I've bedded my fair share of rifles but I have never really grasped the reasoning behind only bedding behind the lug. Why would bedding the whole thing hurt accuracy?

Bedding only behind the lug prevents any any extraneous particles from allowing the action to seat fully in the inletting, which can definitely affect accuracy. Since the rear surface of the lug is what actually presses against the inletting during recoil, this can work pretty well.

On the other hand, in many actions fully bedding the lug prevents the front of the action from flexing during firing--at least theoretically.

I know more than one custom gunsmith who beds both front, rear and sides of the lug, but leaves some space at the bottom to prevent particles from allowing the lug to seat fully.

When the lug is part of the action you want the action to stay or settle back to the exact same spot.

If there is no room in front of the lug it may not be able to settle or may work it's way up during firing.

To me, bedding the action and a couple of inches of the barrel shank helps stiffen the action. You can see this, stock in padded vice with wet glass. If you flex the barrel back and forth, you can see the wet glass bulge as the action flexes. Once the glass sets up, there is no flex.

Gotta see this to believe it.

DF

i have heard that many times, but then why are benchrest rifles, with very heavy barrels, typically bedded with the barrel completely free-floated? And the most accurate factory rifle I've ever owned was a Rem. 700 varmint-barreled .223 with only the back of the lug bedded.

There is a reason to bed the first couple inches of the barrel on a 98 Mauser, because the front action screw is in the middle of the lug. When the screw is tightened, the front of the action can bend if the barrel isn't supported. But most bolt actions have the front action screw behind the lug.

A recent build, a 7RM MkV/Brux/McM Woody Express, is bedded like that per my smith's recommendation. And it shoots great.

Either way, bedding the full action seems to me to help stiffen the action. The shank as part of the bedding may help with the stiffness. But, my smith said the full free float to the receiver is better for even vibration harmonics vs. the shank being involved.

I guess,old habits are hard to break. My latest build, a 26 Nosler 700 BDL, is bedded the old way, full action with 2" of shank. And, it shoots good, too.

DF

I think The bigger problem with bedding is that people put stress on the action by putting too much torque on the screws when doing the bedding job.

Put that on top of bedding up into the barrel change and things can't get out of whack quick.

Spotshooter,

Oh, I've seen that too, even from supposedly professional gunsmiths.

I pillar mine, and take great care to have nothing in a bind especially the box mag, making sure it moves some.

DF

MD,

Yes Sir, I learned that in Gunsmithing class from one of the best smiths in then industry. Best class I ever took.

I pillar mine, and take great care to have nothing in a bind especially the box mag, making sure it moves some.

DF

Does stressing or flexing really matter so long as it stresses or flexes exactly the same way every time? My objective in accuracy bedding is to get that precise repeatability, not that I'm an expert by any means. Neutral bedding is desired but not an imperative. Insofar as bedding behind the recoil lug only, bedding the sides and front make for more contact points which makes for more potential variables. If you consider the stresses in firing they are mostly back and in rotation vertically. Other forces like twisting are relatively minor and should be handled by the friction between the stock and the action - if properly inlet or bedded and torqued. No?

In the final analysis many bedding methods seem to work just fine.

As an aside one benefit of bedding is to couple recoil forces from the lug into the stock equally across the entire area of the lug. Wood is not homogenous in compressive strength. The weaker parts yield first and more force is borne by the stronger parts. You can get splits doing that.

It does.

a few common issues are the release agent being too thick, which results in wiggle room, and varied friction points.

think about the way you move a springy piece of metal, you clamp it down, and then bang it and get it to move and hold. That's something you really don't want here.

Getting a stress free, now wiggle where it counts bedding job is the key to getting a rifle to settle down and run.

Spot

I think we're talking about two different things. Take the M98 action mentioned above and how bedding the shank of the barrel relieves stress on the action. IF the action is perfectly bedded (meaning no change in the action/stock interface from shot to shot) with the barrel free, does stress on the action affect accuracy SO LONG AS the stress on the action is the same for every shot?

Now I mean this as a general example regarding the state of the action from shot to shot. Floating at the shank means the barrel is a longer moment arm and forces can as a result cause more variation at the muzzle. Shorter is stiffer. So normal shot-to-shot variation in forces causing the barrel to vibrate may (may) cause more variance in how the muzzle reacts.

I bed both behind and in front of the lug however when I put the rifle back together I put a tiny bit of grease on the lug and have no problems at all. My bedded rifles have all shot under an inch and most of them are factory barreled rifles not customs.

Shod

JB pretty much nailed it in his first 2 posts...

