Greener developed the .310 cartridge in the early 1900’s as a target round. Shortly after the Australian Government identified the potential of the mild round for military training purposes and adopted it for ‘cadet’ musketry; hence the assumed name of “.310 Cadet”.
In line with the British tradition of naming cartridges relative to bore dimensions and not groove the Greener round has, as one might expect, a .310 bore with subsequent groove diameter of .318 and features a heel style bullet. Essentially it is an over grown .22RF and factory ammo I have dismantled featured a cupped based bullet to aid the sub diameter heel to slug up to groove dimensions and firm crimp; just like a .22RF. ‘Cartridges of the World’ list velocity for a 120gr bullet of 1530fps.
I was fortunate enough to be gifted a Wesley Richards Cadet with a brand new BSA barrel. All advice was that converted .32-20 brass would suffice for the little rifle however from day one I was not able to achieve any degree of accuracy with smokeless powders. Black powder duplex loads with a compressed main charge shot perfectly but accuracy with all manner of modern propellants remained elusive. Long story short, .32-20 brass neck wall thickness runs .007, bullet heels were .309 and the chamber measures .333 at the case mouth. Doing the sums I had .010 difference and upon ignition of the smokeless charges the case walls released allowing a massive blast of hot propellant gas to whistle by the unsupported heel canting the bullet, destroying accuracy and causing leading in exactly the way all under sized bullets do. The black powder duplex load shot well on the basis that BP as a propellant has different burning characteristics and upon ignition facilitates undersized bullets to expand to maximum allowable (slug up). That and a compressed charge of powder acting as a consumable over powder wad blocking any initial blast and keeping the bullet square to the bore. Original factory ammo, as mentioned already, featured a crimp and cupped base allowing the heel to expand and seal in the same way .22RF does however these features were not available to me.
In line with the British tradition of naming cartridges relative to bore dimensions and not groove the Greener round has, as one might expect, a .310 bore with subsequent groove diameter of .318 and features a heel style bullet. Essentially it is an over grown .22RF and factory ammo I have dismantled featured a cupped based bullet to aid the sub diameter heel to slug up to groove dimensions and firm crimp; just like a .22RF. ‘Cartridges of the World’ list velocity for a 120gr bullet of 1530fps.
I was fortunate enough to be gifted a Wesley Richards Cadet with a brand new BSA barrel. All advice was that converted .32-20 brass would suffice for the little rifle however from day one I was not able to achieve any degree of accuracy with smokeless powders. Black powder duplex loads with a compressed main charge shot perfectly but accuracy with all manner of modern propellants remained elusive. Long story short, .32-20 brass neck wall thickness runs .007, bullet heels were .309 and the chamber measures .333 at the case mouth. Doing the sums I had .010 difference and upon ignition of the smokeless charges the case walls released allowing a massive blast of hot propellant gas to whistle by the unsupported heel canting the bullet, destroying accuracy and causing leading in exactly the way all under sized bullets do. The black powder duplex load shot well on the basis that BP as a propellant has different burning characteristics and upon ignition facilitates undersized bullets to expand to maximum allowable (slug up). That and a compressed charge of powder acting as a consumable over powder wad blocking any initial blast and keeping the bullet square to the bore. Original factory ammo, as mentioned already, featured a crimp and cupped base allowing the heel to expand and seal in the same way .22RF does however these features were not available to me.
Long story short, a generous benefactor in Australian sent me 20 ‘Super’ brand Cadet brass made to correct specifications (neck wall thickness 11-12 thou) such that a fired case did not require any sizing and held an as cast bullet snuggly with thumb seating. Instant accuracy, no leading, headache suppressed. The addition of another 20 Bertram Cadet cases from Australia produced identical results and my woes were over…………..until recently when I purchased an additional 50 Bertram cases.
When the brass arrived I measured the neck wall thickness and to my horror found it to be .009 that upon loading of either of my bullets with heels of .308-.309 would give me .005 ‘slop’. How much harm could that do I thought? Accuracy was no existent with bullets hitting sideways at 50m and the illustrious leading returned. Queue head pounding on loading bench. What to do? There was only one solution and that was to increase the diameter of the heel of the bullet to match the inside diameter of a fire case. Bullet heels needed to increase in girth to .312-.313 in order to restore the equilibrium.
I have a pair of CBE Cadet moulds. 320-120 RN and 323-125 with a more pointy profile. I decided to leave the 320-120 as is for use in the existing thick walled Bertram brass and with the black powder rounds with converted .32-20 brass. The 323-125 originally casting heel at .308 in 40-1 alloy would be altered to suit the new brass with the thinner walls. No reservations were had about altering the mould as the 50 new cases would last indefinitely as no sizing is requiring when case and bullet are matched so I fully expecting them to ‘see me out’. Calling on a services of a retire gent (Tony) nearby where I live who happens to be a gifted benchrest shooter and extremely clever machinist I had the heel of the mould opened up to .313 and commenced further load development.
