Ammo headspace

[m1a_scoutguy]

For bolt guns, I bump the shoulder back on fired brass .001-.002"

Semi autos my require more, as much as .006" bump, as they tend to stretch quite a bit. I take new factory ammo, measure and fire it, then measure again. The difference is what I usually set the sizing die to bump.

I bought these awhile ago for all my bolt guns and they seem to be working pretty good. Not really cheap but its a buy once cry once kinda thing I guess. I have been setting my shoulder back .002 and everything seems to be working good. https://www.whiddengunworks.com/product/case-gauge-3/ Wilson case gauges are a great tool also,especially for the semi-auto rifles. https://lewilson.com/case-gage

[HKGuns]

I bought these awhile ago for all my bolt guns and they seem to be working pretty good. Not really cheap but its a buy once cry once kinda thing I guess. I have been setting my shoulder back .002 and everything seems to be working good. https://www.whiddengunworks.com/product/case-gauge-3/ Wilson case gauges are a great tool also,especially for the semi-auto rifles. https://lewilson.com/case-gage

Just to be clear, so people don't get confused.

"Bumping the shoulder .002 ONLY works reliably when you are measuring and bumping the case fired from the rifle you're reloading for.......You may get lucky, but eventually, your luck will run out.

That isn't how I load.....I load, as stated above. Every round fired may have been fired from a different gun or not by me......I load in lots of 100 at a time and I could grab any box and use it with any rifle.

Which is exactly why I take them down to fit into the case gauges.

[m1a_scoutguy]

Just to be clear, so people don't get confused.

"Bumping the shoulder .002 ONLY works reliably when you are measuring and bumping the case fired from the rifle you're reloading for.......You may get lucky, but eventually, your luck will run out.

That isn't how I load.....I load, as stated above. Every round fired may have been fired from a different gun or not by me......I load in lots of 100 at a time and I could grab any box and use it with any rifle.

Which is exactly why I take them down to fit into the case gauges.

Yes,you are correct,I should of been more clear. I use these for specific rifles in each caliber I have and use only brass that has already been fired out of that bolt gun. You do not want to just pick up range brass or even buy once fired brass and trust this setup. ONLY after running it through your specific rifle.

[grizzman]

In loading for "automatics", have y'all done any headspace/bullet seating measurements on factory and reloads before and after chambering to see what effect the "violence" of chambering has? I believe it also takes some math to determine actual bullet movement in the neck because of headspace change..... (And I don't have anything to measure runout with so haven't done that...)

No, I have not. With a properly loaded cartridge, chambering into a rifle once should have no affect on the shoulder location or cartridge overall length.

Any 5.56 ammo I make is loaded so that it's usable in any of my ARs. Any semi-auto 308 Win ammo I make is also loaded so that it's usable in any of my semis, or bolt guns. Bolt guns have ammo that is specifically made for them, and not used in other rifles.

I don't know of a minimum headspace measurement for 5.56. Unless you're installing a barrel on a rifle that doesn't have fixed headspace due to the rifle's design, it's generally not something that matters.....since headspace isn't the same for all rifles.

[triggerjerk]

As I said, for me, 3 rifles of differing headspace. Shorter chamber with blue/h2 and 4 thou longer chamber with white/h both pushed shoulder back same distance. 2nd chambering pushed longer victims back that last thou to shorter hs. 2nd chambering did not push those shorter from 1st chambering at all. Factory PMC, American Eagle, Monarch Brass and handloads (un-annealed)......

[Clint]

Both the cartridge and chamber are specified in the SAAMI prints.

You can see there the 5.56/223 chamber headspace min dimension is 1.4636 +.010

The Cartridge headspace dimension is 1.4666 -.007

A little careful math will reveal that for most cartridges, there is potentially .003 of "crush" built into the design.

In other words, the max cartridge is .003 longer than the min chamber.

Although this seems fundamentally wrong for an autoloader, in practice, most factory ammo is made toward the minimum spec of .007 shorter, which provides .004 of clearance rather than .003 of interference.

The short version of all that is, yes the min/max values are right in the prints.

I think I understand the guages and their headspace measurement along with measuring of fired cases to get an idea of individual chamber headspace. Admittedly my googiefie is suspect, and I haven't spent much time looking, but on the unfired ammo itself, I cannot find "headspace" max/mins. Just distance of shoulder breaks from the base.

Would someone please straighten me out and educate me as to the minimum headspace for unfired 223 and for 556 ammo? Thanks

[HKGuns]

Both the cartridge and chamber are specified in the SAAMI prints.

You can see there the 5.56/223 chamber headspace min dimension is 1.4636 +.010

The Cartridge headspace dimension is 1.4666 -.007

A little careful math will reveal that for most cartridges, there is potentially .003 of "crush" built into the design.

In other words, the max cartridge is .003 longer than the min chamber.

Although this seems fundamentally wrong for an autoloader, in practice, most factory ammo is made toward the minimum spec of .007 shorter, which provides .004 of clearance rather than .003 of interference.

The short version of all that is, yes the min/max values are right in the prints.

Can I ask where you got that drawing Clint? Never seen one done like that before with both on one drawing.

[triggerjerk]

Thanks, Clint. If you hadn't specifically said it was on that drawing, I wouldn't have found it, glasses or not, on my grainy magnified phone image. Maybe I should get my computer fixed.... Nah, need more ammo/equipment....

Best I remember (it's been a few years) I was amazed that all the factory ammo measured right at that 1.4636 go guage....

[Clint]

They're all right from the SAAMI web site and all in that format.

https://saami.org/technical-informat...mber-drawings/
https://saami.org/technical-informat...ami-standards/



Interestingly, Hornady did a good job with the 6ARC and others to eliminate the potential headspace overlap.

You'll see the headspace is 1.190 and 1.1901 to guarantee NO overlap if both are in spec.

https://saami.org/wp-content/uploads...2020-07-29.pdf

Can I ask where you got that drawing Clint? Never seen one done like that before with both on one drawing.

[HKGuns]

They're all right from the SAAMI web site and all in that format.

https://saami.org/technical-informat...mber-drawings/
https://saami.org/technical-informat...ami-standards/



Interestingly, Hornady did a good job with the 6ARC and others to eliminate the potential headspace overlap.

You'll see the headspace is 1.190 and 1.1901 to guarantee NO overlap if both are in spec.

https://saami.org/wp-content/uploads...2020-07-29.pdf

Got them thanks. For anyone else interested, the other than new or modified cartridges are all in one of the PDF's in his second link. (I was looking for individual cartridge links.)