I am planning a AR15 300 BLK pistol build. If I purchase a completed lower at what point do I get the serial number registered as a pistol, does that take place when the FFL fills out the paperwork? Do I need to take it to the sheriffs office after it is finished? I do hold a Michigan CPL.
Is using an 80% lower a bad idea?

Not until it has been built into a pistol. And you have either 10 days, or 30 days after that point. (I don't remember which.)

When the lower becomes a pistol, you have 10 days after taking possession to submit the completed RI-60 to your local LE agency. You must also keep a copy of the completed RI-60 with the pistol for the first 30 days it is in your possession. After those 30 days, you can do whatever you want with your copy of the RI-60.

If you purchase a completed lower, it must be transfered from the FFL as a pistol on the 4473. It must have been a pistol it's entire life; if it has been transferred as a rifle ever, it is always a rifle thereafter.

If you are finishing an 80% lower, I would consider it a pistol upon assembly into a functional firearm. However, it can't hurt to register the lower with an RI-60 as soon as you've milled it to 100%.

Nailed it. Great explanation.

For the 80 percent builder when the pistol is done, you then send in your RI-60.  It asks for a serial number.  The law does not require you as the builder from an 80 percent to place a sn on the receiver.  Just put "none" and for manufacturer put "self."  If you elect to put a SN (and its up to you) on the receiver then put your SN on the form.  The local agency will call you and say you need an SN.  You have to explain nicely that neither federal nor state law requires a SN, they only prohibit obliteration of a sn.   They will call the MSP and then should back off. That is my experience  

If you get a stripped 100 percent lower from an FFL, its not a pistol under state law though the FFL may record it as a pistol on the 4473.  Then you take the stripped lower home and build it into a pistol and attach an AR upper, say 7.5 inches.  Now you have an AR pistol.  You now fill out the RI-60; list your self as the seller and not the FFL, and your self as the purchaser.  The FFL Sold you a lower, not a pistol.  You "sold/transferred" to your self a pistol you made.  Put the mfgs sn on the form and the other information.  Your local agency will call you to confirm you did not make a mistake.  Explain politely that you previously purchased a stripped receiver which is not a pistol under Michigan law because it has no moving parts or barrel.  When you built it then you sent in the RI-60.  They should be satisfied.

You will need to put overall length and bbl length on the RI-060 but your 100 percent milled lower will have neither.  Wait until it is configured as a pistol rather than trying to register a receiver which is not a pistol under Michigan law.

Unless you still have a pile of the old carbon copy RI-60's, from prior to requiring overall length. They still accept them (in Midland at least, probably elsewhere), without batting an eye. "Unknown" or leaving overall length blank, are also accepted. This has been for any and all pistols I've registered since the change, not just AR's.

YMMV, depending on county/city.

Barrel length is still required. But adding a threaded barrel, or a different length, on any pistol, at a later date, or even purchased WITH the pistol, don't have to be documented. Which simply points out yet ANOTHER stupidity factor, of handgun registration in our state.

Anything coming down the pike that will make it so you don't have to register your pistols?

Maybe a new governor in the election? Lol. Otherwise, not a snowball's chance in hell.

There was a bill last year that would have gotten rid of pistol regisration. But Snyder vetoed it just after Sandy Hook

So I think there's a chance of another bill coming through, but not while Snyder is in office, I think.

Are there any further restrictions or minimum/maximum OAL? I am doing an ar pistol build now just got the receiver and made sure on the 4473 that it was marked as a receiver. Going to register it as a pistol once I get the barrel.

The OAL stuff always confuses me. With the SIG sb15 brace, kak pistol buffer tube, and 10.5" barrel I think I'm going to be a little over 26" OAL. Should I be okay or is there something I am missing?

If it comes out over 26" you can't register it as a pistol.

The Sig Brace is not considered a stock, correct? Therefore, the AR would not be designed to be fired from the shoulder. Thus it is a pistol no matter the OAL. The definition of a rifle states it must be designed to be fired from the shoulder.

If the Sig Brace is considered a stock (which it is not at the moment to my knowledge), then the AR in question would be a federal and MI SBR (requiring a tax stamp) due to the 10.5" barrel, but would not be registered in MI as a pistol due to the OAL being greater than 26".

If its over 26" it's not registered as a pistol. Pistol, rifle or sbr.

Correct, the sb15 brace is not considered a stock, the ATF has recently also stated in a letter that shouldering the sb15 is legal and does not change the classification of the firearm. So correct me if I'm wrong, the 10.5" AR pistol I am building, despite having an OAL over 26", will still need to be registered as a pistol. But also does not qualify as a state or federal SBR.

Thanks for the feedback I don't want an oopsy when dealing with these things.

Nope, 5x5 was correct. I was incorrect stating that it needs to be registered. I forgot about the OAL portion of the pistol definition.

MCL 750.222 states:

So by definition, the AR pistol with a Sig Brace is not a pistol in MI because its OAL is greater than 26 inches. It is not a rifle because it is not intended to be fired from the shoulder. It is not an SBR because it is not made from a rifle. It is simply a firearm I guess.

Depends on what length the barrel is, and what length your buffer tube is.

I have a 7.5 inch upper on mine, which puts it under 26, even if I used an A2 buffer tube. I'm using a relatively short PISTOL tube on the back end, so I could use up to a 10 inch barrel, most likely.

It all depends on what length barrel you want. Mine IS a pistol. Well under 26'



Look into the Franklin Armory ATF opinion for what ends up being a "firearm" rather than Pistol, Rifle, or AOW.

With a 10.5 inch barrel, you do NOT want to use the KAK tube. Especially not the one they designed specifically for the SB15 brace. It ends up being too long. I'm using the pistol tube setup from Phase 5 tactical brownells link They're actually quite nice, and are made to hold the detent pin and spring in, with a small cutout, rather than just a lip. Kind of a nice feature. I'll probably use their rifle tubes in the future.

The Sig Brace stays put just fine, at whatever position you put it on the tube. It's VERY tight, and somewhat difficult to get on in the first place. I put mine onto the Phase 5 tube about halfway, for proper length of pull. The ATF has also issued an opinion letter, approving firing from the shoulder with the brace.

And, you'll find a LOT of useful info in the AR pistols section on here.

Or use whatever barrel or buffer tube you want. Add a DDLES folder and measure it in the folded position.  Should come in under 26".

Thanks for all the helpful responses.

Yes I plan on using the KAK buffer tube specifically for the SB15. I like that it has a shoulder to stop the brace from moving around and adds about 1.5" LOP.  http://www.kakindustry.com/ar-15-parts/lower-parts/buffer-tubes-and-parts/sig-super-sb15-pistol-buffer-tube
I really don't care if the firearm comes out over 26" unless there is a law prohibiting me from doing so. But I don't believe that there is a limit on OAL for a pistol configuration AR, whether or not it is then a pistol by Michigan definition, which is what my original question was really about.

If we break it back down, regardless of what my personal AR build OAL turns out like, I was just trying to make sure that I don't accidentally  make an SBR and that I meet Michigans registration requirements, whether I need to register or not.

OAL under 26" - needs to be registered as a pistol in Michigan.

OAL 26" and over - no registration

Didn't think of that. Good point :)

Damn, might have to do that, and get a LaRue 12 inch upper.

I can't seem to find info on how michigan measures overall pistol lenngth. I am going to build a 300aac pistol. It seems that with a phase 5 buffer tube it will be just over 25 inches if I include the muzzle break in the measurement. If I were to go with a kak tube that would add an inch and get it over 26. Don't know if I can count the flash hider though since I don't think it's permanently attached.