7mm SAUM?

[sigstroker]

This cartridge has been in a mini-resurgence, probably because a couple of new brass manufacturers are now supplying brass at an almost reasonable price. There are also new chassis becoming available and old ones going on sale, making it a good time for a cheap build on old rifles.

I have a short action Savage 12. Would cartridges with the bullets seated a bit long still cycle through it? With a chassis that uses AICS mags, could I make cartridges that still fit everywhere but can still be long enough to use the good bullets? I assume I can't put the short Savage in a long MDT chassis and use long action mags?

[ar15barrels]

I have a short action Savage 12. Would cartridges with the bullets seated a bit long still cycle through it?
With a chassis that uses AICS mags, could I make cartridges that still fit everywhere but can still be long enough to use the good bullets?
I assume I can't put the short Savage in a long MDT chassis and use long action mags?

The "good" bullets have always needed to be deep seated in any of the short action magnums to fit within a 2.9" magazine length.
The RSAUM's are a slightly shorter case than WSM's though.
If your action won't take the 2.9" length, you can always have it notched to clear the bullet tips.
This is common when you go longer than 2.8" by removing the spacer in AI mags or using the 2.9" mags that don't have a spacer.

You are correct in that your action length defines what length stock and magazines you must use.