A few more bedding questions

[goodgorilla]

For the barrel, do you tape it up before or after you remove stock material? I was thinking that I should tape up the barrel before I remove stock material, so that the thickness of the tape at the front would hold the front part of the barrel at the original height after bedding. Another thing that I am confused about that part is the thickness of the tape, a bedding video I was watching said that the damn in front of the recoil lug area needs to be higher than the support at the front of the barrel, to me that doesn't make sense. My other question is about removing material from the recoil lug area, most people I have seen write about it said that you should remove material behind the recoil lug, but what about underneath the recoil lug?

 

[DCS]

"original height" may be a secondary priority. The highest priority is to have the two primary contact points between receiver and stock on exactly the same plane. On the factory rifle, install the gun in the stock and tighten the front screw until it is snug. Then install the rear screw and tighten it snug while holding your fingers on the seam between the barrel and forearm. If the seam expands or contracts, then the stock is applying a bending force to the receiver because the contacts points are not on the same plane. Repeat the test while feeling or observing the seam between the tang and stock.

This test determines whether you will (either) remove some material from the front or rear contact area, or vice versa, add some material to either point, with the ultimate goal of no "seam creep" whenyou tighten the screws. This is easily done with various sanding drums for removing, or shims and epoxy for building up.

Once you have created a flat plane, you can then observe the relationship between barrel and forend to decide whether the barrel is adequately floated by the new flat plane, or if you want to remove some material from the forend. I don's use any tape at this stage. I just eyeball and progressively sand away until I get a combination of good looks and adequate free float gap.
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You can remove a little material from the bottom of the lug slot if you want. It helps with epoxy adhesion.

Put release agent everywhere (I use canned shoe polish applied with a q-tip. I also wet the screws with clp when tightening the receiver into the wet bed.)

Bed the rifle with compound at both contact points. Use clay dams to keep the compound in the desired space. You want a little ooze-out during assembly. Just wipe it off the taped stock as it oozes out. Tighten screws to appropriate torque and let it set.

The goal for the front section is a perfect bed for the receiver (in front of the magwell) and a perfect 3-D slot for the lug. Wrap 3 layers of masking tape around the barrel nut (just in front of the lug). Put release agent on the tape. Place the clay dam such that the epoxy will contact about .75" of the barrel nut area. When the job is over, you will have a 3/4" section of compound in front of the lug that clears (free floats) the barrel nut after you remove the tape. I don't know what "dam in front of lug higher than support" means. Most free float jobs incorporate the idea of zero barrel contact in front of the jug. If you use a really long heavy barrel, you need a beefy receiver, or you may need a full bed or an adjustable (tunable) single contact point in the forearm. But for moderate barrel weights and lengths, FF from the lug forward.

The goal for the back section is a smaller little "pad" bed for the rear screw contact area.

The overriding goal is that the receiver only has one home, and the home does not apply bending force to the receiver. By mating the stock to the receiver, you create a situation in which the receiver always goes back to the same home after each shot.

Nothin to it...after your first one.

 

[goodgorilla]

Most of what you said makes sense to me. But what direction would the seam expand or contract? I would imagine vertical displacement would be natural if your tightening down the action. Also, what kind of displacement would make you want to add or remove material? You just said if you see it move you do either one, but which action do you take for what circumstance? Lastly, when you said to tighten one screw down snug, feel the crease, then tighten down the other side, I thought if you tighten down one side completely before tightening down the other side actually causes a bow.

 

[DCS]

The bow, if it exists, is the problem that you want to remedy with bedding.

Sometimes a new rifle in factory configuration will have no bow. When you get lucky and find one of these, it will pass the aforementioned test. Neither the gap between the barrel and forearm nor the gap between the tang and rear stock area will change perceptibly when you do the test. In this case, the two contact points are on the same plane. You then bed this rifle as is, and the main goal of bedding on this particular rifle is to eliminate "slop" in the fit between receiver and stock so that the receiver only has one home. It can only lay in the stock in one position, even after each "recoil shock".

Other times, the two contact points are not on exactly the same plane, and the gunsmith can see or feel slight changes in the "seam gap" when the test is performed.

If you feel the gap between the barrel and forearm increase, this suggests that the rear contact point is lower than the front. The act of tightening the rear screw is putting a downward bending force on the tang area, with the front screw contact point being the fulcrum. To fix this, the smith would either sand/grind down the stock at the front contact point until the rifle passes the test, or, build up the rear by (prepping and) epoxying a shim in place.

Alternate scenario: If you lay the rifle in the stock and it seems to rest properly on both contact points, but you feel that the act of tightening the front screw is applying a downward bowing force to the front of the receiver, then the front contact area may be lower than the rear, and you would take opposite action. This scenario is a little trickier to perceive. When one tightens a stock screw, it should find home and "hit the wall" (get tight) suddenly. The "wall" exists because the receiver is laying "flat" in the stock bed, and the screw "gets tight quickly" because the screw is compressing the receiver surface against a well-matched stock surface. If however the screw gets snug but takes another half turn at "snug" before it gets tight, then the screw is trying to flatten the receiver against a poorly-matched stock surface. This is occurring because the front and rear contact points of the stock are not on the same plane. If they are both flat but not on the same plane, then they are forming a "step", and the screws are trying to mate a flat receiver to a stepped stock.

I thought if you tighten down one side completely before tightening down the other side actually causes a bow.

