What is the correct port pressure for the Garand?

[fatelvis]

I know the Garand was designed to operate at about 50Kpsi chamber pressure, but what is the proper pressure range for the gas port? I'm trying to check powders and charges on Quickload, and want to know which ones are a good choice to operate the action, without overtaxing the gas system. Thanks in advance.

[M-Tecs]

I am out of town and I don't have my references handy but if memory serves me correctly it's 6,000 to 8,000 psi.

[Outpost75]

I am out of town and I don't have my references handy but if memory serves me correctly it's 6,000 to 8,000 psi.

That sounds correct to me. I don't trust memory much anymore at my age...

I know that if you stick to 4064, RL15 or Varget and load 175 Sierra MK to get 2640 +/- 30 fps you are OK, but slower powders will bend the op rod and faster ones will go over-pressure before you reach 2600. In LC Match brass 46.5 grs. of 4064 or Varget or 47 grs. of RL15 is a good place to check using WLR primers, and tweak from there to get your desired velocity to approximate M72. Increase the charge 1.5 grains with 150-grain bullets to approximate Ball M2.

Today's IMR4064 tracks closely in charge/pressure to old military IMR4895 made before 1975. Current 4895 is too fast for 175-grain bullets in the Garand, but works OK with 150-grainers, 48 grains to approximate Ball M2 in LC brass.

[fatelvis]

I'm looking to use cast boolits loaded light enough so that they juuuust operate the action. Light recoiling and accurate.

[fatelvis]

28grns of RL7 under a 311299 looks pretty good. 1809fps, with a 5925psi port pressure. Has anybody tried that load, or something close?

[Outpost75]

I use 40 grains of 4064 with HM2-.311-160-5 to reliably cycle my Garand,for 2200 fps.

Tried 30 grs. of RL7 with #311299 and would not cycle.

Should add that my rifle was a CMP rebuild with new spring kit.

If your springs are old the charge can be reduced, many people have good results with 35 -36 grains.

[Scharfschuetze]

I've found that 33 to 35 grains of 4895 or 4064 under a 190 to 210 grain boolit functions reliably and is accurate in my Garands. I personally like the 311334 or 311299 Lyman designs and they fall into the above weight range.

[Ford SD]

I'm looking to use cast boolits loaded light enough so that they juuuust operate the action. Light recoiling and accurate.

If you Read Bruce B Work on the M1a A Very high percentage of the powders Bruce used should Work in the M1 grand
if he found it did not work in a 308 it probaly will not work in a 30-06
the same for Boolits but in the 30-06 some of the heaver ones should work better

http://castboolits.gunloads.com/showthread.php?3558-7-62x51-NATO-(-308-WCF)-in-the-Springfield-M1A

you might have to add 1-2 grains of powder from Bruce loads -- ie 308 to 30-06 (I do not load 30-06 so you will have to do your own research and look for your own data --Some one on here will load cast for 30-06 and will have posted some data

of the cast bullets/ load data Bruce used should give you something to look at

if you push them too fast you will loose Accuracy

[BUCKEYE BANDIT]

+1 , and they land at 3:00 about 3' away in a nice little pile :smile: PING!!!
I've found that 33 to 35 grains of 4895 or 4064 under a 190 to 210 grain boolit functions reliably and is accurate in my Garands. I personally like the 311334 or 311299 Lyman designs and they fall into the above weight range.

[Motor]

That sounds correct to me. I don't trust memory much anymore at my age...

I know that if you stick to 4064, RL15 or Varget and load 175 Sierra MK to get 2640 +/- 30 fps you are OK, but slower powders will bend the op rod and faster ones will go over-pressure before you reach 2600. In LC Match brass 46.5 grs. of 4064 or Varget or 47 grs. of RL15 is a good place to check using WLR primers, and tweak from there to get your desired velocity to approximate M72. Increase the charge 1.5 grains with 150-grain bullets to approximate Ball M2.

Today's IMR4064 tracks closely in charge/pressure to old military IMR4895 made before 1975. Current 4895 is too fast for 175-grain bullets in the Garand, but works OK with 150-grainers, 48 grains to approximate Ball M2 in LC brass.

