How is everyone coming up with their overall length? Is there some chart to go by that says - "an ar15 with a 10.5" barrel has an overall length of _____"? I would like to Form 1 two lowers, but I am not sure how to come up with an overall length for an 11.5" barrel and a 12.5" barrel? I have also heard conflicting information regarding whether or not the stock should be collapsed or extended?

Any suggestions?  Thanks!

Stock extended. It wouldn't be overall length if the stock was collapsed.

Seems to me you would want to put "under 26 inches" that way you are covered if you are under, same way you would want to put "under 16 inches" for the barrel length to cover you regardless of what upper you put on it.

A standard AR15 variant with a 11.5 inch barrel and a typical 6 position collapsible stock is 30.5 inches overall.  Just add or subtract based upon your barrel length.  

Barrel length is measured from the face of a closed bolt to the end of the barrel which does not include a muzzle device unless the device is permanently attached. (pin/weld or silver solder).

Overall length is measured with the stock extended as per the previous post.

ETA: Martinsburg will no longer approve forms with "less than 16" or similar statements or forms listing two lengths.  You must list the length of the gun/barrel as you intend to initially "make" it.  Once you make it that length you can change the length at will.  Martinsburg "asks" that you notify them if you make a "permanent" change.

This comes up once a week.  Hey Tony_K––-can this be a sticky?

19" added to the barrel length to establish OAL of the gun.  Once the stmap comes back you do not have to keep the same length upper on the lower receiver.   You can put a 5" 9mm upper onto the gun even if the Form 1 says 11.5" 5.56, etc...

Good luck OP on dual Form 1s.

Thank you everyone for the replies, I appreciate it!

LMTRocks - my apologies if this is a frequent post. I did search, but I guess my searchfu is weak today. Thanks again!