Neck turning for 50 BMG


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usmcpmi
November 26, 2008, 05:33 PM
My cases are sticking on a regular basis in my 50 BMG rifle. I have bought a neck turning set up and understand the idea/principal and have played with a few cases. I have read that one should turn just enough to make the neck the same dia. all the way around, down to the shoulder. What if I have to cut off more material or less material from case to case? Should I try to keep the neck wall the same thickness? I have measured the fired brass and taken an average of 20 rounds. I have read on other posts, to turn down to get .002 clearance between the neck of the loaded round and the inside of the chamber. I have not found a minimum thickness for the neck wall. Any help would be great. Thanks.
Semper Fi
MG

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243winxb
November 26, 2008, 06:30 PM
http://www.hevanet.com/temple/index.html Neck turning in general is to make neck wall thickness the same on all cases. As for the minimum thickness for the neck wall on a 50BMG i have no idea. :confused: I would guess .014" is the minimum wall thickness. Just a guess????? http://www.hevanet.com/temple/MatchPrep.html Quote:
" Neck turning
There are a number of reasons to neck-turn your brass. Some benchrest rifles are cut with extra-tight chambers and require neck turned cases, just to chamber - I'm going to assume that if you have such a critter, you know all about it. For those shooting 'factory' rifles, there are still some advantages to be had. Neck turning uniforms the wall thickness. A uniform wall thickness results in more uniform release tension, the case lets go of the bullet evenly, directly contributing to accuracy. Uneven tension while seating bullets can cause the bullet to cant, increasing runout. Finally uniform necks present a uniform amount of tension for each and every case, minimizing one more potential inconsistency.

To determine how much to neck turn, I will take four or five cases from the lot to be prepped and set my neck turning jig to just scrape some brass off. I'll turn all five and then examine them. What I'm looking for is a depth that cuts about 75% of the way around the 'average' shell. It may cut all the way around one, and barely cut at all on another, at the extremes, but for three of the five, I want 75%. Now on this first pass it's unlikely that I got there (if I did, I was rushing things...) so I'll adjust the cutter in ever-so-slightly and try again. I repeat this procedure until I get the depth I want. (~75% on most of the cases.) If you use the K&M, or another trimmer that allows you to measure your turned thickness, you can just adjust right down to your desired thickness. (Probably .001" more than the thinnest measurement from before, although maybe the same as that measurement, or a thou under, there's no magic here - go with what seems right to you, and experiment. Just remember that you can always take more off, you can't usually put any back...

I've motorized my turning setup, by using my drill press. It works just as well, if not quite as conveniently, by hand. Note that my drill press has a DC motor and can be turned very slowly - I go probably 30 rpm. Note also that the trimmer isn't actually clamped in the photos, it's 'floating' in the clamp jaws - this allows it to align naturally to the shell." Quote:

usmcpmi
November 27, 2008, 01:19 AM
243..Thanks. I understand all the reasons for turning. And yes, the chamber on my rifle is a little tight. Mostly what I'm asking is, should I turn a group of cases down to the same outside dia. , or just enough to remove the "75%" around each neck? My thinking is that if all the necks are the same outside dia., when the bullet is seated it will expand each case the same ammount, making each round the same outside dia. the wall thickness should be very close to the same, allowing for the same tension on the bullet. Hopefully allowing for an equal resistance as the bullet leaves the case upon firing. I am trying to reduce the variables that affect the bullet. Cases, all the same lot and length. Primers, same lot. Bullets, same lot. Powder, each charge weighed. I suppose I'll turn down 10 cases and load them all and see what the groups look like. Right now, I can hit a 16"x16" steel plate at 600 yards. My goal is a 12"x12" plate at 800 yds. Any suggestions are welcome. Thanks, MG

243winxb
November 27, 2008, 10:47 AM
usmcpmi, when i neck turn for my 243 win. the cut is 100% . The 75% cut, only hitting the high spots never made sense to me. I did not test the difference between 100% & 75%. But the more metal you remove the more slop you will have between chamber and case neck. I only neck size half of the 243win neck with a bushing die. This centers the round in the chamber as i am sure you know. You should do testing, start with 75% and as the article said, you can turn more off later. When turning dont let heat build up in the brass, it can affect the depth of the cut. Some times the 2nd cut at the same setting on the tool, will remove just a little more. I do not have a lot of experence. And i neck turn with a Lyman tool that works off my trimmer. One more think, be very careful, DO NOT turn/cut into the shoulder.

243winxb
November 27, 2008, 11:06 AM
the minimum thickness for the neck wall on a 50BMG http://en.wikipedia.org/wiki/.50_BMG If the loaded round neck diameter is .560" and bullet dia. is .510" Wall thickness should be in the area of .025" Turning would take off a maximim of .002" But i doubt that a loaded unturned neck really measures .560" So my guess is that you will end up with a minimum thickness for the neck wall of around .020" This means a neck turned loaded round would measure a minimum of .550" ?????? All a guess on my part. You should contact the guy at Questions and comments to 50shooterATThevanet.com (replace the 'ATT' with '@')

50 Shooter
November 27, 2008, 03:14 PM
Have you measured your chamber? CH4D makes a neck sizing die that you can swap out bushings. Another thing to check is your chamber to insure that there's no carbon build up.

Check the CH4D site for more info on their neck sizing die.

243winxb
November 29, 2008, 01:01 PM
Reply from Questions and comments to 50shooterATThevanet.com (replace the 'ATT' with '@') The case neck is cut too thin when:
1. There is insufficient tension to prevent the bullet from seating deeper in the case, given the type of handling *your* loaded ammo will be subjected.
2. Your case necks split prematurely.
I can't give you a number it will vary with the rifle and how you use the load. As the neck gets thinner it can't hold the bullet as firmly. If you shoot a match rifle, carry your ammo in a padded case, and single-load that may never be an issue. If you load up a magazine of five - that's a different story. If you cut it so thin that it's a sloppy fit in your chamber you'll split case necks.

Take care,

GeneT

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