I use a small Rigid pipe/tubing cutter for any “serious” (i e > 0.2”) case shortening.  I use a universal expander to straighten out the “roll crimp” on the shell, and then do the final trimming with a case trimmer, powered by an electric screwdriver.

If I had hundreds of cases I needed to shorten on a routine basis, like friends who convert 5-gal buckets of range pickups into .300 Blackouts, the Harbor Freight chop saw would be a cost-effective investment.  Kind of overkill for feeding a single-shot, IMHO.

Like marlinguy, I have done the same thing an it works great.   

ron

There has to be someone else who has found how great the Forster power trimmer is?

marlinguy  - It doesn't sound like you are using a Forster. The forster power case trimmer is set up on a drill press. I attached mine to a block of aluminum and clamp it in a drill press vice to make set up simple. A mandrel is provided to mount in the cutter head to properly align with the case, which is held in a collet mounted on the aluminum base and attached with provided screws. Once things are alligned, the depth of cut is set with the stop on the press and you are set to go. This system may not be as practical, time wise, if you are only doing a few cases, but if the intent is to trim many, as in wildcat varmint rounds, and some precision required, then this system is hard to beat. I have a table mounted drill press set up just for trimming and chamfering. For preping cases for breech seating a lot of fuss is not as necessary as the case is just a vessel for fuel. But, I have to say, that I bought this setup long ago when I was still shooting varmints and needed to speed up the process. On some cases, 219 Donaldson, for example, I bought a Harbor freight type cutoff saw to speed up things when removing 1/2 to 3/4 inch. other wise the Forster was just as fast and does a cleaner job of it. For the chop saw I use Wilson case holders to hold the case pependicular to the blade, and a stop to keep length the same. In my experience, the difference in time to trim with either setup is very little if at all.  Krag

As I have always said, whatever works for you is good. Just trying to pass along what works well for me.

Well, I took the good advice offered here on the forum and picked up one of the Harbor Freight , 2" chop saws.  I made up a shell holder from a piece of hard wood.  It indexes on the case rim.  Just had to align it so I got the correct cut.   
Some unfired RWS cases I had measured 1.825" OAL so this was my target length.  I found if I cut the 30-30 case to 1.810" it came out of the 8.15X46R sizing die at 1.834".  I only have a hand driven Forester-Appelt trimmer set up for this case, but removing the excess 0.009" isn't difficult and it trues up the mouth end perfectly.
Interestingly, the WW 30-30 brass has a rim diameter about 0.015" larger than the RWS cases. However, the chamber on my rifle accepts this without any difficulty (thankfully  ).
I attached a photo of the set up. My loading bench is not very big (tight quarters  ) so I inletted a 3/16" thick steel plate that I have drilled and tapped for the various tools I need; shot shell press; luber/sizer; powder thrower, etc.
The chop saw has its place now.  Next step will be to trim a bunch of cases and load them up for final fire forming.
Thanks to everyone for all your helpful suggestions!
Mike.