M1 c.u.p ?

[tcrocker]

Does eny one know the max C.U.P for an M1 Garand?

[spqrzilla]

I'm not sure your question makes any sense. M1 Garands are chambered for .30-06 and their designed pressure limits are based on that cartridges' pressure specs.

However, what is more important in loading for M1 Garands is that the ammunition generate the correct pressure curve. Use of powders much slower than IMR 4895 can cause excessive port pressure, even if the peak pressure is not excessive, and that excessive port pressure can damage M1 Garands.

[Lead Fred]

The 30-06 CUP is 60k, but that has little to do with the operating rod bending pressure limit.

The general rule of thumb is do not exceed 2700fps.
If you are using a 150-155gr bullet. 48gr of IMR-4895 will put you right close to 2650-2670fps.

If you are darning you can 1/2 grain up from there.

Mine shoots real nice at 2670fps, so thats my load.

[tcrocker]

I'd like to use IMR 4198 I have a few pounds of it on hand when I load my 45-70. I was going with a cast bullet 180gr lee. I tryed 23gr and max in theLyman cast manuel is31 gr thats at 2040fps and a cup is 28,800. And thats useing there 187gr bullet. The 23gr didn't work the action .I'd like to go up but don't wont to bust my op rod$$$$. And do you think it would be ok to load a 167gr Remington core lock with this load?

[spqrzilla]

If its not operating the action, then you know the port pressure is low. With a fast powder like that, you will have trouble getting enough port pressure, and should not have a problem with too much.

Outside of the port pressure/op rod issue, Garands are very strong actions.

[BruceB]

tc, sir;

As spqrzilla said, 4198 is NOT the correct powder for the Garand, even with cast bullets.

The gasport is at the extreme forward end of the barrel, and the action needs a good shove from the port pressure to function.

To keep that pressure up at a satisfactory level, a SLOWER powder is needed, and I think most of us who use cast in Garands consider something in the area of 4895 to be about as quick as we prefer.

Personally, I find that 4350 and IMR4831 are about ideal, since they give moderate pressure and velocity with the cast bullet, while maintaining enough pressure at the gasport for proper function.

Go to the "CB Loads/Military Rifles" forum and search for "Garand" and "M1"...there's plenty of information.

Trying to use a powder which is not suited to the task runs a variety of risks, and it's false economy. 4198 is a wonderful cast-bullet propellant, but NOT in the Garand.

Best of luck to you.

[hamour]

If memory serves me right, the gov't spec for m2 ball is:
2785 @ 75ft from muzzle (Slightly over 2800 fps at muzzle)
150gr flat based bullet
IMR 4895 not to exceed 52grs (different lots gave different powder weights but the velocity was key)

Most people over time have settled on 48-50grs of IMR-4895 and 150 gr bullets to duplicate m2 ball

IMR-4895-4064-4320 are 3 good powders for full power Garand loads, just shoot for:
2800fps with 150 gr bullets
2700fps with 165 gr bullets
2650fps with 180gr bullets

If you want slower powders, you can buy and adjustable gas plug to protect the op rod.

Slow powder damage accumulates or builds up over time

Ifyou use low doses of slow powder that barely functions the rifle you will be fine, if it concerns you get the adjustable gas plug.

PS: Take caution not to have any high primers! Slam fires are trouble, but this is the same for any semi auto not just the Garand

[Multigunner]

Hatcher wrote that the Garand was destruction tested with special proof loads of 125,000 CUP, it held up to a great many such overloads with no damage to the receiver, and continued to function even after one bolt lug had broken off.

Herter wrote of converting Garand actions to straightpull operation for use with ultra high performance wildcat cartridges.

[BruceB]

Hamour says,:

"If memory serves me right, the gov't spec for m2 ball is:
2785 @ 75ft from muzzle (Slightly over 2800 fps at muzzle)
150gr flat based bullet
IMR 4895 not to exceed 52grs (different lots gave different powder weights but the velocity was key)

Most people over time have settled on 48-50grs of IMR-4895 and 150 gr bullets to duplicate m2 ball

IMR-4895-4064-4320 are 3 good powders for full power Garand loads, just shoot for:
2800fps with 150 gr bullets
2700fps with 165 gr bullets
2650fps with 180gr bullets"

Up to this point, he is quite correct. Now, he strays a bit when we consider CAST BULLETS.

