AL Barrel Nuts, Alloy Handguards and Heat

[StoneHendge]

I finally managed to get the ball rolling returning my [barrel nut and chamber insulating] Faxon Carbon Fiber handguard to Brownells. While my credit marinates on the journey through the USPS system, its time to start thinking about its replacement. I'm leaning towards one of the V Sevens - either the lithium alloy or the magnesium alloy. Although i'm sure I'd do much better today, let's just say I passed undergrad Physics 101. But that's it. Google isn't very helpful answering some of my questions. So here they are. I will predicate by stating my current belief is that BSF's carbon fiber system works to some degree helping cool a barrel, but that it will still retain more heat than a plain steel barrel. Therefore any system that might help cool the barrel is a plus. Even at the expense of a warm handguard (happiness is a warm gun, after all).

Aluminum barrel nuts: Aluminum absorbs (and conducts?) heat rather rapidly. So from a barrel cooling standpoint, this should be a good thing. The barrel nut will pull heat away from the chamber and likely result in lower temps of the steel around the chamber while also presumably limiting the heat that may travel down the barrel. BUT, aluminum expands more rapidly than steel when heated. Does this become an accuracy issue under "spirited" rates of fire. Is it possible for the expansion to loosen up the interface and create increased dispersion (in Litz-speak). It's not a big deal if it makes a 1/2MOA barrel MOA, but with the 8MOA shift I got with the cf handguard and subsequent return to zero after cooling, I no longer know what to expect!

Lithium Aluminum Alloy Handguard. The best I could find was that lithium acts as a heat sink and that this property makes it popular in industrial coolants. Okay - good to start - a lithium aluminum handguard should then pull heat from an aluminum barrel nut and then maybe even pull heat from the warm air between the barrel and the handguard. But if it acts as a sink, does this mean it gets hot? Or will it conduct that heat to the cooler air around it.

Magnesium Aluminum Alloy Handguard. I couldn't find anything about how well magnesium or magnesium Aluminum alloys conduct heat. Anyone know? I also understand that magnesium Aluminum Alloy may not be as strong and is susceptible to corrosion. But they are absolutely insanely light - 5.4 oz for a 15"er plus 1.1 oz for the AL Barrel nut. I would only buy one from Brownells.

Titanium barrel nuts. I know titanium does not expand nearly as much as steel when heated. But how well does it conduct heat vs steel and aluminum? I would go this route with a "pure" aluminum alloy handguard if I decided against one of the V Sevens.

[Splatt]

Wow !

[The Profit Joseph Sith]

Heres the method ive been waiting to see for years. Use your hand gaurd to tension the barrel and tie it all together. Get the air in between the barrel and HG. Glad someone finally made it and boy oh boy these things really are masterpeices. Now the only thing left to do is put a fan blowing air down the inside actively cooling the barrel. If the combined that with something like the JP Enterprises thermal heatsink thing it might be pretty "cool"

https://www.masterofarms.com/index.php?main_page=product_info&cPath=1&products_id=65

They use 7095 Tennalum for their receivers.

On the other end of the spectrum but equally as posh is the Turnbull steel receiver's. (Diabolically sexy!) I mention this because its basically the same (steel) material for all the interfacing parts. Looks like they discontinued the ar15 pattern.

https://www.turnbullrestoration.com/turnbull-mfg-company-introduces-the-turnbull-tar-10-rifle/

And then theres these guys who ive been waiting for around 5 years or more to release to public, which i know doesn't help your query but theres no doubt that when a rifle is made entirely out of the same material the thermal expansion dilemma is negated.

http://amalgamatedti.com/phone/index.html

If i remember correctly the last time i asked my dad about this (hes a QA/engineering guy at boeing) the thermal expansion of most materials is basically negligible your talking like .0001" for most common alloys around a few inches in size. The bigger it is the more this matters. The main issue is the thermal dissipation. Ive always been skeptical of those CF sleeved barrels. I want to see someone put a thermistor or other sensor under the CF before wrapped and one on the outside to see what the variances are.
Also keep in mind virtually all AR's out there have a steel or SS barrel in an alum. receiver so a alum barrel nut wouldnt be any worse. And if what your saying is true. The nut will expand and get tighter as it heats up. I highly doubt thermal cycling will loosen it up if torqued correctly.
Good luck though.

[A5BLASTER]

The biggest issue to worried about when using non steel or titanium materials to build a compression fit device i.e. barrel nut is thread lose due to over tourqe also know as qualing.

