Mythbuster#1 | Stresses in the Barrel

I was once again on a colleague's website and thought to myself...

... this really ought to be cited, but then everyone would immediately discover who I'm referring to. And since I don't want to disparage anyone, but merely express my (partially contrary) opinion on the subject, I'll paraphrase it...

The statement concerns arguments in favor of single point cut rifled barrels (SPCR for short) – i.e. Barrels using this process. It claims that:

1. Barrels manufactured with SPCR are stress-free.

2. With button-rifled Barrels, precision issues can arise due to material stresses when cutting the Muzzle Thread.

Theory – I'll keep it brief and clear, I promise!

Strictly speaking, the entire discussion revolves around what are known as residual stresses in the material. These can arise, for example, from rapid cooling processes during raw material production, but can also develop later through forming processes and machining. In practice, therefore, you will never find a metallic component that is completely stress-free. Now, some might ask: What about stress-relief annealing? Yes, precisely! It's important to note that we are not talking about stress-free annealing, but rather stress-relief annealing. The reason is that this heat treatment process only eliminates residual stresses that exceed the hot yield strength. Any stresses below this threshold will still be present even after annealing.

What does that mean in terms of Barrels?

Barrels no such thing as Barrels stress-free Barrels . The question is therefore whether my Barrel has Barrel too much" or "sufficiently little" internal stress. Since this question is difficult to answer, there is often debate about which is the better method...

• SPCR: In this process, the rifling grooves are cut into the Barrel using chip-forming machining. Any metallurgist who has ever worked with nitrided steel knows that chip-forming processes have absolutely nothing to do with stress relief. While many Barrel manufacturers in the USA use materials like 416R, which is not comparable to nitrided steel, stresses still arise during processing with SPCR.

• Hammer Forging (Forging/Hammering): Forging itself creates considerable tension in the material, which can normally be controlled by subsequent heat treatments such as the stress relief annealing mentioned above. While this process has not becomeBarrels used forBarrels , there is nevertheless a well-known Austrian company that uses it to manufacture very precise weapons. You just have to know what you are doing, then a lot is possible.

• Button Rifling: I always explain to my customers with a technical background that button rifling is like thread forming, but with an extreme pitch and small flanks. And that's precisely the point. One must consider this purely numerically. For a 6.5 Creedmoor, we are talking about a land-to-groove difference of 0.21 mm (according to CIP). Back-of-the-envelope calculation: We are talking about a forming process where the material is displaced by approximately 0.05 mm. If one then considers the amount of material that counteracts and keeps the resulting residual stresses in check, what are we even talking about? Furthermore, there is also the option of subsequent stress-relieving annealing.

And what about the muzzle?

If a Barrel has Barrel internal stress in the material, it can actually happen that the field and tensile diameter change during thread cutting. In the worst case, this has a negative effect on precision – in the best case, the change is "CIP" 😂 and leads to a kind of choke that actually increases precision (theoretically possible but unlikely). Ultimately, the same applies here: if you purchase reasonable blanks from reputable manufacturers, you will usually not encounter such problems. We have never had a single case like this and have so far used almost exclusively button-drawn Barrels... so much for that topic.

Conclusion

Barrels no such thing as Barrels tension-free Barrels . That will probably remain a fairy tale that is repeatedly used by some Gunsmith and semi-professionals). Nevertheless, the issue of internal stresses in the material of barrels is essential for their precision, which is why renowned Barrel are strongly concerned with this issue. As with so many things, there is no simple yes or no answer here. Therefore, here is a practical tip: if you Barrel a precise Barrel , you should turn to reputable manufacturers.

Backpedal! - I don't want any trouble 😎

There is no question that the Barrels made Barrels colleague using SPCR are in a league of their own – at least, the manufacturers mentioned there are Barrels worldwide for their excellent Barrels , and the shot patterns I have already seen from his weapons leave nothing to be desired. Hats off! However, I don't think it's fair to portray other methods as being so much worse.