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.

Tuesday, September 21, 2010

Umarex Walther PPK/S

An extremely generous fellow surprised me with a Umarex Walther PPK/S BB pistol yesterday, just turned up in the mail. I emailed him and he replied that the slide kept popping off while firing and that he wasn’t able to get it back together. So he sent it to me as he knew I’d get it working and enjoy it. Sometimes airguns are like that, they drive you nuts until you just can’t stand the sight of a particular problem gun (I know I have several I’d like to run over with a steam roller).


As received.


The slide was detached. Googling around for information I came upon an excellent Youtube video detailing the disassembly and reassembly. Although I’m not a big fan of using a drill bit as a pin punch, but you do what you can with what you have.


Spring in place.


Unlike the pistol in the video, a previous owner had replaced the trigger guard with a laser sight made for the pistol. The pin that retains the stock trigger guard is not used. The trigger guard is pivoted down.


And twisted slightly to stop it against the frame.


Then the slide is slid on.


And down. It needed a bit of wiggling.


Part of the problem is that instead of using a pin to retain the trigger guard, thus locking the slide in place, the laser sight used two socket set screws. So I tightened those down. I think I’ll make small dimples in the frame to more securely lock them.


Looks cool…makes me want a “real” PPK.


Not a big fan of the bulky CO2 screw knob. But it does provide good leverage.


Four magazines loaded with steel bbs.


Inserting the magazine.


The gun felt stiff, and the plastic shroud around the barrel seemed tight. Several times when first shooting it the slide locked up, requiring manual recocking. I greased it up and it worked better but I’ll probably smooth it a bit.


The slot the CO2 cartridge fits in is pretty tight which makes replacing cartridges a pain. I think I’ll trim a little off the sides. You can see that it pinches the cartridge enough that it stands up…


It was getting late but I ran it a bit to test. The blue group is with steel bbs at about 10 feet. The red circles are a 5 shot group using lead bbs (not .177 lead round ball, will try that later) used in the Haenels.

The pistol isn’t particularly accurate and the laser needs to be zeroed to the point of impact (it was shooting low), as well I think it needs some gentle tuning. I’ll work on that later this week. It is a fun pistol, and while the “blowback” action serves absolutely no purpose, it looks and feels realistic.