Are you talking about the Walther branded one, it has kinda flat sides....there is also a round one I got for my Hammerli years ago.....I think it might be branded as hammerli but not sure.
Anyhoo I have them both.....both have worked just fine for me. The walther branded square sided one is a little shorter....it will fit in things like the walther lever rifle just fine....the round one is too long.....both will work in my 850.
I can also tell you that I have lost 88g cartridges. Not ever seen one that will self seal....have had several turn into a frozen block of metal before, but never seal.
I do not care for the 88 gram....I am not going to shoot that long. You don't get any more pressure, there is just more in there before it starts to fall off....and I think the extra mass helps keep the temps up....they don't seem to get cold as fast. On a gun like the 850 just take off the guard if it gets cold and let the warm air get to it....the lever gun no luck.