Jimacat will by by shortly to explain, but here's a Garand converted to 458 Win Mag he found. It's been fired 20 or so times, so it functions fine.

WOW!
I remember an article by Jack Lott on making a 458 on a Browning 338 semi. He said it was a bitch to make feed, and didnt reduce recoil like he hoped.

I cannot wait to hear about this.


I always wanted to redo one in 9.3x62.

I applaud the gunsmith. But it ia very bad idea; do not shoot it!
Back thrust is way more than an M1 was designed for. Fortunately M1 receivers and bolts are very strong, but the CMP doesn't even want you shooting 30-06 ammo in them.
I know, it will work fine, until some day, it cracks.

To paraphrase the late, great Jeff Cooper, "an ingenious solution to a non-existent problem."
I read about these several years ago. Never understood the reason for this other than someone wanted one.

Oh, I completely understand the appeal and the rationale and impetus for the build. Doing something that has never been done is my forte. If we didn't have creativity and ingenuity, everyone would just shoot a 30-06. Boring. Just that the M1 components were not designed for Magnum level back thrust.
Now, Garand components are also very strong, so it will probably work fine. How long?

Since the Garand is a gas operated system I'd think the gas could be regulated so that it would be about the same as it would be with the 30-06. The thickness of the steel around the bore and chamber would be another matter.

My question is where can you use it?

Maybe some of the Alaska bear guides who favor the .458 but as far as I know, none of the African safari destinations will allow import of a semi-auto.

If it's just to have it for the fun of having it ... yeah, I get it.

It would perfect for hogs. Elelphants. Or anything. Plinking; need is not ever a question.
Clowd; of course the gas can be regulated by the size of the gas port; we do that when converting to 7.62; open up the gas hole from .078 to about .090 or so.
However, that is not the issue, nor is radial strength of barrels; modern CM barrel steel is very strong so that is not important. What is important, is the back thrust on the bolt lugs. 60K PSI, and a .532 case head, produce an axial (back thrust) pressure that the M1 was not designed for. Again, they are very strong, so it will work; but for how long? And the M1 was not designed to shoot 30-06 either; in fact, the CMP recommends against it.

That thing scares me!

The .458 Win. Mag. is a far cry from M2 Ball or M72 Match.

No thanks.

Aw, It is just a ladies gun for the gals that are bad shots!

Hip

quote:

Originally posted by dpcd:
Fortunately M1 receivers and bolts are very strong, but the CMP doesn't even want you shooting 30-06 ammo in them.

Might you clarify this? I took a CMP Garand build class a few years ago, and we all built rifles chambered for .30-06. Now, the powder burn rate is important for this gas-operated rifle, and there are recommendations in this regard.

As I said; the CMP does NOT recommend that the M1 be fired with 30-06 ammo. That has higher pressure than the rifle was designed for.
NO M1 was ever built in 30-06 caliber!
ALL of them were built for the M2 Ball and M72 NM ammo. Those are not 30-06 as defined commercially, in any way.
Do not confuse the commercial 30-06 with the Military ammo specs.
So, while you might have an M1 with a chamber called a 30-06, the system was not designed to fire current commercial 30-06 ammo. Pressure is higher than the rifle was designed for.
And yes, gas port pressure is important because you will bend the operating rod. Ok, they are already bent twice, but I mean in the wrong direction.

I’m not saying a 458 Win Mag Garand will work well for very long… but I’ll have one to play with. I promise I’ll report back after 50-100 rounds!

RC

Wear lots of protection like space suit.

Tom,

Leather jacket, Ray Bans, driving gloves. I’m going to look like a boss.

RC

i don't know when pressures will defeat materials - but i know it will be interesting

You will definitely make a cool looking corpse!
M1 receivers are made from case hardened 8620 steel. They are actually very strong. I have never seen one fail.

Tom.

I understand accelerated wear…but catastrophic failure…? I’ll call you when it happens…and it’s on me when it does…

If you can’t tell, I can’t wait to shoot it.

RC

It's been a long while, but I remember reading an American Rifleman article about a 458 conversion while waiting in a barbershop as a kid back around 1980 or so and thinking it was the coolest thing I'd ever heard of.

(I remember the time frame because we'd just moved to a new town and the shop closed very shortly after we arrived).

EDIT: Given the decades that have passed, I assume that if these sheared the lugs and blew up after 50 rounds we'd have heard about it. On the other hand, given the decades that have passed if this was a great idea that set the world on fire I assume we'd have heard about it!