As far as aluminum goes in a barrel nut that is the only worrie you should have over a steel or titanium barrel nut is over tourqing it and ripping out the threads are completely locking the two peices together due to not using a proper lubricate when thighting the two interfaces together.

Hope this helps.

Edit to add make sure the nut is made of 7075 t6 aluminum.

[sneaky one]

A5 meant galling, on the threads surfaces. Bill A is the expert on bbl nuts and torque, upon his beloved Grendel idea. 60 ft. lbs., is max.

Never use any heat to separate, aka- a bbl. change. Kroil oil- seep- soak - wait-

Shoot less quickly, don't overheat all the components-- better groups on target.


Galvanic corrosion is the result of aluminum and steel connectivity- Not good, Bill A reduced that by using the Loctite, Permatex threadlocker, as a barrier to the


dissimilar metals,,, and as the lube on the threads.- Plus to help keep all parts together for the best accuracy possible.

Slow the rate of fire for best groups.

[grayfox]

One of my longer projects (in my past life) had to deal with an aluminum alloy that was supposed to be qualified for nuclear, not to mention, naval specs and QC. The trouble came in from the manufacturer not being as in control of the heat treating as was originally thought... and the upshot was over some time, that the aluminum leached away leaving a porous, leaky and weak metal lattice-architecture behind... that weeped, leaked, and even broke through a few times with just a pencil push. This came from corrosion occurring down at the grain-level and grain boundary level, and, like I said, alloy was qualified for safety-level systems in plants.

So now every time I read about this or that aluminum alloy with more reactive metals (think Li, Cu, etc etc)... even in small %s, I just get leery of all the promises, b/c the mfr in the case I dealt with, didn't know or didn't control or wasn't aware of the actual alloy-formations going on down at that inter-granular level, and they all swore that the heat treating etc was all gtg. I'm sure the guys who use these other alloys will swear that they are great and have no problems but I've had engineers, professionals and executives swear that also regarding this other alloy... and they all proved to be wrong. Got kind of expensive for them when they had to fix it.

Just a caveat. Maybe that couple of oz's you're looking to save aren't worth it after all.

[A5BLASTER]

A5 meant galling, on the threads surfaces. Bill A is the expert on bbl nuts and torque, upon his beloved Grendel idea. 60 ft. lbs., is max.

Never use any heat to separate, aka- a bbl. change. Kroil oil- seep- soak - wait-

Shoot less quickly, don't overheat all the components-- better groups on target.


Galvanic corrosion is the result of aluminum and steel connectivity- Not good, Bill A reduced that by using the Loctite, Permatex threadlocker, as a barrier to the


dissimilar metals,,, and as the lube on the threads.- Plus to help keep all parts together for the best accuracy possible.

Slow the rate of fire for best groups.

Thanks for the spell check Sneak, been a ruff last few days on bed rest.

[StoneHendge]

Thanks everyone! There's a reason why my Physics professor was never going to be proud of me -lol. Thinking that aluminum will expand faster than steel and therefore potentially become looser. Well, duh, it expands in both directions! I feel as dopey as Jeff Sessions looks. Comfortable with the idea of AL Barrel nut now. I always use anti-sieze on my barrel nut threads and if I go the V Seven route, I would certainly check with them to confirm it would work or use whatever they recommend. Their barrel nut is made out of "T7068 Super Aluminum" allegedly harder and stronger than 7075. Doing research, it turns out the V Seven guy was Noveske's lead engineer.

Going to stay away from the magnesium alloy. If it looks too good to be true, it probably is. Chances are that when it breaks or bursts into an intense white flame, it will be at a rather inopportune moment. The V Seven Lithium alloy is made by Alcoa so that gives me some comfort. And if I go that route and it gives me problems, maybe licking it will impart some of lithiums medicinal properties

But I'm not feeling very adventurous at this point given what a steaming pile of hot garbage the BSF barrel ended up being. And my handguard options have increased since I now don't have to worry about fitting a 0.936 gas block under it.

[Kswhitetails]

You will be well served with an AL barrel nut. I was sceptical too, and read somewythat in the millions of AL barrel nuts issued, and used in civi guns, that if there was an issue we’d have been told about it long ago. Good enough logic for me.

[The Profit Joseph Sith]

Looking at the log books for each of my builds i torqued all my 7075 ALG barrel nuts to around 75 ft lbs. One even hit 90. If i remeber that one was kinda weird. I specifically over shimmed them by like .003" and that one wasnt jivin for some reason so i just left it. Well see if it breaks down the road. ALG sells their nuts separately.

Another reason why i will ONLY buy forged...