No, Varget is a great .223 propellant.
Looking at the Hodgdon website, 25.5 is in fact a starting load for that bullet weight. If you'll also notice, the max load 27.5 has a C next to it. That means the max load is a compressed load. With a compressed load, sometimes you'll hear a bit of crunching when you seat the bullet. Slight crunch is ok...when you start changing kernel shape because you're crunching the heck out of it...that's not ok.
In addition, LC brass is fairly thick which in turn reduces your internal capacity.
Those two factors are the culprit.
You have two options. 1. Start with a lower charge. 2. Change brass to a different commercial manufacturer.
Personally, I would lower a half grain (start at 25 grains) and work up from there.
Ed