Hi Lew and a Happy New Year.
I have been going through the Ordnance Board Proceedings and Small Arms Committee Minutes and I think you have probably answered your own question with regards to the origin of the 115grn bullets, but I have also found something else of interest (see below)
First, the Italian connection. A Beretta machine carbine (SMG for non Brits) was tested in OB Proc 5,157 in March 1940. It performed well with its own Italian ammunition (4,000 rounds delivered with the gun) but failed with Kynoch ammo. No mention is made of bullet weight at this point.
The comment was made that the Kynoch ammo had now failed in the Suomi, Schmeisser and Beretta weapons.
The report of the acceptance tests of the S & W carbine was detailed in OB Proc. 6,778 of June 1940, and although the rate of fire of the weapon was far too high (1,200 rpm), the important comment was “I.C.I. ammunition functioned the weapon correctly, but does not possess the accuracy of the Winchester ammunition received with the weapon.” Thus we know that Winchester ammuntion was being supplied to the UK in early 1940.
OB Proc. 7,849 of August 1940 is basically about the failure of Kynoch ammunition to function properly. They were lent a Beretta carbine and 100 rounds of Italian ammunition, but said they would not make special bullets if the order was only 200 rounds and suggested using commercial soft nosed bullets from stock for the next trial. The military concluded that Kynoch’s product and their attitude was “poor” and that “one of the new S.A.A. factories be set up to manufacture this ammunition and no reliance be placed on messrs. I.C.I. (Metals).”
In OB Proc. 8,189 of August 1940, which was a further test of the Schmeisser, the ammunition used was Belgian FN and Kynoch. Again the FN functioned well and the Kynoch failed. It reveals that the FN bullet was round nosed but the Kynoch was truncated cone, and the overall weights were 189 grns for the FN and 188 grns for the Kynoch, showing that they both had 124 grn bullets.
However, the crucial paragraphs occur later in the report. The Board wished to ascertain whether M.C. ammunition of American manufacture would function satisfactorily in the Schmeisser, and that 500 rounds of 9mm Winchester special ammunition was left over from the trials of the S & W. Note the use of the word “special”. It also stated that 110 million rounds of M.C. ammunition had just been ordered in America.
OB Proc. 10,478 of January 1941 was a report testing several different makes of 9mm ammo in various SMGs, including the British made Schmeisser (i.e. Lanchester). There was an accompanying ammo breakdown and the Winchester ammo had a bullet weight of 117 grns. Whether this was some of the early deliveries of Winchester contract ammo, or some of the earlier Winchester “special” ammo is unclear, but it could easily be the latter. The order for the contract ammo was not placed until 30th July 1940 and the trials in OB Proc. 10,478 would have been held some time before the Minute was actually printed in January 1941, so it is uncertain whether any of the contract ammo would have been delivered in time.
Conclusions? It seems that the Italian 115 grn ammo performed well and was liked, and that a small order was placed by us with Winchester for “special” 9mm ammunition that was used to test the S & W carbines. This ammo was probably 115 grn also.
It does not answer the question of the date of your box, but it is another piece in the jigsaw.
I will go back and check the Ministry of Supply contract ledger at our National Archives as I remember seeing orders for ammunition for the S & W carbine there.
I apologise for the length of this post as I know you probably have copies of most of these Procs., Lew, but I thought others might find it interesting.