I was wondering what the advantages would be to using a small base die in .223 for my AR-15 over regular full length resizing?

A small base die is usually a full length sizing die. It merely reduces the case base down a bit further than normal dies to make them chamber easier. They're commonly used in semi-automatic rifles, and some lever actions, neither of which have the same strong caming action of a bolt rifle. I used to have a set for my Savage 99 lever action. Best wishes.

Cal - Montreal

Seldom do you need the SB dies for an AR, but they are offered just in case.
Brands vary in how much they size the brass, which is something else to consider, but before I invested in a set of SB dies, I would borrow or buy standard dies.

IF your rifle works satisfactorily with just the use of regular dies, there WOULD BE NO ADVANTAGE AT ALL in using the small-base type. These dies are only needed for resizing brass to be used in a weapon (auto, semi-auto, pump, lever, etc.) that will not reliably feed cases sized in regular dies.

The less you work your brass, the longer it will last.....

Hi There:

A unique thing about the M-16/AR-15 style rifle is there is no National Match "spec." like you find with the M-14/M1A rifles of the 60's and 70's.

As such, different manufacturers and gunsmiths use different chamber reamers, etc. when building AR style rifles.

The chamber reamers are sightly different from one-another (hence the references to Wilde chambers, 556 chambers, .223 remington, frank white, etc.) as there is no exact accepted standard.

These differences may require a small-base die in order for the cartridges to reliably function in the rifle in question.

For example, I had two AR's. One upper was built by Frank White (with a tight .223 chamber) and another used an old Colt barrel (with a 556 chamber). My Frank gun required a small-base die in order to get reliable functioning in rapid-fires. In fact, a checked each case for proper resizing before going into matches.

On the other hand, my Colt barrel gun did not need the small-base dies in order to function. I never checked ammo and it always functioned.

The bottom line is: do your current full length sizing dies work (read this "provide the gun with ammo that functions")? If so, then there is no need or advantage to a smallbase die for resizing. In facgt, there may be a disadvantage as you are working the brass which leads to hardening, separation and the need to trim more often.

If your AR doesn't function (and your cases are the correct length, chamber cleaned, etc.), then you might need small base dies.

Hope this helps.

Gurrie