| Strathcona |
| (.224 member) |
| 15/03/17 05:37 AM |
Head space for 303
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Here is an interesting thread regarding head space and the 303.
http://parallaxscurioandrelicfirearmsfor...=1#.WMg3mo-cF9B
| DarylS |
| (.700 member) |
| 15/03/17 07:32 AM |
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Re: Head space for 303
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That is good - thanks for posting it. Here are 2 of the important photos from the link.
Same thing happens in ALL guns - all cartridges, rimmed, rimless, rebated rim, or belted if they have excessive headspace.
This GIF is quite a good representation of the actual circumstances.
| DarylS |
| (.700 member) |
| 15/03/17 07:43 AM |
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Re: Head space for 303
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Will say, this is the second article or post concerning putting a compressible spacer above the rim, to hold the case back against the bolt.
This will not work in belted, rebated, nor rimless cases. It might work OK with semi-rimmed cases.
Necking the case up then forming a new shoulder for a crush fit on bolt or action closure PRIOR to firing the first time, is a better method, imho.
I measured some various makes of .303 brass that were in a junk bowl on my bench. They ran from .055" to .064" on rim thickness - how about them apples?
By the numbers
1. The firing pin shoves the case forward, rim against the breech.
2. The primer detonates. If it's not heavily crimped in place, it backs out, shoving the bolt and barrel as far apart as it can.
3. The thin, forward part of the case expands to fill and grip the chamber while the bullet moves out of the case and down the barrel.
4. The solid case head can't expand and grip the chamber, so it moves rearward, re-seating the primer, stretching the case walls just forward of the head, and stopping when it hits the bolt face. (In rear-locking actions like the Lee, the bolt and receiver also compress/stretch to add a little more movement. The higher the pressure, the more they move.)
5. If (and only if) the amount of head movement exceeds the elastic limits of the case, the cartridge separates into two pieces.
New cartridge cases can normally stretch a lot before breaking. Even with a minimum rim .054" thick and maximum "field" headspace of .074", the resultant .020" head clearance is well within the limits of new brass and it's very unlikely a new case will separate even if the headspace is somewhat more than the field maximum (which is pretty rare).
| Marrakai |
| (.416 member) |
| 15/03/17 09:37 AM |
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Re: Head space for 303
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Quote:
First I took a case that had been reloaded with heavy loads enough times so it was stretched near breaking.
And.......?
I acquired a set of 3 Arrowmark go/no-go gauges many years ago, and they get a fair workout at times, especially shuffling the Lee Enfield bolt-heads in the spare-parts bin to correctly headspace recent acquisitions of self and friends.
| Strathcona |
| (.224 member) |
| 15/03/17 11:36 AM |
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Re: Head space for 303
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I think Daryl was pasting in the text from the link and it just ended real quick like.
Re changing out the bolt heads, if i understand correctly, the MkIII and earlier were not marked with a size?
I compared the bolt heads from my 2 x SMLE and they seem the exact same as the head on my matched bolt from my BSA sporter?
Thanks
| DarylS |
| (.700 member) |
| 15/03/17 12:23 PM |
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Re: Head space for 303
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I thought all the bolt heads normally had a number - 1 through 4 - perhaps - my memory is not good on the different headspacing bolt heads.
Edit - just checked my Mark 3's.
#3 on the sporterized mil-spec (only have an action and sporterized (poorly) mil. stock, and the other is full stocked SMLE w/matching numbers, stamped ENGLAND on the front action ring & also stamped 1953 with a #6 bolt head. The stamp is at the front on the right, down side of the bolt head.
| Marrakai |
| (.416 member) |
| 20/03/17 10:27 PM |
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Re: Head space for 303
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When in my late teens, I had the excess headspace on my No.3 pattern Lee Speed corrected by an old cane-farmer who had been an armourer in WWII. His toolbox contained boltheads numbered 1 through 7. The numbers of his spares were marked on with electro-pencil!
His fee for the replacement bolthead? I had to shoot the boar that was getting into his newly-planted sugar-cane from the adjacent rainforest. Got him on the second night...
Still own that rifle.....
It was my first centrefire!
| Strathcona |
| (.224 member) |
| 21/03/17 02:24 PM |
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Re: Head space for 303
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| DarylS |
| (.700 member) |
| 22/03/17 06:42 AM |
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Re: Head space for 303
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Interesting both of mine are .625", well, actually the 1953 stamped #1 Mark 3 measures .625 on the bottom side and .623" on the top side. Both appear to be stamped with a #3 when I use a magnifier.