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[leman77]

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[yzErnie]

Is there any letter stamped ont the top of the floor plate tang?

[DaveInOroValley]

Here you go:

Post-WWII M1911 series .45 magazines:

Commercial Colt (pre-1970). Marked "Colt .45 Auto" on the bottom of the
floorplate, with no rampant stallion. Beware! Many of the after-market copies
carry similar markings. However, the "counter" holes in the side of the magazine body
are generally over-sized. The other dead give-away is the typeface
("font") used--it is not the same style font used by Colt.

http://www.rawles.to/M1911_Mag_FAQ.html

[Riodog]

Yep, that's the real thing. Worth prolly around $1000.
Rio