I've owned a couple of the Sears rifles and both had H rings. I think they were all made after the change. I also had a 1951 FN deluxe .270 with the H ring.
Last month, I picked up a sporter on Gunbroker built on a 1948 FN barreled action with a left-handed stock. It has the C ring. As noted above, 1948 appears to be the cut-off date for the C rings.
I was glad to get this rifle, but would have still bought it, C ring or not as it's a great rifle and was a bargain at $456. The C ring is a nice touch, but really not that big a deal. Any FN of that era is well worth owning and using. The C ring is supposed to handle escaping gas better. A better idea is to avoid doing things that generate escaping gas. That's how I've managed to hunt with the notoriously gassy pre-64 M70 for thirty-some years and keep my complexion as lovely(!) as ever.
