Thanks for the reminder. I had forgotten about this while the Howa was at the gunsmith waiting 3 months for parts for the new sight.
I did some work with the mags today and there are definitely problems with the "open U" type mags, or at least with mine. More specifically, I have 4 mags, 1 is the "closed U" type, and 3 of the "open U" type. I tried the closed U type first, 6 times, and no problems at all. The open U were different. I tried each 6 times: Open U mag #1 failed to feed the last round and jammed all 6 of 6 tries. Open U mag #2 worked fine 5 of 6 tries, jammed and failed to fire the last round once of 6 tries. Open U mag also failed to load/fire the last round 1 time out of 6 tries. In the first course of testing I made no special effort to work the bolt smoothly, be sure not to short stroke, etc. After the first round I have described, I tried Open U mag #1 again, being very careful to work the bolt smoothly and fully stroke the bolt--it failed 2 times out of 4. The bolt operation on the Howa is not very smooth in any event. Other than the failure to feed/fire the last round, all the mags worked as they should. All of this testing was done with Tac 22, which in my experience will feed in just about anything. This problem with the open U mags is not acceptable in my opinion.
So, I am going to take the mags apart to see if there is a spring reversal situation causing these problems. If that does not help, I am going to contact the distributor again and see if I can exchange the open U mags for the closed U variety. I will post the results of that.