resizing mystery

[krains]

I sat down last night to resize some 270 Win brass and had some results that puzzle me. I measured the brass with Hornady's comparator using the C .375 bushing. It measured 2.045. I wanted to bump the shoulder back to 2.043 so I placed the die in the Forster Co-ax and screwed the die (full length bushing die) down till it touched the shellholder. I had previously lubed the case with a homebrew (90% isopropyl alcohol and 10% lanolin). Ran the case up into die (expander ball removed) and pulled it back down. Measured a cool 2.047...……

So I repeated this process with the remaining 49 cases. Exact same measurements before and after.

Why did that happen?

Luckily it was a 3 die set from Redding that included a shoulder bump die that I placed in the press and ran all of the brass down to 2.043

 

[spife7980]

You didnt have it screwed down enough. You size the neck down and the expander ball pulls it forward as it gets extracted. Screw it in another itsy bitsy bit and try again.

That said, how many times are they fired?
If they are new then they probably arent fully expanded so that little bit of growth may be just fine to work with. If they all chamber fine then I would wait to measure them when fired again to see what they measure then and adjust from that. Oh shit, I forgot you used the body die on them. They should certainly chamber just fine in the current state, fire again and see what the result is.

 

[Supersubes]

You sized the case down radially (body got smaller in diameter the full length of case), and that material had to go somewhere. Your press deflects during sizing, since a lot of force is being applied. Some presses do this more than others. You can counter this somewhat by screwing the die down slightly till the press “cams over” a bit.

Edit: You can actually use this as a technique to find your actual chamber length when you have a bunch of brass that fits the chamber already.

 

[krains]

I just got the Forster CO-AX press and was hesitant to cam over with it. I'll try that.

 

[Changed]

If this is "New" brass or 1F brass it may be that you didn't fully expand the case on the first firing. In other words you fired case was smaller than your chamber. This happens quite frequently.

 

[krains]

2x fired brass

 

[padom]

You got that measurement and didnt keep screwing down in 1/4 turn increments to reach your desired bump? What you see is normal. Keep screwing die down in small turns till you get your number.

 

[Huskydriver]

The touching the shellholder method of instructions should get you near sammi specs but will not get you optimum shoulder bump without slowing taking your die in and checking with your comparator or using your feelers closing a bolt on a sized piece of brass. Some chambers may need to be a little higher or a little lower than just barely touching when screwing the sizing die in. Your brass grew as a result of the die being set slightly larger than your chamber. Body was resized to spec but your should was pulled forward to fill the die. Brass follows the path of resistance in your die so if your die is set larger than your chamber, your brass will try to stretch to fill it as the body is squished inwards.

 

[krains]

Will do

Thx