Garand Chamber Pressure

[Bart B.]

From an earlier thread:

https://web.archive.org/web/20000620...rpo/M1load.htm

If not . . .
https://www.sportsmansguide.com/prod...unds?a=1791292 (w/ which the OP shot at nice target )

https://www.midwayusa.com/product/95...l-metal-jacket

and for light reading
https://www.guns.com/news/2011/08/16...-garand-part-i
https://www.guns.com/news/2011/08/23...garand-part-ii
.[/QUOTE]
Again, links to sites stating arsenal 30-06 ammo chamber peak pressures are 50,000 psi and commercial ammo pressures are 60,000 psi.

Does it matter that arsenals (and early commercial ammo plants) used copper crusher pressure test systems whose tarage table for the lot of copper discs used translated their crushed dimension to 50,000 cup but they stated "psi"? And up to date SAAMI specs for that same system lists 50,000 copper units of pressure using crushers and 60,000 psi using pressure measuring transducers?

[44 AMP]

Does it matter? I don't think so. I don't think it matter if modern pressure measurement systems yield a different number than the old copper crusher system. Its just a number, and when properly placed in context, doesn't matter if what they thought was 50K was actually discovered to be 42K or 60K, today, what matters is what they thought, and did, at the time.

sites stating arsenal 30-06 chamber peak pressures are 50,000 psi and commercial pressures are 60,000 psi.

It is important to remember that the GI .30-06 and commercial .30-06 ARE DIFFERENT LOADS. This should be obvious just by looking at the velocity numbers. GI 150gr ball is spec'd to run ~2740fps while commercial 150gr ammo from REM/WIN/FED/ etc is all listed in the 2900fps range, some even a little higher. This is DIFFERENT ammo than the WWII GI ammo the M1 Garand was built to run on.

[Bart B.]

Originally Posted by 44 AMP

Does it matter? I don't think so. I don't think it matter if modern pressure measurement systems yield a different number than the old copper crusher system. Its just a number, and when properly placed in context, doesn't matter if what they thought was 50K was actually discovered to be 42K or 60K, today, what matters is what they thought, and did, at the time.

It is important to remember that the GI .30-06 and commercial .30-06 ARE DIFFERENT LOADS. This should be obvious just by looking at the velocity numbers. GI 150gr ball is spec'd to run ~2740fps while commercial 150gr ammo from REM/WIN/FED/ etc is all listed in the 2900fps range, some even a little higher. This is DIFFERENT ammo than the WWII GI ammo the M1 Garand was built to run on.

Does it matter that arsenal ammo was chrono'ed at 78 feet with a different system than commercial stuff at around 10 feet, both with different cartridge and test barrel specs?

[Jim Watson]

That sort of legacy data led a lot of people to believe that .308 Win. was a 20% overload for a 7.62 NATO.
The Merrill article you link makes the same assumption, that SAAMI maximum is "half again" the pressure of late GI. Which took advantage of IMR4895 to get the velocity older, less progressive burning propellants required higher chamber pressure for.

Old time velocities are at "78 feet" because the leBoulenge electro-mechanical chronograph screens were 50 yards apart to get adequate resolution. With the start at 3 feet and the stop at 153 feet, the midpoint was taken as "the distance."

[mehavey]

As many have brought up before, CUP ≠ PSI (although many worshiped "published" references
simply equated two as editions were updated ...and erroneous pressure units then became gospel.)

SAAMI does translate between the two for the `06, citing 50,000 CUP ** or ** 60,000 PSI

THAT SAID:

Originally Posted by BartB

...important to remember that the GI .30-06 and commercial .30-06 ARE DIFFERENT LOADS.

Just so . . . quoth Master Po.

[Bart B.]

Originally Posted by Jim Watson

That sort of legacy data led a lot of people to believe that .308 Win. was a 20% overload for a 7.62 NATO.
The Merrill article you link makes the same assumption, that SAAMI maximum is "half again" the pressure of late GI. Which took advantage of IMR4895 to get the velocity older, less progressive burning propellants required higher chamber pressure for.

