Gunsmithing Rifle bedding life span

[Dsparil]

Curious,

For a stock like a grayboe with aluminum pillars already machined in, what is the typical life for say Devcon or marinetex bedding of a remington factory action?

 

[Sonic Crack]

Thats going to depend on how well the stock was prepared, correct mix ratio of epoxy, how much epoxy used, how much solvent and cleaning products you dump into your action/ect when cleaning. Ect ect. All things equally well, Im not sure what the life of the bedding would be. Im sure a good long time if done correctly.

 

[Mordamer]

I expect my bedding jobs to last for multiple lifetimes. I have no idea what could go wrong with the bedding unless someone soaked it with some pretty nasty solvent and left it. I once read a book about benchrest shooters and their techniques and I believe there are bench rest shooters that periodically have their actions re-bedded. There is a lot of other crap that goes on in the bench rest world that borders on mental disorders and superstition.

 

[Wannashootit]

There is a lot of other crap that goes on in the bench rest world that borders on mental disorders and superstition.

I just spit my coffee on the keyboard...

 

[JMGlasgow]

I expect my bedding jobs to last for multiple lifetimes. I have no idea what could go wrong with the bedding unless someone soaked it with some pretty nasty solvent and left it. I once read a book about benchrest shooters and their techniques and I believe there are bench rest shooters that periodically have their actions re-bedded. There is a lot of other crap that goes on in the bench rest world that borders on mental disorders and superstition.

Same goes for service rifle/high power.

 

[scharfschutze762]

Same goes for service rifle/high power.

Because back in the days the crap used for bedding was acraglass and its nowhere near whats common today like Marine-tex and Devcon which out performs acraglass in both strength and solvent resistance 100X over. Even mild solvent like Hoppes will eat up acraglass.

 

[Terry Cross]

Agreed.
When properly done, bedding should be there until they excavate the remnants of our civilization.

Every year I continue to get in rifles for the 3rd or 4th rebarrel / rework that I originally bedded in the 80s and 90s. All were with MarineTex and I continue to be impressed with the longevity of the material. No soft spots or issues at all.

It must be noted that roughly 1 in every 10 come in completely soaked in solvent. I have no clue what someone would do to get solvent and oils between the receiver and bedding but they sure as hell do. When I remove the action from the stock and the bedding is wet with Hoppes or ShootersChoice solvents from years of whatever the hell they do to them yet the bedding is still hard and stabile, I have to think that the material and methods are good to go.

./

 

[308pirate]

Same goes for service rifle/high power.

Maybe you're thinking of the olden days of M14s/M1As. They ate bedding because of the way the barreled action attaches to the stock. A double lug job through bolted from the bottom up fixed that.

And in any event, service rifle stopped being an M14 game by the late 90s.

So no, bedding is one of the things NRA service rifle competitors do not worry about. Because their rifles don't have or need any.

 

[Fursniper]

I just spit my coffee on the keyboard...

LOL!

 

[Mr.BR]

Bedding might last a life time on your every now and then 0.5moa - but generaly 1moa rifle from what you can tell .

Its the material shrinkage that is bane of good bedding jobs (not so good bedding jobs suffer from other issues to the degree where shrinkage is least of their problem.

If you look the net '' http://bulletin.accurateshooter.com/2017/01/what-are-the-best-bedding-materials-speedy-speaks/'', on various bedding materials
lets just say that if you have any trace of a wet patch of oil or solvent ,water , when you take the action out of the stock then bedding is not really in full contact.,

Of course depending on stock material, Grayboe stocks should rank among the shitier ones in terms of holding dimensions as they are basically cast out of filled epoxy , no fiber matrix at all.,samo fillers greatly reduce shrinkage but those also make them products very heavy , we will see what gives on Grayboe , tough i am suprised at how they are priced considering how cheap they are to make in relation to hand laminated McMilans.

Benchrest shooters do bed their rifles many times or better yet glue them in like AI. depending on the stock type , on wooden stocks that can be each year .

