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A fat chamber isn't necessarily bad...

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No4MK2 View Drop Down
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    Posted: December 17 2009 at 2:16am
If load data was developed in test barrels and not in an actual Enfield or other rifle with the dreaded "oversize chamber", and such loads are then fired in a typical L.E. rifle there is a n increase, however slight , in the volume of the chamber and said load will produce lower pressures( and most likely velocities). It might also provide a little extra measure of safety for those liking maximum loads. Just a thought...My '55 MK2 has a chamber that is EXRTEMELY close to minimum chamber demensions.Now if US companies will just start making properly demensioned cases all would be perfect!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: December 18 2009 at 2:34am
Could be that US companies proportion their cases according to the original Royal Standard which was how the Canadians manufactured .303 cases before WW1 and that is a commonly accepted cause of the jamming problems the Ross rifles had when Canadian troops used British supplied ammo that was allowed a looser acceptance standard.
 
Another possible cause of thin rims is that due to the similarity of the cases, and the fact that both Krag and .303 were not that high volumne production during peacetime, .303 cases were probably formed from the same drawn and turned blank used for the Krag cartridges.
The US Army specs for the Krag gives a .060 rim thickness, commercial cartridge drawings give a .064 max rim thickness for the Krag. A series of rim thickness measurements done in the 1960's showed that rims as thick as .068 could be found with some brands of Krag ammo. Since the original specs for the Krag called for a headgap clearance of from .004 to .006 a Krag in new condition or fitted with a new bolt, which was a common repair procedure, might not chamber these thicker rims. So I suspect that more recent production Krag cases are at the low end of the acceptable limits (.059-.060), and .303 cases made with the same machinery would also use the thinner rim.
 
Also I've heard that some double rifles and other sporting rifles built before WW1 won't always close on a milsurp .303 rim. Photos I've seen of pre WW1 sporting .303 cartridges seem to show a thinner and smaller dia rim.
 
Since until recent times British target shooters almost never reloaded fired cases, making any accomodation for reloading probably wasn't high on the cartridge companies list.
 
Chambers of .303 rifles may not be so oversized other than the extra clearance at the shoulder, but loose head gap coupled with a tapered chamber gives the same effect as an oversized chamber.
Find Boxer primed military spec cases for reloading for a milsurp rifle if you want a good fit, commercial cases are manufactured for commercial sporting rifles and don't often make accomodations for loose military chambers and headspace.
 
If the US military chose to cut the chambers of their .300 Winchester Magnum long range sniper rifles oversized and loosened the headspace requirements to allow for dirt and fouling during military operations, one would hardly expect Winchester to begin manufacturing all .300 Winchester magnum cases to fit a military chamber tightly to allow easier reloading for the milspec rifles, and end up with their ammo no longer fitting a commercial sporting rifle chamber.
 
PS
The US Military recently put in an order for 50 million dollars worth of .300 Winchester Magnum ammo at $1.60 per round. It will be interesting to see if any alterations have been made to the case. And when milsurp .300 Winchester ammo begins to show up in a few years we can expect a lot more shooters will become interested in the cartridge.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 18 2009 at 7:01am
FWIW I beleve that US specs (SAAMI) are designed for 101% lawyer proofing. If this can be "Seasonally adjusted" to reap 1% additional profit that doesn't hurt either.
The premise is that maybe, just maybe, ol' Billybob may have an old, oh so old, Enfield rifle that is overstressed, has never been cleaned, and has been further strained by the use of high power "continental" loads.
 
This is the rifle that has to be 102% safe so there is no possibility of a lawyer suing for even "emotional distress" due to a loud muzzle blast, much less any kind of structural failure.
 
Based on the low-ish pressures the weakest rifle ever built should be safe with brass that saves corporate 0.001c per round too.
 
Thus we have RemChester min spec brass to deal with (which is why I only use Prvi Brass)Clap
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: December 18 2009 at 9:50pm
I wonder what the percentage of sales of centerfire rifles ammunition in the US is .303?
 
With cheap surplus, and the European import .303 I have to wonder if sales of .303 Enfield ammo is a big enough incentive to the cartridge companies bother with product improvements.
If there were many sporting rifles chambered in .303 in the US things might be different.
 
I think they passed up a good deal when they chambered the reproduction 1895 Winchesters in .30/06 and a few in .30/40 but not in .303 which is a much better cartridge choice for that action, and also historically correct.
The break down Handi guns are another good action for the .303. A auxillary barrel in .303 would allow a wider range of game than some other chamberings, and the rimmed case is a far better choice for a breakdown action.
A Combo rifle/shotgun OU would also benefit from a .303 chambering.
 
