Bedding issue....why?

I have bedded more than 5 rifles and all, even the first effort, came out swimmingly. What I never did was a "before" and "after" comparison. There certainly are enough of those in the form of "after bedding the groups tightened up" variety. Testimonials abound. Can't argue with success. At least i can't. I am not really challenging anything though it often appears so to others. Let it be known that I not only am a true believer in Pillar Bedding but I use the process on all my rifles.

So here is the issue: Background) RJR sent me a most excellent post on the impact of tightening the action screws or having protrusions subject the action to stress that deforms the receiver. The impact on the guns integrity was beyond my imagination. It also raised questions about what I had been doing and the actual result.

I have seen terrific videos about pillar bedding and the final shot always shows a stock with the perfect cast of the bottom of the receiver and the recoil block. Really photogenic castings of the receiver bottom covered with a gleamingly smooth slab of epoxy with nary a bubble or fold. But under that epoxy sits some wood of either lam or solid personality. Laminated wood is superior to solid because of grain, color options and that the stock has a much less chance of warping into a twist or bend with environment fluctuations. Terrific stuff. BUT, lam and solid woods still expand andf "grow" as the humidity goes up and down and so does the action with temp. From where I sit you cannot get rid of this relative movement between the receiver and stock unless the stock is metal and somehow lets the action move withing it while the action is captured. I guess in my theoretical options a SS receiver would be best served by a SS receiver. But following the current wisdom we fill any void between the wood and receiver with epoxy that also has little give. Wetting wood has long been a trick used to cause horrendous pressures sufficient to crack granite. I know that as the humidity goes up that wood and epoxy are subjecting the receiver to pressures beyond that of any screw. It may be a tiny bit of movement but it is there.

The same must be true for the receiver dimension associated with temp. It must be moving and if there is contact that contact might be a pivot.

All that should provoke some enlightening conversation among people far smarter than myself. I expect I will benefit.


Now to another angle: There is a way to mount a rifle without touching the receiver. I am referring to the method where the barrel is clamped in a block and the front of the barrel and the entire receiver are left to float. From the targets shown in these articles I assume that there is no other way to "bed" a rifle that wouldn't result in better accuracy and precision. And that completely ignores the defeat of the last vestige of recoil. I have never seen one of these block mounted guns sporting a brake or flip suppressor barrel device. Pardon the humor. Does this device prove that "no contact and distortion" is the optimum? Would never work with a Mountain Rifle, I'll grant you.

My thought was to bed the action on pillars that sit proud of the stock and free of any pressures from the stock whether it be "now" or in the future. I also thought that it would be better to bed the entire recoil lug if the rear was allowed to float/slide along the rear block. I imagine the loosening and then re-tightening the action on the rear screw alone would neutralize the action/stock union till either warmed or became wet. The "rules" call for ever so slight torque/pressure from the rear pillar anyway.

Happy new year

Good read, brings up some questions. I am no expert, but here is my rebuttal:

Bedding a wood stock, especially with devcon and metal pillars, takes the swelling out of the equation. The bedding material is harder than the wood and should stay true no matter what happens to the wood around it. The pillars make sure you have metal on metal on metal contact for two reasons. One is to make sure the action is straight and not being distorted when the action screws are torqued. The other is to make sure there is no wood between all the pieces to be compressed or deformed.

Heating and cooling of the action I think is minimal. We are heating the inside of the barrel, in front of any bedding material and ideally in a free floated chamber. This should take care of any swelling. As hot as my barrels have been, the action has never been hot. The difference between 0 and 100 degrees, ambient outside temperatures, is not going to swell any metal enough to make a difference.

lastly, the bench guns that are clamped down, there is hardly any weakness in that system because you remove the stock completely. the action is bolted directly to the heavy base for support. If your action is completely floated on pillars, I think you are going to bend screws and break stocks. Like holding the gun tight to your shoulder to manage recoil, I think the action needs to be supported to keep from damaging itself or the hardware it's mounted in.

I glass bedded many of my Savages that came with the synthetic (tupperware) non-accustocks and their accuracy didn't improve any after being glassed.

Savage tupperware stocks are just fine with the factory pillars. But because I like a piece of mind, I glass them anyways !

IF after bedding or both pillar and bedding, after all set and hardened i have having good luck testing as follows if the results are successful, i actually put a dial indicator mounted to the barrel and the indicator tip at the end of the forend, i loosen up the rear screw a little and if i see more than .002 or .003 movement, it is not a stress free job.

chet

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Originally Posted by chetc

IF after bedding or both pillar and bedding, after all set and hardened i have having good luck testing as follows if the results are successful, i actually put a dial indicator mounted to the barrel and the indicator tip at the end of the forend, i loosen up the rear screw a little and if i see more than .002 or .003 movement, it is not a stress free job. chet

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Chet,

Thank you so very much. That is a fantastic way to evaluate the quality of the bedding job. What is the torque that you tighten to, which screw do you tighten first, do you walk the torque down or fully tighten with the first stage? Have you ever had one that didn't move at all?

