Looking for some help

[Cap8523]

hello I have a x caliber barrel that is 416r stainless steel. When I was tapering it I got a little a head of myself and after threading for the action and the recoil lug (Remington 700) the area behind the recoil lug is about 1.17 for 3 inches then tapers down to 900 at the muzzle.

My question
I have tried multiple times to figure out the hoop strength but I guess I can't understand the math. When I do the math I'm getting 98k. Does anyone know the strength of the 416r and how to figure out the hoop stress? Is the 416r at that size strong enough or should I get a chrome Molly barrel? The barrel will be done in 338 rem ultra mag. Thank you in advance for any help on this matter

 

[savagedasher]

hello I have a x caliber barrel that is 416r stainless steel. When I was tapering it I got a little a head of myself and after threading for the action and the recoil lug (Remington 700) the area behind the recoil lug is about 1.17 for 3 inches then tapers down to 900 at the muzzle.

My question
I have tried multiple times to figure out the hoop strength but I guess I can't understand the math. When I do the math I'm getting 98k. Does anyone know the strength of the 416r and how to figure out the hoop stress? Is the 416r at that size strong enough or should I get a chrome Molly barrel? The barrel will be done in 338 rem ultra mag. Thank you in advance for any help on this matter

I would call the barrel company . Larry

 

[Cap8523]

I did and not much help couldn't tell me anything

 

[savagedasher]

I did and not much help couldn't tell me anything

Call them back . Never take a non answer when it comes to safety. Larry

 

[savagedasher]

I did and not much help couldn't tell me anything

Call them back . Never take a non answer when it comes to safety. Larry

 

[riflewoman]

For 416r the prperties are a bit dependent on the final heat treatment. The lowest heat treated grade has a static strength of about 110 ksi. With a chamber diameter this gizm calculated a hoop stress of 110ksi for a magnum chamber. http://www.engineeringtoolbox.com/stress-thick-walled-tube-d_949.html

Hoop strength is complex but one thing to consider is that the hoop stress is maximum at the chamber wall. One thing to consider is that if the barrel yields it will only yield a small amount and then actually be stronger. The military does this with some cannon barrels. The phenomenon is called auto frettage. Call the barrel manufacturer and ask for his heat treatment and Brinnell Hardness.

 

[carlsbad]

Using conventional formula for hoop stress, I get 90ksi also. However, the hoop stress formula is for thin walled, large D/t geometries, which a gunbarrel chamber isn't. I don't know of any analytical formula to calculate stress in such a thick walled, small diameter pressure vessel but I haven't done a search. Stress goes up with diameter so the inside diameter of the chamber is stronger than the outside diameter.

416R is good stuff and 100ksi yield strength minimum should be a good assumption.

But, if 90 ksi was the real stress in 100ksi material, you wouldn't want to get anywhere near it. However, your stresses aren't significantly higher than a 308. Using the same traditional formula, I get about 65-70 ksi for a 308. This would not provide adequate safety margin. So we know that the actual stresses are lower. Looking for bounding real iife examples I googled "savage small shank 338" and found that while people are scared to build a 338Lm on a small shank, several people claim that 338 RUM is perfectly fine and they have done it themselves. That calculates out to 103ksi and bounds your barrel. NO, I'm not saying that I recommend it.

Your barrel stresses may have eaten into the safety margin. I would bet a whole lot of money it wouldn't fail. But injury or death is another subject. I like my barrels 1.25' at the chamber but most are finished at 1.200 so .030 is pretty minor.

All of this said, you have to make your own call but lots of experimental data says you'll be fine.

--Jerry

 

[carlsbad]

Call them back . Never take a non answer when it comes to safety. Larry

You're not ever going to get them to drop everything find an engineer to calculate a barrel stress for you. Only internet nerds will do that for free. --Jerry

 

[savagedasher]

You're not ever going to get them to drop everything find an engineer to calculate a barrel stress for you. Only internet nerds will do that for free. --Jerry

A friend had his come apart after he had the barrel octagon . Blew his thumb off . He nearly died. I gave my best advice .
If the barrel company couldn't tell me I would trash it. Larry

 

[carlsbad]

An octogon removes almost 8% of the diameter which can be a much higher percentage of the wall thickness around the chamber--up to 33%. Additionally, any non-round shape adds significant stress intensification factors associated with geometry. If he started with the Savage small shank, he was really adding all the factors up against himself. I am glad he survived but sorry for his loss.