Benchrest is full of voodoo but they have general idea what maters and what doesn't in their quest for ultimate accuracy , and bedding is pretty high up the list of what is considered most important list goes like this->Barrel ,Bullet, Bedding everything else is very far down the line in relevance in their world..

 

[Clark]

Bart Bobbitt, the guy who shot a 3.25" 20 shot group at 800 yards with a 308 in 1997 in Precision Shooting ad by Krieger, used to say that the bedding breaks down under a round bottom receiver. He used a Win M70 at Camp Perry with a flat bottom. That info can still be found with Google.
60 years ago I saw my father calculating the counter rotational force of rifling on artillery, with pencil, paper, and slide rule on this desk.
I could do it for rifles, but there are too many out of control variables to say any rifle would break down. I try to get all the recoil torque of a round bottom receiver into the pillar undersized concave top pre stressed into the epoxy or into a Vblock.

 

[JMGlasgow]

Maybe you're thinking of the olden days of M14s/M1As. They ate bedding because of the way the barreled action attaches to the stock. A double lug job through bolted from the bottom up fixed that.

And in any event, service rifle stopped being an M14 game by the late 90s.

So no, bedding is one of the things NRA service rifle competitors do not worry about. Because their rifles don't have or need any.

Yes, the M14 is a bit of a maintenance queen. I was also talking about some of the barrel replacement intervals, and cleaning regimens some competitors follow.

 

[Long_Action]

Devcon is some tough shit. I use it to plug channels in 80/20 aluminum to keep coolant out at work. I applied it close to 10 years ago and it doesn’t split, crack, or shrink. The 80/20 bars wear out or are destroyed long before the devcon would be an issue. I’ve even used it as a quick patch on coated vibe bowls. If your barrel lug is properly bedded, it will never wear out.

 

[308pirate]

Devcon is some tough shit. I use it to plug channels in 80/20 aluminum to keep coolant out at work. I applied it close to 10 years ago and it doesn’t split, crack, or shrink. The 80/20 bars wear out or are destroyed long before the devcon would be an issue. I’ve even used it as a quick patch on coated vibe bowls. If your barrel lug is properly bedded, it will never wear out.

+1

I LOL at people who say Devcon epoxies are somehow less than tough as shit. They are meant for serious industrial/MRO use and they perform in conditions far more abusive than under a rifle's receiver.

 

[308pirate]

Yes, the M14 is a bit of a maintenance queen. I was also talking about some of the barrel replacement intervals, and cleaning regimens some competitors follow.

There's all kinds.....

I was never a stickler for crazy cleaning regimes, nor was anyone I shot regularly with. Everyone has their pet routine and products, but that's the same as here in this game. The benchrest guys are the ones who do all the crazy shit that's mostly unnecessary in practical riflery.

As far as barrel replacements go, the rule of thumb was to ditch it once it would not hold X ring at the longest distance you needed it to (600 yards for the across the course game). That same barrel was probably still a hammer at 300 and many guys would run two uppers (one for practice and one for matches) with the practice/training receiver getting the old barrel. Easy practice when you can rebarrel an AR in about 30 min (including messing with the FSB/gas tube) in your basement.

 

[Mr.BR]

Again you are missing the point Devcon is not the No1 choice not because its not tough enough but because it shrinks to much as material shinks action is not even close to full contact any more. I am not bedding every day but do up to 20 bedding jobs per year and prefer Araldite to any other compound

'' My only preference of one epoxy over another is their stability over time. My buddy who works for the Texas State Weights and Measures Department had me cast several of the most common types of epoxies used for bedding into 1.000″ machined blocks. After one year of being kept in a controlled climate and measured for shrinkage monthly, the Marine Tex shrunk only 1/10th of 1% (i.e. 0.1%) whereas almost all the others (including Devcon Steel formula, Devcon Aluminum formula) shrunk 3% to 6%. The only other compounds that matched the Marine Tex were Araldite 1253 and Araldite 2014, with the latter being quite expensive for daily use.