Thank you again. My dial indicator has been loafing far to much. John

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Originally Posted by schnyd112

Good read, brings up some questions. I am no expert, but here is my rebuttal:

Bedding a wood stock, especially with devcon and metal pillars, takes the swelling out of the equation.

There is wood under the middle of the receiver and it is covered with a thin coat og epoxy. As that wood absorbs moisture it swells. The epoxy cannot contain the wood swelling and its elastic property lets it move back and forth following the wood movement. Not talking about waving in the wind movement here but a few thousandths of arch in the receiver will have a serious affect on the impact point. FURTHER, the distance between the mounting screws will change with the weather cause the wood grows in length when it gets wet. Wood has almost all it movement in the thickness dimension but it does grow in the long axis. Right? We are talking thousandths of an inch.

Heating and cooling of the action I think is minimal. We are heating the inside of the barrel, in front of any bedding material and ideally in a free floated chamber. This should take care of any swelling. As hot as my barrels have been, the action has never been hot. The difference between 0 and 100 degrees, ambient outside temperatures, is not going to swell any metal enough to make a difference.

Using my scientific kitchen range/oven to heat the action and a digital caliper to measure a Striker action we get the following: at @ 68 degrees the length of the action is 152.47mm. After heating it to 120 degrees that length grew to 152.56mm. Total growth is .09mm for a delta T of 52 degrees F. That seems to be .018mm growth for every 10 degrees. That is the T instability of the receiver at approx the mounting holes. That will probably only be a lot if you calculate the Impact point variance. Or just compare the groups if you start out with .25" groups. The thickness of the receiver must also have a bearing but that would only matter if the stock/epoxy is actually touching the receiver to move it. The idea to mount the rifle in a fixture and mount a caliper to measure the tip of the barrel movement is great. That can be done here as well to eval the changes in action temp.

If your action is completely floated on pillars, I think you are going to bend screws and break stocks. Like holding the gun tight to your shoulder to manage recoil, I think the action needs to be supported to keep from damaging itself or the hardware it's mounted in.

The recoil lug takes the recoil strain. Yes there is a shock in the stock and action but they are traveling together thanks to the lug. I agree that the mounting screws would snap under this pressure and certainly no epoxy would resist and certainly there would be variances between shots.

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I just finished bedding a Boyd's, and this time I used a Savage pillar for the front. Because I don't like the rear hole any bigger than necessary, I used lamp rod there. I have a full bull barrel on that action, put the right amount of tape at the front of the forend, so everything was lined up perfectly. Everything came out very clean. Front and rear pillars are metal to metal from bottom to top.

When torquing the front, it is just like a bedding block. Screw bottoms, the next fraction of a turn, its torqued. From 20in/lbs up to 30in/lbs, there doesn't seem to be anymore movement at all. Perfect.

Not so on the rear. Even though it is metal to metal all the way, I'm not getting that solid lockdown like on the front. I am convinced the installation is stress free. The screw bottoms, then tightens up gradually. Unlike the front, it's still moving all the way up to the max torque. I don't need a dial indicator, I can feel it.

After doing many stocks, I'm convinced this movement comes from the magazine hole and general lack of support material in the magazine, trigger area. And that's not a "wild exaggeration" :-).

Now...with torque tuning, this rifle can still be made to shoot well, in spite of the lack of perfection.

But, once one has experienced the precision action seating that can be achieved on a solid bedding block or a metal chassis, anything else seems "whimpy".

But, good groups can be achieved anyway :-))

FW,

Great post and thanks for the info.

I agree that the front is perfect. I agree that the rear should operate like the front. Are you positive that the lamp rod isn't the culprit? I don't think it should be but still it is the only variable so far.

I'm convinced it's that big hole for the action and the trigger hole right next to it. The action screw would strip before I could contort the lamp rod. But like I said earlier, you can still make it shoot very well.

just want to add to this topic, i have a new model 10T in 6.5CM, i decided to check the bedding on it, to my surprise the front of the action was not in contact with the bottom of the alum bedding block, it took some filing on the sides to let the action finally make contact with bottom of the block. what i did was start by smearing some red lipstick on the bottom of the block and the sides, the action was rubbing hard on the sides, i kept taking it apart and you can see where the lipstick was showing shiny marks, keep filing equal amounts on each side till the bottom just starts to show contact. hope it helps the groups which were not too bad, but should help.the rear was good.

Chet

FW,

Could you loosen the front screw and tighten the rear first to see if it acts better if it goes first?

Thanks,
John

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Originally Posted by chetc

i have a new model 10T in 6.5CM, front of the action was not in contact with the bottom of the alum bedding block
Chet

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Wouldn't you think a rig like that would be perfect going out the factory door? I think your 6.5 CM should be a single ragged hole performer. let us know, please.

John

I had the same experience as FW after bedding my 12BVSS laminate stock. Rear screw creaking as I tightened it down and not the same solid feel as the front screw.

That was when I realized that there is another piece to the bedding puzzle......the trigger guard!

