Durability of .32 H&R revolvers converted to .327?

[Cosmodragoon]

Since far too few revolvers were made for the .327 Federal Magnum, many shooters have taken to having them made. Since most of us don't have thousands of dollars sitting in a custom gun budget, a popular choice has been to convert guns chambered for the .32 H&R magnum. Given the much higher operating pressure of the .327, how much extra wear and tear should we expect?

Are there specific models of revolver that are better than others? Are there models that you would definitely not recommend converting? Are there suggested limitations on what type of ammo you should use?

Since they only ever made it in a 3", I'm planning to have a 4" Sp-101 converted from .32 H&R Magnum to .327 Federal Magnum. It seems like Rugers are generally built tougher than many other guns but any thoughts would be appreciated. Thanks!

[Dixie Gunsmithing]

Anything that will alter the chamber bores of a cylinder, especially opening them to a larger diameter, shouldn't be done. The cylinder is designed to withstand a certain set pressure, and if the chamber wall thickness is thinned, that pressure rating drops. The only way to do it would be to make a larger cylinder, but it wouldn't fit in the frame. Then, even if the chambers weren't altered, a hotter load would exceed that set safe pressure. This all is why the manufacturers have different frame sizes.

The barrel is next, and is designed towards the rear for the pressure it will see when the bullet passes into it. If it is exceeded, it can rupture, or actually be blown out of the frame.

Last, is the added stress to the top strap, which could cause it to crack.

The only way to safely do it, would be to use a revolver that is designed for a greater load than you want, and downsize it.

[James K]

Given a fairly modern revolver chambered for .32 S&W LONG, reaming to .327 H&R Magnum is iffy, but not usually that dangerous. But to ream to .327 Federal Magnum is a whole different ball game. Unless you enjoy picking pieces of gun out of your eyes, don't do it.

As for reaming any of the old solid frame or break top gun chambered for .32 S&W, to anything else that would be a disaster looking for a place to happen. Even shooting .32 ACP in those guns (a common practice) is dangerous!

Jim

[Cosmodragoon]

Please forgive any confusion. When I said ".32" in the question, I assumed that people would understand it to mean the aforementioned ".32 H&R Magnum". (Did they even make an Sp-101 for .32 S&W or S&W Long?) I edited the original post to clarify. I am thinking about converting an Sp-101 in .32 H&R Magnum to .327 Federal Magnum. Thanks again.

[Old Stony]

I don't think I would be afraid to convert a single six from the .32 mag.
I have a J frame S&W I converted years ago from 32 long to 32 mag and have fired it many times. It actually shoots really good in that caliber, but you are talking about converting to something with a lot more pressure involved.

[warrior poet]

Rugers are usually tanks... and it will PROBABLY take it... but, and a very big but at that, is that you are asking LESS METAL to withstand MORE PRESSURE. You would probably be better off to get a cylinder made with one less round. (A six shooter becomes a five shooter, etc...) Then you have the extra metal to withstand the extra pressure. Just a thought.

[Jim Watson]

Since the SP 101 was available in .327 and is still available in .357 Magnum, and since Ruger actually authorized M. Ayoob's gunsmith to rechamber the early .38s to .357, I would expect the .32 H&R model to handle .327 quite well.

Hamilton Bowen will convert a Single Six .32 H&R or S&W K frame to .327 with a new cylinder. He will rechamber .32 H&R to .327.

[Dixie Gunsmithing]

Ruger would know what their guns could handle, and would be the only advisable way to proceed. It's rare that a gun manufacturer will tell you this, liability wise, unless they are sure it won't fail. Everything is designed around a safe pressure, plus a safety factor of some percent, and in some cases double pressure. I know of some European guns that were proofed at X2 pressure.

I once saw the chamber of a cylinder blown out on a S&W 44 mag, the whole outside gone, and the thought of that happening just raises goosebumps on the back of your neck.

Update:

I thought I would include the below screen capture (not the .44 mag), and a few links.

Photo (C) Werner Mehl (www.kurzzeit.com)


Exp-Rev by matneyw, on Flickr

Link to video of above:

http://www.youtube.com/watch?v=AIi1Nw6GUZ4

A similar video:

http://www.youtube.com/watch?v=epKyIfAJEOY

[James K]

Hi, Cosmodragoon,

You mentioned the SP-101 but your title says .32 H&R revolvers, which would seem to indicate H&R made revolvers. I agree that the SP-101 could probably be converted with no problem, but converting an old H&R breaktop .32 would not be a good idea even if the round would fit in the cylinder.

Jim

[PetahW]

.

Yeah - I'd be more worried about creating a surprise hand grenade, given that the .327's operating pressure is approx 3x that of a .32 Long's & 2x that of the .32H&R Magnum's.



.

