Recoil lug thickness studies

[Bob Wright]

Recoil is a force that will displace the containment that it rests in. Whether it reacts in the long axis or flexes the stock or receiver, it must return to its resting point I would think, to be repeatable. A well bedded receiver that flexes, then rests almost exactly as before will give repeatable results. If one of these components in the bedding goes to a different position, I think it gives up that repeatable "at rest" result. That's the best I can figure. A lot of dynamic and static b.s. that has to be contained through bedding.

 

[MagnumManiac]

Nobody that works on many rifles said in this thread that a well bedded, aluminium bedding block or fibreglass stock that was bedded are the rifles bending recoil lugs. It is cheap plastic injected stocks, wood stocks soaked with oil and other poor designs that do not have proper bedding abutment.
To bend anything there needs to be movement and a hinge…these are adequate on many cheap stocks to allow movement. My REM 700 SPS in 300RUM has already bent the stock, so I bedded the rear of the stock, the sides and left an air gap underneath, when removing the stock now, there is no further bending evident.

Cheers.

 

[Mike Matteson]

Well I guess I've been doing somethhing wrong again. ****. I have let my action into pre-cut stocks. Being left hand in the right mind . That was the only way to have a stock to fit me. It's been awhile that I have bedded an action in. I would make sure the action would fit. Then bed the entire action in from back of action to the barrel. Also bedded the trigger-magazine housing in. In the screw areas. I left material inbetween the action and trigger-magazine housing so there wasn't any movement between the too. I didn't use any piler posts. There wasn't much room between the two. They were 98 action with a recoil lug on the action as the aciton were machined. I think if you bent one of those, there is a real big problem. Now on other actions that a different story. The one thing I do do it float my barrels in any action. Just never done a 700 action. I didn't like therr saftey on their trigger set up. Being left handed, and carry the rifle on my left side would work the saftey off. So I changed actions or don't carry a round in the chamber while hunting.

 

[tobnpr]

This is simple physics.
No different than on a jobsite when I see a framer use a right angle clip for a structural attachment, and his attachment points to the structure (pins, screws, etc) are an inch inside from the bend, instead of as tight to the inside corner as you can get it. Forces will easily flex the angle away from the structure in the first scenario- but there's no room for movement when properly installed in the second one.

If you imagine the contact surface where the lug will seat, if it's not precisely at 90 degrees to the bottom of the receiver/parallel to the receiver ring- but rather angled outwards/downwards, the bottom of the lug is where contact is first made- and there is a gap above. Under sufficient recoil impulse, there is space for the lug to flex/bend. This can be easily checked with some contact blue or stock inletting black, but it's so easy to bed a lug that there's no reason not to...

 

[Coldfinger]

Oversized lugs are a gimmick, Look at the lugs on a Sako TRG 42 or any Tikka, They flat shoot and the lugs are minimal, I think Remingtons are boring, But I have barreled a bunch of them and installed oversized lugs. The more important thing is being precision ground. The factory lug is very substantial. One of the more famous Gunsmiths even said Oversized lugs are not necessary, I can't remember which one it was though.

Custom actions that have integrated lugs seem to have much smaller bearing surfaces. Smaller = stiffer less leverage to aid in flexing. Even mausers and Winchester 70 lugs are much shorter than Remington

 

[North Idaho Hunter]

Ran through all sizes that you can think of on 700 clone builds. The biggest issue ---- bad bedding or no bedding at all.

Saw a 338 lapua Ai shear a lug clean off! That was a good one

 

[MLN1963]

I have to wonder if some or all these Savage and Remington stamped lugs are slightly bent to start with from the stamping process?

 

[Rflshootr]

Of course they are.

 

[ntsqd]

It is possible to stamp such a shape without bending the lug, but it requires well maintained good tooling, and it will both drive up the part cost and lower the output volume.

 

[Rflshootr]

Not really. It takes a fairly large amount of force to shear a piece of steel 3/16" thick. Even if the stock started out flat and parallel, there is always distortion, especially at the edges, when shearing/stamping. I guess it depends on what a person considers "flat". I don't consider .001-.002 flatness/parallel acceptable. There is a difference between the two. The only way to get something truly flat and parallel is through lapping and grinding operations which, like you said adds more operations, drives the cost up and lowers production. When I rework a lug, I grind as flat as possible, lap the best side as flat as I can get, then skim grind the opposite side a 2nd time to insure parallelism. They're usually within .0002 or less. When I make one from scratch, the blank gets rough ground flat & parallel, the hole drilled and bored square to the faces, the outside profile milled, deburred and then check-lapped one side and final grind on the other to a thickness of .200. I pick that thickness for 2 reasons...one it adds a bit of beef over the standard 3/16 factory lug, and .200 is an easy number to work with when setting head space.

 

[ntsqd]

Back starting in the late 1920's up into the early 60's Burroughs Business Machines stamped most all of their mechanical calculator parts. Due to processes carefully worked out those were flat within your described unacceptable tolerance, they had to be or the machines wouldn't work. They also exhibited very little of the "rounding" of the top surface edges that we see in typical stampings today. When ever someone says it can't be done I call BS because I've seen some of those parts. It can be done, but it costs money to do it. That is partly why Burroughs is no longer around (incompitance at the highest levels is more of the reason - nepotism can be a business killer).
While that tolerance may not be acceptable to most here, it is very likely a lot smaller than what a mass rifle producer will accept. Would not surprise me if it is flatter by a factor of ten than what they will accept.

If you set the barrel or barrel nut install torque high enough then the flatness of the area of the lug around the barrel hole becomes moot. Particularly at the OEM thickness (thinness?) of the lug. Parallelism in the area around the barrel hole is a separate issue and will mostly be dependent on the material supplier's controls. It would be educating to see, say, Savage's production print for their recoil lugs.

 

[Doom2]

Ran through all sizes that you can think of on 700 clone builds. The biggest issue ---- bad bedding or no bedding at all.

Saw a 338 lapua Ai shear a lug clean off! That was a good one

Bet there was a lead sled involved.

 

[Randfal]

Aluminum bedding blocks, properly bedded...those facts make the difference.

I never waste time bedding an aluminum bedding block.
For the record I was discussing standard calibers up to 300 win sizes. The big safari guns are a different subject.

 

[gunaddict]

Chad Dixon surface grinds factory lugs and uses them. At least he did. I would think if he had any bending issues he would not continue do use them. I wish he was still on here to reply.