So I removed the rear most screw from the trigger guard and then tightened down the rear action screw again. Solid, no creep.

Then I tightened down the rear trigger guard screw and watched the trigger guard settle down into the stock. Apparently it was not sitting square on top of the rear pillar, and the creep was the trigger guard bending under the torque of the rear action screw....with only 25 inch pounds of torque.

Lesson learned.

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Originally Posted by johned

Wouldn't you think a rig like that would be perfect going out the factory door? I think your 6.5 CM should be a single ragged hole performer. let us know, please.

John

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hello John

out the factory door is ???? on any rifle especially Production jobbies, i was very surprised when i checked it, I have a habit of taking all my rifles apart and checking everything, trigger is at 1 1/4lb now and i am sort of satisfied with the bedding and tang area is fully floating. might add some bedding compound to some areas before all said and done.

Chet

#2 poster pretty much said it all.

I have bedded several rifles and rebedded a few. I am no expert, but IMHO based upon my own experience, metal to metal is the key. As to pillars that actually lamp rods, be aware they are soft metal at best and poor quality metal at the very least and subject to stress. Steel will serve you better.

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to my surprise the front of the action was not in contact with the bottom of the alum bedding block,

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I think that is intentional on the part of Savage. The idea is to pull the action down into the sides of the stock. The sides of the stock prevent the barrel from vibrating side to side. You should watch your setup now to make sure that over time it doesn't start to loosen in the sides.

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Originally Posted by upinthehills

I think that is intentional on the part of Savage. The idea is to pull the action down into the sides of the stock. The sides of the stock prevent the barrel from vibrating side to side. You should watch your setup now to make sure that over time it doesn't start to loosen in the sides.

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it's possible, i still have side contact, no issues there, but as you said it very well may be intentional. i don't feel confident with the gap under the action, will find out next time out if it helped or not,

Chet

Some other things to consider regarding laminated stocks and epoxy bedding. Think of the bedding this way; the barreled action, bedding, pillars and screws are a solid unit, and the stock is the interface to the shooter. Only when they form a solid unit is consistency in groups going to be the best possible.

Epoxy, properly mixed and cured, generally will not expand or move with temperature or moisture, UNLESS you exceed the curing temperature, and then it will re-harden to the shape it is in at the higher temperature.

Note to those who do the bedding work in a cold garage in the winter! Make sure your epoxy curing is done at a temperature at least 10 degrees higher than any temperature your gun will ever experience, including being locked in a car in the hot summer months when interior temps can exceed 140 degrees.

I use a hot box technique utilizing a common hair dryer and cardboard box with thermometer pushed through the side to monitor temps. I like to cure epoxy ( i.e. Devcon 10110) at 170 degrees F.

You can also cure at a lower temp and TEMPER the epoxy using heat afterwards if it is convenient. You can, for instance, place it in a cars trunk with the action screws properly torqued on a hot summer day and leave it for the day (or two) to temper the epoxy. But if you cure it at a lower temperature, say 50 degrees, and then go out on a warmer 80 degree day and do a bit of shooting, the epoxy will be heating up, softening, and moving as you shoot, and probably causing some shift in point of impact. This factor is probably why some "home smiths" might feel epoxy bedding is not worth the trouble.

This same characteristic of epoxy is why laminate stocks are less susceptible to moisture creep. Laminate stocks are composed of thin layers of wood oriented with the grain being mostly parallel to each other. The Urethane glue used is quite stable when cured, and saturates the wood fairly deeply. If you look closely at the feather edged portions of a laminate stock, you'll see how the wood is saturated with the glue. This is also why finishing a laminate stock in linseed oil is not a good idea as it cannot soak into wood that has been saturated with glue. But it will soak into the unsaturated wood and cause swelling, which in turn stresses the wood and can cause small cracks to form at the interface with the glue saturated wood. I have experienced this first hand.

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Originally Posted by Texas10

Some other things to consider .........

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Excellent advice. I can verify all this and second the motion. Thanks T10

Very interesting stuff!

thanks, Brian

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Originally Posted by upinthehills

I think that is intentional on the part of Savage. The idea is to pull the action down into the sides of the stock. The sides of the stock prevent the barrel from vibrating side to side. You should watch your setup now to make sure that over time it doesn't start to loosen in the sides.

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well after i got thinking about possibly intentional, well why only a few threads caught and a springy feeling when tightening the front screw, can't be intentional, then i forgot my buddy bought the same gun a few weeks later, so i go over to his place and borrow it, took it apart and there it was both front and rear screws were tight and you can see where the action was setting on the bottom of the aluminum frame and the sides were making a contact. so my gun is now where it is as it was to come out of the factory, this can happen to any rifle, so no flame to the mfg. you have to get the action down on the aluminum block, or you will not get the right amount of the screw in the action for proper torque settings, with only a few threads caught the screw may pull the threads one way or the other.

Chet

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Originally Posted by chetc

........ i forgot my buddy bought the same gun a few weeks later, so i go over to his place and borrow it, took it apart ...
Chet

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Good work and thanks,

John