TargetTalk

I may be looking for a newer 3 p rifle <i have an Anschutz 1813 ,but was considering a Walther KK300 or 2313 anschutz with an aluminum stock,what are the pros & cons of alum. vs. wooden stocks.
I hear alum. has problem with temperature extremes,any truth to this ?
Any other problems?
Any help greatly appreciated.
regards,Rick.

The coefficient of thermal expansion of steel and aluminum are significantly different. This means that aluminum will change dimensions more rapidly than steel for the same temperature change. Those different expansion rates cannot be good for a stress-free action bedding.

It seems to me that unless one wants to be continually loosening and retorquing the action bolts, it would be best to stick with wood or a composite like fiberglass.

think i'll stay with he old reliable......wood.
How come 3p rifles aren't synthetic stocked.
would it possibly be because of weight?
regards,rick.

How much do wood and aluminum expand or contract over a difference of 20-50 degrees? Is it really that much?

Wood expands and contracts with changes in humidity.

I would think that the best thing to do is to use a torque wrench and make sure your stock and action are properly mated to each other.

The main advantage I've seen is that the aluminum stocks offer more adjustments than the wood stocks do. But, that can be a blessing and a curse. A lot of shooters will spend so much time fiddling with adjustments on their aluminum stocks they don't work on other things they need to.

TWP wrote:How much do wood and aluminum expand or contract over a difference of 20-50 degrees? Is it really that much?

I couldn't find the linear CTE (coefficient of thermal expansion) for walnut, but I found one for oak (close enough, IMO). It is 4.9 micrometers/meter-deg. Celsius.

The CTE for 7075-T6 aluminum alloy (what I assume most rifle stocks are made of) is 23.6 micro-m/meter-deg C.

Aluminum will change in length 4.8 times MORE than wood for each degree C of temperature change. That, to me, is a significant difference particularly when walnut's succeptibility to expansion due to moisture absorption can be virtually eliminated by (a) using properly dried and aged stock blanks and (b) sealing the wood properly. Both (a) and (b) are done as a matter of course by competent stockmakers.

IMO, the best stocks for competition rifles are made of foam-filled, laminated glass and carbon fiber composites.

I think looking at the thermal expansion coef of wood is not so useful. I am pretty sure the variation with moisture changes is more significant. Still, I like the late 90's version ans. free rifle stocks very well.

pdeal wrote:I am pretty sure the variation with moisture changes is more significant. Still, I like the late 90's version ans. free rifle stocks very well.

Walnut's succeptibility to expansion due to moisture absorption can be virtually eliminated by (a) using properly dried and aged stock blanks and (b) sealing the wood properly. Both (a) and (b) are done as a matter of course by competent stockmakers.

the coefficient for thermal expansion of walnut is 6.58...

Guys,
All debate is concentrated around thermal expension, but how about elastability of wood versus allu and fibration dampening of wood versus allu?
I do not have any practical experience, but feelings tell me wood has a better dampening factor than allu. Or am I wrong here?

By the way, on the Bechrest Central Forum a while back someone did a test with POI of cartridges shot with the powder loaded in the front (near the bullet) and in the back (near the rim).
We did the same test here in The Netherlands with a Walther GX-1, shot prone from a frontrest and a Anschutz 2013 clamped in a machinerest with different makes of ammo and had matching results: a vertical change of POI of aprox 6mm (1/4") between the 2 groups.

Albert,
The Netherlands

Anonymous wrote:the coefficient for thermal expansion of walnut is 6.58...

OK, so aluminum expands 3.6X the amount walnut does instead of 4.8X. Still a huge difference.

OK Jose, since I'm not a mechanical engineer,

Explain the expansion coeficient to me.

If I understand it correctly it means that 1 meter of Aluminum will expand 23.6 Micrometers for every degree celcius change?

If this is correct, we are talking about the expansion difference between the aluminum stock and the steel action.

Since I don't know the expansion ratio of steel I can't add that into the equation, but it should be expanding and contracting as well. Just not at the same rate, so the actual movement difference would be even less than that. The little I could understand of what I read quickly on the net is that Aluminum's expansion coeficient is about twice that of steel.

What is the expansion coeficient of the steel in the action/barrel?

The aluminum stock is going to expand/contract in 2 directions that concern us, front to back and up and down. The front to back distance that concerns us would be from the rear of the action to the forward action screw. A distance of about 1/3 of a meter (or 1 foot for us non metric guys). You are talking about movement of less than 8 millionths of a meter for every degree celcius of change in temperature. IF I'm correct that steel expands about half as much then the actual difference in expansion would be only 4 millionths of a meter for every degree celcius.

I'd venture to guess that the movement is well within the manufacturing tollerence of even an Anschutz rifle.

While proper drying and sealing of a stock will minimize expansion of the wood, it will not eliminate it.

I just don't think your calculations show a real superiority of aluminum over wood.

The fact is that both will change dimensions over time, temperature and/or humidity.

The real solution it to properly torque your rifle before each use.

If you like the adjustability of Aluminum get one, if you like the look and feel of wood, then get one. Either one will work fine if you use it properly.

Hi guys,
I think the Anschutz alloy stock gets around all the steel/wood/alloy expansion and contraction issues by by having it's own rubber like bedding material set into the stock. This has a "memory" that ensures that the bedding pressure is the same all the time. This means you don't have to re-torque the bedding screws everytime you use the rifle.

It appears to work very well. I have an alloy stock (not Anschutz) with expoy bedding and I have to re-torque the bedding screws everytime. It seems to work OK for me. However I do strip the rifle every 1000 rounds and re-lube the screw threads. Very important for getting consistant torque settings.

Also important is the care of your torque wrench. A friend had his Anschutz torque wrench tested and it performed much better than many professional torque wrenches. The comment to him was he should unwind the torque setting knob after he uses the wrench so as to preserve the spring inside.
Cheers
Martin

Funny, I was told that repeatability is a problem with these small torque wrenches and that once you find your rifle's "sweet spot" you should never touch the adjustment!?!

Jack

I seems that I always ended up with a real good barreled action for my daughter and no stock. I bought a grunig stock. The action that I have is a round bottom so I bought the anschutz adaptor. I found that on an aluminum stock that it takes about twice the amount of touque that it does on a wood stock to get the gun to come in. I think hers shoots best at 65 in lbs on the 4 adaptor bolts and 50 on the 2 reciever screws. The 4 socket head cap screws that come with the adapter are a little week and too short and until I changed those to a little longer to bick up the remaining threads, I was having to retorque. Now I check it a couple a times a year but it does not change. I think that the reason for requiring higher torque on the aluminum is because of the harmonics of the aluminum. Just a guess..