Lately, I’ve been working on developing a 140-grain jacketed accuracy load for the scouterized M96 Swede. Today’s testing consisted of 44.5 and 45.5-grains of IMR 4831, per Hodgdon’s web-site and 2017 Annual Manual (each have the same data). The published minimum load is 43.0-grains at 39,100 CUP, and the published maximum is 46.3-grains at 45,400 CUP. SAAMI's MAP is 45,000 CUP.
There were no problems with today’s first 44.5-grain round. However, after firing the second round the bolt required some extra effort to lift, and on checking the primer I noticed that it was cratered and there was a partial impression of the bolt face. I, then, checked the first round’s primer and it was cratered, too, but there wasn’t any bolt face impression. I packed up the rifle and shot the S&W Models 24 and 624.
Qualifier: I weigh every charge, including plinking loads. Even with the 45.5-grain load the powder was below the case shoulder, and bullets were seated to just above the shoulder.
Back home, I rechecked Hodgdon’s web-site and manual, just to be sure I read them correctly from when I loaded the rounds yesterday. Yep, the loads were well below the 46.3-grain maximum.
I measured the case heads of both fired rounds, full length sized them, and measured them again. The first head expanded .0025" and the second one .0035". WOW! Thanks to Mr. Mauser and Swedish steel the rifle held together.
Speer’s 14th edition manual and their 15th manual’s web-site list IMR 4831 data as 39.0-grains minimum and 41.0-grains maximum. Hornady and Sierra do not list IMR 4831.
Lesson learned: Though I have more than a dozen manuals, and always check at least three of them before starting on any new cartridge and/or bullet experimenting, I didn’t pay enough attention to the huge disparity between Speer’s data and Hodgdon’s. I will forego any further IMR 4831 testing.