.303 incendiary, ctge, Inc. B Mk VII, 168 gr projectile, solid point, gliding metal jacket with steel tube and a steel/ lead bottom. Headstamp - DA /BVII /1944, Quebec Canada, 36 grains (?) of cordite, blue tip.
Is that how you measure cordite, by grains?
I would assume cordite would be measured in grains but only Tony E would be able to confirm that. Anyway this reply nudges it back to the top of the list so some good will come from this rather vague reply.
It is a Bit of Chicken and Egg situation with Cordite…It is supplied as a Cord of strands, cut to a set length (close to 50mm (2 inches) and a set number of strands…the weight resulting ( from observation of various loads across the years and different manufacturers) is always 37 Grains ( +/- 0,5 grains)
The Only way to change significantly the mass of Cordite is to shorten the Bundle at the "cutting"stage, and that can only be to “calibrate” the load to get the normal 2440 fps standard valocity for Mark VII ball. Other Bullets ( Tracer, AP, Incendiary, etc, will have different masses, so the Cordite will have to be adjusted in Length (or maybe even in “Strand Count”) this latter variation having to be done batch by batch at the Cordite Factory, where the strands are extruded(Spaghetti style) and wound into a “cord” for rolling on a drum for delivery to the “filling factory”.
The Cordite is fed into a filling machine, which cuts the cord to length, and fills (pushes the cutoff section into) the Untapered-unnecked case in the manner of putting a cork into a wine bottle, adding the wad above the load, prior to the filled case being sent to Bullet placement, taper/necking, and crimping ( one dial-feed type press).
Cordite over its 100 year history, was maintained at pretty close specifications around the World ( UK, Canada, India , South Africa and Australia/NewZealand)
Such was the consistency, that Cordite MDT for .303 loading could be made anywhere in the Empire and shipped to other Factories to be loaded without any problems. And the “trim length” could be varied so as to maintain the standard velocity quite easily.
The "36? grains would be close to the correct Wt. for a 168 grain projectile, but I would say that the Cordite wt should be a little higher than 37, as this is a Lighter projectile than the Mark VII 174 grains. Although as I have found with other types of Specials (US and German) the Powder charge often does NOT vary from the standard Ball round, unless the wt differeance in the projectiles is significant ( such as the differance between Trace and Ball ( 142 and 152) in US .30 cal…also taking into account that the trace loses mass as it travels, thereby travelling faster as it progresses ( like a discarding sabot round).
Military ammo is loaded to a set of velocity Parameters for a particular projectile and sighting calibration, so as different Powder lots can vary slightly, so can the final load in the case as well. Military Lots of Loading Powder of course, are kept to strict “velocity” parameters, even by blending several sublots of Powder until the correct velocity per load is reached…In the “Plate Loading “system used by the USA up to the 5,56 era, any change in Plate calibration required a lot of expensive tool work…so if one could vary the consistency of the Powder to suit a set” powder measure” it was more economical. Powder measuring in the European Loading systems, being a variable setting, could be easily calibrated for different Powder characterisitcs, Lot by Lot…But even the Germans had ONE standard Rifle cartridge Powder ( Nitrozellulose Gewehr Blattchen Pulver) with a fixed dimensional design ( Flakes, 2x2x0,45 mm) which with correct coatings, gave a standard Burning rate and standard Load densities, repeatable from Lot to Lot of cartridges. Only their Luftwaffe Loadings used Tubular Powder ( also standardised to a particular size and Burning rate.)
What a contorted path thru propellant technology a simple question regarding Cordite can lead…
I believe that other criteria enter into the picture, some more important than velocity. Chamber pressure, loading density, and pressure/time/velocity curve being three.
Your mention of the other factors (pressure, density etc) were effectively “eliminated” by the nature and consistency of Cordite MD-T of the standard dimensions used in .303 cartridges… With these factors a known constant, the “velocity” requirements were arrived at by simply varying the Number or length of strands used… The “Burning rate” and “pressure curve” of a strand of cordite was a constant factor, and so did not have to be allowed for ( except when comparing Lot to Lot of Cordite, and it was held to very close tolerances of Nitration, Burning rate, etc. so that all the “filling Factory” had to do was ensure that the Cordite gave the mandatory 2,440 fps required using the stated MD-T.
THis was easily done by adjusting the overall volume of cordite in a case by trimming the charge by length…which worked out to about max. 50mm OAL or slightly less I have not measured a cordite charge recently.
Given that a .303 case is 56mm ( +/- 0,5mm) long externally, and the Bullet seats about 6 mm into the case, and the base Web is about 4mm thick, and the cordite is usually compressed in place ( sometimes the charge comes out distorted, other times straight) the 50mm estimate is probably a bit high, with about 46mm about right… so anything between 45 and 50mm Strand length would seem correct, and allow for Lot-to Lot Burning variations.
With correct Blending proportions ( NC, NG and Vaseline) the “Density” of the strands should be a constant for the diameter and actual volume of compound in a strand ( ie, the Burn rate per metre, the normal Expolsive parameter).
So the volume of gas produced will be proportional to the length of the Strands in a charge. The Burning rate ( and pressure curve) will be constant from load to load, as the Conformation of the load is identical from cartridge to cartridge
( Not so in Tubular Powder Loads (is, US NC type Powders) due to load variations, placement variations in the orientation of the case…even though the Powder density is such that the Powder “fills” the case with little or no airspace;)
Your comments of pressure etc have validity when dealing with a multitude of Powder types , Loading variations, different Primer types and brands, and so on as occurs in “Hand Loading”.
But in the Standardised atmosphere of Large scale Military ammo manufacture, as many “Variables” are either eliminated or minimised in their impact, by rigorous standardization of the components over very large numbers of production, by standards of QA which would make other production systems shudder.( “over-Picky”)
When I was at S&B back in the 1990s, I was shown the operation of an automatic projectile weighing Machine ( of German origin, pre WW II)…the Bullets were selected out according to a +/- toerance of a few grains ( they were doing 9mm Para projectiles) and Lotted according to several weight ranges. ( several 100K in each Lot)…then the ammo was loaded, projectile Lot by projectile Lot, allowing for a Powder charge variation between Lots, to give the Bullets a constant instrumental velocity over all.
The difference in Powder charges in a small round like a 9x19 may have been “inconsequential” to our eyes as “handloaders” etc, but as an economy and accuracy measure, over several million rounds, can amount to quite a lot.
Example: I load Blanks for a Theme Park; I used 0.33 grams per load, and that made 3,000 loads per 1 kg Powder; when I adjusted the case length ( using recycled Blank cases, for the same sound and flash effect, with the reduced case volume, ) I could use effectively 0,30 grams ( ie, 3,300 loads per Kg, and increase in production of 10%. I won’t go further into details of manufacture ( board rules)
Note that to our unmetricated friends, 0.30 grams is ( 0,3x15,43 grains)==4,63 grains so a change of 0,463 grains ( aka “1/2” a grain ) is significant in Pistol loading terms. And 1/2 grain over 14,000 cartridges is a Pound of Powder
( or an extra 1400 cartridges) and at a retail cost of say, $0,80 each, that is a bit of moolah…
Our yearly production is in the 25-30,000 of this particular blank…think of the Financial effects when dealing with Millions of rounds per year…
Ammunition is interesting…teaches you Chemistry, Physics, Engineering Economics, Politics, and Languages…and best of all, getting on with people with different views.
Regards, Doc AV
AV Ballistics Film Ordnance Services
AV Blankfire Pty.Ltd.