If you've got the cash, I'd go for it. I recommend going the trust route rather than as an individual when filling out your form 1. Going this route, you don't need CLEO signature or fingerprint cards, and it speeds up the process significantly. Just google 'form 1 trust' for info.
You'll also want to know how your SBR will perform compared to a 16" carbine. The below is copied from an earlier post of mine:
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The info below is from my own measurements, use of a ballistics calculator, and research using respected sources. I'm no expert, but the info below has helped me to understand the performance differences of my SBR. The numbers below presume the use of M193 ammo. Other ammo will likely perform differently, but generally be in the same ball park.
Muzzle velocity with a 16" barrel is ~3165 fps. Muzzle velocity with a 10" barrel is ~2865 fps. There is approximately a 300 fps drop in velocity going from a 16" to a 10" barrel. After leaving the barrel and stabilizing, a bullet fired from a 10" barrel will behave very much like a bullet fired from a 16" barrel that has already traveled ~80 yards.
Bullet spin rate is also effected by barrel length: ~326,000 RPM with a 16" barrel compared to ~295,000 RPM with a 10" barrel. This lower RPM from a 10" barrel is approximately what you would get from a 16" barrel with a twist rate of 1:7.75 to 1:8. Choose your ammo based on this lower 'calculated' twist rate and lower muzzle velocity.
If you are zeroed at 50 yards, your POI will be will be the following:
25 yards = 1.1" low
50 yards = POA
75 yards = 0.8" high
100 yards = 1.3" high
The effects of windage on a bullet fired from a 10" barrel is about 15% greater than from a 16" barrel. At 100 yards with a 20 MPH wind at 3:00, a 16" barrel will hit 2.2" left, and a 10" barrel will hit 2.6" left.
My experience is that I get my best groups with 62gr ammo, followed by 55gr, and 75gr comes in with the largest groups (even with match ammo). The lower spin rate at the muzzle is likely the biggest factor for this.
Even though I used M193 above for my measurements/calculations, I wouldn't recommend using it in a P556 for self defense. The reason is that he primary wounding mechanism with M193 ammo is fragmentation, which is relative to velocity. For M193 (and most ball ammo), fragmentation doesn't occur properly when impact velocity drops below 2700 fps. When fired from a 10" barrel, velocity drops below 2700 fps at just 47 yards. If you want to reach out further, you need to use soft tip or hollow point rounds that don't rely on fragmentation and maintain their wounding potential at lower velocities. The P556/SBR is really best suited for close quarters where distance isn't as important as reduced size and maneuverability.
Anyway, hope this helps
http://ammo.ar15.com/project/AmmoOracle_061808.pdf
