Glass bedding?


July 6, 2006, 10:49 PM
Please define and explain glass bedding. How does it improve accuracy?

It sounds fragile... if it is really "glass" being put into the gun, what happens
if the gun takes a shock?

I recently picked up my first bolt-action rifle, and am trying to understand the new terms. While I've been a pistol shooter for 20 years, I'm relatively new with rifles...

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July 6, 2006, 10:57 PM
In the old days, fiberglass cloth was epoxied into the stock. Today's epoxies are tough enough to be used without the fiberglass, but the term "glass bedding" stuck.

The fit between the stock and action is far form perfect. When the action screws are torqued, the action and stock deform. This creates a "spring" that changes the harmonics of the barrelled action from shot to shot.

Bedding with epoxy forms a custom fit between the stock and action and eliminates the "spring" effect. This, in theory, makes the harmonics of the barrelled action repeatable every shot. Repeatability is accuracy.

July 6, 2006, 11:05 PM
I don't think that my new bargain Remington (model 700, SPS) has glass bedding. So, is this a mod that one without technical skills can do easily?

July 6, 2006, 11:08 PM
Back a couple months ago there was an article in the NRA's American Rifleman about do-it-yourself bedding jobs. I think the author said he ended up with the action permanently affixed into the stock and didn't have any holes to put screws into. :D

You could always get a stock that doesn't require custom bedding, like the HS Precision or Accuracy International stocks. The barreled action bolts directly onto a big aluminum chassis block that runs the entire length of the stock on the AI.

Thin Black Line
July 7, 2006, 07:53 AM
+1 on the HS Precision bedding block. If you have a standard action/barrel
this will be your best bet.

I used glass bedding on a ruger 77v in a McMillan stock. There was not a
bedding block molded into it, nor did I want to do pillar bedding since it was
cut to fit the action as is. However, there was still a little bit of a gap
--especially around the rear tang. This would have caused major play
due to recoil and affected accuracy. I glass bedded it and consistently
did sub-moa with handloads including hole in hole. BTW, I like the solid
feel of the McMillan over the HS.

If glass bedding is done right, it is nearly as strong as steel. You can do
this job yourself, but I would suggest practicing on scrap wood/metal before
you try it on your firearm. Think of this more like painting a portrait rather
than caulking a bathroom when it comes to application. A little goes a long
way. Be sure to use the release agent and don't get any of the bedding
compound in the trigger mechanism, safety, mag well, etc. It literally just
provides a "bed" for the *receiver* (up to the sides where it becomes
exposed outside the stock). I've seen some people recommend doing the
first couple inches under the barrel as well, but it seems to me that would
mess up the barrel harmonics. I did not do that on the 77V and the results
speak highly of leaving the barrel like a tuning fork. :D

July 7, 2006, 08:28 AM
Bedding block or not, you may get an improvement... Smear your action with Johnson's paste wax, with the screws in it, also smeared. Cover the surfaces in the stock with epoxy, place the action in, and let it cure. Should pop right out. Dremel the epoxy as needed, and drill the screw holes a little.

July 7, 2006, 08:36 AM
Here's an excellent article about bedding an action and all the steps involved:

July 8, 2006, 01:33 AM
I have the standard HS Precision stock for a Rem 700, and just finished bedding it. Although it wasn't really necessary, I did the whole action rather than just front and rear, and initial tests seem to show a nice improvement.

I can post pictures etc if anyone's really interested.

September 10, 2006, 10:08 PM

The square is 1", distance was 125yds. Identical (as much as possible) HS stocks, one of which was bedded. I shot with the original stock, then unbolted it and swapped in the new one. Conditions weren't great, and the test was haphazard, but it confirms what I've seen at other distances etc.

September 10, 2006, 10:22 PM
The 'glass' is the glass fibers added to the resin to reinforce it. Make sure every bit of metal has release agent on it !! Some just glas bed the receiver but others like myself bed the receiver and about 2" of the barrel. With a proper bedding job the rifle is made more stable against moisture and temperature changes .Made more rigid which is important for accuracy.If I take the barrel and receiver out of my stock and return it the point of aim doesn't change nor is it necessary to fire a few rounds to "seat" the receiver in the stock.

September 18, 2006, 02:54 PM
Does it matter if the stock is wood or synthetic? I have a wood stocked Savage bolt action rifle that I'm considering bedding.

