Sionics Weapon Systems is now offering what they call Rail-Ready Uppers. These are complete uppers including the BCG that come ready for you to bolt on your GI barrel nut compatible rail! There is nothing to cut, nothing to remove, and nothing to waste.
Most manufacturers offer uppers with a standard FSB, delta ring assembly, and handguard cap which is wasteful if you are just going to install a rail that uses the standard barrel nut when you receive the upper. You end up cutting off the delta ring and handguard cap. It is even worse if you have to remove the FSB in order to replace it with a low profile gas block. Rails that attach via the standard barrel nut are common now yet, no one that I know off sells uppers with this in mind.
Sionics’ Rail-Ready Uppers are available in 2 lengths, 11.5″ carbine gas or 16″ mid-length gas, and 2 main configurations, with an FSB or with a low profile gas block. If you are choosing the 16″ mid-length set up with a low profile gas block, you may also choose their medium or lightweight barrel profile.