What's the difference between a transferable machinegun on Form 3 and Form 4?

Thanks

Basically nothing.  When sellers post the "Form" the gun is on, often "on Form 3" means the seller is a SOT, and that they'll be able to transfer it to your in-state dealer without an additional $200 tax, but that really depends on the seller's current licensure/tax status.

A gun is transferred between SOT dealers tax-free on Form 3.  A gun transferred on Form 4 could have been between private sellers, or a SOT and a private seller, and involved a $200 transfer tax.

Regardless of which Form the gun is registered on, however, the CURRENT SOT status of the seller and buyer is what counts.

If buying in-state, you can buy direct from the seller without involving a dealer (provided your state law allows this), for one $200 tax.

If buying from out of state, the gun has to first be transferred in-state to your SOT dealer before you can start your Form.  If coming from out of state from a non SOT, there's a $200 tax to get it to your dealer, and another $200 to get it from your dealer to you.  If coming from out of state from a SOT, it's tax-free to your dealer, and then a $200 tax to get it from your dealer to you.

Thanks for the information.

Reason I ask is my friend (a non SOT) up in CT has a reg'd BAR on form 4 and he agrees he will sell it to me.  I live in PA so it'll be an outta state transfer and I really want to start moving on it and get it in my possession.  I just found out what form it's on so now I can start talking to dealers down here and get started on the paperwork.

If it's an original C+R qualified BAR then you could get your C+R license pretty quick and cheap and then he could sell it to you direct.

If he owns any property or some type of vacation address in your state he can do a permanant change of address on form 5320.20 into your state then once that is approved sell it to you directly because the gun will not be selling across state lines.

Otherwise someone's gonna pay 2 transfers to get it into your hands.