September 18, 2006, 05:04 PM
is fine. Did it with my 03A3, got great accuracy results.

September 18, 2006, 06:00 PM
Thanks for posting the pictures, Jonathan.

Can anyone else provide some figures or photographic evidence for the improvement they saw after bedding? I will be bedding a thoroughly ratty Mosin-nagant M44 into a heavily chopped ATI stock (this is my 'home gunsmithing practice' rifle) and would like to know what accuracy improvement I should expect.

This is the same rifle I will be re-crowning (the counterbore has been worn out by a cleaning rod it seems- rounded rifling edges) and doing trigger work on. The best groups I get out of it are around 4 MOA with Wolf 200 grain SP. I'm hoping to get around that with surplus (usually around 8 MOA right now) after this work is done.

Edit to say: I'll be threading the barrel for a muzzle device too. After removing the bayonet adapter and sight assembly my groups opened up quite a bit. I remember someone saying that Mini-14 accuracy could be increased by putting a flash-hider on the end, changing the barrel harmonics a bit. I'm willing to give it a try, and a big ol' AK-74 brake just looks awesome on M44s. :)

September 18, 2006, 06:02 PM
One thing's for certain, I won't be, er, bedding my action until after hunting season. I'm all sighted in and don't have time for another trip to the range :)

September 19, 2006, 02:03 PM
I don't have photos. My 03A3 is a 1943 2-groove GI barrel. In a sporter stock it gave me 2" 100 yd groups. After bedding, I get 1/2" to 3/4" groups, and I think the limitation is my eyesight. I use a fixed 4X Burris scope.

I was careful to keep contact with the recoil lug only on the rear face, not sides or bottom. I also opened up the channels for the action screws, so they don't touch wood or bedding. Barrel is free-floated.

It's easy to do. Go for it.

Thin Black Line
September 19, 2006, 02:15 PM
Can anyone else provide some figures or photographic evidence for the improvement they saw after bedding?

Sorry, don't have pics nor the pile of cash that was paid and I later spent
after selling the Ruger which did hole in hole. :D

September 19, 2006, 02:32 PM
Remington 03A3 1944,200yd X ring shooter without glassbedding.Sometimes glassbedding can be a henderence instead of a benefit,depending on the weapon.

September 19, 2006, 03:14 PM
I did it to my first .22 without ever having seen a bedded rifle in person. I just searched the web and got all the info I needed. Pictures are priceless in doing this. I got some brownells acra-glass and bedded my marlin 25n. It cut group size by nearly 25 percent, and combined with the free floated barrel groups were round instead of oval. Also when I pull down my rifle, the rifle still needs to be re-zeroed but its a small amount compared to before.
You will have no problems doing this with a wooden stock, in fact some say bedding is easier on a wood stock. Think of glass bedding as more like epoxy than anything else. On some magnum rifles they add steel shavings to this epoxy to make it stonger, but this is rarley needed.
Unless this is a high dollar rifle, I am confident that you will be happy doing it yourself and learning as you go. If youve got a rimfire around, give it a try too.

September 19, 2006, 09:26 PM
I'm another guy who did a successful bedding job without seeing one in person first. Look online for pictures. Bonus points if you can find pictures of your rifle being bedded.

Two things I screwed up: first, I opened up the hardener, measured it out, then went to measure out the resin, but instead used another measure of hardener, mixed it up (thinking that the two just looked similar) put it in the stock, set it to dry, then wondered why it never hardened. I cleaned it out, remixed the epoxy properly, and it turned out great. Lesson learned: hardener and resin look different.

The second thing I screwed up is on a mauser (sporterized vz24), I didn't fill in the indentation at on the front trigger guard screw pillar with clay, so the trigger guard is now permanently part of the stock. It's not as bad as sticking the barreled action to the stock, but dumb nonetheless. Lesson learned: make sure you fill in all notches and groves and other "terrain" with some clay before applying the release agent. (And don't forget that either)

If you're careful, read the directions, read other people's directions, etc. until you understand what you're trying to do and don't get cocky (I remembered to fill in that indentation on the first rifle I bedded, but rushed the second), you'll be fine. (And, if your rifle is really nice, you might want someone else to do it for you, learn on a cheap rifle. The one I did first cost me $100)

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