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Using A Dial Indicator To Check Bedding

10K views 20 replies 4 participants last post by  Mainspring  
#1 ·
Glassbedding is a method to increase accuracy. When done, stresses are eliminated between the metal parts and the stock. "Stress" is usually caused by one part being forced to do something it does not want to do. If the relationship between the barreled action, the stock and the bottom metal is not perfect, then the action will be bent when the guard screws are tightened.

We try eliminate to these stresses by pouring a liquid goo of our choosing between the action and the stock and waiting for it to dry. Once dry and all the parts are cleaned and reassembled (including all the other necessary fitting of parts), we trot off to the range to compare targets from both before and after the addition of our magical liquid goo. Most try to guess their results relying on their experience in bedding.

If the rifle is bedded correctly there is no need to torque a stock screw, it serves no purpose and can be detrimental to accuracy. "Torquing" is used to overcome imperfections, but we strive for perfection. Once bedded correctly get your itty-bitty screwdriver and with two fingers tighten the stock screws, all you're trying to do is keep the action from bouncing around. Adding a drop of thread-locker is preferable over extra tightening.

One way to check for stresses is to used a dial indicator that has a magnetic base attached. The dial indicator will show errors in bedding as small as the increments on the dial. It's use is simple but care must be exercised to achieve true results. A pressure point in the forend will null-and-void this measurement, so remove it, add it later if you want a pressure point. Also remove the magazine spring and follower, the pressure applied to the bottom of the bolt will affect readings.

When you are ready to measure, flip the rifle upside down and put the barrel in a padded vise, leave a couple of inches between the forend tip and the vise. Set the magnetic base directly on the barrel and rest the indicator tip on the "bottom" of the forearm. Zero the indicator. Loosen and tighten each guard screw one at a time. If they are both loosened at one time the stock will want to fall off, so...one at a time. Check the readings and record them for each screw. If there is stress, when the screws are loosened the action will want to move back to it's relaxed position and will move the needle. If the needle "bounces" it can indicated a bent guard screw or bind on the screw. For "target" guns we strive to keep the needle between 0.000" and 0.001", for hunting guns 0.001" to 0.002" is fine.
 
#2 ·
Well, I'm not a gun smith and totally self taught by what I've learned through the school of hard knocks, trial and error and read from different sources over the past 50 years and I don't totally agree with you. I agree 100% with your post as far as a proper bedding job being stress free but that barreled action is not going to remain stress free when a bomb goes off in the chamber with 60 to 70 thousand pounds of pressure pushing a heavy chunk of copper and lead down the barrel. When it does, that barreled action is going to dance all over the place if the mounting screws are not properly torqued. There is this little thing called bolt stretch that has to be controlled and minimized, as well as crush pressures on the pillar post and other compents between the head of mounting screws and the actions.

It's apparent you will not agree with me either but two of the finest precision rifle builders I know are very specific on their toruqes so I think I will continue to torque mine. Right or wrong, it has always worked for me.
 
#3 ·
It's just a different school of thought, one of the many. Using the indicator, try torquing the screws in different increments and record the results, a picture of your bedding will develop and it can be done at home on the bench while drinking coffee. The results of course will still need to be done on the range.

Bedding is an attempt to make a rifle more consistent, so that the last shot fired mirrors the first. Two methods to achieve this; let the rifle do what it wants or force the rifle to do what you want. A properly bedded, pillared 'glass stock shouldn't need torquing whereas a skim-bedded wood stock may benefit from torqued screws.

I like letting the rifle do what it wants, and the stock is just something to hold on to. When the primer ignites, things are gonna bend and twist and buck and torque. A properly bedded rifle with lightly tightened screws allows this to happen and the action to return to the previous position all on it's own. Torquing is an attempt to force the action to be consistent, to force the rifle to return to it's previous position, in spite of all the bucking and twisting.

Torquing definitely has a place.Many rifles can't allow consistency and torquing the stock screws will enhance accuracy. When Remington brought out out their VS/Sendero line is when torquing came into vogue. The HSP stocks were the first major attempt to produce an over-the-counter target rifle (not just adding a heavy barrel and yelling woo-hoo). The aluminum block's radius is undersize for the round action and the action literally rides on the top edges of the block, But, per factory specs, when the screws are torqued to 65in/lbs accuracy returns. In lieu of proper bedding this method works well and allows the consumer an easy way to improve or return the accuracy.

Today of course there is a market for torque wrenches, and guys with their tool catalogs have another "need" for a tool. The forums are full of people looking for "factory torque specs" on their favorite rifle. "Good-and-snug" just doesn't cut it anymore.
 
#7 ·
That goes a long ways to help, but the action still needs to be retained in position. I still use screws, it just takes 10-15 minutes to tighten them though. Cleanup work afterwards is more critical than many people realize as well as contact between the action and all the other parts. If the bottom metal is slightly bent then stress is added to the action, or tight mag boxes, sling studs, triggers and so forth.