Speedy added: The Marine Tex Grey has no atomized metal in its makeup even though it appears that it does. This can be proven by the use of a strong neodymium magnet. What is humorous to me is that people don't like aluminum yet will bed their actions atop aluminum pillars that have twice the coefficient of expansion (COE) of steel. Like Devcon, it is what people have always done and used. Thus [they] perpetuate the same old stuff. That's my two cents’ worth. But as I tell everyone, I'll tell you what I know or do, but it's not my job to convince anyone to do it my way''

 

[Edds]

I was told, by someone that should know, that metal filled epoxy is not the best choice for the application. He said that most of the epoxies used for bedding start getting soft at around 200° and that the metal causes it to absorb heat faster. That person uses Marine Tex.

 

[Ledzep]

I was told, by someone that should know, that metal filled epoxy is not the best choice for the application. He said that most of the epoxies used for bedding start getting soft at around 200° and that the metal causes it to absorb heat faster. That person uses Marine Tex.

When was the last time you shot at 200°?

I think a lot of people's expectations are a little higher than reality. I'll let you in on a secret... Epoxy shrinkage is negligible. I bed my stuff with JB weld. I also only bed about 1.5 square inches between front and rear pads and I don't use pillars in modern composite stocks. No loss of accuracy, no compressed material, no POI shift, no problems.

Would it blow your mind to know one of the shops that gets all the praise for their beautiful bedding jobs, beds actions BEFORE cerakote (Oh noe!! 1:1 fit???). I bet they've never heard a complaint.

Consider the thermal expansion coefficients of bedding epoxy and your steel/stainless/titanium receiver. Where's your 1:1 fit?

There's doing things that work because they work, and there's doing more because it's a sales pitch or better presentation, or peace of mind, or overkill for the sake of "better". Don't confuse the two.

If properly mixed and not exposed to sunlight the stuff will outlast you. If you're smart and put a couple layers of tape on the sides/bottom and front of the recoil lug your action will slide right out much less chance to physically damage the bedding.

 

[my human host]

Feeler gages will give some indication of how much the compound has shrunk on a conventional bolt action. I have had 700's that would take a .001 roughly 3/8" down in between the stock and the sides of the action, but they still shot like they were just bedded.

 

[Edds]

When was the last time you shot at 200°?.....

When was the last time you checked the receiver temperature on a 100° day after firing a few dozed rounds?

 

[Hookturnr]

When was the last time you shot at 200°?

I think a lot of people's expectations are a little higher than reality. I'll let you in on a secret... Epoxy shrinkage is negligible. I bed my stuff with JB weld. I also only bed about 1.5 square inches between front and rear pads and I don't use pillars in modern composite stocks. No loss of accuracy, no compressed material, no POI shift, no problems.

Would it blow your mind to know one of the shops that gets all the praise for their beautiful bedding jobs, beds actions BEFORE cerakote (Oh noe!! 1:1 fit???). I bet they've never heard a complaint.

The thought in doing this is that once the bedding material cures and slightly shrinks, it will be an approximate dimensional equivalent of what the cerakote adds to the dimensions of the reciever. It actually makes for a VERY close fitting bedding job

 

[Edds]

Chad has previously discussed this. I thought he did it simply to prevent damaging the finish while bedding.

 

[Ledzep]

Oh, but what about the coat of release agent on the receiver when you bed it? Probably pushes the OD out like 5 microns at least... lol

I think you missed the point.

Consider the guy that beds before cerakote.
Consider the guy that beds after cerakote.

Both rifles shoot. Does it matter?


As far as heat transfer, point taken the front ring can get warm. The back 3/4 of the receiver, not so much. Regardless,

1) The bedding is typically less than 0.100" thick and two-part epoxies are not like polymers or metals where they will get soft, reshape, and resolidify in a new shape. So as far as "getting soft", they may get more flexible, to a point, decrease in Young's modulus with increased temp. What effect is that going to have on elastic deformation in this scenario, considering the back half (or more) is not going to be affected by temp? I'll venture to say "Negligible". At least lost in the noise of everything else that happens when you fire a couple dozen rounds in rapid succession. If you have research showing otherwise, I'd love to see it.

