How tough is it to bed a stock?

[NesikaChad]

Mark,

Take a good hard look at most pillars that are contoured to match a receiver. The one's I've seen have a rather poor surface finish at this point of contact. That and they aren't always accurate in the radius. This tells me you either have two points of contact at the edges or a single point at the center. Either way your asking a material to yield to another material. Some guys try to make up for this by allowing a thin layer of resin to squish between the stock pillar and action but what ends up happening in most cases? The thick goo of wax used as a release penetrates the resin and inhibits good adhesion. The resin then begins to flake off the pillars. I chose to go the other way by accentuating the amount of resin. It keeps the pillar surface away from the stock so that a .050" thick layer of bedding can take up some of the compression load. The rib down the center takes on the task of resisting any compression. A 1/4-28 fastener isn't going to develop enough tensile load to yield a .125" wide strip of stainless steel that is closely contoured to an action.

The whole idea with bedding is a tension free environment inert to ambient condition changes. The pillars job is to avoid crushing fibers in the stock from the tensile load applied by the screws. That's it.

My pillars have the small rib in the center because it actually allows bedding to match this radius for me. The small point of contact is more than enough to thwart off any distortion caused by the screw loads. All this works together to get a pretty fair mirror image representation of the receiver when it's cast in resin. That's really all were doing here. Making a precision casting of the receiver's outside contour.

The REAL feature with this pillar is the fact that when properly installed it virtually guarantees that the action and barrel are resting exactly on their radius and the stock's "water line". Meaning it's a half in/half out relationship.

No more barreled actions that either point up, down, or sit above/below the stock line.

I've posted quite a few redundant pictures of my bedding jobs, here is another showing all this stuff in a finished state. The bore is enlarged to ensure the screws don't act as recoil lugs. A guy has to engineer some clearances in the right spot on a rifle. Especially with repeaters and when dealing with the transmission of recoil. The stock doesn't absorb recoil. Least it shouldn't really. It transmits it to your shoulder via the recoil lug. The path the recoil takes goes right down the sides of the stock to the grip and then out the back to your body. The sides of the stock are where some of that energy is lost. They spread slightly which means the action continues to move to the rear at a slightly different rate than the stock itself does. Guard screw holes, tangs, and bolt handles need to be tailored accordingly or accuracy will suffer.

It's why single shots are so much simpler to build and probably why they have this mystical reputation for being so much more accurate. I seriously doubt its because of rigidity because a properly built repeater will run right next to a single shot all day long. Too many 700's and P64's on the firing lines at Camp Perry to really dispute this.

 

[MontanaRifleman]

Chad, I really, really appreciate the explanation. I have a good handle on marksmanship, ballistics and handloading (I think) but this is one area that's always been a little fuzzy to me. This statement turned on the light... lightbulb

It transmits it to your shoulder via the recoil lug.

I knew that the action/guard screws were not supposed to touch the pillars or stock but wasn't sure why. I basically thought the barrel/action was tied into the the stock by the recoil lug AND its contact with the stock bed/pillars.

Looking at my HS Sendero stock, the pillars in the aluminum bed are recessed in the bedding area no contact with the action at all. The beddimg block is carrying the tensile load via the pillars and judging by the rub marks on the receiver bedding block, the contact points are on the edges. If I wanted to skim bed the stock, the action would have to basically float on the bedding compound. Any thoughts?

Are those pillars your creation? If so, do you sell them? If not, where can I get some?

Thanks for taking the time to educate me,

Mark

EDIT: If I wanted to get an aftermarket recoil lug down the road, when I get a rebarrel/ blueprint, would bedding now be a bad idea?

 

[NesikaChad]

IMO a good bedding job is the most rewarding, nerve wracking, tedious, and fun job a guy can do to a gun. A close second is threading/chambering a barrel.

That being said its a job best done once and only once as reworks are always a pain in the arse.

As a practice I do not bed a stock until the barreled action is 100% complete. The only exception to that is if it is getting plated, coated, or blued. I bed them first as none of these add enough film thickness to get worked up over.

So, I'd advocate leaving the stock alone until the barreled action is 100% complete. Worst case scenario:

You've bedded this thing and then ship it off to get the action trued up and a new barrel installed. The smith has a big woops and crashes a tool into the receiver ring while facing/threading the action. Now you have to get a new receiver and bed the stock all over again.

If it's worth doing right it's worth doing ONCE.

Hope this helped.

C

 

[Clark]

Pillar bedding and glass bedding make a lower compliance fit between barreled action and stock.

The forward momentum of the projectile and gas causes a rearward reaction in the barreled action.

[Mass of the bullet][velocity of the bullet] + [Mass of the gas] [ 1.5 time velocity of the bullet*] = [Mass of the barreled action] [Velocity of the barreled action] + [% coupling of the barreled action to the stock before bullet escapement] [Mass of the stock] [ Velocity of the stock]

What does all that mean?
If we can get the stock to move with the barreled action before the bullet escapes, then we can count the stock mass in when we calculate how far the gun moves before bullet escapement.

