Newbie.

I am building my first AR-15. I am hoping to build a 300 BLK SBR. My issue is getting the total length to get the NFA stamp. The barrel size I am looking at is 8.5. I have AP Gen 2 lower and upper receivers. But, I have not ordered a stock or buffer tube. Is there a standard carbine stock/buffer tube length? I am looking at Magpul Mil-Spec CTR, expandable stock. I have no idea what buffer tube, yet.

Any help on estimating the total length is greatly appreciated!

You'll have to pick a receiver extension / recoil system.

If you use a standard carbine receiver extension and measure with the stock extended (If I recall correctly that's what the ATF wants) would be 27.75" with an 8.5" barrel.

Add 19-20" to your barrel length

Thank you for the reponses!