op rod piston diameter

[Bob K]

What is the minimum diameter acceptable for an op rod piston and still be serviceable for the M1 Garand?

[Milwroad]

.525 but it might work if a little under if the gas cylinder is tight.

[Sunray]

Go here and download the free .pdf TM and FM manuals. Note the need for the provided UN & PW.
http://www.biggerhammer.net/manuals/

[StockDoc]

If the rifle functions, then it is fine.

[Ron H.]

What is the minimum diameter acceptable for an op rod piston and still be serviceable for the M1 Garand?

Sir, per Kuhnhausen, 0.5253" is minimum and 0.525" is no-go.

That said, I do have one op rod that mikes 0.525" and works fine so long as the ammo is up to spec. Weak ammo, like some of the LC 69 the CMP was selling 10-ish years ago, won't always cycle the action.

Hope this helps, and Semper Fi.

Ron H.