Thursday, September 23, 2010

Finishing up the Marksman Mod. 70

Just a few more things to complete on the Marksman.

Since the barrel/breech were off the compression tube, it was a fine time to do a quick clean with the JB Non-Embedding paste. It was absolutely filthy.

Had some concerns about the sloppy fit between the OD of the mainspring and the ID of the piston body. The piston had a liner that was approximately 0.0115" thick. I sourced a piece of sheet steel that was 0.0260". Some measurement and guestimation on my part hoped that this would tighten up the fit, better support the spring, and help prevent spring buzz/vibration.

Pulled out the old liner with a small pair of needle nosed pliers.

The inside end is folded inward. End of the mainspring presses against it--holding it in place.

Found a piece of 1" delrin rod to use as a form.

Rolled the sheet metal around the rod. A dead blow hammer added some persuasion here and there.

Wonder of wonders, it somehow actually formed a straight tube.

Cut with tin snips.

Had to do some test fitting and resizing before finally getting it right.

Cut and folded the piston end. After getting this end flat, I smoothed out the sharp ends and ground enough clearance for the piston stem.

Notched out the key way clearance for the scope rail.

Eyeballed the insertion length...

and cut to size with a Dremel tool and a cut-off wheel. I cleaned up the end, dressed it flat and deburred.

Installed in the piston and test fit with the spring and guide.

Turned my attention to the roughly finished cocking lever slot.

Deburred and cleaned up the slot with various diamond hones.

Spent a significant amount of time on this slot. A good finish here will really reduce the cocking effort and allow for a smooth cocking gun without a ton of break in time.

Sanded off the machining marks on the cocking shoe, then took it to the buffing wheel.

Before installing the piston, the compression tube was thoroughly cleaned then burnished with moly.

Bonus. The compression tube had been nicely cross-hatched by Weihrauch during manufacturing.

Piston installed and the polished shoe.

Moly for the cocking shoe/slot interface.

Cleaned and moly'd the pivot shim washers.

I'll wipe off the excess moly later.

Mainspring got a thin coat of copper anti-seize/Beeman Laser lube.

I'm glossing over the reassembly as it's really just a reversal of the initial blog post here.

Trigger unit slid home.

Trigger block safety reinstalled. Do not install the snap ring with the holes facing rearward. It will block the sliding safety tab on the trigger unit and the trigger will not fire.

Finished fitting the screw cups and blued them. The screw holes are different depths on each side of the gun so it took some time to get the cups flush. Wanted the screw heads flush with the ends of the cups, too. It all turned out OK. I much prefer the allen heads over screwdriver slotted bolts any day. Maybe Torx next time around?

Installed the trigger guard and snugged all the bolts down. Put a sizable quantity of RWS Hobby pellets through the gun then ran it over the chronograph again. Around 935 fps--just a touch faster than the velocity numbers in the Blue Book. So, the tune lost about 20--25 fps compared to the box stock rifle, but some of that loss is no doubt due to some dieseling. It shoots with a solid thunk with no vibration or spring noise. Fires like tuned R1.

Played with the sear adjustment I added to the trigger unit. Screwing the bolt in decreases the engagement. It's possible to dial out any and all of the second stage travel. Of course, it's also possible to set the sear overlap to be so minimal that the gun will fire as the barrel is closed--I stayed away from that. I played with the adjustment enough to satisfy my curiosity as to how fine this trigger can be before backing it out to the original factory setting. Tiny amounts of screw travel have big effects on the overlap (and safety). Give serious consideration and use great care if you touch that screw. Since I didn't want to send Frank a super-fine hair trigger and a potential accident waiting to happen, the trigger is back to the stock sear engagement--save for a better finish on the components and some lubrication on the moving parts. The stock trigger set-up is actually quite good--almost as nice a full-on Rekord.

Frank, thank you very much for letting me re-connect with the first real air rifle I ever shot. I had a great time working on this one. You should receive it later today.

I'll be sharing a gun that Frank sent me soon.


Frank B said...

Derrick,you are a credit to the hobby....and I don't know how to thank you sufficiently for the kindness you have shown me.However,I can assure you I will figure out a way.....your friend,Frank B

Josh C. said...

Excellent photos-keep up the great work. Based on results between various greases, what specific grease/lubricant would you recommend to put on after a trigger job.

derrick38 said...

There are so many good quality greases out there. It'd almost be difficult to pick a bad one. Moly is always a perennial favorite, but you could also try Buzzy's Slick Honey if you can find it--it's insanely slippery stuff. Any of the better quality wheel bearing greases from a decent auto parts store are also outstanding. Lucas red grease, CRC Sta Lube, Castrol Syntec MP...