I searched for this, but couldn't come up with a good answer.

I have a #2 Shilen stainless barrel in 30 Cal that has had the cylinder portion cut back about 1.5". It was rechambered from .308. This leaves enough to thread, but only about a .375" cylinder at the barrel shoulder before it tapers.

The current chamber is 30-06. I don't see an issue with that cartridge.

Could it be rechambered to .300 Win Mag and have enough meat in front of the chamber?

Jeremy

A #2 in .300 win is certainly going to set you back a bit. But not considering that factor, have you thought about contacting Shilen for their opinion? It would seem at least that they might be in the best position to know.

Some years back another prominent barrel maker declined to cut a particular custom contour for me citing a potential strength problem such as you describe.

I wasn't sure if they would venture and answer since it has been cut back so far. Still it is worth a try.

Thanks,

Jeremy

I think he is saying the straight (1.2" or so) part is .375 long.
IIRC the Winchester FW goes down to 1" diameter over the camber.

Mark

Yes, the straight portion is 0.375" long, 1.15" in diameter at that point.

0.98" at the shoulder of the cartridge (estimating where the .300 Win shoulder would be), 0.89" at the throat or a little in front of the throat. Then it tapers to 0.75" 2" further on where the taper changes.

Jeremy

TC Encore barrels are 1" diameter and available in ultra mags.

Mark

I sent Shilen an email to see what they think.

I appreciate the thoughts on it. Mark, good point on the Encore barrels, and they weld a lug to the chamber.

Looks like I have some more research to do, or just leave it be. Maybe just questioning it makes it a bad idea. It shoots great as a 30-06.

Jeremy

Everyone should have a good shooting .30-06.

quote:

Originally posted by Toomany Tools:
Everyone should have a good shooting .30-06.

Very true.

Jeremy

quote:

Everyone should have a good shooting .30-06.

I've been building and buying rifles for 50 yrs. Never owned (that I remember) a 30-06 or 270. Loaded for a number of them. Simply never owned either.

Jeremy,
Shilen is closed for the NRA show. A couple questions. Shilen list their breech ends as 1.220 in diameter. How long is your barrel?


http://www.shilen.com/contours.html

I have never owned a sporting 30-06 or 270 either; too common. Plenty of M1s and 03s though.

The barrel is 23.75" long. I don't know how long it was when it started life, or what might have been done to it. It came to me on a rifle that wouldn't group. I pulled it and found that the threads were improperly cut. They looked like the wrong angle was used to feed the tool in.

I cut off the shank, re-threaded and chambered it in 30-06 for a Remington 700 that had a pitted barrel.

I have a need for a lightweight rifle and like .300 Winchester better than 30-06, so I was thinking of rechambering it if it would work.

Jeremy

It's pretty simple to figure out if you have a cartridge, the barrel and a micrometer. Most of the American factory barrels have .250 inch wall thickness over any given point of the chamber. As a rule, I think .200 inch wall thickness is the crazy, European person minimum. I have heard and read of barrels being turned to .125 over the chamber and surviving 55,000 PSI but you would have to be nuts or just experimenting to do it.

As far as stainless bursting at low temps. I think I read they are talking about -40F to -50F. At -45F the tires of your car are frozen with a flat spot for the first 5 minutes of your drive to work in the morning and spit freezes in the air. The coldest I have ever seen it here in Edmonton is -46F. So unless you happen to live in Alaska or have a winter home in McMurdo, I wouldn't worry about it.

I have a chart that was given to me in gunsmithing school. I'll see if I can dig it up.

There is meat surrounding the cartridge. The thinnest area is at the shoulder and it calculates to 0.23" wall thickness.

However, the taper at that point is pretty steep and I am more worried about the few inches immediately in front of the chamber.

That section sees the main pressure peak.

I pulled out my textbooks from college. Looking at Charpy impact values for 410/416 stainless versus CM. At -40 degrees, the impact strength is lower for stainless, but not horrible. It is very dependent on the heat treatment of the steel and the specific alloy.

The higher concentration of chrome carbides in stainless contribute to the lower impact strength at low temps. Chrome carbides are angular and allow for tiny stress raisers in the steel structure. Again, it is very dependent on the heat treatment.

There is the science lesson for the day.

I did hunt once up by Augusta, MT when it was -43F out. I shot a big muley buck and immediately wished that I hadn't. My hands were froze cleaning him and the rest of me froze packing him out.

Jeremy

At roomtemperature, the shearstrength of most CrMo steel Used for barrelmfg. is about 30% stronger than 410/416 used for barrelmfg.
At 40deg below freezingpoint Most CrMo has lost 20% of the strength, compared to 410/416 that has lost about 50%.

Sorry i dont have the numbers in psi or whatever you use, i only have them in metric.

