I am one of the die-hards still trying to make the 5.7mm Johnson (.22 Spitfire) round work.
The case is formed from .30 Carbine brass. The case is lubricated, run into a forming die that starts forming the neck. The case is then run into a trim die that also further forms the neck and then the case is run into the sizer die that brings the case to its final dimension. To get the neck properly formed, the expander plug has to be in the sizer die when the brass case coming out of the trim die is first put in the sizer.
Because the process crunches a .308 diameter case down to .224, the brass has to go someplace and so the neck thickens. If the neck is more than 0.012 thick (it always is), it must be turned or reamed. At present, I use an inside neck reamer on my Forster case trimmer to both trim the case to length and ream it to the proper thickness. But after being reamed, the neck is too big to properly hold the bullet and so must be run through the sizer die a second time to correct the dimension; thus cold-working the brass.
I was wondering about turning the outside of the neck to bring it into specification without the need for the second trip through the sizer die but was worried about creating a stress concentration where the undercut portion of the neck joined the shoulder.
Does anyone have any experience with neck turning versus neck reaming that they could share and explain why I should choose one other the other?
Thank you.
The case is formed from .30 Carbine brass. The case is lubricated, run into a forming die that starts forming the neck. The case is then run into a trim die that also further forms the neck and then the case is run into the sizer die that brings the case to its final dimension. To get the neck properly formed, the expander plug has to be in the sizer die when the brass case coming out of the trim die is first put in the sizer.
Because the process crunches a .308 diameter case down to .224, the brass has to go someplace and so the neck thickens. If the neck is more than 0.012 thick (it always is), it must be turned or reamed. At present, I use an inside neck reamer on my Forster case trimmer to both trim the case to length and ream it to the proper thickness. But after being reamed, the neck is too big to properly hold the bullet and so must be run through the sizer die a second time to correct the dimension; thus cold-working the brass.
I was wondering about turning the outside of the neck to bring it into specification without the need for the second trip through the sizer die but was worried about creating a stress concentration where the undercut portion of the neck joined the shoulder.
Does anyone have any experience with neck turning versus neck reaming that they could share and explain why I should choose one other the other?
Thank you.