the ACP cylinder rarely gets used.
Mine sure does! I shoot almost as many ACP's at the range. Plus, if I need a box of ammo quick for targets and haven't found the time to reload recently, I can grab a box of .45 acp under 20 bucks at several stores in my area. .45 Colts (other than a small supply at Walmart this time of year only) are SUPER hard to come by most times. That's my primary like. Also, if you get a good heavy load, it performs stellar and uses 1/2 the powder to do so. My goto load for target & plinking is 5 gr. Unique and a 200 gr. RNFP bullet, which also shoots great in every 1911/auto pistol I've tried them so far. My target load for the colt is 8 gr. Unique. Plus the brass is cheap and readily available. I was given over 1000 and have access to about 4000 more from the same source if desired.
With my LC brass, I haven't been able to get Starline at all and even the Winchester can be tough to get. I've had to wait 6 mo. recently to find a bag, which really stinks. Here's an article with some loading information about RUGER .45acp cylinders only too. Using this data, I get the equivalent to my 23 Gr. H110 loads in velocity with 12gr. Longshot. They are stiff if you try them though.
Dohh their database is having issues today. I was there yesterday and it was fine. If it comes back online, Use this link and then under recent tests at the left is the .45 acp in the convertible article:
http://www.handloads.com/