hi there. i have a heym express bolt rifle in .505 gibbs. i've just done an article on it in this months "shooting sports" on it in uk- may issue if thats of help.
good solid rifle- key issue with this (and any other bigbore DG rifle for that matter) is the ammunition- terribly important you specifiy the ammo you want to run through it and stick to it. i had some issues with various makes but my .505 now loves the norma PH. cycles like a dream...i suggest you ask heym to feed, eject, regulate and test card the rifle to fire the new norma ph in .500 jeffrey- norma uses woodleigh solids and softs which are magnificent-
as a back up tool the heym will serve well. just ensure you test it and the ammunition thoroughly before you hunt with it.