New IMR-4895 seems to work pretty good with Sierra 180gr BT Match bullets. I was using the start load from Hornady's Garand specific data so your statement may be true if top end velocity is wanted.

Motor

[Scharfschuetze]

I'm looking to use cast boolits loaded light enough so that they juuuust operate the action. Light recoiling and accurate.

Getting a Garand (any gas operated semi-auto) to shoot both accurately and operate reliably is a balancing act and I've found the heavier projectiles between 195 and 210 grains to be more efficient in this regards. Remember that the Garand was designed for jacketed bullets at much higher pressures than we normally use with cast boolits.

In previous threads, mention was made of using 4350 powder with cast boolits to up the port pressure. Perhaps this is an option, although with light boolits, it might not combust well for good accuracy or ballistic uniformity.

One of my projects this summer is to try and get the 170 grain Lyman 311041 (30/30 design) to shoot well in my Garands after a similar question to yours was posted a few months ago.

For light loads in the Garand that do not produce enough port pressure, you might consider an adjustable or vented gas cylinder plug. With it opened fully, you can then operate your Garand manually. While not achieving your goal to "juuust operate the action," it may achieve good accuracy for you as well as light recoil.

[Artful]

Pretty good memory guys . . .

As the M2s original 42,000psi pushes the bullet down the bore, the increasing volume between the chamber and the bullet drops the pressure to about 8,000psi near the muzzle, where a port taps off about 6,000psi (+/- 2,000psi)4 worth of that to operate the Garand’s gas system. (http://en.wikipedia.org/wiki/John_Garand)

Commercial ammo may have different pressures...

The Hornady Reloading Handbook 7th edition recommended M1 loads are all safe to use.

http://www.garandgear.com/m1-garand-ammunition

http://www.radomski.us/njhp/cart_tech.htm

http://www.guns.com/2011/08/16/the-secret-to-a-long-life-a-garand-diet-or-what-to-feed-your-m1-garand-part-i/


https://www.youtube.com/watch?v=78t7Yi5v9uE

[wiljen]

one of the Schuster adjustable gas plugs is a big help for getting good cycling out of different loads

[Bert2368]

Somewhere on the net, there is an actual TABLE showing gas port pressure for various Garand loads. Including cast. I have seen reference to this, but have had no luck in finding the table... Anyone know?

[fatelvis]

After reviewing commonly accepted loads on Quickload, they all have been around 9500 psi at 22" from the breech. I use that measurement because I figure that's approx where the gas port is on the Garand.


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[Bert2368]

I do not have Quickload.

Quickload costs $150 +, AFAIK?

[fatelvis]

Yes, somewhere around there. But it is a super fun toy!!


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[Multigunner]

"If you Read Bruce B Work on the M1a A Very high percentage of the powders Bruce used should Work in the M1 grand
if he found it did not work in a 308 it probaly will not work in a 30-06
the same for Boolits but in the 30-06 some of the heaver ones should work better"

The Garand gas system is far different from the M14 gas system.
The M14 system captures a limited amount of gas which them expands in the piston chamber. This allows for a much wider range of gas port pressures and slower propellants than would be safe in a Garand.

Heavy bullets and slow powders can wreck the Garand's op rod or lead to early opening.

[madsenshooter]

Somewhere on the net, there is an actual TABLE showing gas port pressure for various Garand loads. Including cast. I have seen reference to this, but have had no luck in finding the table... Anyone know?

I used to have a quickload workup that parashooter did posted on this board! It was based on the port pressure generated by a standard ball load. His loads for a cast bullet in the 200gr area targeted 2000fps and showed what the port pressure would be for a wide variety of powders. Even a caseful of 860, not boosted, won't get you beyond the port pressure of standard ball. If I can find it, I'll link you to it.

[Larry Gibson]

I don't know the "correct" port pressure for the M1 Garand but having measured the time/pressure curve of numerous lots of M2 Ball, one lot of M1 Ball and a couple lots of M72 Match the pressure at 22" runs from 9,500 to 14,500 psi(43). That is equivalent to measurements with transducers not CUP.