The maximum headspace specs for the .303 British in older journals is given as .068, with .064 as the mimimum. Military cases that I've miked run around .063. Near as I can tell my No.4 with No.3 Bolthead has a .0035 headgap with those cases, which puts it at a .0665 headspace, my Remington cases seem to last forever so long as single loaded, though problems with the mags usually result in a cut neck or shoulder sooner or later.
 
So long as headspace is within the standard acceptable headspace for a new Enfield , around .068 or so, reloading doesn't present that much of a problem. Much more than that and commercial cases start getting annular rings. I suspect the same would be true of other cartridges in this class if headgaps were the same.
If US commercial cases were given a .063 rim then rifles with max acceptable headspace for a well used slightly worn Enfield would still suffer from annular rings and ultimately partial separations.
I can't think of any commercial sporting rifles in this power range that would be considered suitable for reloading if head gap was .01, not without fireforming at least.
 
Come to think of it , military cases with thicker walls are often recommended for fireforming when reloading for a rifle with loose headspace, such as well worn .30/06 or 8mm Mauser rifles.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 18 2009 at 9:58pm
I think that the rim thickness is vastly over stated in respect to annular rings.
What is far more relevant is the actual case diameter in the area directly in front of the rim itself.
If you mic unfired PPU (NNY) brass, MilSurp brass & compare it to RemChester brass you'll find quite a difference, this difference copies over into brass expansion during firing.
The expanded areas the ones causing the annulus, have expanded by very close to the difference in the unfired case diameters.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: December 19 2009 at 7:06am
Could be at that, I figure the very tight chamber, diameter wise at least, plus its very slickly polished chamber wall, is the main reason Remington cases fired in my MkIII don't show a ring.
Its likely that burning rate and pressure curve are another factor. I don't crimp , relying on a close neck fit, not crimping is an old time suggestion to reduce the effects of variation in neck pull strength. Not crimping may allow a slightly slower build up in pressure which would allow the casehead to move back before pressure locks the case wall to the chamber wall.
 
Seller and Bellot fired in a slightly less polished No.4 chamber before headspace was tightened up would ring and crack more easily than Remington cases.
The S&B cases might have a thicker rim and thicker case wall but the web was no where near as thick and the brass not as good.
 
PS
I remember someone mentioning sorting through his Milspec cases and choosing a bunch with rims that miked at .068 for reloading, a rim that thick would be over specs and probably be unusable in most commercial sporters in good condition.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 19 2009 at 9:58am
I don't crimp either.
I have reduced the diameter of the expander ball slightly, by polishing, so I get a good tight pull, but without the hassle of crimping.
 
I also resize to fit my chamber, but using a full-length die, adjusted to resize with minimal shoulder setback.
 
The interesting thing I've found is that the Rem brass has the ring, the PPU doesn't. This is true when fired in the same chamber, or a different one. This is with all other things being equal as I test loads I work up with a chronograph & adjust brass batches as neeeded for the same velocities.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 19 2009 at 9:59am
Sorry, let me clarify that a bit.
It doesn't matter which chamber I resize for the ring, or lack of one is the same. I do not use identically sized brass in different chambers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: December 19 2009 at 12:24pm
I neck size only, and only 2/3 the length of the neck. I also use an undersized expander, a homemade one.
I polish away any rough spots inside the neck, and chamfer the casemouth, but don't bell.
I use fired expanded cases once each as snappers for dry firing before decapping. The striker fall is just hard enough to loosen the case in the chamber slightly for easier feeding.
Once fired cases are rotated 180 degrees when next fired, so subsequently the cases will be equally expanded and pin strke will be perfectly centered.
 
Leaving 1/3 of the neck expanded helps in centering the neck in the chamber neck, so the bullet starts into the throat already well centered.
 
I seat 150 gr bullets well forwards with cannelure exposed to reduce jump. Thats individual to the particular rifle they'll be used in. If not sure of the throat clearance I seat to the cannelure.
 