2) Considering the small thickness of the bedding compound involved, and considering that what you're saying is that we consider the change in heat conduction coefficient of mostly epoxy with some atomized metal mixed in, and that of pure epoxy... I'm going to hazard to guess the time difference it takes to heat soak is probably a matter of a few seconds at most. What's more, having a higher heat conduction coefficient, the metal mix would shed heat faster to the stock (or receiver, if it cooled off first).

There's also the point of change in compressive strength (at all temperatures) caused by mixing metal into the epoxy...

Anyway... I haven't done or seen any testing on any of this so maybe I'm just talking out my ass, but everything I see says "negligible" insomuch as you won't see any meaningful difference regardless of which way you go. Put another way, if there is a difference, almost nobody is going to be able to see it or pinpoint THAT as the reason for it, so why worry about it? IMO, YMMV, etc.

 

[LRI]

I've bedded guns for a long time now. For the last 9 years I've offered an unconditional lifetime warranty on the bedding work we do here. To date, that is one thing I've never had to replace or repair.

The argument regarding coating before after has been demonstrated time and time again to be trivial at best. It matters not one bit to the gun. Back to back tests on multiple calibers ranging from 22LR to 338's with a variety of barrel contours came to the same conclusion.

If anything, it could be argued that a slight interference fit is desirable. A certain level of compressive loading isn't a bad thing. Bottom line is with modern resin systems and thoughtful, detailed preparation, there's no reason not to expect a pillar bedding job to last almost indefinitely. The issue I see more than anything is if the overall setup has flaws.

Some examples:

A Surgeon DBM is physically larger than most and it requires more material being removed in order for it to fit in the stock. If you were to say run a 338LM with a spaghetti barrel and stuff all this into a lightweight hunting stock, the potential for failure is raised. Why? The recoil is going to be a brute for starters and with thin cross section sidewalls, it's going to be a lot more work for the stock to control it. The stock's core isn't going to respond well to the violent compression forces that apply when the fires are lit. The sidewalls are going to distort under this recoil and this will raise the possibility of the bedding fracturing. -Almost all repeating type composite/wood stocks flex like this to some degree. One also needs to address cross pinning the stock to mitigate the trigger well blowing out or behind the recoil lug.

-Something we do to every single stock job we run here. You never see it, but the stocks are pinned.

The other issue is Aluminum pillars. Forget the heat expansion rate argument crap. Just let that topic die the death it needs to. If your rifle gets hot enough for that to be a factor you have bigger issues to worry about. Aluminum is kind of a little asshole at times. The moment you machine it, it starts to oxidize. The difference is the color. Shiny, chrome line finish vs satin gray looking. Aluminum Oxide is the byproduct of this. In most cases, this is a good thing as the layer forms on the outside and then stops. Atmosphere cannot get under it to continue the party. Why it works so well in so many environmental conditions.

With stocks there's something to consider, especially if you have an all carbon stock. 1, AL and CF are literally polar opposites on the galvanic table. What does this mean? It means if you have an all carbon stock fitted with AL hardware and you find yourself in a very electrolyte heavy environment (salt water, salt spray, heavy sweat, etc) its going to start behaving like a battery. A corrosive action will take place. It may not happen instantly, but it does happen. It's simple chemistry.

2nd is the adhesion thing. Oxidized AL does not bond with resin systems the way it's supposed to. The development of composite/AL wing structures in airplane shit discovered this a long time ago. it takes a bit of work to make them behave for the long haul. I see evidence of this on stocks where the pillar contacts the action. The resin is paper thin here and it doesn't take much for some level of erosion to take place. No, this does not mean AL pillar bedded guns are junk. What it does say is a guy should take some precautions. First, etch the OD of the pillar with an abrasive and then immediately submerge it in a neutral solvent. Leave it there until you are ready to use it, going forward; Handle it with gloves and coat it in resin immediately when it's time to use it. Make sure you dry it off. That will go a long ways to avoiding an issue.

