So, from my observation of original Colt 601 & Colt 602 receivers, it seems that they are marked: "COLTS PATENT FIREARMS" to the left of the sear pin hole.  It also appears that XM16E1 AND early M16A1 receivers are marked "COLTS PATENT FIRE ARMS" to the left of the sear pin hole.  On later M16A1's when ALL of the address info is to the left of the sear pin hole they appear to have gone back to "FIREARMS" as one word.  Does anyone have any photographic evidence of ORIGINAL receivers that deviate from these observations? Thanks.

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I have a few 601 demilled receivers I'll have to dig out tomorrow and look at. Never really noticed.

Since You're discussing it, is it just the angle or does it seem to alternate between using a comma and using a period after Hartford?

I THINK that they are all commas, however the lighting and angles make some look like periods.

After more research, it appears that the XM177E1, the XM177E2, and the GAU carbines all said "FIRE ARMS" as well. It looks like I had a couple of my early receivers engraved incorrectly, but most are OK.

So keeping on this topic, what years did they have 'Colt Firearm Division' on the lowers? Pic for details.

I am not 100% sure, but what I have seen, the last “Colt Patent Fire Arms” was on the xm16e1. I t was replaced by the “Firearms Divison” on the m16a1 with this Property and export markings .