Greetings all. I was perusing Youtub videos regarding Ruger Mini's and one producer made a statement regarding the barrel material (paraphrased): the stainless barrels "bend" more than the blue when hot (in his experience).

So, for the more knowledgeable, is that statement true? Do stainless barrels get hotter and bend more?

quote:

Originally posted by craigcpa:
I was perusing Youtub videos

Here's your first problem.

quote:

Originally posted by craigcpa:
regarding Ruger Mini's

Here's your second problem.

I don't know if there is any difference in expansion, contraction, or bending properties between the two types of steel. I do know that thin profile barrels and/or rifles not designed for high accuracy exhibit accuracy issues as their barrels change temperature.

A heavy profile barrel on a rifle designed for accuracy exhibits very little, if any, accuracy issues as the barrel heats up and cools down. IMO this does not describe a Ruger Mini.

Oi.

Everybody is a metallurgist.

The short answer is no.

Given two identical rifles, where one has a barrel Of CM, the other stainless, they are going to behave the same.

Stainless does not "get hotter," or "bend more." This is just silly. In terms of rifle barrels. If you'd like to talk about welding, then there are a lot more steels for different purposes, and I wouldn't say any of the stainless "bends more" than hot or cold rolled, and those are just general terms to boot.

Mini-14s are notorious for "barrel whip" because of the profile.

If you've actually bent something, you've damaged your barrel with sustained automatic fire. By that time your crown and throat are probably long gone too.

Heat can change tolerances, and what is rifling if it isn't tolerances?

Steel, like many things, has a modulus of elasticity, and this is the area where it can be loaded or flexed, without bending. You can apply some heat to it, and you might change its "harmonics," but you haven't changed its strength or cross section.

So, "bending" the barrel isn't at all the right term, and under typical use, the thing you're most likely to beat on with repeated use of powerful ammunition, or sustained fire, is the throat, first. The wear on the chamber headspace tolerance from direct contact with the wee explosion and friction of the bullet.

CM and Stainless wear differently, through the life of the barrel, but having had a variety of rifles in both types of steel, it is profile that is going to determine whether a barrel will "open up" when it gets hot.

One also wonders, if you're shooting enough to sufficiently heat up a barrel, how accurate are you trying to be, and how much accuracy do you need to deliver that much lead down range?

If the handguard is smoking, you might want to just take it easy.

Thanks, Arc, for the narrative explanation. Gave me my answer.

And I'm not a rifle purist or heavy user, so my knowledge is very limited.

quote:

Originally posted by fritz:
<SNIP>
IMO this does not describe a Ruger Mini.

He was referring to the "thermal stringing" problem that the early, thin barrel Mini did have. On gradual heat-up as the rifle is shot, the barrel would indeed bend as a response to internal thermal stresses, then recover on subsequent cool-down. This would manifest as stringing error, and you can actually see your shots walk up and down the target.

Stringing error is a completely separate issue from barrel whip, but both are endemic to thin barrels.

As to your question whether stainless has more of an issue than chrome-moly steel, I don't know. I certainly saw a lot of stringing during the Accu-strut's R&D phase, but I did not do a differential study on that specific issue.

I do know that cryo-treatment solves the problem. Saw this many times. We routinely send all our test rifles for cryo before we even begin testing.

It's really just the welding and engineering in me, but "bending" is for when a beam or other structure is altered.

Deflection is what we'd call a movement under a load where the structure returns to its original shape once the force or load is removed. Or, flexure that doesn't exceed the elastic limit.

I suppose it's easier to just call it "bending," but when you're trying to describe and understand why bullets go somewhere else when a barrel heats up, you don't really mean bending.

Uneven thermal expansion would be the most accurate description.

quote:

Originally posted by kkina:
He was referring to the "thermal stringing" problem that the early, thin barrel Mini did have. On gradual heat-up as the rifle is shot, the barrel would indeed bend as a response to internal thermal stresses, then recover on subsequent cool-down. This would manifest as stringing error, and you can actually see your shots walk up and down the target.

Stringing error is a completely separate issue from barrel whip, but both are endemic to thin barrels.

As to your question whether stainless has more of an issue than chrome-moly steel, I don't know. I certainly saw a lot of stringing during the Accu-strut's R&D phase, but I did not do a differential study on that specific issue.

I do know that cryo-treatment solves the problem. Saw this many times. We routinely send all our test rifles for cryo before we even begin testing.

What is the "cryo treatment?"

quote:

Originally posted by fritz:
A heavy profile barrel on a rifle designed for accuracy exhibits very little, if any, accuracy issues as the barrel heats up and cools down.

Thank you, fritz, for that comment. It directly addresses something I’m discussing in a guidance document right now.

quote:

Originally posted by craigcpa:
What is the "cryo treatment?"

Something like this (available from several vendors).

quote:

Originally posted by sigfreund:

quote:

Originally posted by fritz:
A heavy profile barrel on a rifle designed for accuracy exhibits very little, if any, accuracy issues as the barrel heats up and cools down.

Thank you, fritz, for that comment. It directly addresses something I’m discussing in a guidance document right now.

My first rifle is a 1948 Winchester Model 70 in .270 -- Dad gave it to me many moons ago when he stopped hunting. This rifle has pronounced POI shifts as the barrel changes temperature. Rifles for that era were not free floated and the barrel has a rather thin hunting profile. A local 'smith worked on the rifle to minimize the temperature shift issues, and his work helped to stabilize the rifle's POI. But I've learned that POI rises at least 1 MOA as the barrel warms, and depending on ammo shifts a little left or right with a hot barrel.

I was quite pleased when my precision bolt action rifles, which have M24 profile Bartlein barrels, exhibit no POI change from cold to warm to hot barrels. The barrels are thick & heavy, and they are free floated.

As I acquired ARs, I was concerned they might show POI shifts with barrel temperature changes. Fortunately, all of them show stable POI. Of course all of my ARs are free floated, however their barrel profiles tend to be more middle of the road.

It is worth noting that there are hundreds of types/grades of steels. Numerous types of stainless, hard steels, soft, tough, etc. Rule of thumb in the past has been that stainless steels are generally softer than good carbon steels. Remember when stainless knives couldn’t hold a good edge? Technology has brought us better, and more, steels. Rifle barrels are made with “alloy” steels. A mixture to give the best properties of things like stiffness, toughness, wear resistance and maybe resistance to rust. It is likely that there are some very good stainless steel barrels being made. Spme may be better than the traditional carbon steel barrels. While all this probably has some truth to it, traditional types (myself included) remember stainless making poor knives and think that it will wear faster and not make as good a barrel as other steels. Probably for this reason stainless has had a harder time being accepted as a viable barrel material.

quote:

Originally posted by Chris42:
...stainless has had a harder time being accepted as a viable barrel material.

Maybe decades ago, but not in this century.

If you want a chrome lined, phosphate coated, or melonite treated barrel -- sure, most of these will be chromoly steel.

Stainless steel barrels are the rule in competitions which favors accuracy. Stainless barrels are common in ARs, hunting rifles, and even some rimfire rifles.

quote:

Originally posted by fritz:

quote:

Originally posted by Chris42:
...stainless has had a harder time being accepted as a viable barrel material.

Maybe decades ago, but not in this century.

If you want a chrome lined, phosphate coated, or melonite treated barrel -- sure, most of these will be chromoly steel.

Stainless steel barrels are the rule in competitions which favors accuracy. Stainless barrels are common in ARs, hunting rifles, and even some rimfire rifles.

my first AR heavy barrel was SS in the early 90's,

and a lot of the competitors I shot with had SS barrels,

while it was button rifled, it was quite accurate,