Tuesday, August 4, 2015

Adding A Sling To My IZH 61

Lotta times, I'm just looking for a simple project.  This was one of those days. My IZH SBR project gun seemed like it would be easier to shoot with a sling for additional offhand support.  Problem is, there's really no provision on an IZH 61 to mount anything easily.  That hollow plastic stock, while nice and light, doesn't readily lend itself to sling swivel installation.

Rather than just guess where to put the front sling attachment point, I thought I'd use a piece of picatinny rail to allow fore and aft adjustment.    An $8 Magpul MOE synthetic rail looked like it would be an almost exact match to the IZH's polymer stock.  The fact that it came with threaded backing plates made the choice even easier.

With the stock removed, I fiddled around with where to mount it.  Bottom of the stock or left side?

Bottom of the forend won.  Barely.  A couple pencil marks on the seam showed where to drill. 

Drilled the holes.

This is where is gets tricky.  There's no easy, direct access for the threaded bosses. They'll have to be fished into location and held while I try to catch the thread of each bolt.  Those bolts Magpul included in the rail kit are non-starters for this installation.  The factory applied thread locking compound will make it impossible to spin the bolt fast enough to advance it through the thread.  It'd stick and just spin the backing plate inside the stock.  A couple #10-24 SHCS without any thread goop were used instead.  To get the backing plates into the stock, I superglued each plate to a bicycle spoke.  The Zip Kicker makes the glue dry instantly. 

Here's where I wanted to pull my hair out.  The only access to the interior of the forend is through the trigger inletting.  This was just an exercise in patience and dexterity.   Honestly, it was awful.  The boss had to be lined up with the hole, the bolt pushed through the rail and stock, then rotated to catch the first thread without moving everything out of position.  Twice. 

Eventually, I got to here.  Bolts are tight and the rail nicely centered. 

Doves flew up into the sky and a beam of sunshine lit my workbench. 
Then the light went out because I still needed a rear attachment point.

Thought maybe (yeah, right) a conventional screw stud would work.

Centered up and drilled. 

And it's  hollow, too.  So, no screw stud.  Wouldn't be enough thread contact.

The only access to the interior of the buttstock, at least at the heel, is through this 8mm (about 5/16") hole.

I went through my "weird" fasteners and found a couple of these.  Don't know if I'd call it a t-nut or just a threaded boss?  This has an M5 x 0.8mm metric thread.  It's probably from a bicycle road brake pad.

Shaved the thread down in height slightly until it would push through the 8mm hole.  Then I rattled it around until I could pull it into position and get a bolt to catch the thread.  For some reason, this was easier than the spoke fishing.  Probably had everything to do with the interior shape of the stock funneling the insert down to the hole.  After I caught a couple threads, a few drops of superglue were used to temporarily anchor the insert...

So I can make a sling swivel stud with an M5 threaded shank.  This was starting to not look like a simple project.  Piece of .375"diameter  O-1 tool steel went into a collet and square block.

Found center.

Spotted and through drilled for the sling swivel hole.

Mic'd across the flats of an Uncle Mike's brand stud as a reference number.   0.312"

Chucked a 1/2" end mill, then set a stop so the piece can be relocated in the vise accurately.  The piece is starting at 0.375" diameter. I need to take about 0.032" off each side to make the flats 0.312" apart. 

Math:  (0.375 - 0.312) / 2  =  0.0315" per side.

Touched off, zeroed the depth readout, then slowly milled downward...

Until the readout showed 0.032".

Turned the piece over and repeated the procedure.

0.3115"  Close enough. 

I'd left extra stock so there would be something to chuck in the lathe.  Turned down the end...

And threaded M5 x .8mm.

Trimmed off the excess thread and squared up.

Flipped the piece around.  Faced and beveled the top.

Blued and installed.  Got lucky and it aligned when it was tightened.  Otherwise, it would've needed a shim washer.

Put the action back into the stock and mounted up a sling.   No gaps between the rail and forend.  Aesthetically, these projects are considered a success if they look like I had nothing to do with them. 

The gun is substantially more stable offhand when using a hasty sling.  If I had to do this again, I'd think hard about using rivnuts--either aluminum or the ones specifically for plastic installation.

Thanks for reading.

Sunday, July 26, 2015

CP1-M CO2 Pistol Disassembly

Tore down the CP1-M this evening.  Took a few pics along the way.

Make sure the gun isn't charged with CO2.

Remove the trigger guard...

then the rear grip screw.

 Grip pulls off.

Remove the single shot tray or magazine.

It's not necessary to remove the bolt handle if you're just servicing the valve, but I unscrewed it from the bolt.

 End cap retaining screw.

With the end cap off, the hammer spring guide and hammer spring can be removed.

Breech screw removed.  --It's the small screw in the middle of the shot tray/magazine slot.

 Here's the top of the transfer port.

Here's the entire transfer port.  Pulls right out.

The hammer cocking pin is a small bolt.

The hammer can be withdrawn now by pulling the trigger to get the sear out of the way. 

Here's the hammer, hammer spring, spring guide and the hammer cocking pin.  I polished the sear contact area on the hammer.  (Call it a striker if you prefer)   Shooters looking for additional power will often swap out the hammer spring with something stiffer.

Another approach is to add an additional spring inside the hammer spring.

 Like so.

 A spring within a spring.

 Inside the gun, it looks like this.

Underside of the breech shows the bolt cocking pin

The bolt withdrawn. 

With the valve screw removed...

...the valve slides out of the gas tube.

 And unscrews.

Face of the valve is similar to the Crosman 38T.  Hollow piercing pin held in place by a threaded retaining ring and a face seal.

Sometime shooters looking for additional power will substitute a weaker spring into the valve.  This also has the advantage of not increasing cocking effort --provided the original hammer spring is utilized.


OK, trigger time.  The lower stop pin practically falls out on it's own.  (That's OK, when assembled, the trigger guard keeps it in position.)


Here's that 3mm threaded hole mentioned in the first CP1-M blog post.  On the first run of pistols, this hole was threaded (thread size is M3 x .5mm), but the adjusting screw was not installed.  I've already added a sear adjusting screw.

Trigger pivot pin is pushed out and the trigger removed.

Use about a 5mm long set screw.  Round over and polish the end.

The trigger as it sits in the gun. Polish and moly all the contact points.

Only the sear is directly spring loaded.  Note that any trigger adjustment requires removing the grip and the trigger pin stop to access the 3mm screw.  This can be done with the gun charged with CO2 and dry fired until it feels right to you.  As always, err on the side of caution when working on any trigger.

The three set screws on top of the forward end of the breech are loosened to remove the barrel.


The barrel arrangement is similar to the QB series of rifles.  The transfer port is located between two o-rings on the barrel shank.


Of course, they're metric like everything else on the pistol. 

Finally, an o-ring at the breech seals around the loading bolt.

Reassembly is a simple reversal of the above.  I found the gun to be extremely easy to take apart. It was encouraging to see viton o-rings in several key spots as well as thread locking agent on all the fasteners.  Build quality was excellent.  And not just "given the price point".  I found this to be a solid attempt at making a very good pistol.  After having it a couple weeks, as a target pistol, it's easier for me to shoot offhand than my modified Crosman 22XX guns, or my Daisy 747.  It'll also outshoot my Gamo Compact, largely due to having more weight at the muzzle for stability.

Oh, that "spring within a spring" power boost took my .177 cal pistol from 365 fps to approximately 525 fps with RWS Hobby pellets.  Probably want to tweak that down a bit.  For paper punching, I'd like it to be around 410-420 fps--mostly to keep the shot count up.

More soon.