They are Tracer.
Most likely Mk 6 or to give them their proper name "CARTRIDGE, S.A., TRACER, .303-INCH, G MARK 6."
I think the headstamp is actually K5, 45, G6 which would make perfect sense for this load.
K5 is Kynoch Factory 5, Kidderminster, UK
CARTRIDGE, S.A., TRACER, .303-INCH, G MARK 6.
Introduced: c.1942
Approved: 3-1945
Description: PS bullet with C-N* , G-M* or coated MS* envelope containing a compound core consisting of a lead/antimony (92/8) front piece, with a copper cup containing tracer composition in the rear. The bottom of the cup is closed by a brass washer and the envelope turned over to retain the core. There is a cannelure round the middle of the bullet.
Crimping: Case mouth coned onto bullet cannelure.
Weight: 151 grains
Tip Color: White
Trace Color: Red
Charge: 35 grains cordite MDT, size 5/2*, with a strawboard wad on top.
Remarks: This is the standard GIV pattern with a bullet using standard components, and was originally known as the "GIV/II" which became "G MARK VI". The above designation was adopted circa late 1944 with the change of mark numerals in British service.
Air service day tracer.
PS= Pointed, Solid
C-N= Cupro-Nickel, an alloy of 80% copper, 20% Nickel. Dull Silver in color
G-M= Gilding Metal, An alloy of 85-90% Copper and 15-20% zinc. Copper in color
MS= Mild Steel
MDT, Size 5/2= Modified, Tubular. Cordite was originally 58% Nitroglycerine, 37% Guncotton and 5% mineral jelly but it caused excessive bore erosion so the mixture was modifided to 30%, 65% and 5% respectively. This was known as "Modified". Then it was pressed into a tubular form to obtain an increased burning surface. The 5/2 indicates the external and internal diameters. (External=0.05" and Internal 0.02")
Source: Identification Manual on the .303 British Service Cartridge, No.3 - Special Purpose Ammunition. Published: B.A.Temple-1987
Hopefully that answers a few questions but if you have more just ask and I'll see what I can dig up.
Nick