"If you want slower powders, you can buy an adjustable gas plug to protect the op rod."

This statement is correct for JACKETED bullets. With our slow-powder cast loads, we are not posing any threat at all to the op rod, and in fact the reason for the slower powder is to get the gasport pressure UP for proper functioning, not reduce it. Therefore, a pressure-venting plug is NOT needed, and may even be a liability.

"Slow powder damage accumulates or builds up over time."

Again, the slow-powder cast-bullet loads function the action LESS violently than normal-powder loads with jacketed bullets.

"If you use low doses of slow powder that barely functions the rifle you will be fine, if it concerns you get the adjustable gas plug."

Proper slow-powder loads will function the rifle quite crisply, without danger to the operating parts.

"PS: Take caution not to have any high primers! Slam fires are trouble, but this is the same for any semi auto not just the Garand."

High primers are certainly to be avoided, and can indeed create slam-fires as hamour indicates. An equally-serious concern is the possiblity of slam-fires caused by firing-pin impacts on the primer BEFORE the action is fully locked. The M1 has a free-floating firing pin, and if we extract a round from the chamber without firing it after it was chambered in semi-auto function, we WILL see a dimple in the primer from the impact of the firing pin. ENSURE that rounds chamber freely (no partial sizing) and use hard primers such as CCI#34 or even CCI#200. Do NOT use Federals or other "soft" primers.

It is perfectly possible to use a powder and charge which gives excessive chamber pressure, and still fails to provide enough pressure at the gas port to function the rifle. This is a dangerous condition, of course. Err to the side of slower-burning fuel, rather than using faster-burning powders.

[hamour]

Bruce B I was just trying to give some general back ground on M1 loading.

You are quite correct that slow powder at moderate velocities are good in the Garand, it is only when you reach full power loads that the slow powders start hamering the op rod.

[BruceB]

Yep, and it's my understanding that it can happen rather quickly, too, as well as the gradual build-up of damage to which you referred.

I usually "read" the ejection pattern in M1 and M1A rifles, as compared to jacketed loads in the same rifle. When a slow-powder load starts dropping the brass in about the same area as the jacketed 'service' loads, I figure that the PORT pressure is about the same as that of the jacketed load. So far, this has kept me out of trouble.

You gave us a very good digest of load performance in the M1, and I enjoyed it. I also agree 100% with your comments concerning those jacketed loads. What I wanted to do was expand on the experiences many of us here have had with the cast-bullet loads.

Sure do enjoy the M1 rifles, and I bought another one (a Danish return with 'VAR' barrel) a few months ago at the Big Reno Show. With the weather improving rapidly, it's time to get after some serious loading for it.

[hamour]

BruceB, I think the competition shooters are the ones which experience the sudden death of the op rod from shooting a large amount of over spec ammo. I think the long range guys actualy carry extra rods per gun!
Where as a hunter would play heck trying to shoot enough over spec hunting ammo to hurt his op rod. Especialy if bullets are in the 150 to 180 gr range.

I have 7 to 8 thousand 170 gr Rem Round noses @ 4.3 cents each and am going to shoot them up prior to trying cast in my Garands but am enjoying learning on how to get the job done.

[Multigunner]

I once put a badly beat up Garand back in working order, including rebarreling it since the original bore was totally shot out. A friend helped with parts and did the rebarreling, using a slightly used but still accurate matchgrade takeoff barrel.
Anyway he noticed that the op rod was the old style with out the radius cut, so he traded me a NIB replacement for it. He was restoring an early Garand and wanted it to be as from the factory.

Apparently a few op rods had snapped for one reason or another so a radius or scallop was cut on later rods to avoid breakage.

I'd heard that the 170-172 gr MG loads were hard on the Garand, but late in WW2 they issued the heavy bullet AP loads on a regular basis. Perhaps the scalloped rod made the difference.

Also op rods were said to snap sometimes if the grease congealed in sub zero weather. Vitalis hair oil was used as a field expediant sub zero lubricant in Korea.

[spqrzilla]

The problem with uncut op rods was when the Garand was used with grenade launching blanks to launch rifle grenades. That use caused damage to the op rod and the cut was to fix that.

The uncut ones are also considered a bit weaker for loads with excessive port pressure but that was not the original motivation of the modification.