When the brass arrived I measured the neck wall thickness and to my horror found it to be .009 that upon loading of either of my bullets with heels of .308-.309 would give me .005 ‘slop’. How much harm could that do I thought? Accuracy was no existent with bullets hitting sideways at 50m and the illustrious leading returned. Queue head pounding on loading bench. What to do? There was only one solution and that was to increase the diameter of the heel of the bullet to match the inside diameter of a fire case. Bullet heels needed to increase in girth to .312-.313 in order to restore the equilibrium.
I have a pair of CBE Cadet moulds. 320-120 RN and 323-125 with a more pointy profile. I decided to leave the 320-120 as is for use in the existing thick walled Bertram brass and with the black powder rounds with converted .32-20 brass. The 323-125 originally casting heel at .308 in 40-1 alloy would be altered to suit the new brass with the thinner walls. No reservations were had about altering the mould as the 50 new cases would last indefinitely as no sizing is requiring when case and bullet are matched so I fully expecting them to ‘see me out’. Calling on a services of a retire gent (Tony) nearby where I live who happens to be a gifted benchrest shooter and extremely clever machinist I had the heel of the mould opened up to .313 and commenced further load development.
The first run of 40-1 alloy dropped bullets with heels of .310 nominal diameter. Loaded on my standard charge of 5.1gr Unique (Lee disc 0.66) the rifle managed to keep them on the paper at 50m but with poor accuracy and a degree of leading also. Tony had told me that if more girth was required to take a suitable drill bit, wrap some 400 grit abrasive paper around it and carefully lap the heel some more. This I did and the next test dropped bullets of .312, better accuracy and no leading but still not back to normal. Another brief tickle with Tony’s technique and .313 heels were achieved and whilst leading was eliminated accuracy with 40-1 was not what I demanded. A forum member had intimated that harder alloy might be beneficial and in an attempt to satisfy my curiosity I ran up a small batch of bullets in wheel weight alloy with a BHN of just under 10 BHN (40-1 alloy is 7.8 BHN). BINGO. Accuracy restored to groups hovering around 1 inch at 50m/55y!
Why did I need to use a harder alloy when previously 40-1 binary had providing excellent results? I can’t be certain however on driving home from range during testing I ran through all the possible variables. Alloy, same. Primers, same. Powder, same. Charge, same. Case length, same. Neck wall thickness, less. Maybe if the walls were thinner the case volume would be greater. At the loading bench I filled a new, thin walled case all the way to the case mouth with Alliant 2400 and weighed the charge. This was then poured into an old, thick walled case and to my surprise did not fill the case. The new case with the thinner walls had LESS volume and weighing both old and new showed a 10% difference with the new brass being heavier (70r v 63gr). On this basis the harder alloy may be required due to reduced case volume increasing chamber pressure. Quite possibly 5.1gr Unique is at the top end of what 40-1 alloy will cope with in my rifle and a small increase in pressure was enough to make it fail. Either way, I won’t argue with success.
Lessons learned. 1) Buy a decent lot of components to avoid disappointment in future. 2) Consider ALL the variables but assume nothing. 3) Don’t give up. These rifles are way too much fun.
One day I would love to be able to try a bullet with a hollow/cupped base as the original ammo did and see how it performs. Interestingly the original bullets I have measure a tiny .304 on the heel with case walls of only .008 yet one can only guess must have shot well or would not have been produced.
Jeff
Why did I need to use a harder alloy when previously 40-1 binary had providing excellent results? I can’t be certain however on driving home from range during testing I ran through all the possible variables. Alloy, same. Primers, same. Powder, same. Charge, same. Case length, same. Neck wall thickness, less. Maybe if the walls were thinner the case volume would be greater. At the loading bench I filled a new, thin walled case all the way to the case mouth with Alliant 2400 and weighed the charge. This was then poured into an old, thick walled case and to my surprise did not fill the case. The new case with the thinner walls had LESS volume and weighing both old and new showed a 10% difference with the new brass being heavier (70r v 63gr). On this basis the harder alloy may be required due to reduced case volume increasing chamber pressure. Quite possibly 5.1gr Unique is at the top end of what 40-1 alloy will cope with in my rifle and a small increase in pressure was enough to make it fail. Either way, I won’t argue with success.
Lessons learned. 1) Buy a decent lot of components to avoid disappointment in future. 2) Consider ALL the variables but assume nothing. 3) Don’t give up. These rifles are way too much fun.
One day I would love to be able to try a bullet with a hollow/cupped base as the original ammo did and see how it performs. Interestingly the original bullets I have measure a tiny .304 on the heel with case walls of only .008 yet one can only guess must have shot well or would not have been produced.
Jeff