How thick should bedding compound be?

C

center22

New member
Today, I had an opportunity to check out a professional bedding job on a buddy's RFBR rifle. I was surprised to see that the Devcon coating was only about 1/32nd in thickness on average. A nice smooth compound layer, but in one area I could see the wood grain peeking through. The XIII action bolts directly on top of the aluminum pillars too. Is this considered normal or good workmanship?

PS: When I do a bedding job on my personal rifles, my goal is to put in at least a 1/8" to 3/16" layer of bedding compound. Lately, I began covering over the aluminum pillars with Devcon, so that the action does not make direct contact with the pillars themselves. Would like to hear from those that do this work professionally, or have experience at it. Thanks in advance, ... John


Posted this on another website as well.
 
If you take into consideration that there is shrinkage in the material when drying, thicker applications will likely experience a larger degree of shrinkage impacting the bedding fit. I would think the thinnest, functional layer would be best.
 
Generally, I believe that pillars should not be metal to metal with the action, and that thicker is better for bedding compound, as long as what is used is something that will not deform under heat and pressure. This is not to say that the difference would be noticeable in many situations where the total quality of the build, quality of load workup, and manner and equipment used to shoot may entirely mask any difference. Accuracy is a weakest link thing, and I find that it is very common to find that shooters are worrying about some relatively small factor, and ignoring several larger ones. BTW the proper way to check a bedding job is with a dial indicator and magnetic base. How does your friend's check out using this method?
 
Just A Thought:

Boyd - Nice Post!
Not everyone has a Dial Indicator but old farts like me have an Accurate Torque Wrench.
A 'Shade Tree Way' to check beading is to is to torque both front & back action screws to maybe 10 or 15 lbs.
Now put your finger at the front of the forearm and barrel and slowly loosen and tighten the action screws.
If you feel it rock in the bedding then you probably have a problem!
Actually you do not need a torque wrench - Think - Sung, Tighten & Loosen the action screws & feel for rock or roll!
Doug

PS: I am sure a lot will disagree with me but I never let the pillars touch the action & that includes any bedding on top of the pillars.
 
Boyd Allen said:
Generally, I believe that pillars should not be metal to metal with the action, and that thicker is better for bedding compound, as long as what is used is something that will not deform under heat and pressure. This is not to say that the difference would be noticeable in many situations where the total quality of the build, quality of load workup, and manner and equipment used to shoot may entirely mask any difference. Accuracy is a weakest link thing, and I find that it is very common to find that shooters are worrying about some relatively small factor, and ignoring several larger ones. BTW the proper way to check a bedding job is with a dial indicator and magnetic base. How does your friend's check out using this method?QUOTE]

Boyd,

I do own a dial indicator with the magnetic base, which I use when setting up work on a lathe. Would you kindly explain the process - "How one checks the bedding using it". Thanks.

My friend purchased this rifle used and has had issues with un-explained flyers/flippers plus overall accuracy for a long time. Attempting to assist him in tracking down the problem(s). Thanks, ... John
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Attach the magnetic base to the bottom of the barrel just in front of the forend and position the indicator so that it's plunger is contacting (slightly preloaded) the bottom of the forarm tip, and its travel is at a right angle to the bore, then do what Doug described. You don't want .000 movement because that is an indicator that something is not free to move, but you do want .002 or less. I have done the fingertip method, but for fine work, I do not think that fingers are as sensitive as a dial indicator, when it comes to very small movement. If you can feel movement with your fingers, you definitely have an issue that needs looking into. I Prefer to grip the stock and action, through the middle of the action with one hand while tightening and loosening screws with the other. Of course this is done with the rifle resting on its butt , with the barrel vertical. If you have the barrel leaning back at the muzzle a little as you loosen the front screw the weight of the assembly will pull it back from the bedding, which is why I hold things with my hand to support it enough so that this will not happen. Play with this a little and you will develop the necessary technique.

There are a couple of other issues that your friend should consider. Action screws should not touch the insides of their stock holes (or even be close to them. Also, a friend was recently driven a bit crazy by what turned out to be a scope issue. The scope is a 36x Leupold that had just come back from service with a note that they had overhauled the objective assembly. Evidently their testing did not include the turret assembly. Has your friend tried another scope. This would be a common source of his sort of problem. Getting back to bedding, there should only be one surface that acts as a recoil "lug" in a rifle's bedding. If there is more than one, the most suitable one should be kept for that purpose, and the rest trimmed back so as not to make contact. Depending on how it was done, bedding can look very good and not be.
 
Boyd Allen said:
Attach the magnetic base to the bottom of the barrel just in front of the forend and position the indicator so that it's plunger is contacting (slightly preloaded) the bottom of the forarm tip, and its travel is at a right angle to the bore, then do what Doug described. You don't want .000 movement because that is an indicator that something is not free to move, but you do want .002 or less. I have done the fingertip method, but for fine work, I do not think that fingers are as sensitive as a dial indicator, when it comes to very small movement. If you can feel movement with your fingers, you definitely have an issue that needs looking into. I Prefer to grip the stock and action, through the middle of the action with one hand while tightening and loosening screws with the other. Of course this is done with the rifle resting on its butt , with the barrel vertical. If you have the barrel leaning back at the muzzle a little as you loosen the front screw the weight of the assembly will pull it back from the bedding, which is why I hold things with my hand to support it enough so that this will not happen. Play with this a little and you will develop the necessary technique.