The dial indicator comes into play before the work starts also. A reading before bedding and a reading afterwards goes a long ways towards knowing how well a job was done.
 
#8 · (Edited)
I think you are over thinking and over complicating this.

You use glass bedding because it fills in any imperfections in the inleting.



Take a set of irwin wood clamps or any other wood clamps with rubber jaws and clamp the action and bottom metal in the stock with the inleting screws already in the action. Go for snug not tight when doing this, If the stock was properly inleted it is a simple mater of making sure that the bore line is level with the rails of the stock. If it was properly inleted it will naturally assume the correct position without much pressure.

use the inleting screws to keep all 3 parts in alignment, the bedding compound will conform to the shape of the action and provide that 1/1 fit. By not using the action screws you save yourself any tension and warping they "might" impart.

Ideally the mag box should not be in contact with anything other than the bottom metal and the action in most bolt actions.

The trigger group should never touch the stock.

The action screws should also never touch the stock.

Lets be serious here how much force would it require to warp a bolt action????

If you cannot warp it during the bedding process than the tension on the screws is irrelevant, the gel conforms to the action and the stock regardless.

If stock crush and warpage is a issue then pillar bed the gun, if that's not sufficient then get a full length bedding block, but at the end of the day a dial indicator can only tell you if you screwed up really bad, not if you got it right.
 
#11 ·
I've been fighting a headache for several days and it's kinda hard to concentrate. I'm also reasonably certain that you have not, nor intend to, stick a dial indicator on a barrel. So yeah...I cherry picked.

The topic of this thread is not something new, in fact it is an old technique. I had the good fortune about 15years ago to spend a week in the shop with Chet Brown and he taught me several things about making stocks more accurate. I thought I would share some of what I learned with the members here.

While I realize you are happy with your technique, I have had a desire to learn more. I have not used the Irwin wood clamps and appreciate you sharing your knowledge and skills in using them to bed a stock.

For those members interested in learning more here is a link ~ Learning More
 
#12 ·
Are you implying that I would be so un-American as to pass up an opportunity to handle my firearms?:D

I did put it on 3 guns that I have glass bedded and installed pillars in trying to discern its mystical powers, the Mauser had just under .001 change incidental it has a full length aluminum bedding block, the Howa had the least change the needle was still on the mark, the A303 had half a mark difference. The howa is the most accurate but that's probably because I blueprinted and trued it then put a new barrel on it and have not done that to the other two.

So why again did I do this? Don't get me wrong getting them out of the safe was fun and all but all it told me was what I already knew, they were bedded properly.

This strikes me as something dreamed up by benchrest shooters.
 
#15 ·
It's in no way a fix, just a method of evaluation. While you have experience, I'm quite certain that the techniques and methods you use today are different than when you started. The results are probably better looking bed jobs that are more precise and are done faster. Someone with less experience may find the before and after comparison useful.


CST?
 
#18 ·
Was Gary Schlomer there way back when? I swear that guy could tell you what rocks to make a gun out of :D and if he doesn't know something he knows someone who will.

Anyway for humors sake i checked a new Remington, It fails horrifically because of the for end pressure point like you said, on the other hand it can sill shoot far better than anyone will ever need from a hunting rifle. As it shoots dime groups as is I'm not gonna mess with taking out that pressure point, if it aint broke don't fix it.
 
#19 ·
Yeah Gary was there, ran the show and taught welding. I'm pretty sure he was directing the crew that poured the foundation for the place. I saw him about a 1.5-2 years ago on TV, there was program called DIY TV or some such and they followed a student through on a build.

Bob Penny was in Pseudo, Don Lucas in Stocks, Gus Crites in Machine Shop, Doc Kroeckle and Bill Spurrier in D&F. A gent named George ran the store. I lived in the apartments up the hill. 40hrs/wk for a year and $2.25/hr.

Day one we were told what we learned was our choice. Lots of knowledge to be gleaned from that place.
 
#20 ·
Same here about the introduction. Different names but they all new their stuff, Seemed like to many of my classmates thought that the class instruction was all there was to it. Lot's of em complained about how much it cost, it's not cheap but I say it was worth it. I think it came out to about $10 an hour for instruction while I was there.

Scholmer was dean of student, but he still walked the shop and answered questions, gave pointers and even taught a few classes.
 
#21 ·
The course was taken fairly serious when I was there, though sneaking out early on a Friday was the norm for many guys. The instructors would write a notes upon completion of a section for future reference by prospective employers. Aside from course requirements, students did need to try and get a variety of projects from the store or bring their own. Some students wouldn't and they tended to get duplicate work projects. Some complaints about tuition fees, but those were also the guys cutting class or who were there for a hobby. I found that time flew by fairly fast and had to pay attention to get what I personally wanted out of the program.