Brass Case Head Separation after 6 firings

[nksmfamjp]

Anybody use this setup to look for thinning brass near the case head?

I do and found my 300 Sherman brass all scrapped after 6 firings. I'm pretty careful about sizing after firing. I target 0.003" shoulder bump because at my normal 0.002", there was still a bit of tightness in the final bolt close. Win 70 action.

I actually think it came from forming. Now the brass showed the brass thinned about 0.01" radially. After forming, I tested and saw 0.002-0.003" of this thinning.

So, my thought is my forming process was bad. I used a false shoulder created with a 0.312 (8mm) expander. I wonder if this wasn't enough. Bullets were jammed 0.005". I was using Peterson brass.

Now all I can find is new Starline. I'm thinking COW method and use 0.338 expander to get this false shoulder more solid.

Other advice? Am I heading the right way? Anything better.

 

[can1010]

when i form something like the Sherman or Gibbs cartridge that move the shoulder that much i will expand to 375 and then come back down to do most of the forming before firing, a 416 expander makes 06 cases straight wall and then just form your shoulder where you want but start with 35 whalen brass if you go that route.

Peterson brass had lots of problems with case cracking and head separation a while ago and does not recommend their brass for forming wildcats. 338 Lapua was the biggest problem

 

[FEENIX]

when i form something like the Sherman or Gibbs cartridge that move the shoulder that much i will expand to 375 and then come back down to do most of the forming before firing, a 416 expander makes 06 cases straight wall and then just form your shoulder where you want but start with 35 whalen brass if you go that route.

Peterson brass had lots of problems with case cracking and head separation a while ago and does not recommend their brass for forming wildcats. 338 Lapua was the biggest problem

I used .270 Peterson for my .30 Gibbs but only with COW method; no load development yet. Thanks for the heads up.

 

[nksmfamjp]

I used .270 Peterson for my .30 Gibbs but only with COW method; no liad development yet. Thanks for the heads up.

How did you do the COW method?

Have you measured case thinning with a setup like I showed?

 

[FEENIX]

How did you do the COW method?

Have you measured case thinning with a setup like I showed?

- Opened up to .338"
- Used .30 Gibbs sizing die to establish false neck
- 11g WSF, fill COW to the base of the shoulder, and then stuff with a cotton ball (packed)
- Shoot and clean barrel as required.

Virgin Peterson brass started with .001X" thicker than Hornady. I do not have the thickness after COW, but I can measure them for you. I do not worry about it until one full load firing off the chamber.

ADDED:

From L-R

1 - .35 Whelen Hornady virgin brass
2 - After running through .30 Gibbs sizing die
3 - After COW fireforming
4 - After firing off the chamber with a full load

 

[bigngreen]

I personally don't like fire forming with a false shoulder or COW, I like a middle of the road load with a heavy jamb, .005 really isn't jambing it enough. Fire forming is so critical I just want to make absolutely positive the brass is forming at zero headspace!!!

 

[HSmithTX]

Jam at least .020" for fire forming. 20% or so above starting loads usually works great. If you have a spring type ejector it doesn't hurt to remove it for fire forming.

 

[nksmfamjp]

I personally don't like fire forming with a false shoulder or COW, I like a middle of the road load with a heavy jamb, .005 really isn't jambing it enough. Fire forming is so critical I just want to make absolutely positive the brass is forming at zero headspace!!!

I respect your opinion a lot. Why not use a false shoulder?

Also, if not 0.005" jam, what is enough for you?

 

[bigngreen]

I respect your opinion a lot. Why not use a false shoulder?

Also, if not 0.005" jam, what is enough for you?

Personally I don't like going through the trouble of a false shoulder and I like to minimize moving brass, really it's just what I find works for me the best to get what I want. How much jamb is kinda bullet specific so I just seat them back till I can cam the round in so a LOT of jamb, like what was said above I pull the ejector if it's a plunger style and grease up my lungs then go to forming.

 

[can1010]

i understand if you're doing something along the lines of an Ackley where there is a light crush on the parent case to help with support but when you're moving the shoulders forward as well as blowing out taper the neck will release the bullet before the case forms enough to support itself in the chamber having a better chance of web stretch. I had this problem years ago trying to max out the rum case.

 

[bigngreen]

The Sherman isn't set up on the .004 crush like an Ackley.

 

[can1010]

I know, it moves a lot of brass like a Gibbs and just jamming a bullet leaves the case unsupported in my experience. for the Ackley type just a jam is ok but when moving brass the case needs more support with a false shoulder to eliminate stretch

 

[FEENIX]

Pm

I know, it moves a lot of brass like a Gibbs and just jamming a bullet leaves the case unsupported in my experience. for the Ackley type just a jam is ok but when moving brass the case needs more support with a false shoulder to eliminate stretch

I agree!

 

[bigngreen]

I don't want the case to center on an over size bulbous shoulder that is randomly pushed back since the body isn't centering the case in the die till it's blown .I want it held in place like it's between center then blown out. The bullet does not leave the case before it's been pushed out, this just gives me the best outcome with the least amount of screwing around.