Dealing with high pressures in the Winchester Short Magnums
Q: I just purchased a Model 70 Winchester in .270 WSM together with three boxes of factory ammunition loaded with the 130gn PHP bullet at a nominal 3275fps. This load seems to be a bit hot as case head expansion prevents fired cases from going back into the chamber after being neck-sized. But I have struck trouble even after full-length sizing them, as they still won't chamber easily in my rifle. Can you advise me the best way to get around this problem?
A: The ,270 WSM works at very high chamber pressure - over 63,000 PSI and occasionally case solid heads expand as factory loads prove to be a bit hot in some guns. It has happened to me more than once with the WSMs. All you can do is pre-load the press until the cases will chamber easily and then don't use a maximum load. I like a margin of safety with any reload. A good load that works flawlessly in one rifle may expand case heads in another. Be sure to use a magnum primer in the WSMs even though it will cause an increase in peak breech pressure because of burning more of the powder charge. For that reason you should reduce top loads by at least 3 grains, and work back up. Back off if you get indications of excessive pressure with any load, such as hard bolt lift or stiff extraction. Don't work up until this happens. That's too hot for safety. In my own Model 70 .270 WSM I load 66gn of W-760 and 67gn of Re-19 behind the Hornady 130gn bullet and get 3230fps, but I'd still advise you to work up to these charges