Even on the 98 Mauser, I prefer to float the whole barrel because there is enogh receiver ahead of the lug for support. On a Sako or Howa, on the other hand,I'll bed a short section of barrel because the lug is at the extreme front of the receiver. I like to clear the bottom of the lug on virtually everything and the bottom, front, and sides on a Remington. For at time, I bedded the sides of the lug on Remingtons in the belief that it would prevent twisting of the round receiver in the bed from torque. I really can't say that it did any good. Since clearing everything but the back of the lug had worked so well, I reverted back to that technique and have been happy about the choice. GD

At KofO I was taught on walnut to bed all around the lug up to belted magnums which then it was necessary to relieve at the bottom of the lug. On the real big heavy recoiling rigs relieve infront of the lug also. These variations were for protecting the stock only. Bedding out the first couple inches of barrel, the chamber area, was never detrimental. But we only did that thousands of times - so it mighta been a fluke. The heavy barrels don't benefit from that, because they're heavy. IMO, it's not done for vertical support, its for stability where a bit of flex, where the big boom happens, translates to the most change at muzzle, whip. I've also developed the opinion that it doesn't have to be pretty and perfectly filled to the rails and it doesn't have to be uber-specialty glue. Just get some Loctite gel, which is readily available and very high quality, and dump it in there with the intent to keep everything consistent and neutral. #1 Acquire rifle, #2 float barrel, #3 make fit neutral, #4 bed lug area without glueing action to stock, #5 mount optics. Then you're on your own.

This is true but the other unspoken fact is that some bedding compounds shrink and lose the mirror reverse fit.

There is a reason Devcon Steel is popular with those that have a lot of bedding experience, it is proven and reliable. I have also used Devcon Aluminium at it was equally good though I didn't own the rifles as long to say whether it was still good after 20 years, like I have been able to quality with Devcon Steel. As the aluminium version is to provide a color change option, it should/looks to be just as good.

John

One reason is that a lot of bench rest rifles are switch barrel rifles and bedding under the barrel/chamber would screw up the ability to change barrels.

Who torques screws when bedding? I was taught to use headless screws to center in pillars or at least in stock, and to wrap the action to the stock with electricla tape or rubber cording, but to never use headed screws or put toque on them?

Am I missing something?

Bed only the rear face of the lug for me. Has worked fine so far.

Yeah, me too. But many people like to make things complicated, especially with handloading and rifles, I suspect because they can then spend more time doing it, away from the "real" world.

I've done lug-bedding both by using screws turned in just enough to hold the action in the stock, and by wrapping the action in rubber tubing, and gotten equally good results. The biggie is to avoid "torquing" the screws while the epoxy sets. Have had to correct more than one supposedly professional bedding job that as evidently done by somebody with a torque driver they simply had to find a use for.

pullit,

Yes, I know that. But it also demonstrates that barrels don't need "support" if most actions are bedded properly.

Based on some experience, I also doubt bedding "support" underneath the rear end of light-contour barrels has much if any effect on accuracy. Though support at the tip of the forearm can have a definite effect on light barrels.

Actually, they glue the actions to the bedding. The action is stable so the barrels can be screwed in and changed out on whim.
John

Why not just bolt the pillars to the action and then glue the pillars in and bed the action in one process?

Just like the more expensive concrete has the steel bars pre stressed in tension while the concrete sets up, likewise the better bedding job has the pillar pre stressed in compression while the epoxy sets up. You may have to make special screws and/or washers and or nuts to make that happen. It was not easy getting a 1/4-32 Whitworth female to compress a rear pillar in a Mosin Nagant.

Here is a home made pillar with trigger relief cut and epoxy grabbing rib cuts. The pillar hole in the stock is tapped to have ribs to also grip the epoxy. The top of the pillar is convex. That cut is done with a boring head to match the radius of the receiver bottom.



Here is a Sav 110 .223 where I have covered the front pillar I made with foam so epoxy will now go down into the pillar. The screws are already torqued to where they will be when the gun is fired.


Here is that 223's first group at 100 yards.

Its always a pleasure clark.

+1.

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JB,
About epoxy at barrel/receiver junction, out a bit, it's not just below but on the sides as well. So it is support, but it's 180 degree support. Flex there, or movement of any kind, would have to translate to movement at the muzzle. Like the fulcrum effect, a little in close is more way out far... Has there been any tests that showed this to be a detriment to accuracy on spoterweight barrels? Ok, or vice-versa for that matter? I hate to think it was intentionally done so many thousands of times without benefit. Surely I can't convince you to try it on a few, same rifle, same load, same shooter, same conditions... But it ain't like it takes an extra glue-up session, just dump it in there. Maybe on some stocks one would have to build a dam with putty or something but it ain't like it's a full-on escape from reality. Just another rifle myth? Insignificant enough that it won't show up on hunting rifle accuracy? Kinda looks nice, especially brown, when you're admiring the innards....