M1 receivers do not wear; they are deeply case hardened, 8620 steel.
Again, magnum 60K psi, .532 case backthrust (I can calculate it if you want), is far more than it was designed for (.473 case head at 50K psi, and you use the ID of the case for the area that the pressure is acting against). This applies to any belted mag on an M1. The fact that it is 458 is immaterial.
You will be fine. Probably. All this is just worse case scenario. After all, we chamber high pressure cartridges for actions that were originally designed and built for far lower pressures, don't we?

Tom,

How do you explain the 308 Winchester M1 Garands that the CMP puts out? The 308 has a SAAMI pressure of 62,000 psi and the CMP makes no statement about using specific under-powered ammunition with those rifles so configured. They would have to work over the gas system to function with 308 pressures but that’s the simple part. If you regulate the amount of energy going into the system and keep up with lubrication, the op rods shouldn’t see any increase in abuse over M2 ‘06 ammo in a standard Garand.

Easy; and I have built many 308 M1s. And so did the Italians, who converted thousands to 7.62, as did the US Navy, both with chamber inserts, and later, new barrels (many of them made at RIA). The 308/7.62 generates less gas than the commercial 30-06, and the port volume is lower 23 inches down the bore; chamber pressure is not the issue in this case.
You even have to open up the gas port from .078 to .090 or more, just to get the action to function. If you don't, you will get short strokes most of the time. I actually have a T35 M1; one of the original test rifles used to develop the T65 cartridge; which became the 7.62 NATO, and also the .308 Winchester. A very rare rifle.
Firing commercial 30-06 in them, will bend your operating rod.
I wonder what the gas port OD is on the .458?

Chamber pressure literally dictates the bolt thrust. Where is the issue?

I’m not one to strike a boot to the equine deceased but…

Fact 1

The Civilian Marksmanship Program (CMP) recommends the use of specific lower power ammo in the 30-06 held to about 50,000 CUP or about 55,000 psi. I think this is why people become uncomfortable at the thought of a 458 win mag Garand. This max load develops a bolt thrust of about 9,900 psi

Fact 2

The CMP also rebarrels Garands for 308 Winchester. The 308 develops 62,000 psi. This max load develops a bolt thrust of 11,160 psi.

Fact 3

A number of barrel makers make Garand barrels in 270 Winchester which develops 65,000 psi. This max load develops a bolt thrust of 11,700 psi. I would argue that this build would use slower powders so there may be an issue with pressure curve Here is the gas system we’re unchanged from the standard locations.

Fact 4

The 458 Win Mag uses a 500 gr bullet at 2050-2150 fps. The pressure tested load data I have available shows 50,000 to 53,000 psi to develop those velocities using Accurate 2230 or 2460 powder. The maximum load develops a bolt thrust of 11,660 psi. Yes, one can select loads that will push 60,000 psi but I wouldn’t recommend pushing any envelopes with this project.

Fact 5

The Garand has a very flexible gas system. We can estimate the ideal location of the gas port based on pressure available to do work in Quickload. You can then drill a small gas port and work your way up until it cycles reliably with any load and any powder that develops safe pressures for the 458 Garand. No op rods need be harmed in this venture!


OK. So who has about 300 pieces of 458 Win Mag brass and 40 enbloc clips to sell me???

Aren’t you being a bit disingenuous about this?

The CMP recommends against newer high velocity .30-06 because of changes in the powder and excessive gas causing op rod bending.

It damages the rifle, but is not unsafe in the sense of hurting the shooter.

Yes the Garand was originally designed around a 7mm round with much less performance. But they did redesign it to function around the then current .30-06 ammo and have wide enough tolerance that it could deal with vagaries of wartime production.

The fact that all of these 80 year old rifles are still working after all these years tends to say they work just fine with .30-06 ammo, at least until the manufacturers started trying to make the .30-06 into a .300 H&H.

quote:

Originally posted by dpcd:
It would perfect for hogs. Elelphants. Or anything. Plinking; need is not ever a question.
Clowd; of course the gas can be regulated by the size of the gas port; we do that when converting to 7.62; open up the gas hole from .078 to about .090 or so.
However, that is not the issue, nor is radial strength of barrels; modern CM barrel steel is very strong so that is not important. What is important, is the back thrust on the bolt lugs. 60K PSI, and a .532 case head, produce an axial (back thrust) pressure that the M1 was not designed for. Again, they are very strong, so it will work; but for how long? And the M1 was not designed to shoot 30-06 either; in fact, the CMP recommends against it.

