i believe commercial, and milspec will have a different rifle tube. simply because its the diameter of the tube that matters. the lenght is simply if its adjustable carbine or rifle. but diameter is based on commercial vs milspec. i would suggest staying in the same group( commercial or milspec) as your stock says it fits.
I have been a silent witness
to all of America's finest hours.
But my finest hour comes
when I am torn into strips and used as bandages
for my wounded comrades on the battlefield,
When I fly at half-mast to honor my soldiers,
Or when I lie in the trembling arms
of a grieving mother
at the graveside of her fallen son.