Re: Anyone own a 7mm 300 Win Mag?
OK, so I've had a little fun w/ this new toy and some consternation. Please let me run some data past you guys and get your feedback if you're bored and ya don't have anything better to do tonite!
So, my bbl. Is a Rem 26” take off 7mmRM reamed out using a 7m/300 reamer. Hey, $50 bbl. is perfect to experiment with!
I’m using Nosler custom 300WM brass necked to .284 w/ RCBS 7mmRM neck die and a little lube to “JUST” size tghe neck just above the shoulder and not crush anything. Case head measuremet just above the belt is VERY consistent at (.5095-.5100).
Worked GREAT for the first 50 fireform loads w/ 154g Hornady bullets, 70 H-4350 and Fed GM 215 primers (about 3204fps ave. & 142ES and no great shakes on accuracy,but again it's a $50bbl.). Bullet seated to cannelure which is WAAY off the lands….. ( .1340 off as I measure it w/ the Hornaday COAL gauge). No pressure problems.
Also, worked up a load w/ 180g Bergers, (.0165 off the lands) using the FF cases and 78 g H-1000 to get to 3014fps ave. f/ 3 shots that went into .9moa at 200yds. w/ no pressure signs. Good enough for me for killing things!
THEN, ran out of H4350 and hadda use H4831sc for the second fireform session of 100 cases. Hodgdon manual (circa 1985) for 300WM and 165g bullets indicate a range of 75.5g-81g and for a 150g bullet, 76.5g -82g of H4831. Since I’m using a 154g bullet, 77g outta be okay, right? Wrong.
Blew two primers completely out of the case. Fired 8 more w/ no blown primers but noticeable ejector marks on the case head AND…..case head measurements JUST above the belt indicate .5165-5.175. Check the all the other FF loads and THEY measure .516-.517 at the case head as well.
So, had a chamber cast made in IT measures .5165 just above the belt. This is 6-7 thousandths case head expansion! I was always lead to believe that .001-.003 was SOP. Input?
This weekend I ran 3 rounds thru w/ 75g H4831sc and the 154g Hornady. No blown primers, but still, the extractor mark is VERY visable. Extraction OK, but case head still measures .517 or so.
I had some of the “upper tier 78g H-1000” 180g loads using the previously FF cases and they all went bang without any issue. Seems like once you get it fireformed, it’s okay.
BUT is there a “kaboom” in my future cuz I’m blowing the cases out way to far w/ this chamber/brass combo, weakening the case head web and cruising for a bruising?
All my data indicates that a 300WM is .511-.513 at the belt anyway for SAAMI specs. Given that, even THEY would expand to .0035 or .0055 in this chamber.
Whaddya think? Any help would be GREATLY appreciated.
Life is short and we ain't gettin out alive!