The CMMG, Inc MK3 Receiver Extension and Stock Kit (MPN:38CA953) features/includes a milspec buffer tube (7.25") and 6-position buttstock. The stock kit (MPN:38CA964) features/includes an A1 rifle length buffer tube (10") and A1 Rifle fixed buttstock. Specific lengths are not provided by the manufacturer. I'd recommend reaching out to them directly for more information.