Curved vs flat op rods

[Patrickd]

Other than the serial #, how do you check? I have looked at both in pictures, but haven't been able to distinguish them apart other than by the #'s stamped in them. Where is this distinct curve they speak of in rod # D35382 3 SA
Thanks

[jak]

Prince Humperdink ( Who is also a member of this forum) posted these pictures on the CMP forum.
The curved or straight exterior region of the op rod is the area where the bolt rides on the inside of the op rod.

http://forums.thecmp.org/showthread.php?t=82485

[Patrickd]

Thanks. I did a search, but must have entered the wrong words because that post never came up. Anyway it was exactly what I was looking for. Now does anyone know why they went from curved to flat?

[TJT]

Quicker to mill a flat surface than a radiused surface. That "serial number" on the op rod is a part number. There is ONLY ONE serial number on an M1 rifle--it's the number on the receiver heel. All the other numbers are drawing, or part numbers.
Jon

[Patrickd]

One more question, I have read that the piston end needs to be .520" in dia., but what is the dia of a new rod? Mine seems to mic out @ .526"

[jak]

One more question, I have read that the piston end needs to be .520" in dia., but what is the dia of a new rod? Mine seems to mic out @ .526"

.526" is in specifications. .525" is the minimum.

[Orlando]

.520 the rifle would never cycle

[TJT]

.520 the rifle would never cycle

Not necessarily true, especially if the gc diameter is on the minimum dimension. I know because once upon a time I had an undersized piston but the minimum diameter ID of the gc allowed it to work. Maybe I'm just lucky. But then, I'd rather be lucky than good.
Jon