Springfield square and round bolt recess on receiver

[RCS]

I use to collect data on the square and round bolt recess cut on receivers. I found that the highest SA serial number for a square cut was s/n 54279 but also found that the round bolt recess cut first appeared on s/n 49928. Springfield was producing both types of receiver bolt recess cuts for a short period. All receivers were revision 2.

Anyone have anything to add to my data would be appreciated

[TJT]

I think you have it covered pretty well.
Jon

[RCS]

Just received SA serial number 49635 with a round bolt recess on a M1D sold by CMP from Ed G.