CrMo at roomtemp 975 kg/mm2 At 60F below freezingpoint 780kg/mm2
410/416 at roomtemp 750kg/mm2 at 60F below freezingpoint 325kg/mm2.

Barresl in CrMo ar normaly designed to handle presures from 200-300% higher than normal

Needed wallthicknes is a product of Steelstrength in relation to the holediameter(internal surfacearea) Larger hole needs more sorounding wallthickness to handle the same presure.
A 416 rigby chamber requires the dubbel in wallthickness around the chamber compared to a 223.

One can't compare wallthickness in the threadarea to thickness in front of the reciever, as the threadarea is supported by the reciever.

dpcd
Your idea is only correct if you use flat thread.
When you use 55 or 60 Deg threads that is thightened against stop, they become radially supporting, and most recievers has quite a bit of radial strength in the front.
So no matter of what you think is the intention, the reviever supports the barrelthread radially.

In theory, the receiver ring is a safety valve of sorts. If the vessel swells beyond its normal, elastic capabilities, the receiver ring will catch it to add to the radial strength. If it reaches this point one can bet that the chamber has permanently swelled and is ruined. As long as common sense is applied and there is enough support in the chamber walls the brass case should fail like a pop valve or sheer pin and sacrifice itself to prevent major damage to the barrel.

In theory.

I always love how people obsess over the diameter in front of the receiver without ever thinking of the thread diameter, especially the minor diameter.

Yeah, while it adds to the radial strength if the barrel fails, it's certainly not designed to provide radial, structural strength on every shot. In all truth receivers are a bit to hard to act as pressure vessels anyway. Their design is to retain moving, hard wearing parts and provide lineal strength to hold the cartridge against the breach face, not radial strength.

At best, the receiver is just like the stock and the mag box. When you eventually do something REALLY stupid they kind of get in the way to slow down or deflect shrapnel.

dpcd
As they says " The devil lies in the detail"

I wrote When tightened against stop
And MOST recievers.

I thinks that those 2 sentenes covers quite a bit of normal rifles.
I dont give a SHI* about what a few selfpronounced miraclemakers do of changes on etc. takedowns or like.
As i also wrote, most barrels is from 200% - 300% stronger than needed.
That is the build in safety from designers, to save the asses on the not so tecknically gifted rebuilders

Sorry dpcd
If a part with equal shearstrength and thicker or equal wallthicknes, is of no relevans in your perspective. Then it might be a Little difficoult to discuss designstrength with you.
It seems a Little as discussing neuclear science with a naive farmers daughter at age 7

I dont think you should need a degre to se that on most barrels/actions, the combined wallthikness of the threaded area is way thicker than the barrelshrank in front of the reciever.

But Again most barrels are 200% -300% stronger as normally needed.

And regarding your statement about that the barrel has already failed before the reciever starts contributing. Then please remember that there is both elasticity and more relevant what they call "elongation" witch is normally higher than 15% on barrelsteel.
Elongation % is the percentage that a piece of steel stretches from the yield strengt, until it reaches rupturestrength. Under the elongation the needed forcr has to increace apx 20% to go from yield to rupture.

Please try to understand, that design and strengthcalculation, is something that mfg's Work with every day,
The fact that under normal condition, you dont need to eat from your safetymargin, absolute don't mean that decent designs doesn't take all factors in concideration.

A barrel in a magnumcaliber kan withstand up to the double preasure before bursting in the threadarea, when tightly fitted in a exc. Remmington or Mauser reciever.
I do though admitt that only on the Remmington or other decent PF actions, you get the full bennefit, because of the lousy caseheadsupport on the Mauser

on a CRF rifle a standardcasehead lets go around 5.500 bar(apx 80.000psi). on a decent designed PF action the casehead is supported enough to withstand from 9.000 - 11.500 bar(apx 133.000 - 161.000 psi)
The more scary parts, is that when a casehead lets go, it often is werry tough on the action, and on several m98 and m96 i have blown up, they were totally werck from beeing exposed to presures that didnt even giv heavy boltlift in a modern PF rifle

The 1917 you mentioned, has to my memory a pretty large treaddiameter, compared to manny other designs, therefor relyes less on action support under extremes.

Designing a firearms just strong enough to handle normal situations, is a disaster waiting.

I have seen several bulged chambers, where the chamberwalls has ben stretched way into its yeldstrength, and where the reciever has ben the factor preventing a total rupture.

If you have a decent casehead support, the need for chamberstrength goes up, as the ability to introduce load, increases. If you only has a CRF action, the normal senario, is that the casehead blows at fairly low presure, creating a Whole different loadsenario, wich often results in blown extractors, split recieverrings and other nasty stufs.