Because I have two of them, I guess you could say I have a collection of .22LR Lugers.
I suppose I have a collection of Contenders, having two frames and about a dozen barrels.
I have a collection of Remington 600 series rifles, .222, .243, 6mm, .308, and .350 Mag, and I also include my XP-100 (.221Fireball) as part of that.
I have or had a fairly complete milsurp collection of WWII and some WWI rifles and pistols. Mausers, SMLEs Arisakas, Moisin Nagants, and others, including our US arms.
and I have a collection of all the post WWII "first generation" magnum semi auto centerfires. Auto Mag, Coonan, Wildey, Desert Eagle, and LAR Grizzly.
Also a collection of Ruger New Model Blackhawks, and Vaqueros, but I sold off the Vaqueros a few years ago.
Had numerous 1911A1 pistols over the years, both GI and commercial, but all have gone on to others, save one, the one I inherited from my father when he passed.
So, I've got, or had collections by model and by caliber, still have most of them.