Any Interest in 6mm ? - Build Thread

[oldpro]

Wow that is some mad skills and well thought out to boot. This will be fun to watch. Following

[MJP]

Nice work Bob, I was looking at the pictures first and was thinking that looks like ART valve right there.
Then I read the text and was ok it is bob art valve. 
Will be interesting to see the strings and groups on this one for sure.

Bob do you thread the bolts around transfer port to the tube also or just to the valve body?
On smaller bore the end of the valve is not so critical but when making a bigger bore they see pretty substantial force from the valve and I would use threads instead of the c clip.
Don't ask me how I know. 

Marko

[rsterne]

The two 6mm vertical screws are threaded into the valve body only, like an MRod.... They hold the receiver against the tube, which has through holes, pinching it against the valve....

I can't imagine that the front end of the valve in an ART/SS design is subject to much end force, and both Lloyd and Travis use a circlip.... but if I have a problem then I can't say I wasn't warned.... Thanks for the heads-up....

Bob

[MJP]

Well not on small calibers, it won't be a problem but something past 500-600fpe and big valve you start seeing some stress on those parts.

Thanks for the answer on the bolts, I usually thread them together tube and valve.
Was just curious that's all.

Marko

[oldpro]

Well not on small calibers, it won't be a problem but something past 500-600fpe and big valve you start seeing some stress on those parts.

Thanks for the answer on the bolts, I usually thread them together tube and valve.
Was just curious that's all.

Marko

 Were all a long way off from your kind of power Marko so its not and issue for us. Someday Ill step it up and take a wack at a BIG BORE!!

[MJP]

That will be an interesting build to follow Travis. 

Marko

[oldpro]

That will be an interesting build to follow Travis. 

Marko

You better hope I dont because I would be PMing you 10 times a day asking How you did this or that LOL.

[MJP]

Naah, I think you'll figure it out just fine, the art valve tells me that much. 
But yeah, asking the right questions is not forbidden. 

Marko

[rsterne]

Today I drilled all the holes for the valve in the long (unregulated) tube.... Here is the right side....



You can see the cocking slot for the hammer, and now you can see why I moved the side valve mounting holes forward, to give lots of material between it and the front of the slot.... here is the left side....



You can see the large hole for the gauge on the side.... I installed the valve, hammer, SSG assembly and trigger group today and tested everything.... With the hammer set for 1" of travel I still have 0.22" between the front of the hammer and the back of the valve, and about 1/16" between the cocking handle and the front of the slot.... This allows for 0.20" of maximum lift and still have a 0.020" gap for the SSG.... The valves have an internal travel of about 0.24", so with the stem protruding 0.20" the hammer will hit the back of the valve before anything else hits and gets damaged.... I also made the second valve body today....



The one in the foreground is for the shorter regulated tube.... Since there is a gauge downstream of the regulator in the tank block, there is no hole in the side of the valve for a gauge like there is in the valve for the unregulated tube in the back.... The valve in the front is also larger in diameter because the regulated tube is 0.095" wall instead of 0.120" wall....

Bob

[rsterne]

Last day in the shop before Christmas.... I tidied up all the loose ends.... no photos because there was nothing new, just a second batch of what I have already made.... I built all the internals for my second ART/SS valve (my version), and drilled the holes in the short (regulated) tube to mount the valve.... Other than cut that tube to length (after I get the regulator for my 500 cc CF tank) and drill the 4 holes to retain the tank block, both "lowers" are now pretty much finished.... I am waiting for some 70D O-rings, once they arrive I will be able to assemble and pressure test them.... Oh, I forgot I still have to lap the valve seats and make sure the poppet face is square....

I finalized the design for the receivers today.... The material I bought wasn't tall enough to allow for slope in the scope dovetail, but fortunately I have enough 1 x 1.5" aluminum bar stock for the two receivers.... The scope rail will be angled 20 MOA to put the scope pretty much on optical center with a POA of 100 yards.... These are both single-shot guns, and I wanted to make both receivers identical and yet set one up for 6mm and the other for .257.... I plan to use an "L" shaped insert in the loading area, sized for each caliber, that will bolt into place.... The left hand wall of the receiver will be full height to increase rigidity, the bullet will load from the right, like on my Monocoque.... at least that's the plan at the moment....

I want to wish all my friends here on the Forums all the best for a Merry Christmas and a Happy New Year.... 

Bob

[skorec]

.. The scope rail will be angled 20 MOA to put the scope pretty much on optical center with a POA of 100 yards....

I want to wish all my friends here on the Forums all the best for a Merry Christmas and a Happy New Year.... 

Bob

Bob,I agree with you absolutely and in the new year I will be really happy to see your 100 yd targets from this future gun. Wow.

[Rob M]

hey bob , happy holidays .. quick question since I cannot find the answer, what barrel will this be ??

[rsterne]

Barrels are detailed in Reply #83 on page 5.... TJ's 6 mm & .257, both in 10" twist, with a 14 mm OD and a 20mm OD CF sleeve over them....