Let me know when you find a barrel manufacturer that will do these calculations for you. If a nameless guy on the other end of the phone says, "Sure, it'll be ok", I'm not sure what you've gained.

--Jerry

 

[savagedasher]

An octogon removes almost 8% of the diameter which can be a much higher percentage of the wall thickness around the chamber--up to 33%. Additionally, any non-round shape adds significant stress intensification factors associated with geometry. If he started with the Savage small shank, he was really adding all the factors up against himself. I am glad he survived but sorry for his loss.

Let me know when you find a barrel manufacturer that will do these calculations for you. If a nameless guy on the other end of the phone says, "Sure, it'll be ok", I'm not sure what you've gained.

--Jerry

You can tell him he is okay. I won't.
Larry

 

[carlsbad]

Larry, did you read what I said? I was very careful not to say that. I've asked myself what I would do if it was mine and I really don't know. --Jerry

 

[savagedasher]

Larry, did you read what I said? I was very careful not to say that. --Jerry

Didn't you read what he said?
It was threaded for a Remington and it was 1.17 for 3" Behind the recoil lug and tapered to .900 at the muzzle. To me that was impossible. Larry

 

[dkhunt14]

Didn't you read what he said?
It was threaded for a Remington and it was 1.17 for 3" Behind the recoil lug and tapered to .900 at the muzzle. To me that was impossible. Larry

I would like to know how it is turned to that diameter behind the recoil lug. Usually behind the lug it is thread diameter. Never seen 3 inch threads. What is the diameter of a Remington over the chamber? Matt

 

[Gundoktr]

"Your barrel stresses may have eaten into the safety margin. I would bet a whole lot of money it wouldn't fail. But injury or death is another subject. I like my barrels 1.25' at the chamber but .008 is really minor."

Carlsbad, I think your math may be flawed, that would be 1.25" - 1.17" = .080"

 

[ab_bentley]

On the WSM Winchester the shank diameter is 1.150" for 1.5" from the shoulder tapering to a little .650" @ 24". Mind you this is a 60k psi cartridge.

 

[carlsbad]

"Your barrel stresses may have eaten into the safety margin. I would bet a whole lot of money it wouldn't fail. But injury or death is another subject. I like my barrels 1.25' at the chamber but .008 is really minor."

Carlsbad, I think your math may be flawed, that would be 1.25" - 1.17" = .080"

Good catch. I really meant to say .030 since so many gunbarrels are 1.200. I didn't finish my thought here. I meant to come back to this. I like the full 1.25 for my heavy barrels but many are finished at 1.200. Large shank savages, used for big cartridges, are 1.119. So the OP's barrel still larger than savage barrels.

I'll go edit my post above.

thanks, Jerry

 

[watercam]

Not that I know what I am talking about but does the receiver ring factor into the calculations at all? Part of the chamber is contained there is it not?

 

[carlsbad]

Today I did some investigation and I'm still not happy with the safety factors that empirical calculations are coming up with. I don't believe rifles would be designed so close to the yield strength of the materials. Especially since they may fire thousands of round resulting in fatigue failure if the stresses are too close to yield.

However, I did find Lame's formula for stresses in thick walled cylinders which is what a gunbarrel is. The simple hoop stress formula is really just too much of an approximation for this geometry. Using Lame's formula and the following numbers: pressure 65,000 psi. Chamber diameter .550" Barrel diameter 1.17" I got the following:

Stress at chamber wall: 100KSI.
Stress at D=.787": 59ksi
Stress at OD: 37ksi

So the stress at the OD is fine. I'm still not happy with the stress at the ID for crack initiation. However, we are ignoring the brass which probably significantly reduces the pressure seen at the chamber wall.

Here are the calculated numbers for a 1.25" diameter barrel:

Stress at chamber wall: 96KSI.
Stress at D=.787": 55ksi
Stress at OD: 31ksi

The real way to calculate stresses today is numerical analysis. However, the guys who designed the Remington 700 and all the rifles that came before it didn't have the advantage of computers. Of course back then a lot of information was obtained experimentally and failed chambers and the injuries/deaths that came with them were not as unacceptable as they are today.

--Jerry

 

[carlsbad]

Not that I know what I am talking about but does the receiver ring factor into the calculations at all? Part of the chamber is contained there is it not?

Yes, this is being ignored. It is backed up by the action that it screws into but the portion below the recoil lug isn't. More evidence that the stresses aren't really as high as we're calculating. --Jerry