Need to replace a rubber buffer on an R55 Benchmark

[Odd Job]

I have two Thompson/Center R55 Benchmark rifles. They both have the same rubber buffer, which is removable and sits at the rear of the receiver.

Here is the receiver with the rubber buffer inserted:

And here is the receiver without the buffer:

On both rifles I have had problems with the rubber distorting and impinging on the bolt to such an extent that the manual bolt catch is hard to engage. Another symptom is when the bolt doesn't come back far enough to strip a round from the mag.
It may well be that some of the cleaning products I use have caused this material to swell, I don't know. But I have had to trim the rubber as a first measure on both rifles. They have both lasted 10k rounds, the one pictured here has gone up to 20k rounds:

Parts cannot be found for these rifles easily. They are no longer made and S&W doesn't provide spares to the public for these rifles any longer.
I want to make my own buffer, which should be easy enough since it is nothing more than a rubber stopper molded to the exact shape of the rear of the receiver.

How should I go about doing this?

 

[LoonWulf]

I would probably use urethane window adhesive for my first try.
Wax the action any where you might get the poly, then dam it up to create a slightly over sized part (id use modeling clay or some such).
Layer in the poly as it hardens while trying to avoid voids
Remove, and cut to final size.

Ive made parts from polyurethane like that before.

 

[Odd Job]

Thanks mate, that sounds like a good plan. Is this the stuff you mean:

http://www.ebay.co.uk/itm/Tiger-Sea...ck-/151665024916?_trksid=p2385738.m2548.l4275

 

[LoonWulf]

Im not familiar with that brand, but it LOOKS ok from my quick research.
Ive always used 3M windshield adhesive, or another one i got at the local hardware store....best to look for 100% polyurethane if going the hardware store route.

There are also two part polys that can be poured in as a single step, but they generally come in larger containers and are more expensive.

 

[Odd Job]

There are also two part polys that can be poured in as a single step, but they generally come in larger containers and are more expensive.

I was just Googling around and found one of those. I like the look of it, will order it now. I will post back when I do the casting.
Thanks very much for the advice!

 

[LoonWulf]

Cool! looking forward to how it turns out.....oh hey watch out for the 2 part Foam ones. Those are not the poly u are looking for.....

 

[Drail]

I would advise making up a test piece and allowing it to fully cure and then glop some of your favorite gun oil on it and wait and see what effect if any it has on it. It could save making a mess in your gun. If you are good with an exacto knife you could make one out of a chunk of Neoprene which is resistant to most solvents and lubes. But test whatever you use.

 

[Odd Job]

Update:

I tried one casting resin which produced a buffer that was too hard, it was more like a rigid plastic than a rubber.
Got another type, a proper casting rubber called Polytek PT-Flex 70 PU and made another buffer. This is the product:



The first one took a long time to make because I cast it to the exact length required in the receiver itself. Used a wax spray release agent which doesn't make releasing very easy. The "dam" on the open end of the receiver I made from a small rubber door stop with the edges sealed with modelling clay. For me to get that rubber door stop to the exact position in the receiver was a lot of work. Here is that buffer, which has been tested to 2000 rounds in two rifles with a variety of cleaning materials:



It remains the same integrity, didn't dissolve or crumble and has maintained shape. All that happened was it became darker. Because the release agent doesn't help it release that easy, I used a wood screw to grab hold of the buffer and pull it out. You can just make out the hole on the buffer where the screw was (nowhere near an impacting surface).

For the second buffer I got a bit smarter. This time I didn't carefully measure it, just made it about 10mm longer than it needs to be. Much faster casting like that. Again I had to use a screw to get it out of the receiver but this time the screw hole is in the 10mm expendable material. So this is the second unused buffer, which I will simply cut to size:



Seems like I am onto a winner!
The material is the right density and doesn't swell or warp, or crumble as far as I can see. It's very dense and won't cut easily with a knife, I will have to get a scalpel to do that trimming. It remains unaffected so far by these chemicals:

Strike Hold
Napier Gun Cleaner
Ed's Red
Otis 085 Ultrabore

I'll let you know if anything changes.

 

[LoonWulf]

Excellent work! Ill have to see about getting some of that rubber, your parts came out much nicer than any ive done.

 

[Odd Job]

One other comment, having cast another two of those and cut one to size: it can't be cut properly with a knife, even if it is a scalpel blade. I found that the best way to get a straight cut is by means of a hacksaw. The rubber is just dense enough to be cut and filed, so that's how I have done it. Seems to work well!

I will post some updates after a few thousand rounds of use.

 

[Jim K]

Another source might be an old tire (tyre?). Cheap, plenty to work with and very tough.

Jim

 

[Odd Job]

The trouble is I can't cut a tire to the shape of this buffer: too complex. That thin rectangular inlet on the buffer needs to fit over a small protrusion in the receiver.

 

[Odd Job]

I thought I would provide an update: after many thousands of rounds, this buffer is going strong! This is the buffer from the other R55, installed at the same time.
All that has happened is a colour change to a deep amber: