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.

Marksman Mod. 70 Forward Progress

Hey! Happy belated birthday wishes to Nick!

As a brief reminder, Nick and I are looking for old airguns as blog fodder. If you've got any old guns tucked away that we can have for free or for crazy cheap--the cheaper the better--as our budget is almost zero. Even parts guns can be helpful as we may be able to salvage a barrel or some such part for a project. Shoot one of us an email if you've got anything we might be able to use. Anyway, we appreciate everyone all over the world who's been following our exploits. Thanks to everyone for taking the time to read our blog.


Back to the task at hand. Made good progress today on Frank's Marksman. I appreciate his patience.

Started in on the trigger unit. I swabbed the inside with moly, but still wasn't happy with the second stage, so I started knocking out pins. The metal plate is part of the safety. The spring tensions the lower sear and trigger.

Upper sear and spring removed.



Here's the trigger unit completely disassembled. It's not as bad as it looks to reassemble--it's actually worse.

No, it's really not that bad. This is the general orientation of the parts to each other.

I polished most of the trigger components.

This surface bears against the lower sear.

Buffed the sides, too, where they rub on the inside of the trigger housing.

That center hole in the trigger housing is in exactly the right location to add a screw to adjust the amount of sear contact--it just needs to be threaded. Some measurement revealed the hole was the correct tapping size for an M3 x .5mm thread.

A bit of Tap Magic for aluminum and a plug tap.

Cut to full size threads.

Reassembled the trigger unit and screwed in an M3 button head.

It's too long--I'll shorten it later--but it works perfectly. It reduces the travel of the second stage by limiting the surface contact between the upper and lower sears. I'll set it up and err on the side of safety. The screw can also be backed out--or even removed completely to return the trigger to factory spec condition.

Excuse the redundancy. Yes, I'm going to make some screw cups. They're functional, dress up the gun and remove the flat head machine screws. Went through the transfer punches until I found a snug fit.

Measured the punch.

Cut a piece of drill rod that was a bit oversize...

and turned it down to 0.408"

Another view. Not shown: measured the depth of the holes in the stock

Spotted.

Through drilled with a #9 bit to provide clearance for the M5 x 0.8mm forend screws.

Counterbored with a flat bottomed drill to recess the head of the allen bolt.

Finished with a tiny boring bar.

Bolt was a tight fit into the counterbore, so I shaved the allen bolt head down slightly in diameter to fit.

Parted off and cleaned up. Made a second cup in the same manner. Fine tuned the length of each cup to a specific side of the gun. The left-side hole in the forend was about .006" deeper.

Not shown: cut a piece of delrin (acetal), through drilled for the piston stem, then reduced the outer diameter to press fit into the main spring. Left a 45 degree angle at the base to interface with a steel washer. Same technique as the Weihrauch spring guide made here.

Cutting the OD of the washer to slip fit into the Mod 70 compression tube. Not shown: cut the matching 45 degree bevel.

I've got the washer mounted on a homemade arbor. I "bumped" it until it ran true then locked it down with the allen bolt. It's a piece of free machining steel.

Spring, guide and base washer.



Still waffling on buttoning the piston. The spring is also a very loose fit inside the piston. Want to increase the liner thickness and snug up the fit, then I think it can all go back together.

More soon.