I would like to add that I believe there is
a small recoil lug under the reciever attached by a screw. Some believe the barrels are hammer forged on the E models, although I have not be able to confirm if that is true. Basically an E is a slightly worked over D model. Dokey, try some better ammo, and I bet that the 52D you have might be your best rifle. SK rifle match,Wolf match extra, Lapua Midas L, or good old tenex from Eley.
They cost more but there is a reason for that. Jakes, the holes for the barrel mounted scope are original to your rifle, and if it were mine I would use these, as I like the old long target scopes, as they bend the light less and I think they have less eye strain than reciever mounted scopes...I'm a bit old school here.
Your rifle is an "E" if the serial number ends with the letter E. If it had the original stock, if would be worth more, but as a shooter it looks great to me.
Best reguards Kirk