I have current VPP policies with both Eastern/Historic as well as USAA.
The USAA policy covers $150K of jewelry/watches/art for ~$1,100 per year. That works out to be ~$7.5 per thousand dollars of coverage.
Eastern/Historic covers $500K worth of firearms for $1,500 per year or $3 per thousand dollars of coverage.
Granted these are a bit apples to oranges in terms of the items with different risk profiles (jewelry and art vs. gun) but when I called USAA about firearm coverage they initially told me they couldn't do it in the amount I needed/wanted and when pushed came back with some ludicrous policy premium amount like $5,000+ per year.
We have all of our insurance through USAA (home, auto, umbrella) but if you want to insure guns Historic/Eastern is the way to go vs. USAA in my experience.
Hope this helps.