I can't speak directly from experience with Express in .177", but in .22" I have only one airgun which actually groups well with the 13.43gr pellets, my QB57 with a 12" cut down barrel. I've tried them in my Brocock Atomic and the thing will put 7 out of 10 on target, but the other 3 will be random, often quite bad misses. My QB78D shoots 18.13gr Heavy JSB perfectly, but the Express start opening up at 20 metres and by 30 they're just not reliable. Every .22" I own loves the Heavy variety. They're just so stable.