Cases used in my No.4 fit every rifle I've tried them in, around half a dozen or so over the years. Fired cases from this Savage chamber look like unfired cases, the shoulder not cut as deep in this particular chamber.
Some No.1 and Longbranch chambers I've loaded for leave a hemispherical shoulder and the case looks to have less taper. I suspect the No.1 chambers like this are late 40's or 50's rebarreled.
Those hemispherical shoulders seem to be more sturdy, and an artical on experimental case design says a hemisphere shoulder somehow gives better ignition and more complete combustion, though the experimental cases illustrated were much shorter. Be worth looking into.
I figure those chambers were to allow more crud to build up before chamber cleaning was necessary. 
Some Enfield chamber shoulders match the chamber drawings while some are very different in profile. Ross .303 shoulders don't seem to be standardized, and from the appearance of some fired cases the chambers look to have been cut deeper using a mauser type shoulder with sharp shoulder set far forwards, perhaps a modified mauser reamer was used.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2009 at 1:48am
Thats a lot of work to do.
I'm wayyyyy too lazy for allthat noise.
I just size till a smudge tells me the shoulder is contacting the chamber front & back off 3 thou.
 
My '50 Faz wont let cases set up for the Savage chamber without some serious bolt manipulation to seat them. Like you've observed the later Faz chambers are tight.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: December 25 2009 at 4:55pm
Originally posted by No4MK2 No4MK2 wrote:

If load data was developed in test barrels and not in an actual Enfield or other rifle with the dreaded "oversize chamber", and such loads are then fired in a typical L.E. rifle there is a n increase, however slight , in the volume of the chamber and said load will produce lower pressures( and most likely velocities). It might also provide a little extra measure of safety for those liking maximum loads. Just a thought...My '55 MK2 has a chamber that is EXRTEMELY close to minimum chamber demensions.Now if US companies will just start making properly demensioned cases all would be perfect!
Just thought of something that should also be considered.
If working up loads using once fired barss, then a max load that shows no pressure signs in a case expanded fully in a average military chamber with generous shoulder clearance might develop much higher pressures if the same load is then used in a fresh factory case of the same type.
The unfired case having significantly smaller capacity.
 
Also I've seen a very wide variation in the thickness of the casehead from one brand of .303 case to another so confirming exact case capacity is prudent.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote No4MK2 Quote  Post ReplyReply Direct Link To This Post Posted: December 26 2009 at 12:13pm
LE Owner, Interesting point on chamber vs case capacity.Actually the chamber governs case volume as soon as the round is fired, but variations in case weight can definately contribute to increased pressures all else being equal. Switching case brands at max load levels is not a wise thing to do with out backing off a few grains.My point originally was that an " oversize" chamber will give a measureable increase in chamber/case volume and a corresponding reduction in pressure( same amount of gas in a larger area to fill ).Its a minor point though...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: December 26 2009 at 12:49pm
Originally posted by No4MK2 No4MK2 wrote:

LE Owner, Interesting point on chamber vs case capacity.Actually the chamber governs case volume as soon as the round is fired, but variations in case weight can definately contribute to increased pressures all else being equal. Switching case brands at max load levels is not a wise thing to do with out backing off a few grains.My point originally was that an " oversize" chamber will give a measureable increase in chamber/case volume and a corresponding reduction in pressure( same amount of gas in a larger area to fill ).Its a minor point though...
Good points.
While an unfired case fired in a oversize chamber can expand to fill the chamber resulting in effectively larger chamber space some energy would be used in expanding the brass, not much so the pressures wouldn't rise much if any over that of a load in a once fired case from the same chamber.
A load worked up to max in such an oversized chamber would have a hair higher pressure if the same load were assembled in an unfired case and then fired in a rifle with tighter dimensions. Unlikely to be a real cause of concern, but loads that work well in one rifle might not work as well in another.
My SMLE has a very generous chamber shoulder, hemispherical in outline. My No.4 has a very tight chamber that looks as if cut with a commercial reamer, due to its tight headspace with No.3 bolthead fired cases are indistinguishable from unfired cases to the naked eye at least. loads on fired cases from my No.4 will work in every Enfield I've tried then in with no problems, as easily as factory ammo and that neck sized only.
 
I fitted a new bolt body with bolthed to my SMLE, So far headspace appears to be very close, no sign of stretching or annular ringing. The hemispherical shoulder should work well in maintaing headspace of the neck sized cases, cases now headspacing on the shoulder.
 
The difference between the two is obvious so keeping cases segregated will be easy. I intend to use only one brand of case for the No.4 the Remington.
I may do most and probably nearly all loading for the SMLE using Winchester or HXP cases, I have a fair supply of each, and probably won't be shooting it that much, so those cases will do for some time to come.
Loads for my SMLE will be with 175 gr SMK and starter loads of H4895, at a lower pressure than loads for my No.4
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