Mark,
I can't be certain, since I have seen and handled only a few of these, but I believe Armstrongs only came with one type of base. They are apparently interchangeable with round or flat receivers as there is a shallow "V" milled into the flat on the receiver side of the base. I'm using it on my flat sided Martini but it looks as if it would work on the curved receiver of the Springfield as well. Certainly not as form hitting as a Lyman. If you decide to sell yours without the base, let me know. Thanks. Terry
