Can Someone Explain This Please

[WVDennis]

Hi there. I’m not new to reloading but I’m new to to this site and case forming. I’m in the process of forming 308 to 6.5 creedmore. I’m using 7mm 08 as step between the two. I am happy with the results but I need to understand two things. Do I need to anneal? And what is neck thickening? And how to fix it. If I have a 308 case with no blemishes, it produces a nice product that only need to be trimmed

Thanks

[upnorthwis]

Neck thickening is when enough material is displaced to make the neck wall thickness thicker than factory spec. It can be corrected by either reaming the ID or turning the OD. It could be a problem if the chamber is tight and the bullet can't release from the case. If it all fits in the chamber freely, it shouldn't be a problem.

[M-Tecs]

In the case of forming 308 to 6.5 Creedmoor in addition to reducing the neck diameter you are also moving the shoulder further down the case. Both of which can increase neck thickness that may or may not require neck turning or reaming.

Using 7mm 08 to 6.5mm the neck thickening will be minimal. Since the wall thickness increases as you move down the case you may have to a thickness issue at the bottom of the neck.

[Mk42gunner]

Welcome aboard. Neck thickening has been explained, except how to detect it. You can go the high dollar route and buy a tubing micrometer, or do as I did before I had one: seat a projectile and use a plain flat jawed micrometer to measure the diameter. A bit of math and you have the neck thickness for that case.

As for annealing, it may or may not be needed. There are a plethora of threads about annealing and how to do it on this site. What it does is soften the brass that has probably been work hardened by your case forming operations.

Robert

[WVDennis]

How would I determine if the walls were too thick.....using a set of calipers?


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[WVDennis]

So I get one of these.......what is a normal wall thickness?


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[floydboy]

Most will tell you it isn't worth the hassle to make this conversion. They are probably right. I started with the 6.5 CM back when brass was hard to find and expensive when you could find it. I got 500 LC brass all the same year and went about converting to 6.5 CM. Made about every mistake that could be made I think. First firings were excellent and probably the easiest load I ever worked up. Upon reloading those cases for the first time I had all kinds of trouble with high pressure and accuracy went to pot. I determined my problem was case neck thickness mainly in the form of the donut. I had trimmed my necks before firing but the donut would form on the first firing. Military 308 brass is especially thick do to the fact it can be fired in a machine gun. When forming into the CM case the new neck ends up being made out of the old case shoulder and is very thick. Neck trimming takes care of this for one or two firings but the new shoulder will migrate into the neck quickly. The 6.5 bullet is so long it will stick clear into the case upon seating which means it uses the entire neck. What ends up happening is the first few thousands of an inch of the neck next to the shoulder will be where the donut forms and the bullet will be held very tight and possibly squeezed by the chamber. I was able to feel the resistance when seating bullets. It would take considerable force to punch through the donut. Reaming, filing or trimming to remove the donut helped but was not consistent. I forget where I read about this but somebody had already figured out how to stop formation of the donut. What I do is use a 308 file trim die to size the neck down and push the shoulder back 2-3 thousands farther than needed for the CM case. My trim die had to have the bottom inch or so cut off to do this sizing. Next I would neck trim to a wall thickness of .013. Next final size and form with the 6.5 CM die. After sizing my neck thickness measures .015 whick is what I want. The shoulder is pushed back so requires fire forming to bump it out. What you end up with is the correct neck thickness and for the first few thousands of the shoulder it will be between .013 and .015. This area of the shoulder will be where the donut moves into leaving you neck untouched by this thick brass. What moves into the neck is about the same thickness as the neck. Hope this is all understandable. If you use commercial brass you may not have as much problem as I did but this does seem to work.

As for annealing I use a propane bottle torch you use for soldering. I rotate case necks in point of flame for a 6 count. About 6 seconds. I came up with a 6 count by testing different lengths of time in the flame. 8 seconds and they were obviously too soft. I would squeeze them with pliers to determine softness. Not to exact but worked for me. Necks stopped splitting after annealing. couldn't tell any problems with accuracy.

Good luck, Floyd

[WVDennis]

Well I guess I’ll abandon my effort. I’m trying to qualify for my clubs’s 1000 yd range. Accuracy is important. Midway has laupa brass for $1.20 case. Trying to avoid that but thanks for the input


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