built 7mm Rum

The RUM length brass is going to limit your choice of bullets and seating depth which will work in the magazine. Best to reverse engineer what you are after, bullet weight, form and velocity desired are the starting point. Then you can determine what your seating depth would have to be to mag feed and that will end up being what you throat your barrel for. I went through all this myself and came to the conclusion it would suit me best to just stick with a 7mm mag and give myself some better options for bullet choice. Something else to think about that doesn't give up a whole lot to the RUM and is a shorter cartridge is the 28 nosler. Anyway these decisions are half the fun, good luck with your build!
 
It's easy to extend the magazine box with a Wyatt's mag box and a few seconds in a mill. That will help you get the length the that the case requires to seat the long bullets out.

I haven't done a 7mm RUM but I'm on my 3rd 300 RUM. They require a different mag box with cut outs in the sides as well as a different follower than the 7mm rem mag or 300 win. They need just that little bit of extra space to get 3 rounds in the mag.
 
The 7 rum should use the same mag box and follower as the 300 rum i would guess. i had a blued 300 rum and loved it with 212 eldx . shot a couple moose with it over 600 yards. it was just factory with a trigger and bedding. Would any gunsmith be able to do this for me with the mag box or is there a few that have done it and are more knowledgeable. I’m heading towards the 195 Bergers.
 
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Are you stuck on the RUM? Ive also been looking into big 7's and a few stick out to me that seem to be easier to source parts for. 7-300 Win (7 Practical) have read of guys breaking 3050 with 180gr Bergers and if you really push it, 2950 with 195gr berger. Easy as heck to form brass too, just run your 300 brass through the neck sizer and there ya go. Another one that caught my eye was 28 Nosler, but brass is way to pricey imo. a 7-300 Norma would be a hammer too. 195 bergers at 3150 rivals the 28 Nosler, but more powder. And 300 Norma brass is quite popular and not bad priced. $230 for 100 Lapua vs $150 for 50 28 Nosler brass. All velocities out of a 26" tube as well.
 
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If your going for the "cool" factor a 7-300 win or 7-300 norma would get my vote. Im still contemplating the norma, nobody in my neck of the woods shoots one and its just a neat round. Id probably even do the 7-300 Norma Imp. 195's at 3250 would flatten anything to 1600 with ease. Sure there are more efficient calibers out there that do the same (7 STW), but if your building a custom or semi custom rifle, your looking to be different or stand out at the range.
 
yea i tryed searching for some info on the 7-300 norma but couldnt find much. how much is involved in sizing brass ? same as the win mag? im really looking at the 7-300 win as of right now but those numbers with the norma are very interesting.
 
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