Bob

[Rob M]

thanks Bob !!

[oldpro]

 When do you expect to see the orings for the valve Bob? Eagerly awaiting this build.

[rsterne]

I have been cleaning up some leftover projects for the last month while I have been waiting for some 1.2 mm CS O-rings to arrive for the poppet in my version of the ART/SS valve.... They finally got here and I made a new poppet which worked out great.... The smaller O-rings allowed a shallower groove, which I moved further down the poppet towards the seat and now it seals great and seems to function fine, even at 4200 psi.... It is holding air pretty well, losing less than 100 psi per day, which is good enough for now, and often slow leaks like this improve with time, as they are often the poppet on the seat.... Anyways, assuming it is good enough for now, the next order of business is to make the uppers, and then ream the chambers and mount the barrels.... After that I can shoot these guns for the first time, as I cast some bullets last week as well....

I started on the receivers yesterday, cut them to length (actually 1" over) and machined the concave bottom to fit against the tube on both receivers, which will be interchangeable on the lowers.... Today I laid out and center-drilled both ends of the bore for the barrel and bolt, high enough above the top of the tube to allow for the 20 mm OD barrel sleeve, plus 0.20" to allow for the thickness of a piece of 1-1/4" ABS pipe which I will be using for the foregrip on the unregulated .257 cal.... That plastic pipe is 0.150" wall, so it will just nicely clear the Carbon Fibre barrel sleeve.... It will be captured between a recess on the bottom of the receiver and the tube, like I did with the foregrip on the Monocoque.... Anyways, the C/L of the bore is 0.60" above the top of the main tube.... Once the locations were center-drilled, I mounted the receiver between centers on my lathe, and then held the back in my 4-jaw chuck.... Having it sit on a 60 deg. center inside the spindle bore allows easy centering of the jaws, you just tighten them progressively on the four side of the receiver until it is secure.... Using a live center (ie one that spins on a bearing) in the tailstock, I machined a 1" long collar on the front of the receivers (which is why I left them 1" too long).... The collars will ride in my steady-rest to support the receivers on center while I drill them full length....

I first drilled a 1/4" pilot hole from front to back, using a foot long 1/4" drill bit, stopping just before I hit the 60 deg. center in the headstock.... I then used a long 1/2" drill to increase the diameter to the finished size, removed the receiver from the lathe (so the 60 deg. center wasn't in the way, and drilled through the last 1/2" at the back.... The hole was straight and true, and parallel to the top of the tube in both planes, which is what I wanted.... A piece of 1/2" CRS slides perfectly through the receiver, full length, so I know that the bolt and the barrel will be aligned and parallel.... I them mounted the receiver back in the lathe between centers, re-checked the steady-rest position, and then drilled the front of the receiver out to 25/32" to accept the 20 mm CF barrel sleeve.... The sleeve is about 0.004" larger than the drill size, but it just starts into the hole, so all it will need is a bit of sanding to be a perfect slide fit....  Here is what it looks like at the moment.... I only have one drilled at the present time, the other one will be done tomorrow, all going well....



The plan is to cut off the collar, it was only there to allow me to support the front of the receiver in my steady-rest.... I don't need it for support, as the barrel sleeve goes 2.5" into the receiver, which is over 3 diameters.... It will be located by two sets of 3 setscrews at 120 deg. so the assembly should be 100% rigid when complete....

Bob

[skorec]

The plan is to cut off the collar, it was only there to allow me to support the front of the receiver in my steady-rest.... I don't need it for support, as the barrel sleeve goes 2.5" into the receiver, which is over 3 diameters.... It will be located by two sets of 3 setscrews at 120 deg. so the assembly should be 100% rigid when complete....

Bob

Nice work,  Personaly I will let the collar.

 I really want to sea haw CF sleeve barrel will work.

[rsterne]

The only significant problem with the collar is that I have to machine most of it away at the bottom where the plastic pipe will be for the forestock.... That would only leave about a 1 mm wall thickness in the center at the bottom.... Since the CF sleeve is inside the receiver by over 3 diameters without the collar I don't think it really has any benefit.... I haven't decided yet, one way or the other....

Bob

[rsterne]

I drilled the other receiver today, and then drilled and countersunk all the mounting holes and drilled through for the transfer port....



The small recess on the bottom just behind the transfer port is to clear the upper valve mounting screw, which is just proud of the tube.... The receivers, like the tubes, are drilled on the same pattern, so the uppers will be interchangeable on the lowers.... Although I intend to build the .257 on the long, unregulated tube with the thick wall (4200 psi MSWP) and the 6 mm on the regulated bottle version with the short tube (thinner wall with 3200 psi MSWP).... the interchangeability will allow me to test the other way around, and change my mind should I decide to....

Bob

[oldpro]

 The countdown has begun 4,,,,,3,,,,,,2,,,,,,1,,,,,,,Launch!!! This is getting good now. What do you think 1 week or so to launch?