.257 cal Monocoque PCP

[Rizen 1]

I love "EARLY" Christmas presents!  Looking good Bob!

[Matt15]

Wow Bob!! That is a big scope!!

[Erockrocket]

 That is a fat tubed scope!  Very nice Christmas gift.
I am anxious to see what kind of beast you build. I am planning a caliber change this winter, gonna go with .257. I have a place I can stretch out to 500+yds. I have a few questions about barrel length and power needed, I will start a new thread soon.

[rsterne]

The bulk of the materials arrived yesterday, and I spent the day finalizing most of the design.... It doesn't look much like an airgun at the moment....



Plastic pipe is for the forestock and cheek piece.... 1 1/4" OD CrMoly tubing for the monocoque upper tube (0.065" wall) and air reservoir (0.095" wall).... The 1 1/8" 2024-T3 Aluminum round bar is for the breech block, valve, front plug, and all other internal mounts.... The rectangular aluminum barstock is for the external parts; the spacer between the tubes, the adjustable stock mounts, and the front bipod/stock mount....

Soon to be converted into a pile of chips, and usable parts, I hope....

Bob

[Job]

No more it cannot wait

[Bruce]

Bob!!!!! You sly dog!

Now I want to do another build lol

Going to be fun to follow this one!

Bruce

[Matt15]

Good luck!!

[rsterne]

The block of aluminum from Watertown arrived and I wanted to see how my new 1-1/4" drill bit worked so the first thing I did was square it off to size and drill it to fit on the Reservoir.... That went perfectly, although there is a lot more to do, machine the Forestock Mount into it and a Picatiinny Rail in the bottom.... The Forestock is a piece of 1-1/4" (ID) black plastic pipe 12" long that slides over the reservoir.... and a piece of it 6-1/2" long, split down the middle, will be used for the Cheekpiece.... Here are those parts....



Inside the Cheekpiece are two "washers" made from 3/8" aluminum, which will form the mounts.... One will be attached to the back of the Breech, and the other to the bracket that mounts the Buttplate to the Reservoir Tube.... arranged like this....



Most of today's work went into making the Stock Bracket, which is shown in the photo below....



It is machined from a piece of 3/4" x 1-1/2" 6061-T6 aluminum about 5" long.... The large hole fits over the back of the Reservoir Tube and will clamp in place with set-screws.... The screws at the top will mount the rear washer that holds the Cheekpiece.... The three threaded holes at the bottom are for mounting the Buttplate, and an optional 4" wide Baseplate that can sit flat on a bench.... Here is what it looks like in side view....



The height of the Buttplate will be adjustable in height, tilt, and length of pull, using a threaded rod, locked by a wing nut as shown.... The center position for the front of the Buttplate is 1" behind the bracket, so it should be good and rigid.... By offsetting the threaded rod by 1/8" in the Buttplate, and with the 1/2" spacing on the holes, I will be able to alter the height below the line of sight over a 1-1/4" range in 1/4" increments (3 holes x 2 positions per hole)....

It is great to finally start making chips.... Next up will be finishing the Cheekpiece mounting washers, and completeing the BiPod / Forestock mount....

Bob

[Matt15]

Looking good Bob!!

[MJP]

Nice looking work Bob, what kind of machine you got? First rough cutting with a mill and looks like belt sander finish? Waiting to see the finished gun, most interesting.

Marko

[rsterne]

My "mill" is a milling attachment for my 40yo Atlas 12x36 lathe.... It lacks the rigidity for precision work, so tends to leave tool marks.... I use a sanding block and sand by hand to get the finish you see.... I kind of like it, and leave my aluminum parts natural.... The biggest limitation is that it only has 6" of horizontal travel, and 3" of vertical, and the vice measures 1" x 2.5".... It's a real challenge to figure out how to hold parts sometimes....



Above photo shows using it as a tool-post grinder.... *LOL*....

Bob

[MJP]

Nice, good old fashion creativity I really do respect that. That's one thing I like about this forum, like minded mad scientists around. 
The sanded finish looks good, sometimes it's hard to decide to paint or not to paint or blue parts.
I use an old Victoria U2 milling machine at home with rotary table and milling head tilts 360deg in Y and X axis. And have a full machineshop at work, but that just makes me lazy.

Marko

[rsterne]

Nice.... Sometimes I feel like I'm machining with one hand tied behind my back.... *LOL*.... No wonder everything takes me so long....

Bob

[rsterne]

Spent most of the day putting up Christmas decorations for the Motel today.... but did manage to get a couple more things done in the shop.... I drilled the two donuts that hold the Cheekpiece in place, drilled the mounting holes in the Cheekpiece, tapped the holes in the rear donut and mounted the back of the Cheekpiece.... I also made a stand that attaches to the bottom of the Stock Bracket instead of a conventional Buttstock to use when shooting from a bench.... It will help hold the rifle level, and act as a compliment for the front BiPod....



It is 4" wide at the base, so will have lots of stability.... You simply remove the Buttstock and bolt this on instead.... Not a lot of progress, but at least some today....

Bob

[rsterne]

I got most of the BiPod made today, and did some more work on the Block that will mount it to the gun.... Here is the adjustable BiPod....