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Curious too if anyone has a reference addressing epoxy shrinkage? I have a wood stocked rifle that was bedded 25 years ago with 3M 20-minute epoxy and it's still a snap in tight fit. Like to see what's been found to work or not. Gentleman below uses Devcon Plastic Steel, says avoid Acra-glass...

I wish I were patient enough to do work like this. He seems to have a clue with the glue.
http://www.6mmbr.com/pillarbedding.html

oregontripper,

I've performed that experiment many times, in at least two different ways. Haven't found any difference in accuracy.

Thanks. Fair enough. I concede, if I do it, it'll be for escape only. Merry Christmas.

Looks like the entire action is taped off. Are you just installing the pillars at this point? Did you bed the action (lug, tang, etc.) after this step?

Just curious - always interested to learn different ways folks do stuff.

Thanks!

I think that is the full-on CF method.

Right. Just the pillars in that step. The barrel is upside down and level in a barrel vise. The stock is put on top, strapped down and leveled. There is still no epoxy behind the recoil lug.


In the next step there is soft epoxy behind the recoil lug and the screws are tight again.

In the end, the barreled action should contact the stock at three points:
1) The front concave pillar
2) The rear concave pillar
3) Behind the recoil lug.

Everything else has clearance.



Then I bought a stock that did not fit, but it was close. It was for a 4.415" receiver [Sav 10 short action].
I have a 4.522" receiver 1972 Sav 110 223 [No one makes anything for them].
I had to mill out the stock for:
a) longer action
b) 1/2" pillars instead of 1/4" screws
c) Bull barrel [not a cow barrel]


I am just an amateur that made up this process for this one gun. That was the first round bottom receiver I ever bedded.
The link further back in this thread shows professional gunsmith Richard Frankin:
http://www.6mmbr.com/pillarbedding.html

Contoured vs. Straight (Flat-top) Pillars
Many factory rifles come with contoured (radiused) pillars, and many gunsmiths prefer to use these. The idea is that the contour provides a better fit with the bottom of round actions. Richard has tried contoured pillars and doesn't recommend them. He explains: "Most of the contoured pillars don't really match the contour of the action anyway. And every action is slightly different. Even some of the most favored custom actions aren't exactly the same from one unit to another. What happens when the contour or curve of the pillar is too narrow is that the action touches just the extended top edges of the pillar (left and right of center). That is not as solid as when the action contacts the center of the pillar where the action screw runs. (And those sharp sides of curved pillars tend to point-load and dig into your action.) Also I feel you get a better match of the Devcon to the action with flat-top pillars. What you want is the bedding compound to cradle the action all the way around. I've found this works best with flat-top pillars and a very strong, hard compound like Devcon that doesn't squish down or shrink."


So he supports the receiver with a knife's edge contact with the flat topped pillar to support the tight screw force, and then keeps the receiver from rolling in reaction to rifling torque with epoxy between the stock and receiver sides.

I did not go through a calculation of how much 1/4 -28 screw with 100 inch pounds 2000 pounds of axial thrust, 1000 lb at 50% efficiency.
http://www.engineersedge.com/calculators/torque_calc.htm
The 1000 pounds is divided by the two ears of the concave pillar top = 500 pounds per ear, calculate the bending of the ear with the preload...

Instead of doing all that mechanical engineering work to find the ideal undersized concave radius, I adjusted the boring head on scrap pillars until it fit on the bottom of the receiver so tight that with a flashlight behind it, no light came between the pillar and the receiver.

You might be better off doing it like the pros.
I did do another round bottom rifle, a Rem700 7mmRM, the same way with concave pillars. It shoots better than I can.

Thanks a bunch for the very detailed reply!!!

Excellent thread! and with nary a discouraging word!!!

Happy New Year!!

These bedding threads always get interesting. There's not just one way to glass bed a rifle. So many ways to skin the cat on this subject. My best advice is keep it simple. Some guys go out of their way to complicate things. With glass bedding, you don't want complications...

Yeah, what's interesting is there have been posts here by good gunsmiths and others who know what they're doing describing different methods and materials. Obviously they all got good results with their favored method. Wouldn't be hard to conclude craftsmanship and familiarity with the bedding compound is more important.

Agree that simple is good, but isn't it always so? Less to screw up or go wrong. (I'll take all the advantage I can get, too often I need it. )