Epoxy bed scope mounts?

Discussion in 'Gunsmithing' started by Supertrucker, Mar 7, 2009.

  1. Supertrucker

    Supertrucker Well-Known Member

    Feb 4, 2009
    I know some of the benchrest guys epoxy bed their scope mounts to the reciever. Does any one know this procedure and what epoxy is used?
  2. Boss Hoss

    Boss Hoss Well-Known Member

    Nov 10, 2005
    First use 400 paper then steel 000 steel wool and acetone and rough the contact area of the receiver and then do the same to the contact area of the base.

    Use a cotton ball with acetone to clean any residual off of the receiver contact area and the base or bases. Set aside the base and be careful not to touch the clean areas. Use a little paste wax on the tip of a toothpick to apply into the threaded areas on the receiver. Apply a very thin layer to the screw threads and to the bottom half of the screw head. Set screws on a clean shop towel -- you get the idea.

    Now use JB Weld (regular not the quick set as it for what ever reason does not work as well) because it can be heated and removed easier should you want to remove this later on. Mix it and use just a little die if you have it to more closely match the color of the bases and receiver. After mixing on your little piece of cardboard or index card set aside for a few minutes.

    Get your propane torch and heat the contact area of the receiver and the contact area of the bases just enough to bring out any moisture that may be present on the surface. When the bases and receiver have cooled back to less than 100 degrees (this will not take long because you did not heat them up that much) using the toothpick that you used to mix the JB put a small amount on the receiver mating surface and on the base mating surface. Don't worry about it oozing now carefully place the bases lining up the screw holes as closely as possible and gingerly set the base on the receiver---immediately place the screws in the holes and get all of them started a few turns.

    Now that the screws are started give a turn to one and move to the next screw. Repeat process until they are all snug then tighten each one to its final tension. This is important-----DO NOT OVER TIGHTEN. We do not want all of the epoxy to be completely squeezed out.

    Now leave the rifle in the vise and let sit for 5 minutes or so (I use rubber inserts so that the barrel can be clamped in) and get your capful of WD 40, cotton balls and Q-tips. First use dry q tips to remove most of the excess then take a cotton ball and dip a small portion in the WD 40 and very gingerly wipe down the areas you just removed the excess JB. You will notice that it comes of very easy but make sure not to press to hard on the edges where the base and receiver meet we don’t want to disturb that line.

    Use the q tip or the tip of a toothpick with WD 40 on it to clean out any of the epoxy that migrated through the top of the screw holes an also into the openings of any of the screws.
    Now look at the underside of the bases where any excess JB could have migrated into the opening of the receiver or just on top of the receiver for example. Note where a one piece base is used it likes to hide underneath. For this area use the q tip with some WD 40 applied to remove.

    Now go off and have lunch about an hour and use the q tips soaked with WD 40 to smooth (gently) the lines where the base and receiver meet. If you have done everything correctly it should look like one piece of metal!!!

    In 24 hours or 6 using a light to position over the bases to heat them you are ready to mount your scope.

    A final note here make sure to pre fit everything because it will really suck if you find out a base screw is too long and the rifle will not operate!!! Also make sure the base is level on the action---placing a base or a scope in a bind is bad juju for accuracy.

    If you ever bought a rifle from Speedy Gonzalez and had him glue on the base this is the way it was done.
    Last edited: Mar 8, 2009

  3. NesikaChad

    NesikaChad Well-Known Member

    Jan 28, 2007
    I admit I've never once glued a scope mount to a receiver.

    Be that as it may I have spent quite a bit of time around resins bedding guns and with my RC airplane addiction. The way I fly the damn things typically results in large quantities of 5 minute and CA being used afterward. Anyway. The above sounds like a great process but there are two items I'd like to comment on.

    One, ditch the 400 grit. Resins bond to steel when it's etched really well. The peaks and valleys cut into the metal increases surface area and provides for a mechanical binder. I'd use at least 120 grit for this, maybe even 80 grit. Once you've sanded the action/base wash them in hot, hot soapy water and use a clean brush and scrub the snot out of the surfaces to be bonded. You need to emulsify any oil and lift it out of the pores. The heat helps to draw it out and the degreasing agents in the water will chew it up. Simple Green is great for this. Once this is done, then go after it with some acetone. I'd avoid using denatured alky because alky is hygroscopic; it attracts water. As mentioned, allow parts to dry or warm em up with a hot air gun or torch to burn off any residual moisture.

    Ok, now onto number Two:

    Resins work best when applied in very thin films. That is when they are strongest. It would seem to me that with "bedding" a scope mount to the receiver you are attempting to maximize the surface contact to mitigate any movement or shifting due to recoil or the occasional bump/bang. That being said I personally would want to tighten the screws to the nominal torque setting that they are intended to run at. In the case of a 6-48 screw that's about 5-6 inch pounds. It's around 8-10 for an 8-40. I'd do this to take advantage of the tensile strength from the screw and to keep the film as thin as possible. A .003" thick layer of resin will bond just fine so long as it has proper surface prep and the stuff gets mixed right. That is the last thing. Resins have to be mixed properly and this is where many fail. You mix it about twice as long as you think you need to. You gotta get the esters blended with the hardener to kick off that chemical reaction.
    Last edited: Mar 8, 2009
  4. Coyboy

    Coyboy Well-Known Member

    Jan 30, 2005
    I do things a little bit different, but that depends alot on the action that the one piece picitiny rail is being bedded to. On custom actions the one piece rail usually sits nice and flat on the reciever.

    When doing remington recivers the rear reciver ring usually tails away on the rear right side, so if you dry fit the base you will notice a gap on the right rear where the base dosn't make contact, this can be measured with a fealer gauge for gap.
    If you tighten down all four screw without a shim of either brass or epoxy you will just twist your rail to match the reciever. Then when you atatch your rings the rear ring will cant off to the right, causing a mis-alignment with the scope to reciever.

    I dry fit the base and find the 2 screw holes that disrupt the base the least, one on the front ring and usuall the front rear ring mount hole.

    I then prep the reciever and base, clean degrease, ect. Wax my screws and screw holes.

    Epoxy the base and set it on the reciever. instal only the 2 screws in those holes that I predetermined will not twist the base. I snug them up just so they make firm contact but not tight enough to start twisting the rail.

    Clean up the uze out and the unused reciever holes.

    After 24 hours I remove the 2 screws used to hold the rail in place, clean and degrease the holes and screws and reinstall all 4 screws to the proper tourqe with blue lok tite.

    I have removed some of the rails I installed this way years latter, when the screws are removed, the rail still holds fast and needs a couple of whacks from a mallet to pop the epoxy joint loose.

    What this process eliminates is any twisting of the rail, or possibly the reciever if using a heavy steel picitiny rail.

    I have also epoxy shimmed Tally one piece ring base sets, but because the front and rear sets are not conected it helps to cut a small brass shim for the rear ring base so that it does not cant to the right. The only difference is I use all four screws snugged up, Hear it is not neccesary for twisting just correcting the ring cant. Then when finished, as always lap the rings.

    The remington high polished recievers, like the sendero, are the worst for this rear reciever ring right rear drop off. As they polish the reciever along it's length they reverse direction at the ends and this seems to work off a little more material in that area causing the dimensional problem.
    Last edited: Mar 8, 2009