Mick Smith initially bought 25,000 of them from the Government in about 1957 and he was selling them re-chambered for 2 pounds 10 shillings each. A fair number of the purchase went to the Numrich Arms Co. in the US.
They had to be re-chambered, if sold in NSW, because the NSW Police ruled that they were military rifles if left original, even though the .310 was originally a civilian cartridge.
I might add that there were as far as I remember, as this is over 50 years ago, two other purchases from the Government of 20,000 and 10,000.
Mick was considered to have finally made a big financial blunder when the rest of the trade heard that he'd bought the initial lot.
Mick took a two page add, a centre spread, in the Sydney 'Truth' and announced the the sale of the rifles and the price and that they would be on sale the following Saturday morning. He recruited many of the Saturday morning regulars [Smith's Sports Store was like an unofficial gun club]and we lined the stairs to the workshop where all the converted .310s were stored. One of the counter staff took the money and another wrote a receipt, then the buyer joined the queue and when he got to the front swapped his receipt for a rifle that had been passed by the 'bucket brigade' down the stairs
It was organized chaos and was repeated the next Saturday but not so hectic nor for as long.
How many were sold in the initial rushes I have no idea but it must run into the thousands and most of them would be out there somewhere. Some may have been stamped '.32-20' but I think very few. One thing that is sure is that there are a lot of people who have .310 Cadet Rifles that really have .32-20s.
Now the reason for all the foregoing is that the .310 doesn't always perform well in the rechambered rifles.
There are some differences in the cartridges and anyone that has 'Cartridges of the World' can easily look them up.
Dimensions: .310 first followed by the .32-20.
Bullet diametre: .314/.3125
Neck diametre: .325/.327
Shoulder diam: .342/.342
Base diametre: .350/.354
Rim diametre: .405/.408
Rim thickness: .038/.065
Length of case: 1.075/1.315
O/all length: 1.492/1.592
All sizes are in inches.
There is .0015 smaller bullet diametre so when firing the .32 there is room for gas escape around the bullet and when firing the .310 there is escape as the projectile jumps the .240 gap to the rifling. Either way it's not going to do the rifle much good.
Then there's headspace, which is going to be .027 or .017more than the probable maximum if the breech block has zero clearance on a .32-20 round, more than likely it will have around .005 clearance which means .022 excess headspace.
No wonder I hear of and see some people having trouble with their rifles, particularly split cases.