[Larry Gibson]

"I'd heard that the 170-172 gr MG loads were hard on the Garand"

There was no such thing (in US inventory) as heavier loads for machine guns with '06 ammo. Some ammuntion lots that did not meet accuracy requirements for rifle use were belted and marked "for machine gun use". The loads and pressures were the same.

Larry Gibson

[Multigunner]

"I'd heard that the 170-172 gr MG loads were hard on the Garand"

There was no such thing (in US inventory) as heavier loads for machine guns with '06 ammo. Some ammuntion lots that did not meet accuracy requirements for rifle use were belted and marked "for machine gun use". The loads and pressures were the same.

Larry Gibson

After WW1 the army went to the M1 ball 174gr loads for long range MG use, the earlier 150 gr 06 load having proven to be of much shorter range than they had thought it would be.

At about this time the M2 ball round for rifles went from the 150gr of the 06 to 152 gr due to a change in the alloy of the lead core velocity was increased as well . AP M2 ammo was about 168 gr.

Any of those rounds could be fired in any .30/06 chambered weapon of course. The increased recoil of the M1 ball made it less desirable for rifle use under most circumstances.

[Multigunner]

The problem with uncut op rods was when the Garand was used with grenade launching blanks to launch rifle grenades. That use caused damage to the op rod and the cut was to fix that.

The uncut ones are also considered a bit weaker for loads with excessive port pressure but that was not the original motivation of the modification.


Myth: Ordnance modified (relief cut) Garand Operating Rods due to damage resulting from launching Rifle Grenades.

The Facts: Ordnance modified Garand Operating Rods because right angle steel cuts have always been a point of failure. PHOTO To prevent cracking Ordnance modified (and later on added the change to production) Operating Rods with a circular cut. These cuts vary in size and shape due to different methods and locations of facilities performing the modifications. PHOTO

Furthermore, during WWII when an M7 GL was attached to an M1 Rifle, there was very little gas pressure in the operating system. A large percentage of gas escaped into the atmosphere due to the vented valve. Anyone who has launched inert rifle grenades will tell you that the op rod moves about 1/2 inch rearward, that's all. The reason is, there is not enough gas pressure to operate the system. If launching a rifle grenade damaged an op rod, then service ammunition would have sent it into the stratosphere. The difference is pressure is enormous.


http://www.billricca.com/myths.htm

http://www.inert-ord.net/usa03a/usarg/spigots/index.html

[spqrzilla]

It may be a "myth", as I cannot recall where I first read it. However, Hatcher in his "Hatcher's Notebook" notes that M1 Garands can show cracking in the rear receiver wall where the bolt strikes when firing rifle grenades, so I am suspicious of the quote above is at the least incomplete.

[Multigunner]

It may be a "myth", as I cannot recall where I first read it. However, Hatcher in his "Hatcher's Notebook" notes that M1 Garands can show cracking in the rear receiver wall where the bolt strikes when firing rifle grenades, so I am suspicious of the quote above is at the least incomplete.

The M7 Grenade launcher does not allow the action to cycle.

I've heard of the bolt impacting the rear of the receiver if slow burning powders with high port pressure are used.
Only pproblems associated with GL and the Garand I've run across is the recoil can beat the stock to pieces, and bores can be trashed quickly.
A friend told me of rocket assisted AT grenades that eroded the muzzle badly.

PS


Hatcher in his "Hatcher's Notebook" notes that M1 Garands can show cracking in the rear receiver wall where the bolt strikes when firing rifle grenades

Found it on page 106.
Unless there were incidents where the gas vent didn't operate properly I can't see how this could occur.

[spqrzilla]

Page 206 on my edition. Perhaps other models of grenade launchers were involved.

[Multigunner]

http://www.garandm1rifle.com/page2.html

Theres a file with correspondence on improvements to the gas cut off of the M7 grenade Launcher here.
Julian Hatcher is one of those who signed off on it.

Could be that previous cut off valves sometimes failed causing damage to receivers.

PS
Correct, page 206 not 106.

Also
http://www.billricca.com/lockscrews.htm


DISASTER WILL HAPPEN IF ANYTHING IS LAUNCHED OFF AN M1 WITH A SOLID LOCK SCREW ATTACHED.
The valve system may not have been recruit proof.