Not sure what the difference is with the Rem 6-1/2 caps, but there is no doubt about improvement in performance in the 22 Hornet, 25/20, 30 Carbine, and 32/20. Flyers pretty much disappeared, and groups got a bit smaller overall. The only thing I've read is that the 6-1/2 was developed to cater to the small-case rifle rounds of this caliber class I listed, while the 7-1/2 was designed for the 222-223 class of calibers. I have used VERY FEW Remington primers during my 40+ years of metallic reloading, and they have always been hard to find in my area of southern California--irrespective of component droughts or maker mood swings. I get mine at the Big Reno Gun Show, which I attend about every 18 months or so. Miwall usually has them at their station along the back wall of the exhibit hall.
I haven't tried small pistol primers in the Hornet or other like calibers. I was always concerned about higher pressures piercing their softer cup metal. Maybe that is unfounded, but that is how I've proceeded to date. Perhaps the Rem 6-1/2 combines rifle primer cup strength with pistol priming mixture intensity. Dunno.