NO idea what your point is. But I wish everyone would stop saying that the M1 was developed for the 30-06; it wasn't, and was never intended to fire it.
As for the 458, I am basing my opinion off the SAAMI max of 60K PSI, and a mag head size. That will give a bolt thrust of almost 14K pounds. Of course, if you use lighter loads, the pressure, and subsequent bolt thrust will be less.
For those who might wonder; axial (bolt) thrust is a function of not only chamber pressure, but the diameter of the piston available for that pressure to push against. Not the case head, the internal surface area.

quote:

Originally posted by Wildcatter:


Fact 4

The 458 Win Mag uses a 500 gr bullet at 2050-2150 fps. The pressure tested load data I have available shows 50,000 to 53,000 psi to develop those velocities using Accurate 2230 or 2460 powder. The maximum load develops a bolt thrust of 11,660 psi. Yes, one can select loads that will push 60,000 psi but I wouldn’t recommend pushing any envelopes with this project.

just to be clear, factory 458 win is 60kpsi -

Which was my point all along.

My point is that you are wrong when you say it was never intended to fire .30-06.

Yes, the original development was with an experimental 7mm round.

However, they redesigned it for .30-06. If it was not intended to use .30-06, then the government would not have issued it for use with it.

Your statement about the CMP is also a misstatement. They don’t tell you to use something else- they state use .30-06 ammo that is made to duplicate the standards of the issued ammo, as using newer higher velocity ammo causes too much gas pressure at the gas port, and can damage the op rod. Not that they say it’s unsafe or that the rifle was never intended to fire .30-06 ammo. As I recall, the military did use AP and tracer ammo, and did use rifle grenades- all of which are probably harder on the rifle than using modern ammo.

If the guy who made that .458 version is saying it’s safe, he’s the one standing behind it.

My suspicion is that if you use a .458 WM Garand, you will have more trouble with wear- and it doesn’t seem like a wise choice… which I get your arguments about- but saying it was not intended to shoot .30-06 is like saying the AR 15 isn’t intended to fire the 5.56 round (because the original design was in 7.62, and then they went to .222 mag, etc in the design phases.)

quote:

Originally posted by dpcd:
NO idea what your point is. But I wish everyone would stop saying that the M1 was developed for the 30-06; it wasn't, and was never intended to fire it.
As for the 458, I am basing my opinion off the SAAMI max of 60K PSI, and a mag head size. That will give a bolt thrust of almost 14K pounds. Of course, if you use lighter loads, the pressure, and subsequent bolt thrust will be less.
For those who might wonder; axial (bolt) thrust is a function of not only chamber pressure, but the diameter of the piston available for that pressure to push against. Not the case head, the internal surface area.

All of this is relative and speculation if you haven’t done it. I haven’t done it yet. I personally would not build a 458 WM Garand and then dump 100 rounds of random factory ammo through it. Then again, I shoot almost no factory ammunition through anything I build and shoot. I’ll bet our 458 Garand lasts many 100s of rounds without bent op rods, cracked bolt lugs, or peened locking areas in the receiver. If there are failures, I’ll be the first to post about it!!

RC

There used to be a company that did 458 WM conversions on Browning BARs (the hunting rifles). They did a nice job.

SAAMI max pressure for 30-06 is 60K PSI. Which 30-06 commercial ammo is compliant with the CMP directive?
I don't know either.
As for the 30-06; I have yet to see any Military weapon that is marked for it; that is strictly a commercial designation; let me know if you find one.

The 458 will be fine if you keep pressures low as you indicate. Just don't shoot 30-06 in it!

quote:

Originally posted by Austin Hunter:
There used to be a company that did 458 WM conversions on Browning BARs (the hunting rifles). They did a nice job.

And those (edit: Factory) BARs were made in .300 WinMag and .338 WinMag.

I remember seeing pics of a Garand conversion in .338 WinMag.

Now I want an M1 Garand in 416 Taylor.

I saw a conversion to 35 Whelen once. I thought that was an interesting and useable combo.

I had an idea of converting a Garand to 35 Whelen at one point and bought the adjustable gas block that McCann Industries made. Replacement gas nut with several screws each with a different sized aperature. Never followed through with it though. I love the idea of a cartridge conversion on the Garand.

While we are wondering away from the original topic, I have wanted to do a .35 Whelen on Browning BAR (the sporting rifle, not the military one).

There's more to this than just the diameter of the rim. A straight wall case will produce less back pressure than one that is necked down. I'm not speculating, or calculating. I have actually tested it to failure.

A 458 Win Mag case, necked to 30 caliber, will in fact produce more back pressure than a 30'06, but with the case straightened out to 46 caliber, that pressure will be reduced. I have no idea if it's reduced back down to 30'06 levels or not.

Tony