That is why .223s do not shoot any better when bedded. They already have good enough coupling with the low action to stock peak recoil force. AND the barreled action is a larger multiple of the bullet and gas mass.

I like Wagner for pillar bedding Mausers:
turkbed1
turkbed2
Bedding the Front of the Action

I like Russ Hayden for pillar bedding Rem700s:
Rifle Bedding

*I learned from Wagner to wrap the screws in tape in order to center the screws in the pillars.
*I learned from Wagner to score the pillars so that the epoxy would get a better grip.

*It took me a while to figure out that I wanted to score action screw holes in the stock with 7/16-14 tap, after drilling with 13/32".
*It took me a while to figure out that I like Devcon Steel Putty, so I don't have to fight time or gravity.
*It took me a while to figure out that I wanted to make reduced head screws (< 13/32")dedicated for fixturing, so I could pre compress and locate the pillars.
*It took me a while to figure out not to use brass or stainless 3/8" O.D. tubing as pillars, but to use Chrome Moly 3/8" O.D. tubing for pillars. The brass makes dissimilar metals and the stainless is hard to machine on the lathe. You might think Aluminum pillars with ~1/3 the Young's modulus of steel, but ~1/3 the density could be made stiff enough, but it has dissimilar metal problems too.
*It took me a while to figure out that I wanted to wrap the barrel with tape with just the right number of turns to locate that end of the barreled action.
*It took a while for me to figure out that I should assemble the barreled action with the pillars and jack some dummy rounds through it, to make sure I have the correct mate between magazine and receiver.
*It took me a while to learn that rifles with the first inch of the barrel supported with bedding shoot better than those with more or less.
*It took a while to figure out that a good bedding job will have sustain on pure fundamental note it makes when the barrel is struck with a soft object while the rifle is supported at the wrist. If it does not make that sound, chisel out some epoxy and start over. A buzzing sound means interference. A short tone means interference and/or high compliance.

Someone on the internet is talking about synthetic pillars made of G-10, getting the material from McMaster-Carr. It is stronger than steel. I did a calculation on cost to weight saved, and it was way over the $10/ ounce that I nominally pay for rifle weight improvements.



*My father, chief engineer over 150 engineers and draftsmen for 40 years, designed guns with "Hayes Elements of Ordinance" that said to use the 1.5 factor for the powder velocity.

 

[NesikaChad]

That is why .223s do not shoot any better when bedded. They already have good enough coupling with the low action to stock peak recoil force. AND the barreled action is a larger multiple of the bullet and gas mass.

Using this as the theme then it would suggest that the lowly 22 rimfire should be even better as recoil is almost nothing. Three years of building Olympic target rifles for resident athletes at the USOTC tells me otherwise. If you want gold medals you better have a pillar bedding job and it better be done in a certain way otherwise you'll likely kick out flyers and lose points.

I know for a fact that if a rifle show's signs of vertical, or round groups that are spread, or has an orphan shot, more often than not a good bedding job will make the bulk of these issues go away. This is assuming of course that the ammunition is right and all the other components are doing their part as well. It also provides a foundation for the rifle that is inert to ambient changes in weather. All the surface contact in the world doesn't mean anything if the stock inlets twist up like a pretzel when it's wet and muggy outside.

There are forces at work here that are above and beyond just the transmission of recoil.

As stated, bedding a gun won't polish a turd, but a good gun will become great and a great gun will become exceptional. Regardless of caliber.



Good luck.

Chad

 

[Clark]

Using this as the theme then it would suggest that the lowly 22 rimfire should be even better as recoil is almost nothing. Three years of building Olympic target rifles for resident athletes at the USOTC tells me otherwise. If you want gold medals you better have a pillar bedding job and it better be done in a certain way otherwise you'll likely kick out flyers and lose points.

I know for a fact that if a rifle show's signs of vertical, or round groups that are spread, or has an orphan shot, more often than not a good bedding job will make the bulk of these issues go away. This is assuming of course that the ammunition is right and all the other components are doing their part as well. It also provides a foundation for the rifle that is inert to ambient changes in weather. All the surface contact in the world doesn't mean anything if the stock inlets twist up like a pretzel when it's wet and muggy outside.

There are forces at work here that are above and beyond just the transmission of recoil.

As stated, bedding a gun won't polish a turd, but a good gun will become great and a great gun will become exceptional. Regardless of caliber.



Good luck.

Chad

What is suggests is ritual.
Like ancient Japanese Sword makers, they knew nothing of the scientific reasons for their process, they just did it.
Like so many accuracy rituals, there is plenty of vestigial processes.
It is less work to do something than have a controlled experiment to get rid of it.

And then there are those in the gun business, that are willing to do anything for more money, and make it look like jewelry.

"Welcome to my gunsmithing boutique! We can make benchrest modifications to your long range hunting rifle AND we can do a French paisley concept on your 1911."

 

[KLC]

Here is a pretty good thread on DIY pillar bedding: Bedding Project - Sniper's Hide Forums