Home Forums Hunting & Shooting Custom Rifles & Wildcats Aluminum Cradles In Stocks

You're not being an ass, John. You do seem evasive though.

Torch was just the way I read "apply heat". I still don't see the applicability of that to a system that is thermally equilibrated - all components at the same temperature.

If a rifle is zeroed and then "thermally torqued" I don't doubt accuracy problems will ensue.



Still don't see any trade secrets in whatever the answers to these might be:

Dog and pony shows don't count, I'm talking killers. I have little use for the AMU after the Army had to ask for civilians to come teach young soldiers how to operate an M14 in order to kill the towel heads shooting at them. What the hell are they drawing a paycheck for?

My M24, nor any other of the dozen assigned to my company got skim bedded, though, knowing what I do now, I would likely have done it myself.

Ironbender,

The optic will expand/contract at almost 3 times the rate of the action. By just heating the optic the user can get an idea of the effect this will cause to the zero of the rifle.

By attaching a block of aluminum to the bottom of the action it will help mitigate the change in zero if the rifle has been allowed to reach thermal equilibrium.

Usually our hunting rifles in the field have reach equilibrium, but not always.

Lay the rifle in the sun and the optic will heat first and quickest, followed by the action, followed by the bedding block. In direct sun light the block inside the stock will never attain the same temp as the optic and there will be a significant shift in zero.

Okay - not busting balls here but if the optics getting warm cause a shift in zero - how does having a bedding block in the stock prevent the optics from getting warm?

Or did I read that wrong - the heating of the optics won't cause the shift, they just happen to get warm first, then the action etc.

So what actually causes the zero shift - warm optics or warm action/bedding/stock?

This appears to be contradictory.

Teal,

It won�t prevent the optic from getting warm.

What causes the shift is the distance between the front and rear ring will grow or contract with the length of the scope and put a differential load on the top of the action.

The length of the scope will change as the temp changes.

If the steel action also grew and contracted at the same rate as the aluminum optic the zero would remain relatively stable.

Attaching an aluminum block to the bottom of the action will introduce a similar load to the bottom of the action and counteract, to a degree, the affect of the scope expanding and contracting at a rate 2 1/2 times as fast as the steel action per deg of temp change.

The short answer is to check your zero in conditions similar to your hunt and try and keep you rifle in a state of thermal equilibrium. Don�t leave it lying in the hot sun.

How? The block isn't exposed to the same temps to the same degree nor by the same manner. It's encased in an insulating material (stock), shielded from the environments.

Not disagreeing with what you're saying as to what happens to the optic, as that makes considerable sense (thanks, btw, never thought of that before), but I'm not seeing where the aluminum block makes as much of a difference as you're saying, for the reasons stated. I might just be missing a few steps here, though. Please, continue.

VA,

The block will come to the ambient temp of the environment. It will just be slower to heat or cool due to the insulation of the stock. It is bolted to the steel action and will stay very close to the temp of the action during a change in temp.

The big issue is how fast the optic can change temp if exposed to a heat source such as direct sunlight. If you take your rifle out of the case and then lay it in direct sunlight the optic will heat and grow much faster than the action and block.

The action is actually fairly flexible in the area between the scope mounts. More of it is cut away than is left with the mag cutout and the ejection port.

The block also adds a degree of stiffness to this area of the action

Listen John, just paint the scope white and that should solve all your problems. Of course you might have to paint the mounts white also..........

This is what gets me then. If the Al block is going to be close to the temp (and thus stretch and constriction) of the action - it's moving right along with it then.

If the larger(est) issue is the stretching and constriction of your optics putting stress and moving your action around - how is the Al bedding block then superior to say pillar bedding (this assumes the block is there to "stiffen" the action in the stock to prevent it from moving)

I am also wondering - modern Leupold scopes are filled with an Argon/Krypton gas mix. Argon is an EXCELLENT insulator and thus the internals of the scope wouldn't be exposed to the same expansion of the scope externals (as describes as heating up in the sun). If the scope tube is getting so warm to cause this shift and due to the insulating power of Argon, the internals aren't - why doesn't the scope fall apart from the inside as the tolerances change?