Old time velocities are at "78 feet" because the leBoulenge electro-mechanical chronograph screens were 50 yards apart to get adequate resolution. With the start at 3 feet and the stop at 153 feet, the midpoint was taken as "the distance."

Thanks for the arsenal chrono system details. I think the same system centered at 300 feet was used for artillery and naval guns; the sensors were 100 feet or more above ground.

Winchester's CUP measuring system was different than Frankfort Arsenal's in the 1950's when they introduced the 308 Win cartridge. They set their 308 pressure spec at 52,000 cup because that is what the arsenal reference ammo produced with their system.

[Bart B.]

Originally Posted by mehavey

As many have brought up before, CUP ≠ PSI (although many worshiped "published" references
simply equated two as editions were updated ...and erroneous pressure units then became gospel.)

SAAMI does translate between the two for the `06, citing 50,000 CUP ** or ** 60,000 PSI

THAT SAID:
Just so . . . quoth Master Po.

Good point.

[Jim Watson]

SAAMI does translate between the two for the `06, citing 50,000 CUP ** or ** 60,000 PSI

Did they "translate" or did they run two separate tests? I think the latter because the tables have several cartridges with pressure data by only one system.

They set their 308 pressure spec at 52,000 cup because that is what the arsenal reference ammo produced with their system.

50,000 vs 52,000 isn't much difference. By SAAMI convention, that is only one standard deviation apart. They do a lot of statistical massaging.

[mehavey]

Separate test. That's why I said "for that cartridge"
otherwise, there is only a rough correlation between CUP/PSI -- and it varies (sometimes significantly) from cartridge to cartridge.

[Bart B.]

There is a conversion formula but it isn't exact. SAAMI specs for both ways are best for comparisons:

https://saami.org/technical-informat...ami-standards/

[Jim Watson]

If you shoot a load listed at maximum CUP versus a load listed at maximum psi, which is "better?"

[Bart B.]

Originally Posted by Jim Watson

If you shoot a load listed at maximum CUP versus a load listed at maximum psi, which is "better?"

Impossible to say unless what "better" means.

SAAMI spec reference cartridges will produce SAAMI pressure and velocity specs in SAAMI spec CUP and PSI test barrel and chronograph using SAAMI specs for prepping and loading the rounds. There is no accuracy spec.

[dahermit]

There is way too much thinking going on here. An M1 Garand, if you are lucky enough ot own and shoot one, is a precious relic that should never be subjected to maximum (or any load beyond those suggested as appropriate for its continued functioning), loadings...there is just no good reason to do so. If there is a "good" reason to go beyond the loads suggested as appropriate for target and functioning, I would like to hear it.

[Bart B.]

Originally Posted by dahermit

There is way too much thinking going on here. An M1 Garand, if you are lucky enough ot own and shoot one, is a precious relic that should never be subjected to maximum (or any load beyond those suggested as appropriate for its continued functioning), loadings...there is just no good reason to do so. If there is a "good" reason to go beyond the loads suggested as appropriate for target and functioning, I would like to hear it.

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 assumes any liability for any damage or injury resulting from the use of this information.

Military teams sometimes used M80 ball ammo using IMR4475 powder rebulleted with Sierra 168 match bullets or 173 grain match bullets pulled from M118 match ammo. No problems shooting these "proof loads" known as Mexican Match in M14 or converted Garands. I've shot over a thousand in Garands without problems. They were loaded and issued by the USN Match Conditioning Unit that rebuilt Garands. much more accurate than M118 match ammo testing sub MOA at 600 yards. The 7.62 NATO M60 proof load at 67,500 cup, about 81,000 psi.

[Reloadron]

Garand Chamber Pressure

Does it matter that arsenals (and early commercial ammo plants) used copper crusher pressure test systems whose tarage table for the lot of copper discs used translated their crushed dimension to 50,000 cup but they stated "psi"? And up to date SAAMI specs for that same system lists 50,000 copper units of pressure using crushers and 60,000 psi using pressure measuring transducers?

I am going to say no it doesn't matter.