There are a couple of other issues that your friend should consider. Action screws should not touch the insides of their stock holes (or even be close to them. Also, a friend was recently driven a bit crazy by what turned out to be a scope issue. The scope is a 36x Leupold that had just come back from service with a note that they had overhauled the objective assembly. Evidently their testing did not include the turret assembly. Has your friend tried another scope. This would be a common source of his sort of problem. Getting back to bedding, there should only be one surface that acts as a recoil "lug" in a rifle's bedding. If there is more than one, the most suitable one should be kept for that purpose, and the rest trimmed back so as not to make contact. Depending on how it was done, bedding can look very good and not be.
Click to expand...


Boyd,

You provided more helpful information than I would ever have anticipated. I'm sure this info will be of benefit to many others. My friends scope is a 45X Leupold and I'll have him try another scope. Thanks again for all the valuable advice. John
 
Action Screw Thread Length:

I have found this to be a problem area, generally, with custom made rifles. Why Smiths are so skimpy on threads is a mystery to me. I have found the lack of threads on, particularly the front action screw to be a significant problem over the years. I cut two or three extra with a die when I think there could be a problem. One must also be sure the screws aren't bottoming out in blind holes as well, another area of concern. As bedding shrinks, screw length can be a problem.

P
 
As bedding shrinks???? I suspect Devcon is likely the most widely used compound. The published shrinkage is .06% there Pete. I'll give you a case of ELEY if it's possible for you to measure how small that is on a 1/4X28 screw thread , or any other popular size.
 
Action Screws

Look closely at the Action screws!
Make sure they are CENTERED in the Pillars with some clearance & Not close to bottoming out in blind holes.
If you do not know how to check then I will try to explain further?

One further thought is to check horizontal movement with your Dial Indicator!
Vertical I can live with .003 but horizontal should probably be less than 002 - think nil.
 
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Dollar Bill Test?

John - This might be a stupid question but did you do the old Dollar Bill test??
 
burtona said:
Pete, take the bet on the case of ammo, as assuming 1/4 inch thick bedding a shrinkage of .6 % would be 1.5 thou. You can measure that with a simple Chinese built dial caliper.
Dave
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That's wrong. The shrink rate is .06%, or .0006" per inch. So a .100" thick layer will shrink by .00006" That's 6/100,000th shrinkage. I want a set of THOSE calipers.:D

Even still, a uniform thickness is what I like to see, so I mill to that approximate , but uniform depth.
 
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burtona said:
Pete, take the bet on the case of ammo, as assuming 1/4 inch thick bedding a shrinkage of .6 % would be 1.5 thou. You can measure that with a simple Chinese built dial caliper.
Dave
Click to expand...

I will, however, throw in a free 6th grade math class for you.
 
mwezell said:
That's wrong. The shrink rate is .06%, or .0006" per inch. So a .100" thick layer will shrink by .00006" That's 6/100,000th shrinkage. I want a set of THOSE calipers.:D

Even still, a uniform thickness is what I like to see, so I mill to that approximate , but uniform depth.
Click to expand...

So, as a pro, what do you figure, that's a screw head that goes from, say 12 o'oclock to about 12.01?
Hardly what I'd call a change in holding ability.
 
On the dollar bill test, it has been obsolete for decades. A reliable barrel float, for accuracy work, requires much more room than that.
 
Boyd Allen said:
On the dollar bill test, it has been obsolete for decades. A reliable barrel float, for accuracy work, requires much more room than that.
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Agreed ... recently pillar bedded my X3L barreled action into a Lidgard Zebrawood stock. When tested, I can easily slide five one dollar bills (when held together) between the barrel and stock channel. Brent does very nice work.

Haven't had an opportunity to test the bedding in my friends rifle, but hope to do so by Wednesday. Will update. John
 
Doodaddy said:
Why is that? Heat?
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Particularly with wood...it moves. Also, as we know, the barrel moves when fired, as do scopes. Ever seen a scope very close to a barrel? I've shown customers the mark on top of the barrel left by the scope and barrel coming into contact with each other, and still be able to slide a $ bill between the two, freely. The look on their face is one of enlightenment. The mark looks like a small wear mark. That has to be hard on optics but also tells us that stuff moves when a 60,000psi explosion happens in there.:eek:

Obviously, the person claiming on another site that the muzzle can only move about a half thou has never seen this and it raises question to his claim.
 
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If I am floating a wood stock, and want to preserve the appearance of some degree of fit, I use what amounts to the thickness of a matchbook cover on on the sides, with more underneath, and pay close attention to the gap being of consistent width along its length and on both sides. I also try my best to keep the top edges of the barrel channel sharp. For pure target work, I like quite a bit more room, particularly if the action is glued in, where clearance to move the largest probable shank diameter and length forward in the stock as the barrel is removed is required.
 
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