View Single Post
Old November 30, 2019, 13:21   #51
Sig Sauer Me
LKY_13's Avatar
FALaholic #: 41000
Join Date: Dec 2008
Location: UTAH
Posts: 1,569
Originally Posted by 2barearms View Post
So can someone explain the 3 screw vs 4 screw uppers?
4-bolt = ER (Early Release) 1st gen, manufactured circa June '07-ish. Will have some/all of the following Swiss parts in addition to US parts: imported cold hammer forged barrel (Supposedly. Personally, I have never been able to confirm this, as there are no roll marks. And, no factual documentation verifying this info.) Swiss gas block w/roll mark, Swiss gas piston, Swiss numbered (but not matching numbers) bolt carrier group, Swiss fire control group w/proof, Swiss lower parts kit, and finally a Swiss pistol grip...

I believe somewhere around JS 5XXX-6XXX the imported Swiss parts started to dry up. So, they might have some of the above listed import parts, but tapper-off after this. I cannot confirm what serial number they switched to 3-bolt uppers. I've not ever owned or handled a 556 in this range. No clue if they still had a few leftover pistons, or FGS to put into these or not.

If anyone knows exactly when they switched to 3-bolt uppers, I would love to know.
“If ye love wealth better than liberty, the tranquility of servitude better than the animating contest of freedom, go home from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains set lightly upon you, and may posterity forget that ye were our countrymen.” ― Samuel Adams

Foi Est Tout
μολων λαβε
SiG for Life
LKY_13 is offline   Reply With Quote