It'll be interesting to see what happens with mine then, as I've ordered the new type 25mm seal (the one that clips over the entire head and eliminates any lost volume) that fits the TX and Gamo type wedge fitting, I'm currently running a short stroke head with a HW seal on my Brocock Indy but I'm finding it hard to get decent power and I'm sure it's harsher because of the extra spring needed.
Pete
Far too many rifles to list now, all mainly British but the odd pesky foreigner has snuck in