Next, a porous stock material. If were to paint some kind of scenario where we have very, very radical changes in weather. Humidity and temperature in particular we raise the level of risk in this regard. If a gun were submerged in water fitted with a stock that is porous and its later froze...were going to have issues. Big issues. Nature will win every time.. . .

Bedding resin: I have an opinion on this that is slowly becoming more factual. A good resin system will have a high percentage of solids. Think of this stuff as concrete. Pour a sidewalk in just cement and it'll fall apart pretty fast. Add the solids like sand/aggregate and it'll go nearly forever. The solids are what makes this stuff work. Acra glass falls short on this as the only solids present are ground up chunks of nylon. Nylon is hygroscopic. That means it attracts moisture. The last thing we want. So, it's out as far as I'm concerned. The high percentage of solids is where the compressive, torsional, etc forces get dealt with. The adhesive just holds the stuff together and sticks it to the substrate (rifle stock). Low shrinkage is good, but if we're REALLY going to split hairs here then we need to respect the FACT that shrinkage is a percentage based on the volume of material. A 1x1x1 cube of the stuff shrinks less in overall dimensions than a 10x10x10 brick. -Yet both have the same percentage.

The rub however is "less is not more" in this case. Back to the sidewalk analogy. If you pour a nice 4" thick slab of crete you can drive just about whatever over it. Now do the same size pad but only a 1/2" thick. Your kids big wheel is going to kill it. It's gotta have some backbone. I am of the opinion that a bedding job should as well. It's why I went down the rabbit hole of developing 3D surface machined cnc inlets for every stock job we do. I can't get the level of control I want from stock vendors the way they inlet. Doing it this way however allows me the freedom to control exactly how much bedding is being applied. When an LRI job is done it will have .05" film thickness. Concentric and uniform in wall thickness.

Now, if all this really, really, really mattered in the form of some secret sauce, then what I'm saying should result in guns that just kick everyone's ass. They don't. There are more than capable folks that I compete with for your money. What I will say is that we have a process that we can repeat and scale up exponentially. We have a look that is recognizable and we have a system that has been tested on almost every continent for a decade and a half. (our guns have not made it to the big ice cube down south yet). It's shown to work and tolerate the application well.


This isn't a jab at anyone. It's just stuff I've learned and conclusions I've come to after doing a whole lot of these for a long time. Take it for what it is and maybe it'll dispel some myths.

Hope this helps.

C.


PS. I have this bad habit of editing shit after I post it. Tried to make some grammar improvements here and there. . .

 

[Edds]

Do you make your own cross pins? Is this something you sell?

 

[LRI]

I use a buried 1/4-28 allen socket head cap screw for the pin. If it's a big boomer with a long box we'll shrink it down to 10 or 8-32. It's just got to bond the two exteriors in a way that will support the cores from splitting in the narrow cross section. Drill a hole, tap it, stuff with resin, stab the screw, then cap it off with more goo. Let it cure and sand flush.

We paint everything in house as we order our stocks as bondo patched blanks. The constraints of trying to do deep, forensic work on finished pieces isn't something I have to worry about very often. It literally takes the gloves off and provides a great deal of freedom to aggressively treat deeply rooted problems.

 

[ejg]

I have epoxy carbon/glass components that I made 35 years ago and they are still going strong. These were made with the same resin brand that I use to this day. Hardeners are also still available. At least I have something to look back on when manufacturing epoxy composite components. We blend our own bedding material with the same laminating resin. These are approved resin/hardener combinations for boats/windmills/vehicles and aerospace. Also we have all these years of experience to look back on as well as info on curing temperatures/times for the oven. When repairing bits off single/twin planes I use the same resin/hardener.
Pre mixed epoxies out of tubes can vary. It is unreal how bad some are. Batch to batch as if complete different base materials were used. I am about to ban them out of our workshops even for small fixture jobs.
edi

 

[Mr.BR]

Bedding epoxys might last but whole thing also depends of the stock stubstrate. In BR where there is plently of wooden stocks the bedding is redone not because material shrunk or cracked but because wooden stock moves.