M1 Garand and operating rod bending investigation

[Swampy]

eclancy oughta have some data about the design pressure at the gas port. I've read--albeit decades ago--that it was around 2,000 psi, but don't take my memory as Gospel.

Art, IIRC, and I could be wrong here too.... the gas port pressure the M1 is supposed to have for correct function is in the 4000 to 6000 psi range.

Best,
Swampy

Garands forever
2007 NRA Missouri State 600 yard Service Rifle Champion.
Score 774-29X.... with an M1.

 

[GarandOwner]

Thanks for the information Swampy, If 6000 psi is the max design pressure, then it would make sence for the rod to be made to withstand a force of about 1.5 times that. Alot of times in engineering (at least in Aeronautical applications) we will use a factor of saftey when designing things of around 1.5 (more for critical components).........although other engineering disciplines think we are crazy for using such low factors of saftey

 

[Art Eatman]

Swampy, as I said, I'm nowhere near positive about my 2,000 number.

It would be nice to have the pressure curve of the 4895 burn, with the horizontal axis being length in inches. That would give a direct plot for the pressure at the gas port.

Again, relying on an imperfect memory, most of the published curves are pressure vs. time.

Grumble, gritch...

 

[redneck2]

...did you take into account the inertia it takes to overcome the mass and get the rod moving? The rod's trying to stay still and you're trying to move it to hyper velocity in a millisecond.

I just looked at the stuff briefly, as I'm off to do something more exciting...

like watching paint dry....

 

[Swampy]

...did you take into account the inertia it takes to overcome the mass and get the rod moving? The rod's trying to stay still and you're trying to move it to hyper velocity in a millisecond.

Nahh.... not really.

While the accelleration rate may be pretty impressive, the actual top speed of the op-rod is only something on the order of 20 mph (29.333 fps).

Best to all,
Swampy

Garands forever
2007 NRA Missouri State 600 yard Service Rifle Champion.
Score 774-29X... with an M1

 

[GarandOwner]

...did you take into account the inertia it takes to overcome the mass and get the rod moving? The rod's trying to stay still and you're trying to move it to hyper velocity in a millisecond.

actually yes thats what the area moment of inertia is for (how the member deals with inertia due to its cross sectional area). The inertial force IS P, because all an inertial force is, is the objects mass times its acceleration

 

[GarandOwner]

If you really wanted to, you can solve for the maximum acceleration. Either by Newton's method where the sum of the forces = ma or by D'alembert's method where there is an inertial force, and the sum of the forces = 0 (Both will give you the same result). I will show it using D'alembert's method:

Sum of Forces along the axis of the length of the operating rod = 0

so from the Free Body Diagram of the Operating rod:

- Pcr +FI = 0

where FI is the inertial force = (w/g)a that acts opposite acceleration


Solving for a we get:

aMAX = ((pi^2EI)g)/(wL^2)

(I cant get a numerical answer for this as I do not know how much the operating rod weighs.)

 

[GarandOwner]

I just looked at the stuff briefly, as I'm off to do something more exciting...

like watching paint dry....

hehe as I said in the OP some may find this information dry, but being an engineer, when I think of a problem, I can not rest until I solve it. I know math is not everyone's cup of tea. We engineers are a strange breed