EDIT: I did this post before I had a chance to see the STM-12 kit parts. As it turns out, it isn't a good candidate for an AMRAAM kitbash.
Sure it looks a bit like the AMRAAM, but the STM-12 kit only has three fins! The AMRAAM has four.
The STM-12 body tubes are already slotted for three fins. You'd have to buy new BT-60 body tubes - and maybe a shorter nose cone so . . . forget I ever brought it up!
Unless . . . you wanted to build a sorta' scale three finned AMRAAM.
The Estes STM-12 is on clearance right now on the Estes website for $6.99: CLICK HERE
Here's the Peter Alway scale data I found after a search:
Let's see -
The STM-12 body tube is a BT-60 at 1.637" diameter.
The AAMRAM is 7" diameter.
Divide 7" by 1.637" to get a 4.27 scale factor.
Simply divide all the measurements in the Alway drawing by 4.27 to get the build sizes needed.
Divide 144.25 by 4.27, the model will be 33.78" tall.
New fins might have to be cut out, the trailing edges of the STM-12 fins aren't flat. (You could cut scale fins from the kit supplied balsa)
That nose cone looks long, but for a sport scale model it'll be close enough.
Those blue bands could be done with a strip of Monokote trim. Decals look to be all black, so home decal printing is easy.
With the forward fins, the OOP Estes AAMRAM kit had two pats of clay to go into the nose cone. THE STM-12 kit doesn't require any clay.
A little time with a calculator and you'd be good to go! Sure there would be some cutting and adjustments. but for $6.99 it's a good start for a semi-scale rocket!
Before you order the STM-12 kit on clearance, bear in mind many bagged kits have had malformed body tubes. The kits are bagged up in China. The tubes are packed tight in bags that are too small.