I would think that a precision instrument like a modern, accuracy minded scope would have some tight tolerance and any expansion of the externals without a corresponding movement of the internals (which can't happen due to an Argon fill - they simply will not and can not thermally change at the same rate) would fall apart rather quickly - especially if subjected to recoil at this time. Or is it that the expansion of the externals really isn't all that much.....

Something expanding 3 nanometers 2.4 times faster than something else isn't all that big of a deal, it's still only 3 nanometers (as an example)

Teal,

The aluminum of the bedding block will expand at the same rate as the aluminum of the optic there for applying a similar load to the bottom of the steel action as the optic does to the top of the action if the block and optic are the same temp.

Argon is not a very good insulator. It is just the best, relatively cheap insulator that you can see through. Hence the use of argon in windows.

When designing things like optics all of the tolerances of fit of the parts are considered over the expected range of temp the optic will be used under. At least in a well designed optic or any other mechanism.

A common way of removing a glued in action from a stock is to freeze the whole thing overnight. The steel will contract more than the stock and assist in breaking the epoxy bond between action and stock.

Take a rifle from an air conditioned environment and attach a collimator to the muzzle. Zero the optic on a reference in the collimator.

Set it in strong sunlight and the differential heating will move the zero over 3 MOA in 20 minute of baking.

But they aren't at the same temp. One's out in the sun and the other is wrapped in fiberglass. You've said this yourself. Wouldn't the optics and block only expand at the same rate if they were the same exact Al alloy? the block being thicker (even if they were the same alloy) would expand slower - it's mass taking longer and more thermal energy to reach the same temperature as the optic.



Going to have to disagree here. Argon is an excellent insulator on deep water dives. It keeps you warm in freezing or below freezing temps for HOURS underwater (think long decompressions after going to 240 feet or so) where minutes of exposure would leave you hypothermic and dead. Hell using regular air would leave you dead.

A weekend's dive on the U-Who might burn a couple of thousand dollars on gas alone - they still use Argon. Granted Krpton and Xenon are better insulators but Argon is still an EXCELLENT insulator.

Tactical aluminum bedding blocks and air conditioned scopes, can't make this [bleep] up.

Next week stay tuned for gravitational influence on cryogenically frozen LR primers..

I'm starting to understand why RPGs are so popular.

John: My only question at this point in time is this ...

IF the aluminum bedding block has the ability (as you assert) to essentially counteract the shift in a scope's zero when encountering relatively extreme changes in temperature, why are none of the stock makers that are using the aluminum bedding blocks advertising/high-lighting this aspect?

Seems crazy (at least to me) for them to NOT make sure everyone knows what the aluminum bedding block can do for their rifle, as I'm sure it would be a great selling point.

I'm not going to argue with what you're saying, simply because I have not tested it myself, nor have I seen the results first hand. However, I have to point out that I have never experienced these changes in zero in my rifles, of which I've got one with an HS Precision PSS stock (which has an aluminum bedding block), and a few McMillans, some of which have the action fully glass bedded, some with pillars and glass bedding, some with only bedding at the lug, and some with no bedding at all ... I guess living in Louisiana where my rifles see temperatures of over 100F, all the way down to the low 20's at times, isn't enough of a temperature change to cause this 3 MOA shift in zero?

I'm just wondering how [bleep] one would be with a steel tubed scope.

Does it have aluminum turrets ?

LOL ... I was thinking the same thing, but forgot to post it. What about aluminum alloy scope mounts vs. steel? What about the Burris rings that have the plastic "offset" inserts? After reading some of the things in this thread, if one were to assume some of these things to be true, it would be hard to fathom any rifle setup holding zero for more than about 15 minutes ...