Gunsmithing - How to Rebore a Rifle Barrel Presented by Larry Potterfield of MidwayUSA [.357 Magnum]

Elric

Well-Known Member
So. Without comment, Larry had a low wall rebored to 35 caliber and chambered it for 357 Magnum.


What's a 357 normal working pressure? Buehler? Buehler?
 

RBHarter

West Central AR
35,000 psi . 45,000 cup . 1974 Hornady data , 1992 Speer #12 data , and 48/49/50 data remain the same as earlier data save for dropping Blue Dot circa 2003 for 140 and lighter bullets .
Some data was said to have been changed with the advent of piezometer gauges and strain gauges for pressure measures . The books available to me at the time of my deep search for 357 data did not reflect said changes to maximum loads .
 

Pistolero

Well-Known Member
Good report. Make a wall hanger Browning 95 into a shooter again is a good thing for the world.

Larry can easily afford a REALLY nice shop with all the good toys.

Bill
 

Bret4207

At the casting bench in the sky. RIP Bret.
I should doa video of all the things that can go wrong relining a barrel!
 

Elric

Well-Known Member
Well, where are the nay-sayers? We have a low wall 1885 being rebored and rechambered to 357 magnum, working pressure 35K, and NOBODY has fallen to the floor in spasms over potential liability. Sure, Larry said he's gonna use 38 Special loads, but what if some galoot down the road sticks in a CORBON +P+ self defense load restricted to Rugers or Freedom Arms?

Makes me want to pull my 38-55 low wall out if all of you think a 35K round is just fine...

Thank heavens my Brittany Spaniel doesn't care as long as she gets fed and run hard...
 

Pistolero

Well-Known Member
The issue isn't pressure, at least not directly, it is end thrust. 35,000 psi over the inside of that small case,
ignoring the friction of the case on the chamber walls, puts a normal force on the breech block
of about 3500 lbs. The Low Wall was factory chambered in .44-40. Guessing at the inside rear
case diam at .450, the area is 1.6 times the .357 case inside area. SAAMI pressures are CUP, so not
directly usable here. I decided that .45 ACP std pressure is probably about what PSI a .44-40 would
do. They could push a 200 gr bullet 1000 fps in a BP revolver, so that is about what
you can get with a 200 SWC in a .45 ACP at max pressure, so pressures are in the same ballpark. SAAMI
limit on .45 ACP is 21,000 psi and that gives a case thrust on .44-40 of just under 3200 lbs. So, with
full magnum loads, he may be giving it 10% more force on the breech block than .44-40. I don't think they
are anywhere near running within 10% of problems with the original cartridges, so it is probably
just fine for them some of the time. Maybe a steady diet of max magnums might be detrimental
in the long term, but probably not. I would bet that the safety factor is more like 2X normal
pressure requried to get an actual failure, likely more.
Two issues on pressure containment - rupturing the barrel, and bolt thrust. Of course the other
issue is how an action would deal with a failed case. In this caliber the only area of unsupported
brass is at the extractor, a small area of solid brass head. Any brass neck or body splitting would be
forward and entirely inside the chamber.
OK, so you say you have a .38-55 the rear case area there is around 1.32 times the .357, the only pressure
for SAAMI is 30,000 CUP. No real conversion, but if we work it out saying CUP=PSI (not really valid
but better than rolling dice, maybe) you get a breech block load of about 4,000 lbs. That is certainly
not a precise number but is at least in the ballpark.

Bill
 
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Brad

Benevolent Overlord and site owner
Staff member
The new sayers are out there, I just happen to be one. I don’t know enough to make a good judgement. Bill, however, does have that kind of knowledge.

I have a feeling that if Larry felt it was even remotely dangerous he wouldn’t do it.