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Another interesting SIG factoid - makes me wonder how ATF approved the 1980s importation of the semi-auto 550 & 551s

larryccf

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Only reason i noticed this was that i imported a number of SIG 552 semi-autos back 2004-2005. When they came in the receivers, while marked "SP" for semi-patronen, the bolt carrier had the slot for the full auto trigger packs FA release lever (see first image on left). That first photo shows the ejection port side bolt carrier with the trip lever slot blocked by a block spot welded into the receiver. ATF regs are pretty clear, once borne as a Full Auto, always a Full Auto, no welding to make it inoperable changes that. In the 2nd photo, the top receiver is a full auto 552 that i purchased for a LE demo - you can see that slot is unblocked.

When i saw the entire shipment of Semi-autos were like the receivers in the first image, my heart rate increased. Then i remembered i had a semi-auto 550, that was a 1980s import, in the safe holding it for a customer. I pulled it and it had the same open slot in the bolt carrier blocked by the same metal block spot welded in.

The only explanation i can come to is that ATF's regulation regarding "borne" - They have to have considered the rifle borne after the serial number was engraved, which means the block had already been welded in and the finish applied to the receiver -

FWIW

I just added another photo - the trip lever that releases the hammer is highlited with a red arrow, as the tail end of the bolt rides over it, it depresses it releasing the hammer just as the bolt is chambering the next cartridge
 

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  • semi-auto sig rcvrs with block welded in place.jpg
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  • SIG 550 551 552 receivers underside 2.jpg
    SIG 550 551 552 receivers underside 2.jpg
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