I am always so amazed at the negative opinions I see on small base dies. And they are so strong!
I called RCBS and the tech told me that a small base die reduced the case head by .002” more than their standard sizing die. I don’t see how that can over work brass.
I use small base dies on every caliber that I can get a small base die. Basically that is .223, 308 and 30-06.
I have a spread of match rifles, hunting rifles, and rock busting rifles all in the same caliber. With the small base die I ensure that my ammo will fit all of my rifles in the same caliber.
I don’t know if there is anything to the “overworking of brass”. It is true that military chambers are huge, and brass fired in a military chamber is very hard to small base size. But I don’t know if that really results in lessened case life. At least for axial case expansion.
So many people reload for bolt rifles that they get used to what would be sloppy reloading practices for auto rifles.
As long as the bolt cams engage, you can crush fit an oversized cartridge in a bolt gun. That is why neck sizing is so popular and hardly any bolt gunners ever set up their dies with a case gage. They just crush fit the ammo in the chamber.
Gas guns will jam with ammo that will chamber in bolt rifles.
Garands and M1'a have the inertia to chamber slightly fat and slightly long cases. But it is a bad idea as bolt closure is delayed as the cartridge is crush fit to the chamber. In that time period, that free floating firing is just tapping the heck out of the primer, and your lugs are not engaged.
That has, and will lead, to out of battery slamfires.
Regardless of the type of sizing die, standard or small base, you should always use a cartridge headspace gage to set up your sizing die.
I own a number of Wilson cartridge headspace gages. They cost about $25.00. These work great in setting up your dies to size the case to SAAMI lengths. These gages are also oversize between the shoulder and the base, so you can drop a fired case in the gage and roughly measure the headspace of your rifle.
I also have reamer cut gages. I have asked the gunsmiths who chamber my match rifles to use their chambering reamers and cut me a dimensionally correct chamber from a barrel stub. I can use this gage to tell me if my ammunition is too fat as well as being too long.
I now can gage brass in a virtual chamber. This has lead me to the use of small base dies. In the attached oicture I found two huge fired WRA 68 cases. One would drop all the way in the Wilson gage, but the other would not drop in the reamer cut gage.
After sizing with a standard Lee sizing die, one case would not drop all the way in the reamer cut gage. After sizing with a Redding small base die, the other case would drop in the reamer cut gage.
This tiny amount of case sticking out of the gage may not seem like much, but the unfired cases on my second out of battery slamfire in a Garand stuck out that much. Maybe if the lugs had been engaged instead of the bolt crush fitting the round to the chamber that slamfire would have been in battery. I had to replace the receiver when the bolt knocked the receiver heel off.
If you search enough threads you will find bunches where some poor guy is using standard sizing dies and his semi auto is choking on his cartridges.
If you want to improve your feed and extraction reliability in a semi auto, you should use small base dies.
A couple of caveats, one is that you must set up a small base die with a cartridge headspace gage or you will set the case shoulder back too much. I think this is the origin of those statements that “small base dies oversize brass”. They will if you don’t gage your die set up. The second is that spray on lubes don’t have the lubricity necessary to small base size. You are more likely to get a case stuck in the die than to get it out with these spray on lubes. Imperial sizing wax and RCBS water soluble work just fine in small base dies and I have sized tens of thousands of rounds with RCBS water soluble.
Wilson gage with new Winchester brass.
Once fired WRA 68, one drops in Wilson gage, the other won’t drop in reamer cut gage.
WRA 68 case sized in Lee sizing die, won't drop in reamer cut gage
WRA68 case sized in Redding small base die, drops in reamer cut gage