I had a similar problem with Winchester AA's in my 1942 vintage Ithaca Model 37 20 ga a few years ago.The rims were slightly out of spec (it looked as if they were flatter than other shells compared to them making them slightly oversize)and they did not feed well.I bought them at a going out of business sale along with a box of PMC shells that had hulls over 2 3/4" long after firing which had trouble getting out of the ejection port due to the excess length.The only shells that gun has choked on in 72 years of use,go figure.