For those who have 55x series rifles and/or pistols, I have a few legalease type questions...

1) Does the 0/1/3/20 lower on a 55x cause the weapon to be an NFA item (i.e. full-auto)? I assume the answer is NO since the upper would have to be different in some way (I don't want to know how... thanks...) Is owning a 0/1/3/30 lower a "constructive possession" offense?

I like the "looks" of having the 4 way "safety" for authentics, just like having the 3 way switch on an AR with a binary trigger is cool but DOESN'T make it an NFA item.

However, in the binary trigger example, the trigger has been reviewed by the ATF, but the 4 way 55x lowers WERE for full auto rifles if they were surplus.

Hence the question, I do NOT want an NFA item NOR even to come close to the line. I assume the 4 way is probably a risk I shouldn't take, but I wanted to know what the SigForum braintrust thought.

2) The "registered firearm" of a 55x series is the upper. However, with serialized AR lowers that are the firearm, you can go from PISTOL to RIFLE, but not RIFLE to PISTOL. If I put a used semi-auto swiss lower that was formerly a RIFLE on a pistol, is that converting the pistol to a rifle and creating an SBR?

I have a US imported 553P with a brace. I want the swiss lower, but I don't want to risk unintentionally creating an SBR. I think SOME swiss lowers are "new", so they have never had a stock on them, but many are "surplus" from previous firearms, most/all were rifles.

If I buy a surplus lower that was once a rifle, even though the UPPER was never on a rifle (the serialized part), would that "convert" the firearm to an SBR?

Thanks for any information!!!

James

Update:

After talking with a vendor, it appears the 0/1/3/20 lower will be "demilled"... YAY! So I shouldn't have to worry about crossing that line!

Anyone know about the other question, RIFLE/PISTOL lowers and the SBR possibility?

James

Lowers are the gun on an AR. Not on a 55x. Unless the resulting configuration is illegal (same for an AR) it doesn't matter the original source of the parts they are not rifle or pistol.

F/A on these guns need more than just a F/A lower frame. Trigger group, F/A bolt and a slot machined in the upper for the bolt are all needed.

The WCA 551's came with the three position lowers with semi-auto trigger installed. The third position has a pinned block for F/A but that was likely just a liability issue vs. a BATFE one.

The FA lower on a Swiss semiauto upper will not be able to be fully installed. The automatic sear release lever will hit the “carriage block” (the full auto block welded into the right side of the receiver under the bolt rail) and you won’t be able to fully close the lower and insert the rear pushpin.

All you need to do is convert the FA lower to semiauto-only. Is very easy. You remove the automatic sear release lever, remove the burst cassette, and you swap out the two sears (left is semi, right is FA) for a semiauto-only sear. You can also grind the catch for the hammer off the FA sear, thereby making it into a spacer so that only the semi sear can engage the hammer.

A four position selector lever in a lower with semiauto internals will not produce FA fire. You get semiauto fire in the single, 3rb, and FA positions.

The lower is NOT A FIREARM on the 55x, so it doesn’t matter whether it was installed on a rifle or a pistol. It’s just a part. Pull the stock, add the brace, drive on.....

I would be leery of buying a “demilled” Swiss lower. First, what does that even mean? Why would one demilled the lower? Does he mean he’s going to convert it to semi?