With a focus on the M1 Garand and only the M1 Garand I figure things this way. When John C. Garand designed the rifle he designed it as a gas operated semi-automatic shoulder weapon. He designed his rifle to cycle using a sample of the gas pressure bleeding off behind a bullet before the bullet exits the barrel. The concern here is not the chamber pressure but rather the pressure at a point about (not looking at a drawing) 1.5" aft of the muzzle. I am not about to look up the hole diameter but how things work is not that complicated. Now if we figure our bullet which began with a given chamber pressure is zipping along down a barrel and the breech end is blocked by the cartridge case the gas pressure is going to be dropping since the volume is increasing. I have seen estimates that when the gas reaches the gas port the chamber pressure behind the bullet is about 8,000 with a rough plus or minus 2,000 PSI. Now it stands to reason that whatever we end up with at the gas port hole will be a function of what we started with. The rifle is designed, like any other gas operated gun, within a specific range of pressure. Too litle pressure and the rifle will short stroke and not cycle as designed. Too much pressure and the rifle will destroy itself and possibly the shooter.

As to pressure. The CUP (Copper Units Pressure) and the PSI Piezo-ceramic sensors each operate on totally different principals and when measuring chamber pressures each used a completely separate method and procedure for taking the measurements. The measurements weren't even taken at the same points in a chamber. The fact that the results are not the same should not come as a surprise to anyone. For decades, years and years the CUP method was used and we did just fine. The new method using technology which wasn't around during early CUP testing not only gives more accurate results but also allows us to see a pressure curve and note when and where the peak occurs.

The idea being we operate a rifle within the limits it was designed to work in. How many reloaders are dragging a pressure sensing out to the range? The majority just work from published load data for a specific cartridge for a specific gun. You have a Garand you either buy the right ammunition for it or you load using data published for it. Arsenals aside nobody on the range is measuring their chamber pressure.

Military teams sometimes used M80 ball ammo using IMR4475 powder rebulleted with Sierra 168 match bullets or 173 grain match bullets pulled from M118 match ammo. No problems shooting these "proof loads" known as Mexican Match in M14 or converted Garands. I've shot over a thousand in Garands without problems. They were loaded and issued by the USN Match Conditioning Unit that rebuilt Garands. much more accurate than M118 match ammo testing sub MOA at 600 yards. The 7.62 NATO M60 proof load at 67,500 cup, about 81,000 psi.

Yes, I am familiar with that being done. However, I thought the focus was the M1 Garand as it applies to the average shooter not as a converted 308 Garand gas system applies to military match team shooters. I thought the focus was a M1 Garand chambered in 30-06 Springfield the way the rifle was originally built?

Ron

[Bart B.]

Peak 30-06 Garand gas cylinder pressure is about 2,000 to 2,400 psi dependent on ammo type and lot number. Bullet velocity spread about 30 fps.

[Reloadron]

Peak 30-06 Garand gas cylinder pressure is about 2,000 to 2,400 psi dependent on ammo type and lot number. Bullet velocity spread about 30 fps.

I thought it was much higher, like around 8.000 PSI at the actual gas port. Then too I am looking at the barrel gas port hole and you are looking at the gas cylinder which I can see would be less.

The end result will always be the same. Going to the store and buying a box of 30-06 220 grain bullets and loading them in a M1 Garand is not a good idea. Buying ammunition manufactured for use in an M1 Garand is a good idea. Loading ammunition using load data, on or near maximum standard 30-06 Springfield for an M1 Garand is not a good idea. Loading 30-06 Springfield using load data considered safe for an M1 Garand is a good idea.

There is only so much which can be said about chamber pressures and the M1 Garand rifle.

Ron

[Bart B.]

Originally Posted by Reloadron

Loading ammunition using load data, on or near maximum standard 30-06 Springfield for an M1 Garand is not a good idea.

Both military and commercial 30-06 average max pressure spec is 50,000 cup. The right combination of charge type and weight for some bullets will be safe, wrong combination will be dangerous with port pressure too high. The barriers not to cross setablished by some is bullets heavier than 185 grains and powders slower than IMR4320

I think all commercial 30-06 match ammo is safe for Garands. And matched by reloading. Many thousands of such rounds were used by both military and civilians because it was more accurate than military M72 match ammo. Some rebulleted M72 ammo with Sierra 180 grain hunting or match bullets that was more accurate, about 8 inches .at 600. The best M72 tested about 12 inches at 600 yards in bolt guns, about 15 inches in the best rebuilt Garands.