[Clark]

CAUTION: The following post includes loading data beyond or not covered by currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.
I have blown up a number of revolvers.
1) Split the cylinders on (3) 38 specials and (1) 32 S&W Long.
The 32 S&W Long was a Colt pocket positive over 100 years old, using a case full of fast powder, and not working up.
Quickload thinks the load was 98,000 psi, which is meaningless.

I have been getting very high velocities with a 100+ year old Colt 32 S&W Long, over 1400 fps with 85 gr bullets. That is using a slow powder, LIL'GUN or 800X. I am not getting great groups. The little revolver kicks.

The cylinder splitting has to do with pressure, wall thickness, stress rising cracks, and inside diameter. It is a very complicated equation to calculate the stress in the steel open ended tubes per Roark's formulas. Those don't even work, as the outside of a chamber is not symmetrically round. But to a first order the stress is proportional to the pressure times the inside diameter divided by the wall thickness. The critical wall thickness is the either the chamber to chamber or chamber to outside, which ever is thinnest.
In the 32 S&W long made in 1907 in the picture that does 1400 fps, the inside diameter is 0.34" while the thickness to the outside is 0.050"

That ratio better than J frame 357 mag revolvers and WAY better than a Ruger Blackhawk 45 Colt.

So with those thicknesses, I am not afraid to work up to the threshold of sticky cases with slow powder in that old revolver. Not afraid of cylinder splitting.

When cylinders split, the pieces go right, left, or up. I have never been hit when shooting. But I have made big holes in wood and metal when the parts went to the right. Don't stand next to anyone trying to split a cylinder. Semi auto pistols and bolt action rifles can throw parts and gas backwards. I hold those differently in testing.

But wait, there's more..
There other things that can get wrecked on a revolver besides cylinder splitting:
2) The bolt the fits in a slot in the frame and fits in a slot in the cylinder during firing, can see stress if the bullet strikes the forcing cone off center. That puts a torque on the cylinder and can open the size of the slot in either or both the frame and cylinder. That makes rotational sloppiness, so the subsequent shots can be even MORE off center. Colts tend to be right on, tight, and stay tight. Smiths start tight, and with a little abuse they get sloppy. Rugers come sloppy from the factory. I have done this with (2) revolvers and bought lots of revolvers that came with this problem.
3) The frame can bend. I have done that once to an Aluminum frame revolver with triple loads.
4) End shake. The cylinder can get loose front to back. I have bought revolvers with this problem
5) The forcing cone can blow out. This has happened to me (3) times with 327 Federal type loads in a 100 year old Colt 32 S&W Long revolvers. Each time I TIG welded up the forcing cone, and re cut it thicker. The repaired thick ones have never failed.

[Cosmodragoon]

So, after similarly stating that:

All the posts in this thread discuss custom modifications to a firearm for use at operating pressures far beyond what the manufacturer originally intended. USE THIS INFORMATION AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.

... it seems that a very important consideration in preventing fatal energy delivery to components is alignment. Either of the smiths I was considering for this project offer a variety of services and I seem to recall "eliminate end shake" on the list. I'll have to have this conversation with them as we explore those other options.

The first potential problem I considered was the forcing cone. Plainly stated, forcing cones see a lot of force! In addition to receiving the bullet, they are effectively ground zero to the propelling explosion of every shot. I may call Ruger tomorrow and try to find out what, if any, differences exist between this forcing cone and the one they used on their shorter-barreled Sp-101 that actually comes in .327 Federal Magnum.

[Cosmodragoon]

BTW, here is the candidate:

[Clark]

Cosmodragon,

Have you got calipers?

[Cosmodragoon]

Clark, I have a basic caliper around here somewhere. Unfortunately, it seems to have been temporarily displaced in my last move. Were you thinking of using it to compare the width of the thinnest section of the cylinders between recently produced Sp-101s in .327 Federal Magnum and the older Sp-101 I have in .32 H&R Magnum?

[Cosmodragoon]

Coincidentally, I called the Ruger in New Hampshire where the Sp-101s are made earlier today. I had the lady in customer service find me the resident expert on Sp-101 design. I asked the expert if there are any structural or metallurgical differences between Sp-101s recently produced in .327 Federal Magnum and the ones produced in .32 H&R Magnum a decade ago. He stated that everything is exactly the same except for the chambering. He said that there was no change to the composition, processing, or structure of any part, from barrel to forcing cone, except for that.

I know from putting a .327 round into the chamber that the difference is only in where the throat starts. The .327 slides in like butter but stops just short of fitting all the way down the chamber. So correct me if I'm wrong, but we are really talking about a very small change to the chambers in this conversion.

If all other things are equal, then I don't see how there would be any large gap in durability between this project and the Sp-101s sold in .327 up until just recently.

[Clark]

I am impressed you got a call through and got answered.

That is rare.

I was on a gun forum 15 years ago and so I called WD-40 and got through.