Crosman MK2 Modifications -- Part 3

Next up on the MK2 is end cap for the shroud.   Essentially, it's a glorified nut.  It will thread to the muzzle end of the barrel and support the front of the shroud.

Dug though my metal stock looking for a piece of 7/8" OD rod to match the OD of the shroud.  No luck, but I did find a piece of 1" stock.



























Faced the end.

Turned the OD down to 7/8" then cut a step to slip fit into the shroud's bore.

 Center drilled.

 Through drilled 21/64".

Countersunk.

Started the 3/8"-24 thread with the tap held in the tailstock for alignment, then finished by hand. 

Parted off the endcap.

Needs some clean up.

In a fit of insanity, I decided to make a fancy interface and special wrench for the cap.

The cap was held in a 5C collet and the collet went into a six-sided (hex) collet block.




























This was then set in the milling vise and a hole was drilled, then the block was rotated 1/6 of a turn (60 degrees) re-clamped and another hole drilled...  A work stop was used to get the block clamped in the same location in the vise each time.

Eventually, I had six evenly spaced holes.  Removed the collet block--being mindful to not move the X or Y position of the mill table.

For the wrench, I faced a thin slice  of 1.125" round stock. 


















Rebated to fit over the end cap.


















And it went into the same hex block using a larger collet.

Back to the mill and the work stop where it was drilled six times.  In theory, the holes in each of the two pieces line up.  

Turned down some thin brass rod and made six pins.

Found center and through drilled the wrench with a 3/16" bit.


 

The (freshly blued) wrench, brass rod cut into small pins, and the end cap.

The brass pins were pressed into the body of the wrench.  Used some Loctite 680 bushing retaining compound to help keep them in place (probably forever).  Chucked the wrench and faced the pins down to the same height.  Not shown:  Cut a handle from a piece of 3/16" drill rod.

Along the way, I added a groove to the cap for an o-ring and used a boring bar to remove about four or five of the 3/8"-24 threads from the muzzle end.  Also chamfered the pin holes and generally cleaned things up.

Wrench and end cap. 

 They practically press fit together.

The end cap threaded into place.  Nice, clean fit with the OD of the shroud.




























Here's the new business end of the MK2.  By removing those forward end cap threads, it looks like a deeply recessed crown.


Still need a new plug for the hammer spring tube.  Oh, and probably a front sight.

More soon.

Crosman MK2 Modifications -- Part 2

I was going to rebarrel this Crosamn MK2 to either .20 or .22 cal, but since someone already took the time to machine a really nice .177 cal loading bolt, I sourced a 24" Crosman 1760 barrel instead.













The stock MK2 barrel is just shy of 8" OAL. 

Cut the new barrel off somewhere around 10.3" long.  Assuming  that the final length will be pretty close to 10" after threading, facing and crowning.

Measured the major diameter of the thread--the barrel needs 3/8"-24 threads at each end.

Chucked the new barrel in the Taig and turned the end down to 0.369"  Cut a slight taper at the very end to make the threading die easier to start.

With a die holder mounted to the tailstock, I started the thread. 

Eventually, the barrel slipped in the chuck, so it was transferred to rubberized jaws in a bench vise and the thread was finished.

Back in the Taig to face then cut a 0.370" shoulder behind the thread.   This will be the breech end of the barrel.  I'll be working breech to muzzle.

 














A little bit of measuring gave the location for the CO2 transfer hole in the breech-end of the barrel.  Clamped the barrel in a v-block (this proved to be a mistake) and lined up to drill the hole.

Spotted.

Drilled with a #28.   Removed the barrel and immediately realized I had no way to line up this hole with the transfer port in the gun.  The original barrel features a dimple for the barrel setscrew opposite from the CO2 hole.  The dimple allows indication by alignment with the threaded hole in the gun's receiver before installing the setscrew. 

Mounted the barrel in a 5C collet and a square collet block.  Took a couple minutes to orient the hole so it faced straight up and was centered under the mill spindle.   Positioned a work stop against the collet block.  Flipped the collet block over and butted against the work stop.  Drilled a shallow hole with a spotting drill.

Began the cut for the pellet leade with a small tapered burr.




















Knew it wasn't going to be deep enough, so I started looking around for something to use.  Remembered I had a set of tapered pin reamers that are likely a few decades older than I am.

The #2 was a likely looking candidate.  Slow speed and lots of cutting oil. Lot of test fitting followed by several small pieces of emery cloth backed with a small brass rod to complete the polishing.

Another test fit.

 Bolt rotates closed. 

Not shown.  Threaded the muzzle end of things.

 Faced.

Recessed, crowned and polished to 500 grit.



















After pondering the various sizes of metal stock in the basement and weighing the pros and cons of steel vs. aluminum,  I finally settled on a 7/8" DOM steel tube to sleeve up the barrel. 

Out in the garage, the tube was chucked in the Shopmaster lathe and the end was turned down to 0.755" OD.  This will slip fit into the breech of the receiver.

Cut the tube 7.125" from the step at the shoulder to the muzzle.

Test fit.  So far, so good.  In the next couple days, I'll make a nut for the muzzle.  It will tension the barrel as well as secure the 7/8" barrel sleeve.  Then I'll need to make a plug to act as a base for the hammer spring and fit (or make) a new front sight.

Please check back soon.