You could do a chamber cast with a product called cerrosafe(?) from Brownells, or find a long shaft, bore or hole gauge.
I had same rifle/chambering in the spring of 21. A short or undersized throat. Ruger said they cleaned & polished on the first trip, a no go & in the meantime I'd acquired a modified case to help me check as well.
I was very specific about the problem when I called Ruger the second time & also put a big note in the box. They sent me another ship label. They replaced the barrel that time & ll was well. A few other members here had same issue about that same time.
