Krag Collectors Association Forum

A different approach:

Utilizing the top part of the Wilson .308 Winchester cartridge gage, I inserted the neck of a new GRAF .30-40 case and a W-W case, until they stopped.
Using the 'depth gauge' feature of my vernier-caliper, I measured the distance from the top of the gauge to the rear of the cartridge rim.

The GRAF case gave a 1.822" measurement. The W-W case gave 1.783". This approximates the distance from the base of the case-neck to the rear of the cartridge.
The difference between the two cartridge-cases was .039". (This is consistent with the .038" difference noted in these cases, earlier in this thread).
The 'problem' GRAF case being predictably longer in that section, which is likely the problem Zach is encountering with his brass.

butlersrangers wrote: ↑Wed Jul 07, 2021 10:34 pm. . . the GAF Brass . . . the GAF shoulder . . . their GAF Brass . . .

GRAF! (Spell checker?)

FWIW, there's a tool to measure cases to a specific datum on the shoulder (such as the .375" datum SAAMI uses). https://www.hornady.com/headspace-bushings#!/


Same idea can be improvised by using a fired pistol case - or boring a 3/8" (.375") hole in an appropriate chunk of metal.

Oh Parashooter, you're going to take all the fun out of re-inventing the wheel.

p.s. Dang, I try to be careful with my spelling. I went back and corrected my GAFF. Now, it's time to watch Hockey and have a SPRITZER.

If GRAF brass measures 1.822", from the rear of the rim to the front of the shoulder, it is within the SAAMI standard of 1.8289" for that .30-40 cartridge dimension.

It is also close to the dimension given in the 1917 manual, of 1.82",
for the distance from the cartridge base to the juncture of the shoulder and neck.

I imagine any mischief of fit, has to do with the case shoulder angles not being quite compatible,
with how the chamber is actually shaped.

Zac,
I did send you a PM, I think. Does the PM stay in the outbox till it is read? If so I did it right. If not I am not holding my mouth right or not pushing the right buttons.

I stacked some gauge blocks up to a height of 1.829 and put the comparator line on top of the gauge. It intersects the case a little shy (.026") of the end of the radius.
Start and ends of radii are very hard to measure accurately. I think that is why Saami uses that point in almost the center (.3799 would be the actual center) of the angle as a reference and draw the cartridges and chambers with straight lines. Intersections of straight lines are easy to draw and measure. It would be very difficult for the makers of the cases to make them like that, so they can leave the radii in there within limits, but those lengths at at .375 diameter will be absolute. That is where Graf messed up. Reading the Saami drawing the max distance to that line at .375 diameter is 1.7821 for the case with a minus .015 tolerance. If we made a gauge with a precision .375 hole and measured to the end of the cartridge I think we would find out how much they violated it.
One of these days when I get some time I will draw the chamber up in CAD with the precision turned up to 7 decimals and see if I am understanding this correctly. When I am programming intersections of angles and radii on the lathes, the machines will not tolerate rounding errors in CAD if done with 4 or 5 decimal precision.

Oh, and Parashooter's photos of measuring said angle are quick and reasonable effective, this post is mostly "why for" it is done that way.

Br, you were on the right track with the 308 gauge, unless the hole is precisely .375 your measurements only compare to cases that chamber without knowing which side of the tolerance those cases are. Sure points in the right direction.

Some people do not know how to send PM. I tried again, shoot me email me if you get it.
Fred

Fred, a PM will appear as a number in your 'out box', until the recipient opens it.

Thanks, Br. There was still an old one in my out box from months ago. That fooled me into thinking the new message was there. I think my first one did not go because I forgot the title above the message. Right now the old message is there plus the new address for Zac. Sure like email better than PMs.

Fred I got your message and sent you an email, should have the sizing die and shell holder sent out today, thank you again