Garand reloading question


June 6, 2006, 02:40 AM
How does the quickness of a powder affect the op-rod?

From what I understand the quickenss relates to how fast the powder will develop max pressure compared to some standard powder.

So, when the primer fires, and the powder does its job, why do the 'quicker' powders bend op rods? The Garand needs about 2kpsi (IIRC) at the gas port to function... why do I care if the pressure is generated at the breech (with a fast powder) or near the muzzle (with a slow powder)... 2kpsi is 2kpsi.

What am I missing?

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bill in IN
June 6, 2006, 07:56 AM
Basic Physics- change in about anything divided by the change in time is the equation for stress. In this case it's change in pressure and the resultant change in op rod position. Too much stress and somethings gonna fail.

June 6, 2006, 10:13 AM
Completely uninformative post.... do not become a physics teacher. ;)

A 'fast' powder will make X-PSI, so will a slower powder.. so the AMOUNT of pressure is not the issue.. just when it is created.

The bullet will have more forces acted on its quicker, but that mean nothing... its not like other loads using quick powder are KB-ing guns left and right.

Only thing I Can fiugre is that the quicker powders will need more pressure as thier gases, when created at the breech end of the gun, are done expanding and will lose pressure as the bullet goes down the barrel (volume and pressure will be inversly proportional, so PSI at the gas port will be lower).

So, WHY will quick powders bend an op - rod?

Jim Watson
June 6, 2006, 10:53 AM
"Quicker" powders don't bend operating rods.
"Slow" powders do.

Assuming full power loads at maximum standard chamber pressure, the "quicker" powder burns, builds to its maximum chamber pressure, and then declines fairly rapidly.

The "slower" powder burns, builds to the same maximum chamber pressure, but is burning progressively so pressure does not decline as rapidly. Therefore port pressure will be higher and can be higher than what the rod will stand.

Garand is designed around "medium" burning powder like IMR 4895. A fast burning powder might not generate enough port pressure to function the action, a slow powder might generate too much and bend the operating rod; yet maximum chamber pressure would have been the same for all three.

June 6, 2006, 11:02 AM
The M1 Garand was designed around a specific round. The powder charge, burning rate, OAL, bullet weight are part of the Garand system. A GOOD loading manual will show loads for the Garand and they work. I have played with different combinations and the MIL SPEC works the best so stick with it. The M1 is not a bolt action which will tolerate extremes in loads. It is what it is so live with it or bend op rods.

June 6, 2006, 11:23 AM
Pressure at the gas port. With heavy bullets/slower powders, the gas port sees higher pressures. Higher pressures at the gas port means more force on the tip of the oprod and more violent cycling.


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