Headspace...

[mike16]

thanks!

very interesting

[CINDERS]

my stupid question ~ if you are going to go to tighter spec's on the chamber are you getting custom made dies to suit like Neck and FLS as I am sure that the manufacturers would all work to the standard form or possibly the SAAMI spec either way would be interesting to know what the die people do as I use a Lee FLS.
I think tbonesmith got a swag of the new Armalon barrels be interesting to know what reamer they used.........!

[Peter Laidler]

Chaps........., listen.......... with a .303" rimmed round it's NOT the chamber that counts, it's the length of the barrel in relation to the face of the bolt head. It is THAT distance that measures CHS. NOTHING to do with the bloody chamber

Pulling teeth or what.......................

[muffett.2008]

You could strap a large field dressing to your forehead Pete.

[Peter Laidler]

Phew............ run out of them Muffer - I need a pillow! The thing that's keeping me sane at the moment is doing the zillion small jobs on my Mini Cooper that I've been meaning to do for the last 10 years. While I'm here, has anyone got a hydrolastic suspension type mini sitting waiting for scrap? But it's a nice sunny day here in Oxfordshire so it's outside.......

[CINDERS]

I thought CHS was measured from the base of the cartridge to the end of the neck oh well there you go. I have about half a dozen WWII 1st field dressings here and a few large shell dressings if you want one Peter........

[Bruce_in_Oz]

Most? RIMLESS, bottle-necked cartridges have their "headspace" defined as the distance from the "base" to a specified diameter on the shoulder.

A notable, recent exception is the .357SiG. This BOTTLENECKED cartridge uses the end of the neck, as per MOST of the straight-walled (9mm Para, .45ACP, etc. Too much "yodelling syrup" for the Alpine boffins one day?

The term, "headspace" was first in use when there were NO "rimless" cartridges around. It just stuck. It's just a short-hand term for what can be a complex subject, requiring expensive metrology, especially gauges.

Anyone know how, or even IF it applied to pin-fire rounds and chambers?

[englishman_ca]

I used to have a Mini, but a wheel fell off.

[englishman_ca]

Peter, put yer helmet on!

Different specs from different standards.

When I went to school, we learnt cursive writing and printing. Now my hand writing is all flcked up as I use a combination of both, cursive printing. Then we changed over our monetary system to decimal. sixpence is worth 2-1/2 P. WFT??? Then we learnt the metric system. Feet, inches, pounds, stone, hundred weight, long ton, short ton, was now cm, kg.

I started a career as a draughtsman. My drawings had to contain nominal fractional inch dimensions in decimal (1/16" = 0.0625") with metric equivalent written below in mm.

Now I am in Canada, it is metric with next door neighbour using Imperial, or rather their own standard of it. 1 US gallon aint 1 Imperial gallon.

So having a set of standards for North America is business as usual for me. Makes sense that north american ammunition is made to north american standards to fit north american manufactured firearms.
It is not just by chance that you can take a shiney new SAAMI spec Winchester made round of 303 and fire it in your old SMLE (and then complain about case life).

Just curious, but to what standard do British firearm manufacturers use these modern times? Is it the old milspec? Does a modern British manufactured sporting arm still need chambers that will accept any manufacturer's ammo in battlefield conditions covered in mud or sand?

I guess what I am trying to suggest is that the world goes around and has moved on. There are still some folks buying commercially loaded 303 Brit ammo and there is also a small demand for new sporting arms chambered in such. The new specs (SAAMI, CIP) are for these sporting arms, they were never intended for use with surplus battle rifles.

If I did work on modern sporting arms, I would have a set of modern gauges.

I understand that chamber dimensions do not have an effect of head space and that they are two separate issues with their own individual gauging. However, they are related and connected in this conversation by the same named set of standards.

Not rocket surgery, mil spec gauges for milspec arms, SAAMI spec gauges for SAAMI arms and CIP gauges for CIP arms.

Mix them up and it becomes FUBAR'ed.

[Bruce_in_Oz]

Pondering further; how many folk have used and maybe still have, "rim-thickness" gauges for .303 ammo.

Back in "the day", no "well-equipped" full-bore shooter would be without one of these.

The idea, and it has SOME merit, is that different rim thicknesses, coupled with "correct" headspace, could produce ignition variations, and thus, different points of impact.

Hard-core competition RIMFIRE types STILL have their own versions of this gauge. These are used to select cartridges having a "rim" thickness" in a fairly narrow range, to reduce variations in the ignition of the priming compound contained within that rim.

It's mostly about thinning the herd of variables, not to mention a bit of "Zen" or, "The Force" or what have you. "Fashion statements" also have a role to play; see; "gadget gamesmanship".

A "THIN" rim will allow the round to "float' a bit, possibly lessening the depth and "speed" of the striker fall, and thus, minutely alter primer performance. Hard-core bench-rest types batch their brass, and gauge the seating depth of their "special" primers, after "uniforming" the pockets and the flash-holes.

Have a close look at the operation of the extractor on a Lee-Enfield: It actually holds the case fairly close to the bolt-face whilst in operation. Going back to J. M. Browning's 1911, the "as designed" chamber had NO distinct "step" where the case mouth could engage, just a taper (leade). The "floating" striker CAN protrude a LONG way forward, but it is not exactly propelled by a Mauser or Lee-Enfield grade striker spring. The extractor is expected to stop the relatively low pressure .45ACP case from "getting away". Browning hedged his bets with the .38 Auto / .38 Super, giving it a minuscule "semi" rim that is supposed to engage a "cutout" in the barrel hood. Not much point, as it turned out. Guns in the slightly shorter and MARGINALLY tapered 9mm para work just fine as well, without much of a chamber mouth "step".

Open-bolt SMGs are a different bucket of bait.