 PM »

Paul, I can only speak for myself here, but, I have never seen a post of yours that contained "clutter".

rsterne · « **Reply #791 on:** January 30, 2015, 10:41:18 PM »

I can't take credit for the solution to the hammer stroke, it was stalwart who figured out to slot the tube wider and let the "T" nut drop down out of the way.... He didn't warn me that the center of it would still hit the hammer, though.... The first time I dry fired it, the hammer came to a screeching halt, causing one of *those* moments.... *LOL*.... Production tolerances at work, maybe?.... Easy solution was a few minutes work with a round file....

The gun is currently sitting on my bench, all the parts bolted together and fitting nicely.... I have a QC issue on the rear adjusting / trigger mount bracket to deal with, one of the holes in it or the receiver is drilled about 1/16" out of whack and has to be moved over.... I'll fix that tomorrow, and mount the action in the stock.... then probably machine the slot for the magazine.... Next week comes the fun of building the reverse tank block.... LOTS of chips to make there....

Bob

Kailua · « **Reply #792 on:** January 31, 2015, 12:07:11 AM »

I can't take credit for the solution to the hammer stroke, it was stalwart who figured out to slot the tube wider

Good job stalwart

stalwart · « **Reply #793 on:** January 31, 2015, 01:52:59 AM »

Thanks, Paul.

You can also get the t-nut to settle in more if you internally bevel the slot with a flat file, to match the nut. Either way, it's a quick fix.

rsterne · « **Reply #794 on:** February 01, 2015, 06:29:44 PM »

This morning I machined the notch for the magazine.... Man, there sure isn't much room to work with.... Anyone tackling this on their own, blind, the first time, had better be very good, very lucky, or be prepared to buy a second receiver and/or tube.... Here is a photo of the finished notch....

Note that when you machine deep enough for the .25 / .30 cal MRod magazine not only do you machine through the receiver, but the tube as well, and may even tickle the top of the valve.... Here is what the tube looks like at this stage, and the magazine sitting in the receiver....

The nose of the bolt protrudes into the magazine notch when closed, so a new shorter bolt is required.... This will lose some of our hard-earned hammer travel, but cannot be avoided to allow the use of the magazine....

Next job is to make that new bolt.... More later....

Bob

moorepower · « **Reply #795 on:** February 01, 2015, 07:30:59 PM »

What wall thickness tubing are you using?

stalwart · « **Reply #796 on:** February 01, 2015, 08:53:01 PM »

.065"

Guys, 3Ks produced for sale here will be skeletonized. This will cut down on machine time (your $), and will be covered by the stock.

rsterne · « **Reply #797 on:** February 01, 2015, 09:32:50 PM »

Yeah, yeah, yeah.... He expected me to remember that!.... Oh, well, spending a half day machine two matching sets of holes in the receiver and tube was good practice for me.... *LOL*....

Anyway, I spent the afternoon making a new bolt....

It's a flow through nose design (with the feed hole in the side not yet drilled) because that style is a lot shorter overall and won't have to be held back against the hammer spring to get the magazine in and out.... It functions flawlessly, popping pellets out of the magazine one after the other....

Now, on to the next problem.... The cocking pin on the hammer now hits the flange on the front of the bolt, not good for either the bolt or pin.... If anything is going to come to a crashing halt, I want it to be the face of the hammer hitting the back of the backing block.... So, now we need a new hammer, with the cocking pin further back relative to the nose.... I was hoping to do some testing with the stock hammer weight, even though I didn't think it would produce enough dwell, but since I have to make a new one, I'm going to maximize the weight, so it will be a straight cylinder, with only flats where needed to clear things and provide a place for the sear to catch....

Bob

stalwart · « **Reply #798 on:** February 01, 2015, 09:51:58 PM »

"Oh, well, spending a half day machine two matching sets of holes in the receiver and tube was good practice for me.... " And it sure turned out pretty!

Nice bolt... getting to the meat and potatoes here...

stalwart · « **Reply #799 on:** February 01, 2015, 11:59:09 PM »

Guys, I remember seeing snap in single shot trays for MRods... who makes those?

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XS60C PCP Repeater project

Author Topic: XS60C PCP Repeater project (Read 455383 times))