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Bedding Compounds

This is a discussion on Bedding Compounds within the The M14 forums, part of the M14 M1A Forum category; I have been tinkering with and reseraching various stock bedding compounds. My expereince with the M1A is 4 beddng jobs - 3 of those repeats ...


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Old May 29th, 2011, 09:48 AM   #1
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Bedding Compounds

I have been tinkering with and reseraching various stock bedding compounds. My expereince with the M1A is 4 beddng jobs - 3 of those repeats on the same stock before I got it right.

The goal is to lock the receiver into the stock to elimnate movement and to mold the perfect stock to receiver match.

We have come a long way with compounds, but we still aren't quite there.

We have glass, aluminum, steel and titanium. Also out there appear to be ceramic and the elusive carbon compounds.

In no specific order, here are my views:

1. The compounds has to be of sufficent hardness to maintain the fit with all the inherent pounding it is going to take. Some are too soft, allowing the bedding to change. Some are too hard, leading to chipping and cracking.


2. Shrinkage - you want a compound that does not shrink while setting up to the specific receiver. Something with a lot of shrinkage really makes the bedding job a futile effort.

3. High abrasion of wear tolerance - you need something that resists wear. For me, I like to be able to remove the receiver from the stock at fairly regular intervals, and don't want to worry about how much bedding life I am using up by that process.

4. Heat resistence. My personal belief is that this is the biggest sleeper in bedding characteristics. Most compounds in general use are rated for 250 degrees (Devcon titanium is rated for 350). But the temperature rating is more or less a failure point. We have all been to the range on bright sunny days that heat the drak metal. Add the heat caused by firing, and the temperature climbs. We may never get to 250, but we certainly get well over 100. All those heating and cooling cycles have to stress the bedding, and even if you never get to the failure temp, getting even close to that on a regular basis has to cause stress that decreases the bedding life.

It seems a higher temp rating for a compound would increase the life of the bedding job.

As noted earlier, Devcon, MarineTex, acryglass and similar coumpounds all come in with temp ratings of 250. Some shrink more than others. Some are too soft, and some too hard (my experience with Devcon titanium a good example of that). None of these are particularly good in terms of abrasion resistance.

So here is the question - with all the advances in ceramics and carbon compounds, is there something out there that passes these tests? I have never used JB weld for a bedding job, but it advertises that it can withstand constant temps of 500 degrees and has a max rating of 600.

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Old May 29th, 2011, 12:29 PM   #2
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JB weld

If you find something better please let me know. Marine Tex is also excellent, bit tricky to mix, shorter working time....... Art

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Old May 29th, 2011, 04:59 PM   #3
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Art,

Funny how when you do the comparison by looking at those factors, we keep coming back to J-B Weld. J-B Weld has a tensile strength of 3900 PSI; which is 65% the strength of filler metal. (J-B Weld only adheres to the surface, so the bond strength is actually only 1800 PSI). Still stronger than the others. Fro what I can gather, JB is made from epoxy, powered steel, a little chalk filler.

Anyone use this? http://www.cotronics.com/WEB%20SHEET...%20%207032.pdf

I have an email into these guys to check it out.

But it compares favorably to JB.

JB - 500 degree rated, 3900 PSI
RK 454 - 500 degree service temp, 10,000 PSI (but a quick 20 minute working time)
RK 456 - 500 degree, 12,000 PSI (same fast working time)
Durabond 7025 - 1200 degrees, 4800 PSI, No work time listed
Durabond 7032 - 2000 degrees, 5400 PSI, "hardening starts in 60 minutes"

Looks interesting, as long as it bonds to wood or fiberglass, takes a release compound so it does not stick, has low minimum working temps, has no or low shrinkage and has adequate work time (20 minutes is pushing it).

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