There were three versions of the .303/.22 Machine gun training cartridge developed between 1925 and 1929, but none ever entered service. They were intended for use in indoor 25 yard ranges in Vickers guns with specially modified barrels. The first pattern used an all lead 40 gr. bullet with 10 gr. Neonite which gave 2100 fps, but also problems with leading. There was also a version that used a 10 gr. all aluminium bullet with again 10 gr. of Neonite to give 2600 fps. This was found to be a little problematic in the sense that they had considerable penetrative qualities and punched holes in the 1/4″ steel back plates used on the indoor .22 training ranges. The final version had a 40 gr. lead bullet with copper gas check and first used the same charge as the previous loadings. After trying various charges it was found that the best performance that still operated the Vickers gun was 8.5 gr, giving 1900fps. Although formally recommended for service the project seems to have quietly died.