Barrel Shroud / Sleeve for the Marksman 56-FTS Part 1

Started the full-length sleeve for the Marksman 56-FTS.   Didn't really get very far yet, but starting often begins long before any chips are made.  

When complete, it'll look like this, but 16" long to cover the entire barrel.  It's strictly cosmetic.  There might be some benefit, as the additional weight should slow down movement to some degree, but I really just want to have some simple, cleanly machined lines.

As I wanted the sleeve to look like a full length version of my modified Crow Magnum muzzle brake, I had to consider how to machine the 15"+ long flats on each side as well as the groove along the top.  The breech end will also need a taper, the muzzle end cut to length and beveled and finally some set screws for mounting.  And a swivel stud for a rifle sling and what else did I forget?  Oh yeah, where do I even start?

This is often just a mental checklist now:  Will this physically fit in the machine?  Do I have a way to hold it?  How accurate does it need to be?  What will (probably) be the most difficult step(s)? Do I need to make or buy any tooling for the project?  What options to I have for each machining step?  Pros and cons of each?  Is this really a good idea?  Am I out of my damn mind?

Purchased a two foot long piece of DOM (Drawn Over Mandrel) tubing last year from McMaster-Carr.  It's 7/8" (0.875") in OD and 0.635" ID.   The Marksman 56-FTS barrel is 16mm OD (0.629" ) leaving about 0.006" clearance to the tube.   For reference, a sheet of paper from the printer is a pretty consistent 0.004" thick.   

I opted to machine the taper at the breech end first then bring in the overall length.

Looks OK.  Some fine tool marks, but the sleeve will be bead blasted in the final steps.  Need to take this to length, finish the muzzle end, and polish out the OD before cutting the flats.  And that's where things stalled out.  I didn't want to cut and polish this thing at home.  And I really didn't want to cut those long flats on my small mill.

Took it to work and got the Ok to work on it after hours.

Metal cutting bandsaw.

XXX marks the off cut.   Coolant and auto feed.  Sure beats my hacksaw with those Harbor Freight blades.  

Cut it to 16-1/4" long. 

I've shown this machine before.  Its a Rand Bright cylinder polisher.  Has a roller than spins and draws the tube through where it's polished by a 4" wide sanding belt.  The belts are something like 90" long.

The white sheets of nylon are adjustable for tube width.  I knew that a co-worker had been running some hydraulic tubes that were the same diameter the day before, so that had also factored into my desire to do this at the shop.

Ran it right through.  Didn't even need to change the sanding belt.  After three passes, it looked great.  Probably equivalent to sanding it to 320 grit--and only took about 45 seconds for the entire job.  Since the Rand Bright was already set up for the 7 /8" width, it took me longer to uncover and recover the machine with a tarp than to do the polishing.   

That saw cut end needs some attention.

Over to the lathe and faced / deburred the muzzle end of the sleeve.   At this point, the sleeve is still about 1/4" longer than the barrel.  Again, just used the tools already in the QCTP.   

Now it was time to go home and finish the length.

 

As expected, just a bit long.

Out to the garage and faced, beveled, then polished the muzzle end to final length.

Decided it might be smarter to polish out and remove those small machining marks from the tapered end now rather than rely on media blasting later.

Final test fit for length.  Next, I'll machine the long flats on the sides.  My milling machine will make the length of cut, but I'd prefer to make these long cuts on a larger, more rigid machine.  And there's a face mill cutter at work that should give a better finish than the end mill I'd have to use at home.

More soon.  Thanks for checking in.

Making Screw Cups for a Marksman 56-FTS.

I know.  I know.  We haven't been posting.  Some stuff came up that kinda pushed airgun tinkering to the back burner.    Waaaaaaay back on that back burner.  I'm gonna try to ease back in.  

So, the, uh, Marksman 56-FTS.  Right.  It needed some screw cups and maybe a nice barrel shroud.  Right there is part of my blogging conundrum.  Speaking only for myself, I waffle about posting another blog about something so mundane as screw cups.  Nick has shown how to make them.  I've done the same.  We hit the wall sometimes on new material.  Nevertheless, its screw cups that I need so it's screw cups for the blog.  

Removed the stock from the Marksman.  That screw cup goes here.  Provides a metal to metal bearing surface for the stock screws to tighten against.  This is helpful because it stops the screws from slowly digging through the wood.

Before I got started,  I looked at some of the other existing hardware on the rifle.  The cheek piece fasteners are blued steel.  I'll follow suit and go the same route so it looks like this was actually planned in advance and not designed by the party committee.

Rather than try to measure directly, I grabbed some transfer punches.  The graduated sizes are pretty handy for a quick reference.

Best fit was a 13/32" (decimal equivalent  0.406")

Found a scrap of .500 diameter 12L14 steel in the scrap pile.   

Cut off an even smaller piece.

Face one end.

Turned down to just over 0.406'

0.408" and a couple tenths should be close enough.  I'm looking for a snug fit.

Some M5 socket head cap screws.

Through drilled

Testing for clearance.

Drilling a counterbore to recess the head of the fastener.

To produce a flat bottom in the hole, I'll finish it with an end mill.  Seems like I never have the diameter I want...

Just took out the drill point and made a flat bottom in the counterbore. 

Test Test.

See how the shank flares slightly just below the head?  If the through hole is too close to the screw diameter, this can hang up and not let the base of the head seat flush.

Rather than making the through hole larger, chamfering the top of the through hole will fix it.

Cut off, flipped and faced to an unshown predetermined length.

Screw cup #1.  

Now for the second.  Since I've made screw cups for various air rifles before, I know that they're not necessarily identical in diameter or depth. 

Screw cup number two ended up about .010" larger in diameter to best fit the factory counterbores.

Test x 3 

Blue time.

And finally, installation and the glamour shots.

Just what I wanted. Looks like they were there all along.

Next up, I'd really like a full length shroud.  Like it to look like the muzzle weight, but run the full 16" barrel length.  The metal is on the work bench, but I'm unsure if I can do the machining here at home or if I'll need a larger mill.   More soon. 

Side notes of note:

I met up with renowned air gunner and just generally good guy, "Volvo", the other day.  I still re-read his blog and wish I had the style and quick wit he wrote with.

https://namericanairguns.blogspot.com/

Ray, thanks for sending me an email checking in with me.   It was good to hear from you