PDA

View Full Version : Bedding question


DBotkin
March 6, 2008, 09:43 PM
I'm continuing the rebuild of my Remington 700. The stock is far enough along I'm going to bed the thing now. I installed Holland pillar bedding posts, and have a Brownell's Acraglas kit ready to go. I'm doing the modeling clay and mold release now.

My plan is to bed the recoil lug and the barrel up to the end of the major taper (it's a sporter barrel), and let the rest of the barrel float. My question is, with the pillars, is there any advantage to bedding the action as well, or should I just do the epoxy bedding from the mag well forward? Doesn't seem like there would be much point to getting carried away with the epoxy (never did figure out why people call it "glass bedding", it's just epoxy).

5whiskey
March 6, 2008, 09:52 PM
Yes, bed the action. That's all I ever bed... the action up to the recoil lug. I leave the entire barrel floating.

Joey

EDIT: I will give my reasoning, which may be feeble but has worked for me to date. I think you especially need to bed the action when you install pillars. The reasoning is that without pillars the action generally rests directly on the stock material. Granted this material doesn't have a form fit finish with the action but under normal torque it should make considerable contact in several places.

When you install pillars, you often take out slight "crush" effect that can cause the action to contact the stock adequately. Sometimes the action will even ride on the pillars making very little contact with the stock material. This basically makes the action bear on a very small point... the surface of the pillar. Recoil could cause the action to rock on the pillar, which will reduce accuracy. Bedding here will provide a nice uniform surface for full contact all around the concave of the action.

Make sure you bed the surface the recoil lug will faces into. If there is an uneven gap between the stock and recoil lug this could cause the barrel/action to shift slightly to one side.

I've never bedded in front of the recoil lug because that was how I was taught. I can't give you the precise scientific reason, though I speculate that I was so taught to ensure there is nothing the barrel can vibrate or "bounce" against. Obviously that is very important once you move beyond the chamber area, hence the need to float the barrel, but I suspect a bed under the chamber area wouldn't turn a .5 moa rifle into a 1.5 moa rifle unless you went to far up with it.

Unclenick
March 7, 2008, 10:17 AM
Much of Wheeler's reasoning is correct. If you have a v-block channel for high torque mounting, like the Choate stocks, then you don't need to bed at all. With pillars, you use a loose enough hole in the stock to require enough bedding material that the pillar can self-center around the screw while the bedding sets up. Otherwise you can get the pillars slightly too close together or slightly too far apart and introduce flexing stress on the action.

Personally, I fit pillars ahead of bedding by leaving them a little too long, and using high spot blue and a scraper to give them a mating fit to the action. Then I use my lathe to final trim the bottom to correct length. At bedding, I make a small (1/8" or so) dam from clay rolled into a string, and work it in around that mating contact edge at the receiver to keep the bedding out of the contact point.

Keep in mind that the pillar is there to keep the stock screws from applying compression to the stock and bedding, which can otherwise take a set over time in a wood stock. They are not a substitute for the bedding at the sides or back at the tang of the receiver. Those places can develop flexing moments and whipping action. If you are using a conventional flat end pillar, there is nothing to stop that slight whipping, which can make the back of the receiver shift a few thousands on the pillar after each shot, unless you have that bedding at the back of the receiver, too.

As to the recoil lug, I was taught to bed the back face and a little of the back edges and bottom of it, but to leave the front of it clear. That scheme keeps it centered and recoiling back a against a surface broad enough to limit rearward recoil force on the pillars and yet be able to be removed from the stock without stressing the rest of the bedding. It can also expand forward if the gun gets really hot.

Bedding the first portion of the barrel does help some guns center in their bedding a little better and may help damp vibration in some. I would not do it unless you are dissatisfied with the gun's performance and are looking for another way to tweak it. You can always add that portion of the bedding later. In most instances all you will accomplish is adding weight to the gun, though a few will respond positively. When I was younger, I did that with a steel-filled bedding to what had been a nice Mauser B&C Carbelite stock and basically destroyed its weight advantage. I tried to whittle it out, and being less experienced at the time, went on to make the stock cosmetically unacceptable. The gun shot no better with all that bedding than it had with conventional action bedding. Lesson learned.

An alternative bedding approach that Bruce Baer developed is to sleeve the barrel back where you are talking about bedding it. He is doing this to long range magnum target rifles, so he can get a straight cylinder that is rather longer than you have for his sleeves. The sleeve is glued to the barrel and engaged to the stock. The whole action and trigger group float. This seems to work well with a rigid custom action, but I wouldn't be trying it on a sporter action because of whipping.

