The reason bullets "keyhole" is they are not stabilised.

This, in turn, is caused by the bullet not spinning fast enough.

Lee Enfield rifling is 1 turn in 10 inches; the reason being that the original, round-nosed bullets were LONG and the lighter, streamlined Mk7 bullet is essentially the same length.

The tight twist is VERY harsh on cast bullets, even quite hard ones. Loading "down" will not help at all with "full-length" bullets, because you will then have reduced velocity AND most importantly, reduced spin rate.

If you want to shoot cast bullets, you need something that will stabilize at realistic velocities AND will not "strip out" whilst being driven up the barrel.

Gas checks are pretty much essential, as is casting a bullet that is a "close" fit in the rifling, which often runs out to .319"

Final caveat: If you MUST shoot cast bullets, be aware that the barrel WILL pick up metal fouling from these bullets and this is a MAJOR hazard if you subsequently use "normal velocity" jacketed ammo. A bulged barrel will eventually happen unless ALL of the cast-bullet residue is removed from the rifling. The jacketed bullet simply "bulldozes" the soft cast-bullet material up until it pushes it aside, thus bulging the barrel.

Wrapping the bullet in Teflon tape may reduce this hazard somewhat, but ultimately, the risk remains.
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