^mm ARC Case Neck Dimension After Sizing

[Zzooomm]

I'm not new to reloading, but I am new to the 6mm ARC and am trying to understand where my issue lies. I cleaned, deprimed, and sized the brass using new Whidden dies. However, when I attempted to insert the brass into the Giraud 6mm ARC shell holder, it wouldn't fit.

I measured the neck and found it to be .007" larger than new brass. I also measured Hornady, Starline, and Alpha brass, and all were the same—.27495 for once-fired brass and an average of .26920 for new brass. I’m only trimming for the chamfer.

SAAMI specifies a neck diameter of .274". I don't have any loaded ammo to measure, but ultimately it seems like the sizing should have resulted in dimensions that would allow the brass to fit into the Giraud shell holder.

What does this suggest about chamber size, die dimensions, and shell holder dimensions?

 

[tdogg]

What size bushing are you using in the Whidden sizer? Are you using an expander ball? What size is it?

Is the neck resized? Can you insert a bullet into the neck by hand? If not, how about seating a bullet in the press and doing the simple bench press test to see if the bullet sets back at all (measure OAL, press nose of bullet into the bench hard by hand and remeasure OAL)?

Cheers,
Toby

 

[Zzooomm]

I'm embarrassed to say I can't remember what size bushing I have in there but maybe .267. My reloading bench is at my office and I'll check in the morning. I'm using the expander that came with the die but will measure it. Thank you for the help!

 

[divingin]

Are you talking about a shell holder or a cartridge checker?

If the former, how did you size the brass? It's possible with an arbor press (doesn't use a shellholder); not so much with a standard press.

If the latter, a) does the brass fit your chamber, and b) does the neck hold a bullet? Loaded round neck diameter should be bullet diameter plus twice the neck wall thickness (.243" plus twice .015"ish, so about .273" depending on your brass neck thickness.) Prior to seating a bullet, neck diameter should be a couple/few thousandths smaller.

Lastly, have you identified what is preventing the sized case from entering whatever it is that it's not going into? Sharpie is your friend: Mark up a case and see where the ink rubs off. Should give you good idea as to what's wrong - this fix should be pretty obvious from there (hopefully.)

Good luck!

 

[NZ_Fclass]

I'm a little confused on the dimensions of the brass - are you saying that sized brass is 7thou too big to use in the Giraud? In which case, the answer is plain - the die dimensions are wrong. - if you are using the expander ball, the problem likely is there. I gave up on expander balls a while ago and simply use a bushing that sizes the brass to the dimension required, to give under 2 thou of neck tension. For a 6 ARC, the finished case should have an internal diameter of .2415 ish plus 30 thou of brass ( I dont know your brass thickness, but Hornady Grendel is 14 thou plus) Which gives a loaded neck dimension of .2715ish. That allows 2.5 thou release in the chamber. I'm not sure why the ARC has a .274 neck, when most 6mm's have 272 or smaller. My no-turn BR is 271. I am assuming that this is for a bolt rifle - an AR would need more neck tension and a smaller neck diameter. I guess measure the expander ball, and talk to Whidden's -I love their dies - 1 have 2 sets for the 6 and 6.5 SLR

 

[Zzooomm]

Reality is my old eyes stuck a .288 bushing where their should have been a .268 bushing! Thanks for all the help. The necks were obviously not touched by the .288 bushing so no sizing was taking place. Kinda like the opposite of neck sizing only!

 

[NZ_Fclass]

Reality is my old eyes stuck a .288 bushing where their should have been a .268 bushing! Thanks for all the help. The necks were obviously not touched by the .288 bushing so no sizing was taking place. Kinda like the opposite of neck sizing only!

Tell me about that one...I once wanted the bush to size down as far as possible - it was my first excursion with bushings. I had 2 different sizes, so decided to keep the spare, larger, as it happens, in the die, above the other. You can work out the rest.