It doesn't look like much, but I think it should function well.... The crossbar, which will bolt to the mount on the gun, is made from a piece of 3/4" x 1" wide 6061-T6 barstock.... It is drilled and tapped for two pieces of 1/2" threaded rod.... The pieces shown are 8" long and 12" apart, and should allow for an elevation relative to the bench of about 6 degrees (360 MOA).... I can make longer rods, or they can just sit on a block of wood to raise the muzzle further relative to the bench if necessary.... The wheels are 2-1/2" OD pulleys with a 1/2" bore, setscrewed to the shaft, with a nut tightened up against them and secured with green Loctite.... The ends of the nuts are radiused so that when you rotate the rods, using the pulleys as handwheels, they won't hang up on the bench, allowing easy height adjustment in very small increments.... There are wingnuts to lock the height, which increases the rigidity of the assembly as well....It is remarkably stable, and I think with the easy adjustment should prove an asset to shooting from the bench.... It will bolt to the mount below....



There is still more work to do to this (you are looking at the bottom of it).... I still have to cut the slots in the Picatinny rail, and drill and tap either side of that for the screws that will bolt the BiPod above to it when shooting from the bench.... The boss on the side facing you fits inside the plastic pipe I'm using for the Forestock, and keeps it positioned so that the top of the pipe is touching the top of the reservoir, offset downwards.... As you can see, the boss is not concentric with the hole for the tube.... This will be attached to the reservoir with setscrews.... I hope to complete these parts tomorrow, and then it will be time to start on the internal parts....

Bob

[rsterne]

I finished off the Mount for the Forestock and BiPod today.... Here it is with the Forestock in place.... The Picatinny Rail is done now....



I also completed the BiPod.... It now bolts to the mount with two #10 SHCSs and has a built in level to check the cant.... which is easily adjustable with the handwheels on the threaded rods.... which are just above the bench....



Used in combination with the plate on the bottom of the rear Stock Mount, which completes the TriPod, the rifle will be easy to adjust to any required elevation by using the handwheels, and then a final set of the cant using the bubble....

Bob

[rsterne]

Made up a mount for the Scope Rail to hold it for machining to cut the radius on the bottom and put in 40 MOA of angle.... This was a time consuming and nerve-wracking job.... Here is the results....



You will notice that the height of the lower portion of the rail is less at the front (left) than at the back.... The difference in the 6" long rail is just under 0.070" which works out to 40 MOA and should put me pretty close to the optical center of the scope at 200 yards.... I had to add one more mounting screw at the back....



I machined the taper into the bottom using a 1-1/4" diameter carbide router bit I got from China for less than $15 including postage.... It cuts very smoothly, and the radius fits the tube perfectly.... Setting the scope rail up so that I could machine it was tricky, though.... I had to bolt it to a backing strip of aluminum (1 x 1.5") with screws in 2 of the 3 holes and move the screws along so that I could machine the entire length.... I was JUST able to manage it without having to move the jig in the milling attachment....

Bob

[rsterne]

This is one of those days you almost dread, and then feel great when it's over..... provided everything works the way it should.... The spacer between the two tubes is 10" long and concave on top and bottom to fit the 1-1/4" diameter tubes, and keep them parallel and 1/4" apart.... It could have been made from a piece of 3/4" x 1" aluminum bar stock, but the only piece I had long enough was 1-1/2" wide.... so the first thing I had to do was saw it lengthwise and then mill it to 1" wide.... Since it was 10" long and I can only machine a bit over 6" of length, that required two setups, and they were critical to match up parallel and exactly 1" wide.... Fortunately, that setup of the vice on the milling attachment on my lathe was also necessary for milling both sides to a radius using the 1-1/4" diameter router bit I just bought.... but again it meant two setups per side, critical that the part be square to the machine in both axis to end up with the same thickness at the center of the web from end to end, to end up with the tubes parallel in height.... and also with the grooves centered in the width of the part, to make sure the tubes end up parallel side to side.... I'm pleased to say that it went very well.... Here is the finished blank....



It fits the tubes perfectly, in fact better than previous breeches where I have machined the bottom with a ball-end mill.... I would definitely use a carbide router bit for this job again, especially with them being a fraction of the cost of a high-speed steel ball-end mill.... It needs to be run fairly fast, with not too deep a cut.... I was running 1270 RPM and removing 0.020" per pass once the full width of the router was engaged.... and using the power cross-feed, that was smoother than going by hand.... Including shallower finishing passes, that meant for about 15-17 passes per setup, times 6 (including milling the width to 1"), so about 100 passes.... It took me 5 hours to produce the piece you see above.... There is a bit more machining to do to this part, it has to be drilled for the transfer port and the three bolts that fasten the upper and lower tubes together.... plus a recess in one end to hold the back of the Forestock in place.... However, that won't happen until the tubes are finished and this will be machined to match.... Besides, I've had enough for one day.... It's time to have a drink and relax.... It's been a very productive few days, and it's time for a break....

Bob

[MJP]

That is nice, this is just the kind of work where the skill and experience comes to play, knowing the limitations of your machines and working around to do what's needed regardless of the limitations.
Good work there Bob. Those are the kind of parts where I'm happy that I spend all that money on an old good mill. To know that I can take 900mm long pass. 
But still I don't have a lathe, I can turn short pieces on the mill chuck but longer ones are must be done at work.
Keep up the good work, enjoying to see it coming together.

Marko

[YEMX]

Looking good Bob!!!  This rifle is going to be awesome!!