Saturday, August 22, 2009

Screw Cups for Gamo and BAM B3-1

I've been working on an ever-growing pile of small stuff; guns that need a relatively straightforward job or two. Seems like there's always a huge pile like this to work on, and it's hard to get to the serious stuff when there's already 3 guns --or more--in pieces on the bench. Lest I confuse anymore parts, I thought I'd knock a few out. And yes, these are mundane jobs. But, I try to remember that it's often the little touches that set the nice guns apart. Well, I try.

This is the palm rest off my old Gamo Compact.

It's adjustable via a single M5 bolt. That M5 adjustment bolt was wearing the wood at the bottom of the counter bore. A screw cup is the obvious solution. A quick hit on the caliper showed the hole to be 0.389" in diameter and 0.221" deep. I'll work with this, but if it was any smaller, I'd enlarge the hole with a forstner bit.

A short piece of 0.50" diameter scrap is chucked into the scrolling 3-jaw and faced. Probably (hopefully) just a piece of mild steel.

I took a quick passing cut, skimming the free length to ensure that it's indeed round. This round end was then chucked into the jaws. I flipped the piece so the freshly cut end was now in the jaws and faced outward.

Started to turn down to reach the 0.389" hole size in the palm shelf.

Once at diameter, I spotted the center hole and drilled the through hole with a #7 drill bit. The hole size just clears the M5 bolt thread.

Used a home grown parting tool in a rear tool post (remember: tool gets mounted upside down) parted off leaving the piece about 0.05" too long for sizing.

Faced the parted off end and brought it to 0.221" OAL to match the depth of the hole in the wood.

Bored it to 0.268" for the M5 bolt head. A typical M5 bolt head is actually larger in diameter than 0.268", so the head will also get turned down to fit.

Installed two M5 nuts on the bolt and tightened them against each other. Now, I can use the 3-jaw chuck and grip 3 sides of the wrench flats rather than the bolt's threads. It's less wear and tear on the aluminum jaws of the chuck. Bolt threads wreck havoc on aluminum chuck jaws. And steel jaws wreck havoc on bolt threads...I see the need for yet another custom tool here.

Turned the M5 bolt head down to just fit into the screw cup. Oops, the head sticks out the end of the cup. That gets faced down till it's flush.

Done, save the finish. Just a small simple thing...

After the rusting go round with Joe's muzzle weight a few month's ago, I've tried a different step in the bluing process. After using my current favorite, Formula 44/40, I washed the parts in cold water for several minutes, then coated them in ProLink lube. It's a wax with a petroleum carrier. The cold water rinse is specifically mentioned in the directions for Birchwood Casey bluing products, but it's NOT on the 44/40 bottle.

If you don't think the grips look stock, you'd be correct. The grip was a bit too large for my borderline L/XL hand and the stippling was poorly executed. Last year, I sanded off all the stippling and reformed the grip to better suit.

Then stippled the grip again with a heavy scratch awl...

Stained the stippled areas with Minwax Ebony wood stain (color number #2718), and finished the rest of the wood with 3 coats of Royal London from Jim Maccari.

Project 2:

Nick sent a waterproof box a couple months ago containing, among other things, a .22 cal BAM B3-1. It's basically a cheap, side-lever, spring piston air rifle made up to look like an AK-47.

Action removed from the stock.

There are 2 bolts that hold the action to the gun. The front bolt goes through the wooden forearm and into a lug in the compression tube. BAM used a phillips headed M6 bolt. It was headed for the same problems as the Gamo Compact and since I was making one screw cup already...

Here's the rest of that scrap steel used above. I measured the hole in the forearm and it was 0.577" in diameter.

Drilled the through hole for the M6 bolt.

Drilled a hole close in size to begin the counterbore for the M6 bolt head.

Finished the bottom of the hole with a small boring bar. Just used it to remove the radius at the bottom of the drilled hole from the point of the drill bit. Made the hole 0.388" diameter to fit the head of a M6 socket head cap screw.

Flipped it in the jaws and cleaned up the outer surface from the jaws. Not show: Parting it off and cleaning up the end. I left it just a bit too long.

Hit it with some layout fluid and let it dry.

Here's where the cup goes.

Assembled. It's long--to leave material to match the angle of the forearm.

With the bolt tightened to pull the cup to the bottom of the hole, I scribed a line around the circumference of the screw cup.

You can just see the fine line in the layout blue.

Vised up. Aligned front/back of the forearm parallel with the jaws. Also angled the cup in the vise so the scribed line is even with the tops of the jaws.

Now, I file perpendicular to the jaws until the file bottoms out on the jaws.

Leaving this.

Took it to 6oo grit.

Test fit. Run a finger across the wood to metal fit. Remove high spots if any (there weren't).

Another view.

Bolted up. Dah! The bolt head is too tall at the front.

The quick (and easy) fix is to just shorten the head of the bolt.


Blued up. The camera flash made it look kinda gray here. It's smooth as glass.

Another view. Really overkill for such an inexpensive gun, but it looks and works better than the factory attachment.

Thursday, August 20, 2009

Reassembling an IZH Baikal 513M, Part 2

Almost there!

The holes in the tube and the bushing are lined up.

And the pins inserted.

You can see the plastic bushing has been pushed out of the spring guide, having done its job.

The trigger has a spring loaded plunger that needs to get shoehorned back into place.

A 1/4" leaf gage works admirably for this.

Then I held it in position with a rubber band.

Aligned with the mounting screw holes.

The blocking lever is put back into place.

The pivot screw is put back in. You'll notice that I accidentally put it in backwards. It doesn't matter.

The end of the pivot screw.

With circular nut and lock washers in place.

The blocking lever was hooked back onto the cocking arm.

Getting that spring back into place was hard! But it all sort of slips into position.

The polymer bushing reinserted into the stock.

And where we started, with the front stock screw back in place.

Preliminary testing shows a slight reduction in velocity with the rifle shooting CP 14.9 gr. pellets at around 770-780 fps. We'll see how that changes after I put a hundred or so through it. As I told Derrick in an email,the rifle has a lot less "grumpy" in it now. It still recoils but isn't nearly as harsh and there's a lot less mechanical noise.