Rebuilding McClure Pellet Trap?

[Gwhite]

I have a pellet trap that I bought about 15 or 20 years ago from Neal Johnson. It's a very nicely varnished oak box, and inside is a vertical galvanized steel plate backed by foam rubber. The pellets flatten against the plate, the impact is absorbed by the foam rubber & the pellets fall down inside the trap. On the back, it says "McClure Model IV, Todd, North Carolina". Neal Johnson closed up shop years ago, and an internet search came up without a single hit on the McClure trap.

I have been practicing a lot lately, trying to get my scores back up to where they were when I was a lot younger. I'm shooting a Steyr LP50, about 300-400 shots a week.

I don't know if the galvanizing is worn off or what, but the pellets have started sticking to the plate. A thin layer of oil stops this for a while, but evaporates and/or gets shot off fairly quickly. Right now, I've applied some waxy stick lube for metal working (Boelube) on the theory that at least it won't evaporate. The stick lube is relatively clean to apply, but I don't know how long it's going to last.

I took a closer look at it this morning, and found several things:

1) The existing plate appears to be just flat (or it was, see below), with no bends at the edges. It's a bit hard to measure, but using a bent paper clip as a hook, I estimate the thickness to be somewhere between 50 & 60 mils. It looks like I should be able to replace it with a polished SS sheet without too much trouble.

2) The plate is bulged out in the center by about a 16th of an inch. It doesn't appear to be lead build up. Somehow the constant hammering with pellets has made the metal expand outward. I'm a bit baffled as to the mechanism for this, it's like a reverse dent. The surface is also rough, but that may just be residual bits of lead sticking to it.

3) The foam rubber is visible though mounting holes in the back, and looks a bit yellow. That may have stiffened up over time, contributing to a harder impact & aggravating the sticking problem. If I replace the plate, I'll have to try to come up with a good replacement for the foam. It may be tricky to get the right stiffness, given what may be available locally, and that my only sample is thoroughly aged. There is a really good foam place in Boston that may be able to come up with a close match. I also have some adhesive-backed sound absorbing rubber sheet that I could put on the back of the plate to quiet the "clank".

Does anyone know what happened to Mr. McClure, or have any experience in rebuilding one of these traps? Getting a stainless plate the right size is pretty easy, but I don't know how fussy the stiffness of the foam is likely to be.

I know this trap was originally designed for air rifle, so I'll post a link over there as well.

Thanks!

[RandomShotz]

FWIW, I may not be able to help with the repair, but I think I can explain t he reverse bulge. Visualize the plate as a stack of extremely thin layers. Obviously, if a projectile strikes the plate with enough force, the plate will bulge in the direction of the applied force. If you visualize how the metal flows in the bulge, there will be some compression of the layers on the struck side and some expansion of the metal on the far side. If the pellet is only powerful enough to plastically (i.e., irreversibly) deform the front layers of the plate, then the front surface will expand and cause a net curvature away from the impact. Obviously, a lead air gun pellet will not move much steel, but the roughness you noted would be the result of peening the surface. With enough pellets over time the overall curvature will become noticeable.

BTW, McMaster-Carr is an online source I use for a lot of tools and industrial materials. They have no minimum order and a fairly extensive variety of foams and rubber sheets:

http://www.mcmaster.com/

Roger

[Gwhite]

Thanks! I think the spreading action of the pellet flattening may also stretch the surface a tiny amount. 10,000 pellets later, and odd things happen...

I'd already checked into McMaster. They have 410 "abrasion resistant" stainless steel sheets, which should be harder & stiffer than the original galvanized steel. If I want to get fancy, I could even have it heat treated to make it really durable. They also have 2" thick polyurethane foam in three stiffnesses. All are available in 12" square pieces, which should be pretty close to the final required size.

I think part of my problem is that I'm shooting 10 or 20 pellets per target. The first shots hit the plate with a nice paper disk on the nose, and can't stick. It's the ones that go through the same hole later that are probably sticking. Because the trap was designed for air rifle where 1 shot per bull is the norm, there wouldn't be as much of an issue.

[RandomShotz]

Actually, abrasion resistance is more a measure of toughness than hardness. When you estimate the thickness at 50-60 mil, that suggests a 16 ga plate which strikes me as rather thin. I'm not sure about heat treating a thin plate like that. Small pieces can be done with a torch if you know what you are doing, but it will be difficult to heat treat a thin 12x12 sheet uniformly that way and sending it out may not be economical.

4130 might be a better choice, since it work hardens - the more you hit it, the harder it gets - McM-C p/n: 4459T31. Still, if there is room for a slightly thicker plate, then that will probably increase durability more than selecting a particular steel.

And the foam probably affects how much the steel is peened depending on how much of the energy it absorbs.

My hunch is that there will be more than a few thousand impacts before there is a noticeable bow no matter what you select

Let us know what you settle on and how it works out.

Roger

[pgfaini]

The pellet trap I built and have been using for about 20 years, uses the weight of the steel plate 1/4" thick, to absorb the impact without any rebound, since pellets are dead soft. The box uses 3/4" plywood for the front and back, and 1"x5" boards for the frame. The steel plate, about 5"x7", is screwed to the back. With the 3/4" thick front, hinged on the bottom, I was able to fabricate a target holder, much like the slide clips on a microscope, by drilling a hole near each lower corner of the pellet opening, a square at about the 6 ring, and using .090" music wire, bend them into an "L" 6"x1-1/2", and insert the 1-1/2" end into the holes, which are a tight fit with the wire. The 6" ends of the wire have small loops turned into them, as knobs. The targets are easily slipped under the clips, which hold both sides snugly. I wear a dust mask, when emptying the pellet and paper waste, about every two years. This is added to my cast bullet lead stash.
I'd suggest you replace the thin plate in your trap with something heavy enough to flatten the pellets without any rebound due to flexing.

Paul