The ammunition that hurt the metford rifling was the Cartridge S.A. Ball, Magazine Rifle Cordite Mark 1 which used a 215gr round nose bullet propelled by hot cordite powder which erroded the lead quickly. It is said to have exited the bore at about 2000 fps.
Cordite powder was very hard on the metford rifling and was adopted in 1891.
The more modern powder was nitro cellulose and was adopted in 1916 and was used throughout both world wars.
What you need to remember is a Lee metford is a black powder rifle and was originally designed go fire a black powder cartridge.
The rounds that you have are the Mark VII ammo which is a 174 grain spitzer bullet loaded to around 2440 fps.
For lee metfords, and long lees I tend to shoot handloads on the light side. Metfords often won't stabilize anything but a cast bullet sized to 1 or 2 thou over bore size. It's not really a matter of "hurting the rifling" it's just the later marks of ammo is loaded fairly stoutly and has a bullet of different shape and weight.
It is of my opinion that the later ammo is a little to hot for my oldies. I shoot 1942 surplus in my Ross, No.1 mk3* and of course my no4. But I don't shoot it out of my long lee. I have a metford here right now which has lots of rifling but won't stabilize .313" cast bullets so it's going to be a matter of finding the right size to make her accurate.
Hope that helps.