Headspace on the mouth questions?
- Thread starter mattri
- Start date
Such a friendly response.
So to reiterate "headspace" is a chamber measurement.
In our example headspace for cartridge x is 1.234".
That being said the chamber has been cut in such a way that a case that measures 1.239" is too long, the bolt will not close on a case that long.
A case that measure 1.230 would chamber fine, and if the extractor or something else held it in place well enough it may get a good enough primer strike to fire and cycle.
In our example headspace for cartridge x is 1.234".
That being said the chamber has been cut in such a way that a case that measures 1.239" is too long, the bolt will not close on a case that long.
A case that measure 1.230 would chamber fine, and if the extractor or something else held it in place well enough it may get a good enough primer strike to fire and cycle.
1911 45 acp inertia firing pin. The firing pin goes forward till it makes contact with the primer. There is no firing pin stop. A type of firing-pin in which the forward movement is restrained until it receives the energy from a hammer blow. It is slightly recessed in the breech face before being struck by the hammer and is shorter in length than the housing in which it is contained. Upon hammer impact, it flies forward using only its own kinetic energy to fire the primer.
Firing pin at full forward travel.
Sounds good to me.
So then how does one accurately keep the headspace/case length "gap" consistent?
In a bottle neck cartridge if our headspace was 1.234" we would use a die to bump a fired case back .002 to appr 1.233", giving us a consistent measurement on all of our rounds.
If straight walled cases lengthened that way it would be a simple matter of trimming them all to the same length, we'll use 1.234" again. But as others have mentioned straight walled cases have a tendency to shrink, not grow.
Do we measure a batch of cases and trim all to the shortest length to remain consistent, say 1.233"
Won't they continue to need to be trimmed, 1.231"' 1.129" 1.127" etc etc?
In a bottle neck cartridge if our headspace was 1.234" we would use a die to bump a fired case back .002 to appr 1.233", giving us a consistent measurement on all of our rounds.
If straight walled cases lengthened that way it would be a simple matter of trimming them all to the same length, we'll use 1.234" again. But as others have mentioned straight walled cases have a tendency to shrink, not grow.
Do we measure a batch of cases and trim all to the shortest length to remain consistent, say 1.233"
Won't they continue to need to be trimmed, 1.231"' 1.129" 1.127" etc etc?
In general terms, brass gets trimmed when it exceeds the maximum length. Some may never need trimming.
Best to buy new brass all of the same lot, keeping it all in the same reloading cycle. All brass fired and reloaded the same amount of times.
The 45 acp head clearance (cartridge headspace) can be controlled with this method. https://thefiringline.com/forums/showthread.php?t=584016 NOTE CRIMP INFO.
But will not work in all chambers and ONLY WITH LEAD BULLETS. May keep the action from fully closing.
In general, not a good reloading practice for auto loading firearms and new reloaders.
Best for 45 acp slow fire Bullseye at 50 yards, for score.
Best to buy new brass all of the same lot, keeping it all in the same reloading cycle. All brass fired and reloaded the same amount of times.
The 45 acp head clearance (cartridge headspace) can be controlled with this method. https://thefiringline.com/forums/showthread.php?t=584016 NOTE CRIMP INFO.
But will not work in all chambers and ONLY WITH LEAD BULLETS. May keep the action from fully closing.
In general, not a good reloading practice for auto loading firearms and new reloaders.
Best for 45 acp slow fire Bullseye at 50 yards, for score.
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Agreed, however if straight wall cases do not "grow" enough to need trimming to the same length what keeps the cases, the measurement, the clearance etc. consistent?
If none of the cases have stretched past 1.234" then none need trimmed, but where are the case lengths presently?
Some could be at 1.233" 1.200" 1.286" etc etc. How does this not have a negative effect on accuracy?
At what point does one straight walled case stop shrinking as opposed to another?
Even 100 cases of the best brass will respond to firing differently, how do we keep them uniform?
If none of the cases have stretched past 1.234" then none need trimmed, but where are the case lengths presently?
Some could be at 1.233" 1.200" 1.286" etc etc. How does this not have a negative effect on accuracy?
At what point does one straight walled case stop shrinking as opposed to another?
Even 100 cases of the best brass will respond to firing differently, how do we keep them uniform?
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When a straight wall case is fired it expands outward to seal against the chamber wall. This tends to shrink the length of the brass. When the case is sized it squeezes the brass down to the original diameter which tends to make it longer. This expansion and compression tends to lengthen the case a little each time. The more pressure and larger the chamber the more the brass is stretched. To maintain the fit in the chamber, once the cartridge gets too long, you trim it.
I would guess the 10mm auto would be one ?? I dont know.
Well, apparently Hornady, RCBS, and Forster want to expand SAAMI's definition of "headspace" since they all market tools that measure a "cartridge's headspace" -either by the products name or in the companies product description. I would argue that since 3 of the top reloading companies use that terminology, let's just go with the flow and allow it to be part of the vernacular. To argue semantics at this point is a futile effort and will only serve to confuse new reloaders. Related to F. Guffy by any chance?
No relation that I know of but I think it is more confusing to use the term head space for the chamber length and the cartridge length. No one will know what the other is talking about. You don't have excessive head space with a cartridge but you can in a chamber. It is simpler to use the correct terms and a lot less confusing. Related to B. Obama by any chance? He likes to use the wrong words for stuff too, like calling semi autos assault weapons.
Why not simply differentiate by using "cartridge headspace" and "chamber headspace"?
I doubt these companies will change the name of their products, so cartridge headspace is here to stay.
You are free to use whatever terminology you want. If I don't understand I will either ignore it or ask for clarification.
I ignore a lot of incorrect usage like substituting "there" for "their" or "they're" and "to" for "too" or "two". It can be confusing but I am smart enough to glean the meaning of it most of the time.
I ignore a lot of incorrect usage like substituting "there" for "their" or "they're" and "to" for "too" or "two". It can be confusing but I am smart enough to glean the meaning of it most of the time.
Me two, to, too................Also! Sorry, couldn't resist.
Agreed- so how do you keep everything uniform in the meantime?
Returning to cartridge x with a length of 1.234"- we load a hundred cases, after firing they have not all lengthened past 1.234". Some are longer/shorter than others. If we trim all to the shortest length we may create excessive "gap" between our case length and chamber dimension, especially if we just keep shortening all of our cases.
How do we maintain a consistent dimension across our hundred cases without continually shortening the cases, eventually excessively so?
LOL
All I can tell you is that I set the trim length on my trimmer with a bushing so the case length is never exceeded. If a resized case is shorter than my trim length it doesn't get trimmed. I know that most new cases are short even after firing and resizing but they do grow over several firings and sizing operations. When they are too long they get cut, until then they aren't cut.
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