One big advantage of using the kits mentioned above is that it puts an end to the Tanaka cartridges' annoying tendency to break the 5mm dia 0-rings regularly.
Mulberry Field conversion kits use 7mm caps, there's no difference in power or anything between the 7mm and 5mm caps as they have the same amount of powder in them both. 7mm 0-rings will last and last as long as the cartridges are cleaned after every firing session. 0-rings should be lightly lubricated with Silicone Grease or Oil.
The kits need careful assembly and setting up for best results. DenTrinity sell them (as stated above) but it's worth asking Francky, Shazhib and John at PFCGUK for prices too
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Cerwyn
Hobby collector of Replica model guns and Militaria.
also member of Living History Reenactment Groups.