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vAgRaNt · Member

This is easily one of the most interesting and thoroughly informative threads, that I've ever read/followed,
on any topic, on any forum anywhere. I applaud your dedication Sir, to the build, but mostly to the documentation
of your steps and proceedures.

Outstanding! Thank you!

Slavia · Moderator

Thank you! It's easier to document things when you do one thing at a time. I have a window of 3-4 days between work cycles, enough time for one or two mods. The documentation is also useful for my own purposes. I can easily go back and refer to what I've already done, and if I need help it comes quickly from other AGH members. Hopefully the combination of what I've done and the suggestions I've received will be useful to others.

yourdaddyjoe · Supporting Member

Salvia, you are such a good Air Gun Mentor…

AirGunEric · Site Admin

"airgun mentalc...", err, mentor, sorry. Smile

Slavia · Moderator

yourdaddyjoe · Supporting Member

Slavia · Moderator

A slight setback - all of a sudden the accuracy went to heck. Like 2" groups at 10 meters.

I had replaced the Crosman one-piece scope mount with a similar Gamo mount that had elevation adjustment. (I got it cheap.) The pivot is nothing more than a rubber pad clamped by a single screw. The pad isn't even cut symmetrically. The screw loosened, and the pad spun around, permitting the scope to wobble.

I put the original Crosman solid mount back on the gun, and everything improved. Stay away from the adjustable one! It's junk.

This is a 10 meter, 10 shot group (from a rest) with the Crosman mount.
Not too bad for a $70.00 USD gun. Maybe not match quality, but certainly good enough for (find your happy place, Yourdaddyjoe) cans.

cw · Banned

Is the fulcrum located at the rubber pad?

Slavia · Moderator

Slavia · Moderator

So, back on track after the scope glitch.

Stock mounting screws put a lot of pressure in a small area. Plastic is elastic and brittle, so there is always the risk of cracking with over-tightening. I bedded brass inserts in the stock so that there is direct metal-to-metal contact from the screwhead to the compression tube, and the stress of the joint is distributed over a larger surface area of the (plastic) stock. (Similar in concept to "screw cups.")

The inserts were turned from brass thumb nuts by spinning them on a screw in a drill while shaping them with a Dremel and file:

They were epoxied in place and trimmed on the inside with a Dremel and sandpaper (the proper diameter screw hole was drilled after the epoxy set):

The mounting screw behind the trigger is slightly larger, but the insert was done in the same way:

I noticed that the compression tube would "rock" in the stock depending upon which end was tightened first. This means that tightening the mounting screws would bend the stock, compression tube, or both, so I bedded the action in the stock. I hadn't anticipated doing this, but I had the materials on hand so I went for it.

I used an epoxy cement (for repairing plastic) left over from another project. I scuffed the plastic with sandpaper, and wiped it down with paint thinner. I used ordinary silicone spray as a mold release on the compression tube. I mixed a small amount of the epoxy and found that it turned to taffy after 15 minutes, was no longer sticky after 30 minutes, was still pliable at 45 minutes, and turned hard at one hour.

Epoxy was applied to the plastic and the action was screwed (lightly) to the stock. I started immediately to remove excess epoxy from the outside of the gun with a toothpick. At 30 minutes I "popped" it apart (finger pressure was enough), and started trimming the inside with a pocket knife while it was still pliable.

I have used commercial bedding kits, and they take 10-12 hours. This is quicker, but you have to be diligent and "stay on schedule." Also, this plastic repair epoxy really smells bad - if you ever use it, be sure to have adequate ventilation.

Slavia · Moderator

A couple more things for this week - I tried lapping the bore. Usually they suggest casting a slug in the bore with molten lead, but I employed a slightly different approach.

I rolled a Sheridan .20 cylindrical pellet between two hard flat surfaces until it was slightly bigger than the .177 bore. Then I pushed it into the breech of the bore with my cleaning rod (a plastic covered coat hanger). This sheared off a little ring of lead, but the lead left in the bore fit tight. I put a dab of automotive rubbing compound on it and pushed it back and forth in the bore until I could no longer feel rough spots. (I held my finger over the end so I wouldn't push the pellet out and ruin the groove/land fit.) I finished up with the brass screw crown polish method (and breech crown as well).

You know what? No change in accuracy. The only thing I accomplished was to make a cleaning patch go through smoother.

cw · Banned

Did you gain any projectile speed from reduced friction?

Slavia · Moderator

broommaster2000 · Moderator