Need some help with tight neck brass


Well-Known Member
Jun 15, 2009
Toledo Ohio
I just picked up a 300 RUM with .337 tight neck. I have not reloaded turned neck brass so I am not sure where to start.

Can you walk me through the process with New brass, once fired but not turned and fired brass that has already been turned?

What size neck dies do I need and which do you recommend?
You need to leave 0.003" clearance between the chamber and the case neck. The O.D. of your loaded round should be 0.334". Measure the case neck wall thickness. Load a bullet and measure the neck O.D. Then calculate how much brass will have to be removed for it to fit the chamber properly. If your bullet diameter is 0.308", then your finished case wall thickness should 0.013".
+1 on Win 69's comment.
I use a Forrester outside neck reamer and do the math like Win69 said and turn the brass down in two passes. Once to get close and the second to get it exact. Don't go fast just take your time. I also use a Redding neck sizing die with the right insert to get enough neck tension. Every now and then when the cases get too large to fit the chamber easily I will use a full length size die to bump the shoulder back.
Its a real PITA to do cases this way but I'm only doing this on a gun I hunt with that I want long range accuracy with and when I did the cases I only did 200. I put 100 away and just use the first 100 to reload and when those are gone I will dig out the second 100. So far I am a long way away from digging out the second 100 as with a load that isn't too hot you get little case growth and the cases seem to last forever. I figure when the cases are gone the barrel with have long been worn out. Next barrel will not have a tight neck. :) At this time I have two rifles with tight necks but man I love the way they shoot.
Thanks everyone for the input. let me see if I got this right

unturned brass: Size neck to standard specs, seat bullet and calulate how much material to remove to give .334 dia. Since this is with the bullet how do I determine which bushing size to buy without bullet?

Turned brass- resize neck to the above bushing dia?

Am I missing anything here?
As Win69 said, Measure the case neck wall thickness.
Multiply it by 2, and add cal to it(.308).
This is your loaded neck diameter.

If you go with .334 OD(sounds good to me), and desire a good bit of tension, say .003", then pickup a .330 bushing. That's .334-.003-.001(springback).
I seat a bullet into a case and then mic the case neck. I usually only go .002 under bore size but do believe you would be better off to go with .003 under, especially if you will be hunting dangerious game with in which case .004 under might be better. The reason for going under chamber size is to make sure it will chamber and alittle dust can make it hard to close the bolt. I also find it very hard to maintain close tolarances with a hand turned neck trimer and recomand a power trumer or one you can run with an electric screwdriver, Much faster and far more accurate and uniform. When setting up your neck turner work down to your final setting. If you go for it the first time you will probly set it to thight and end up takeing off to much brass.
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