Comments on: Lothar Walther UltraLight Barrels — Less Heat, Half the Weight

By: Mike

Mike — Wed, 16 May 2012 19:44:39 +0000

Forget fluting – it`s only for optic.
The Aluminium tube must be glued to the barrel with loctite – than it works well.

By: Jon

Jon — Wed, 16 May 2012 04:06:46 +0000

I’d certainly consider one for hunting…like a 16.5″ barrel on an action I could drop into a chassis stock when not shooting long distance.The weight savings would be attractive.

By: Steve Blair

Steve Blair — Tue, 15 May 2012 04:36:27 +0000

The reason heat sinks are made from aluminum is that copper is expensive and gold is even more expensive. Heat sinks are shaped to present more surface area than the heat source to which they are attached. An aluminum barrel jacket of equal diameter to a homogeneous steel barrel will not transfer heat to the surrounding air any faster. It is limited by the air’s conductivity. Heat is simply trying to achieve equilibrium. When the barrel is hotter than the surrounding air, it will transfer heat to the air until they are the same temperature. Aluminum will transport the heat more quickly and the steel-aluminum barrel assembly will achieve stability faster but the barrel assembly will not lose heat to the air more quickly. Again, these schemes have been tried many times and simply do not provide a worthwhile benefit. Take a look at a Lewis Light Machine Gun barrel. It has large fins and many times the surface area of a conventional barrel and it did not appreciably improve the sustained fire rate. If it worked well, we would see many machine guns with finned, aluminum barrel jackets. Other than the Lewis, how many are there?

By: Rick

Rick — Mon, 14 May 2012 22:40:15 +0000

Steve re read. I am stating that as per robs experience with pulleys, the alu sheath will need to be bought to high heat before the clearance is sufficient for press fitting. the hole will enlarge when heated… and shrink when cooled.

the complete process may likely involve cryo treatment of the barrel liner also.

By: DanielC

DanielC — Mon, 14 May 2012 15:01:23 +0000

“.. a metals expert we contacted said that a bi-metal system employing fluted aluminum over steel, if assembled properly, could dissipate heat much better than steel alone (given the same diameter). Stainless steel has a thermal conductivity factor of 16. Aluminum has a thermal conductivity factor of 250.*”

Find another expert; there’s not going to be any useful improvement in heat dissipation.

Yes aluminum conducts heat better than stainless – but it’s not the thermal conductivity of the barrel metal that is limiting the cooling rate. The limiting factor is the thermal conductivity of the air layer/film surrounding the barrel (it is a *much* poorer conductor of heat than stainless) – and this is unchanged.

EDITOR: Some points. The air layer is not static, but moves over and around the barrel and is essentially infinite. Two, if what you say is correct, then why are heat sinks most often made from aluminum: “The most common heat sink materials are aluminium alloys. Aluminium alloy 1050A has one of the higher thermal conductivity values at 229 W/m•K but is mechanically soft. Aluminium alloys 6061 and 6063 are commonly used, with thermal conductivity values of 166 and 201 W/m•K, respectively.” Wiki. If you doubt that aluminum disperses heat more quickly, you can do your own experiment with cast iron and aluminum cookware. Any cook knows the answer to that one. Also, if the air layer’s thermal conductivity was the only limiting factor in heat dispersion then why do we even bother to insulate heating and cooling pipes at all? Likewise, if a metal’s thermal conductivity is irrelevant, then why do engine builders carefully select materials for radiators, engine fins, cooling lines etc. based on heat-dispersing properties (along with other factors).

By: matt

matt — Mon, 14 May 2012 12:03:37 +0000

I live in Columbus Ga. where it gets real hot. Here’s a tip to keep the heat down, just slide a copper pipe over that barrel melt some aluminum pour that into the pipe. Your good to go just saved you alot of $$$.

By: Neil Gibson

Neil Gibson — Mon, 14 May 2012 08:07:11 +0000

Steve, you are quite right, for starting tubes 10 mm in diamter changing from 20 to 120°C, the aluminium would expand to 10.0222 mm and the steel to 10.0173 mm, so a gap of 0.0049 mm (0.2 mils). Not much of a change, but a change none the less. Don’t know what I was thinking of?

By: Steve Blair

Steve Blair — Mon, 14 May 2012 01:14:41 +0000

Neil, Rick & Robert:
You boys need to review your thermodynamics texts. Only Robert got the expansion correct.

By: Robert Burdge

Robert Burdge — Sun, 13 May 2012 23:54:30 +0000

Concerning the varying rates of thermal expansion …

Aluminum sheds heat so much faster than stainless steel that it would always be cooler than the stainless steel liner, the liner being the source of the thermal energy. This would tend to offset the fact that aluminum expands more at a given temperature than steel.

As to the outer aluminum tube expanding inwards … I believe this is incorrect. I have personally heated pulleys to slip them over a shaft. The inner hole expands when heated.

By: Neil Gibson

Neil Gibson — Sun, 13 May 2012 21:40:00 +0000

Josh – The coefficient of thermal expansion for aluminium alloy is about 22 and steel between 10 and 18, if anything the effect of the higher thermal expansion ratio for aluminium alloy would result in the tightening of the fit between the two metal alloys. The expansion is in three dimensions remember, so for a tube this would result in the outer diameter increasing, and the inner diameter reducing, compressing the inner steel liner.