Alliant made 20/28 as an alternative to Unique for 20 and 28 gauge shoshell reloading. It is denser to make the stack height easier to achieve in the narrow shells. If 20/28 was make as an alternate for Unique in shotshell loads, what do you think it will do in metallic loads?

During the Unique drought, I was buying guess what? 20/28!
It worked very well in 9/38/357/40/45. Yes it's denser so you don't get an overflowing case on a double charge, but it performs very well and burns cleaner than Unique. My guess is that it's because there is a higher concentration of nitroglycerin in 20/28 than in Unique (virtually zero). I surmised that with my powder coat test where I found that higher levels of NG caused more powder to stick to PC bullets when left standing upside down for hours/months/a year. Powders with no NG like Red Dot, Clays, Unique had no powder stick to the polymer coated bullet bases while high concentration powders like Titegroup, Bullseye, Power Pistol, 20/28 and BE-86 had lots of powder sticking to the powder coat.

You also need to be sure to empty your powder hopper after each session with 20/28 and BE-86. The Hornady LnL AP measure will get smokey colored after years of loading even if you empty between sessions but at least it won't bubble up or blister which it may if you leave a high NG powder for long periods of time (RCBS is the worst).

But I digress. Use 5-10% less 20/28 in working up from your Unique loads and you'll find it is a very good performing powder. I have not bought any more 20/28 recently because I just picked up an 8# jug of BE-86 and will be using that for the next year of pistol loads.