The term glass bedding is generally a misnomer. Epoxy glass, like Fiberglass, is a glass cloth-based composite that uses epoxy resin instead of the polyester resin in Fiberglass. The epoxy resin is more dimensionally stable and heat tolerant than polyester, so it became popular as a phenolic resin and paper insulating board replacement for printed circuits. I expect that when composite stock layups of epoxy glass became popular for heavy target shooting stocks, the term just carried over to the resin, erroneously, but became part of the vernacular, nonetheless. I suppose you could use epoxy resin impregnated glass mat to fill big gaps in a very loose stock, but it is very hard on cutting tools when you trim it. The conventional filled epoxy bedding materials are better for that, IMHO.

fisherman66
March 7, 2008, 10:24 AM
Great write-ups Nick and Wheeler! Thanks for taking the time to put those thoughts into words.

DBotkin
March 7, 2008, 10:30 AM
Thanks for the input. This is just a rehab on an old friend, not building a benchrest rifle, so I'll skip the sleeve. :)

I have the rifle setting up now with the epoxy poured. I've never done a bedding job before, so we'll see how it works out when I pop the action loose in a couple of days. If it's not right, I have a Dremel and enough epoxy left for a second run at it. I think I can find suitable epoxies locally, too. I just ordered the Acraglas kit because I was ordering stuff from Brownell's anyway; if I were doing it again, I'd use something a little thicker so the stuff would stay where I put it and not run ALL OVER EVERYWHERE. Yeesh. I have a couple layers of tape over the front and sides of the recoil lug, nothing but release agent on the back.

I did leave the barrel alone. I'll probably try it and see how it does with the whole thing floated from the recoil lug forward, but I have read in many places that the sporter barrels usually need some bedding.

fisherman66
March 7, 2008, 10:36 AM
Art used a small roll of wax paper near the tip of the forearm to apply gentle pressure upward to dampen the vibrations. It's totally reversable and worth shooting a couple groups with to see if there is any improvement after the bedding job is complete and you have shot a few groups to see what good it did, IMO.

Unclenick
March 7, 2008, 11:01 AM
Jack O'Conner used a method of placing two shims near the forend of a stock under the barrel at 120° apart. He sized them so the assembled gun applied 10-20 pounds of upward pressure on the barrel at these points. Harold Vaughn describes it in his book Rifle Accuracy Facts (p.p. 78-79, 2nd ed., Precision Shooting pub., 2000), and uses epoxy coated cardboard shims. Paper match stems are what I've seen used. You just try them at different locations along the barrel until you find a maximum effect, then glue them in place. Vaughn says it works well enough to improve group size 20-30% in most commercial sporter rifles.

I bought, at a gun show — NRA convention show, I think — a little steel trough with a Nylon insert on a long screw that ran the length of the trough. The idea was to inlet the stock and glue the trough in. The Nylon insert applied upward pressure against the barrel, and the screw adjusted the Nylon insert's location until you found a sweet spot. I put it in a Carbelite stock on an early ersatz scout rifle with a very thin barrel profile, and it seemed to work about like the O'Conner method. It just cost a little more.

I will add that synthetic and composite stocks will work best for any barrel pressure method just because they are less temperature and humidity sensitive than wood, and less prone to take a set over time. For those reasons, you probably want to loosen the stock screws on a wood stock with this setup when the gun is to be left unused for a spell, thus to relieve that tension until you need it.

5whiskey
March 8, 2008, 12:37 AM
Thanks for the additions to my initial explanation nick and fisherman...

As always I discover that the more I learn, the more knowledge I understand is out there that I don't know. From reading follow on posts I can build on my feeble base of knowledge and perhaps one day be good enough to build rifles for other people and not just for myself...

BTW I had heard before that some barrels/actions DO like contact at the forearm. I haven't played with this any at all, but from seeing your posts I am assuming it's more of a "firm and steady pressure" contact and not a slight touching. Makes sense, slight touching would bounce but firm and steady would likely help keep bounce at bay. Thanks again gents

Slopemeno
March 8, 2008, 12:54 AM
In my experience, Rugers needed forearm pressure. Remington 700's preferred to be free floated.

KEN K
April 6, 2008, 06:32 AM
I bedded a couple of surplus rifles with bondo, yes the car stuff, it's just another form of epoxy, it's nice and thick so it stays were you put it and it sets up fast, in minutes not days. This stuff sets plenty hard and handles the heat fine. I know it's sissy pink but a black magic marker fixes that. You can get it anywhere and its cheap, you just have to have things ready to go and work quickly ounce you mix it up. I just spray the metal with WD-40 as a release agent. I work with wood and have used it for years to repair holes and gouges in wood, you can work it with regular wood working tools.

Harry Bonar
April 6, 2008, 10:58 AM
Guys:
I must be behind the times.
I thoroughly detest "pillars." I always full float the barrel.
When bedding with Brownells Steel Bed I bed only the recoil lug area and if there is a paralel section on the barrel maybe I'll bed 1/2" of that. I don't just float barrels - I get a thick business card clearance there.
I know other bedding methods work but I remember a quote from "The Modern Gunsmith" "Good sound inletting needs no other help - such help is a cover-up for a sloppy bedding job."
Now, I don"t agree with that entirely but I've seen old world rifles, not glass bedded that the recoil lug and all was in great shape. Not differing with you guys - just - well, I don't know?
Harry B.:)