Heat-Treating Barrels: Rifle Mag Article

[rodclark]

Full disclosure up front - I'm not a gunsmith (as you will see from my question). I'm hoping to tap into the experience of you guys who are by asking your reaction to the article in the current issue of Rifle Magazine on heat-treating barrels. The article was the first thing I read in this issue - the title grabbed my attention. Some interesting claims were made relative to the various rifling methods, which I had heard before. However, the author made some statements which he appears to support with pictures of target groups which, to my eye at least, were not super impressive. I'd sure be curious to hear reactions from those of you who have read the article - or - who have had experience of heat treating finished (i.e. already rifled) barrels.

[waksupi]

I am dubious of the advantage.

[country gent]

Heat treatment of materials isnt always to harden it but may be stress relief, annealing to soften or normalizing grain structure.here was a barrel maker ( black star???) that made a much harder barrel blank a few years back. Must smiths didnt care fr them since they were so much harder on tooling. Reamers and cutters. A few in this area refused to work with them for this reason. Another issue will be when tubes are heat treated by heating and quick cooling they tend to warp or move. Keeping a barrel straight and true is going to be hard. I havent heard a lot about it lately but the process of stress relieving a barrel thru freezing ( 300*below)was quite popular and most top end makers do this in house on the bar stock then the finished barrels.This dosnt harden a barrel but removes stresses and makes the grain structure more consistent. This gives several benefits. 1) the blank is easier to machine since it isnt "walking" from internal stress. 2) The cutters give a better finish 3) barrels stress relieved thru the process require less straightening 4) A blank that relieved tends to walk shots a lot less when it heats up. Something to think about is that light sporter contour that walks it 4 and 5 shots as it heats, is this do to the contour or all the turning taking that 1 3/8" blank to the light sporter contour and the resulting stress?

In my match rifles the barrels were fitted, contoured, Chambered then removed and sent to 300 below and stress relieved. This is one of those things that is hard to prove or disprove as it takes 2 barrels to test one treated one not and differences in the blanks may be the causes. I did a long range model 70 target barrel in 300 mag. Before it would start walking shots up and right around shot 14-15 as it heated ( this was one of the hammer forged barrels so a lot of stress), this showed in its score book. After the deep freeze it stayed put much better.

One of the claims for these blanks is increased barrel life, number of rounds fired. On some of the barrel burners this may be a consideration but

[lefty o]

without reading the article, i would also tend to believe its more about stress relief. stress relieving a barrel isnt a big deal for those guys who shoot 3 shot groups, and shoot 1 or 2 rnds at a deer, but it can be a benefit for a barrel that is going to get run hot.

[country gent]

In the timed events (10 shots 60 or 70 secs) or running a 600 yd slow fire at quick pace (22 rds may be fired in 8-10 mins) to "keep ahead of the wind" every little bit helps. LOL.
The above model 70 was like that at 1000 yds around shot 14 it would start walking and every 2 shots or so after it need 1 clk down and 1 clk left to finish the string in the center. Keeping a good score book shows this after a couple matches

[akajun]

It’s stress relief , most barrels are made from pre hardened steel, fully machined, then stress relieved. Believe it or not barrel steels like 4130 and 416 machine better in a slightly hardened state than when annealed.

[truckjohn]

He may have been referring to cryo-treating barrels.

The thing here is to know your barrel maker. Most of the high end barrel makers already do all the treatments they have tested as "Beneficial" before they ship it to you....

It's the next tier down of "Budget barrels" such as Criterion, Shaw, Green Mountain, and Douglass... Those are good barrels but usually benefit significantly from these treatments as the "Base price" has no allowance for additional services/treatments to be included beyond rifling and profiling.

[Geezer in NH]

Cyro was a big whatever a few years ago. Meh

Green mountain heat treats for stress relief. Don't think they are cheap barrels because of there price.

[M-Tecs]

Haven't read the article but for heat treatment melonite is most common after the fact process https://www.sst.net/barrel-nitriding-service/

[EDG]

Heat treating before and during manufacturing processes is done to make the manufacturing processes faster, more precise and more reliable. Not for any direct accuracy benefits.

I discussed cyro treating of barrels with a coworker who was a masters degree metallurgist.
He could not think of even the slightest benefit for the accuracy in a rifle barrel.

I have not given the subject much thought since then. Then was about 1990.

[TCLouis]

A friend had an Enfeild Musket with a markedly curved barrel.
It would walk rounds significantly (even at musket distances) when he first started shooting it.
He put it on a rotisserie over a low flame "cooked" the barrel for a while and the curve developed.

Shot perfectly stable ever after.

What little . . . LITTLE I know about metallurgy came from inspecting a primary aluminum smelter and learning some of their aluminum billet treatment techniques.
I always wondered who/why someone ever came up with the voodoo treatments they used.

[country gent]

The cyro treatment of a few years ago was a very precise, controlled procedure, It wasnt done with higher temps but with sub zero temps. Blanks were loaded into the chamber and slowly filled with liquid nitrogen ( I believe it was just went blank there). This was at -300* Then over a weekend the load was raised and lowered in temp. TThis converted the autenise grain structure to martinese making a much more uniform grain structure and relieving the stress from machining. We did some tooling at work and after this it finish machined much better with better finishes and less warp. Our basic procedure was machine part .015 oversize, heat treat to hardness, rough grind .005-.008 big, send out for cryo when it came back in it was ground to size. Tool life was increased by a good margin.

I believe most barrel makers now employ some form of this either on the bar stock or thru the process. It makes machining and maintain finish much easier

[Texas by God]

About five thirty round mag dumps as quickly as possible from an AR15; then dunk it in cold water. Voila!