Not if the contact points are flat and on the same plane. That is the number one priority. For any stock that achieves this goal, it should make very little difference (perhaps no difference) whether you fully tighten one screw and then the other, because neither will applying a bending force to the receiver, because the stock is properly mated to the receiver. Theoretically, in a perfect bed, it shouldn't matter, because as you tighten one screw, it is bedding both contact points, because the contacts points match perfectly. That said, if I am shooting a match, I will barely snug each screw and then gradually tighten each in equal movements, just because it's good form.

Parting thought: because the bedding compound is fluid, it will flow. This does most of the work for us. I mention this because the physical act of building clay dams and half-filling the void with goo and then slowly inserting the receiver into the goo and tightening the screws, this is all wonderfully easy. It really is a snap, because gravity and fluid properties work in our favor.

The more challenging aspect is to ensure that the final bed will have contact points that are on the same plane. Do that first, then do the main bedding job.

HTH!

 

[goodgorilla]

On another thread I read a post about using a gage that would detect vibration changes on the stock or barrel when tightening down the screws. He also said there was an acceptable range of vibrations, but I can't find the post. Do you know what he was talking about?

 

[DCS]

I guess I can envision the concept, but I would concur more with the view that "a range of vibrations" is acceptable. In other words, total perfection is not possible. IMO, a vibe sensor to analyze receiver-to-stock fit is overkill.

The goals are to determine whether the screws are applying significant bending force to the receiver, to fix that problem if it exists, and to simultaneously create a bed for the receiver and lug so that they have nowhere else to go. That's it.

Another perspective - if a rifle is bedded well enough to consistently shoot a half minute, it is unlikely that fine-tuning the bedding will reliably get you tighter groups. That final leap, if you choose to pursue it, will be more affected by loading, technique, atmospheric conditions, and how well you are shooting that day, than it will be by any difference between a very good bed and a perfect bed.

Caveat - I'm a working-rifle guy. My goals are achieving consistent .7 minute with relatively lightweight, relatively inexpensive rifles, while expending only reasonable amounts of time loading. So clearly, I'm not a benchrest purist, and some of my views would be unacceptable to that type of competitor.

Good luck!

 

[goodgorilla]

" I don't know what "dam in front of lug higher than support" means"

If you bed in front of the recoil lug area and want to stop the flow of epoxy forward of that, you need a clay dam to do that. Most videos that I have watched say the two contact points for the rifle should be at the tang, and the other would be at the forearm of the stock contacting the tapped barrel. However in Nathan Foster's bedding video, he claims that the dam near the recoil lug should be the second contact point opposed to the forearm. I'm a little confused by that, and in my mind the 2nd point of contact should be at the forearm.

 

[DCS]

IMO, you should change your mind.

In my approach, nothing touches the barrel in front of the recoil lug.

I make two epoxy beds, one at each screw area. The rear bed is small.

Front bed: I tape the barrel nut with 3 or 4 layers of masking tape and coat the tape and receiver with release agent. Put release agent in the screw hole, and put a light film of clp on the screw. Build a clay dam about 3/4" or so in front of the recoil lug, so that it will contact the tape on the barrel nut. Put the other dam just in front of the magwell.

Rear bed: I usually remove the trigger group. Put release agent on the receiver and in the screw hole. Put a light film of clp on the screw. Build two small clay dams for the rear contact area.

Use just enough epoxy. In the front, you want it to ooze out the sides. In the rear, you want only enough "oozing" to ensure that you create a nice bed, but you don't want it running into areas you can't see.

Make all clays dams "thin wall" so that they will compress easily. Work in a warm environment, otherwise the clay will be hard to compress when you install the receiver.

If it's a plastic stock with voids in the bed area, fill those voids when you are pouring the bed. Go slow, and wave a hot-air gun briefly over the half-filled voids to encourage air bubbles to come out. Do not over heat, it only takes a little heat to reduce fluid viscosity to allow bubbles to escape. Too much heat will accelerate the chemical reaction (set).

That's pretty much it.

If you have a really heavy really long barrel, it may shoot better with a contact point well up the forearm. Maybe. I don't do this, again because my focus is working rifles, not huge heavy bench monsters. If you decide to do this, then bed the rifle as I have described above. Then, after everything has set and you have "proved" the bed job with the tests described in this thread, go back and do a 2nd bed job on the entire forearm, with the barrel wrapped in 4 layers of masking tape. Once this has set and you have removed the tape, you will have a consistent gap between the barrel and forearm, extending the length of the forearm.

If your masking tape is 7 thou thick, you'll have a 28 thou gap. Get some high density foam and cut a slice that is 45thou or so thick, in a 1" x 2" rectangle. Insert it in the gap, and slide it forward or back until your group is tightest. Also try it without the slider, to see what works best. When you change loads, you'll have to tune the slider again.

This slider concept can work for any rifle - heavy or light. I use them on plane jane 10-22's. Some rifles get better with a slider, some get worse. Some get better until the barrel gets really hot, then they get way worse really fast, as in holy cow, what happened?!

You've done good research and mental prep. After a while, you just have to go shoot. So bed it and shoot it. Find a load, and test variables. Every rifle is different in what it takes to get that rifle to shoot.

BTW - if you totally screw up the bed, put a pink chain-saw sharpening stone in a dremel. You can remove a bed in minutes with that bit. It will make dust, so wear a mask. Once you know this, it takes the pressure off.

On the other hand, if you overlook something completely and end up permanently gluing the rifle into the stock, there will be no convenient recovery. So pay attention.

One more: if you are working with Savage rifles, go buy some black cap screws of the same length as the factory stock screws. They will have a much deeper hex socket on the head of the screw, and you will be very happy about this some day.

Good luck!