[agtman]

The end result will always be the same. Going to the store and buying a box of 30-06 220 grain bullets and loading them in a M1 Garand is not a good idea. Buying ammunition manufactured for use in an M1 Garand is a good idea. Loading ammunition using load data, on or near maximum standard 30-06 Springfield for an M1 Garand is not a good idea. Loading 30-06 Springfield using load data considered safe for an M1 Garand is a good idea.

The invention of adjustable gas plugs for M1s - Schuster Mfg.'s unit and the one from the GarandGear guy - have mooted the old warning, 'never-shoot-'06-hunting-ammo-in-your-M1.'

These adjustable plugs allow you to do exactly that - ask me how I know.

In fact, for my '06 'hunter' M1, which runs the Schuster plug, I've got a deer/hog load dailed-in using Hornady's 220gn RN bullets over Varget. It pretty much duplicates Remmy's 220gn CoreLok load. Quite accurate too.

Mucho port pressure data here with various commercial '06 'hunting' ammo:

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

[Reloadron]

Agtman, that's right and I forgot to mention the use of an adjustable gas plug such as the Schuster plugs.

Thanks
Ron

[Bart B.]

Delete

[Reloadron]

Bart:

Arsenal tests have military bullets passing the gas port about 1,300 usec, not 490 stated in the link.

While I have not seen the arsenal test you mention I can see the 1.3 mSec as being reasonable. Where are you seeing this 490 number you mentioned? 490 what? 490 uSec which is .490 mSec?

Bart:

Why is http://www.garandgear.com/m1-garand-ammunition data about half?

The Garand Gear article, while interesting fails to describe their detailed test procedure and method. Apparently they drilled out a gas cylinder plug and placed a pressure sensor in the plug. They do not mention anything about the equipment used? I have no idea why there is a disparity simply because there is not enough information to draw a conclusion.

Ron

[Bart B.]

Ron,

My error. Deleted earlier post. Cylinder pressure peaked 490 microseconds after bullet passed gas port. Not after hammer fall.

[Reloadron]

Cylinder pressure peaked 490 microseconds after bullet passed gas port. Not after hammer fall.

I really don't know if that would be accurate? When we think about it from start to finish (ignition to muzzle exit) the whole show is over rather quickly. Now granted rather quickly is a matter of reference and depending on perspective a period of 1.5 to 2.0 mSec can be a long time but for our purposes it's pretty quick.

Looking at the 490 uSec I am a little hard pressed to buy off on that. The M1 Garand has a 24 inch barrel. Now that includes chamber but even with due consideration to the chamber our bullet is traveling at roughly 2650-2700 FPS and in the case of M72 2640 FPS when it exits the muzzle. The gas port hole in the barrel is about 1.5 inches aft of muzzle. So the bullet has about 1.5 inches to travel when it passes the gas port, not very far.

1.5 inches = 0.125 feet
0.125 feet × ( 1 second / 2650 feet ) = 0.000 047 seconds
0.125 feet × ( 1 second / 2700 feet ) = 0.000 046 seconds

The way I figure it, give or take a little, that bullet is gone about 46 to 47 uSEC after it clears the gas port in the barrel. The 490 microseconds just seems a bit of a long time for the pressure to peak in the gas cylinder. They are telling me the gas cylinder pressure peaked about 440 uSEC after the bullet has left the building so to speak.

Something else I have noticed is much of this seems to depend on what we read. As you mentioned, this link including a chart, reflects a peak gas cylinder pressure of maybe 1100 PSI. That pretty much runs with the prior Garand Gear link. Maybe it does take that long for the pressure in the gas cylinder to peak, I really don't know and I am not about to try and instrument a M1 Garand and drag it out to the range. I have a few other projects ahead of that.

Really, while this stuff is interesting all I really care about is how well does my rifle shoot? Does it cycle without any flaws ans how are my group sizes?

Ron

[Bart B.]

Read post #14 in

https://thefiringline.com/forums/sho...d.php?t=532499

on Garand cycle times.