Larry Gibson

[fatelvis]

After trying progressive powder charges through one of my Garands to see if they would function the action, I have found that it requires about 6900 psi minimum to fully function the action. (36grns H4895 w/311299 boolit).
As a sidenote, this Garand has new springs throughout.


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[Scharfschuetze]

After trying progressive powder charges through one of my Garands to see if they would function the action, I have found that it requires about 6900 psi minimum to fully function the action. (36grns H4895 w/311299 boolit).
As a sidenote, this Garand has new springs throughout.

Your load is very close to what most are shooting with that 208 grain (my mould) and 4895. Good accuracy with reliable function.

In the end, each rifle will vary a bit given gas cutting or wear to the actual gas port, the diameter of the piston head, the diameter and wear to the gas cylinder's internal dimensions as well as the springs, and general finish or wear to the metal to metal parts, particularly the primary extraction cam between the right bolt lug and the op rod.

[fatelvis]

Good point about the variables allowing or preventing the cycling of the rifle. I was a bit envious of those who were getting complete functioning with 32grns of H4895, as it showed better accuracy from my rifle. It didn't have enough oooomph to strip off a new round though.. I'll be checking my gas cylinder and piston tolerances soon. And maybe I can dig up my old, worn out recoil spring!

[Larry Gibson]

That's the trick to M1 gas guns having 10" twists with cast bullets; balancing the weight of the bullet with the burning rate of the powder to achieve sufficient gas port psi to function reliably all the while keeping the velocity below 1940 fps.

Larry Gibson

[fatelvis]

What is the significance of the 1940 figure? Any faster does it over spin?


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[mac1911]

I have found if I push most of my alloys over 2000fps I get leading and poor accuracy no matter the rifle.
My most worn in M1 will cycle reliably on 36 grains of H4895 with a Lyman 314299 sized to .310" gas check and tumble lubed. Will hold the black.
In a not so worn in rifle I need 38grains and that rifle/load will hold the 10 ring when I can.

[Larry Gibson]

What is the significance of the 1940 figure? Any faster does it over spin?


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It's called "The RPM Threshold".

And yes it has to do with over spinning a bullet, especially a cast bullet in this case. Note that "over spinning" in reference to the RPM Threshold has nothing to do with, and is not the same as, "over stabilization". They are two separate phenomenon.

Larry Gibson

[.455 Webley]

This is a great thread. Thanks for all of the information that you guys have looked up and recalled here.

[Scharfschuetze]

It's called "The RPM Threshold".

And yes it has to do with over spinning a bullet, especially a cast bullet in this case. Note that "over spinning" in reference to the RPM Threshold has nothing to do with, and is not the same as, "over stabilization". They are two separate phenomenon.

Larry Gibson

That certainly fits well with my experience with not only the M1 Garand, but the 1 in 10" twist 1903 and Krag-Jorgenson as well. 190 to 210 grain cast bullet between 1,800 and 1,900 fps. Good accuracy with lots of weight and good ballistic coefficients to hold well to way out there when shooting at long range.

[fatelvis]

I am out of town and I don't have my references handy but if memory serves me correctly it's 6,000 to 8,000 psi.
Good guess!
After trying many low-powered loads, trying to find an accuracy niche for this particular Garand, I've narrowed down that it needs a minimum of 7500psi port pressure to cycle reliably. And low and behold, 36grns of H4895 produces 7485psi at the port! A decently accurate load, and a good place to consider a baseline for further tweaking.
My next attempt is 40.8grns IMR4831 under a 312299 for 1840fps (130 fps slower than the H4895 load) @7492psi port pressure.
I want less kick, good accuracy, and proper cycling....

[madsenshooter]

When you start with the 4831, make sure you have a chamber brush handy! I tried shooting a match with H4831 at about where you're starting. I got yellow bits of unburned powder all through the action and all over my shooting mat, though I was using a magnum primer! Had to use the chamber brush after each string. Dented up my brass too!