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**44 AMP** · March 12, 2024, 02:29 PM

While a micrometer is the most precise, even a cheap plastic caliper measuring the round will give information accurate enough for a reasonably good identification. The OP need to get one (or borrow one) and take photos of it measuring the width and length of the round.

ALL the old rimfire rounds used heeled bullets. So did some centerfires, in the early days. Only the .22 rimfires are still using heeled bullets these days (other than reproductions of the old rimfire round if any are being produced.)

The round pictured is probably a .41 rimfire, could possibly be a .38 rimfire, there's not a lot of dimensional difference between the two and a tape measure isn't quite good enough to tell which it is.

March 12, 2024, 02:29 PM	#13
44 AMP Staff Join Date: March 11, 2006 Location: Upper US Posts: 28,944	While a micrometer is the most precise, even a cheap plastic caliper measuring the round will give information accurate enough for a reasonably good identification. The OP need to get one (or borrow one) and take photos of it measuring the width and length of the round. ALL the old rimfire rounds used heeled bullets. So did some centerfires, in the early days. Only the .22 rimfires are still using heeled bullets these days (other than reproductions of the old rimfire round if any are being produced.) The round pictured is probably a .41 rimfire, could possibly be a .38 rimfire, there's not a lot of dimensional difference between the two and a tape measure isn't quite good enough to tell which it is. __________________ All else being equal (and it almost never is) bigger bullets tend to work better.