303 HPBT 174 Gr.

[Bruce_in_Oz]

The problem is not bullet weight; any bullet maker worthy of the name can deliver that.

The burning issue is the FORM of the bullet and its relationship with the real world of Lee-Enfield rifling dimensions.

The original Mk7 bullet has an open base; the slinky hollow-point boat-tails do not.

That open base will "bump-up" a little as it gets booted up the backside by 40K plus psi. - solid-based boat-tails; not so much.

So, if your slinky HPBT does not even attempt to bulge a little to obturate the rather generous grooves of a Lee Enfield barrel, you will get high-pressure gas bleed around the bullet. This will cheerfully burn the throat and the beginnings of the rifling.

Another problem with "slinky" bullets is that they are long for their weight. To feed reliably, A Lee Enfield requires a bullet that is a fairly close fit to the internal length of the magazine. If your "magic" bullet is significantly longer that a Mk7, then you have to seat it down into the cartridge case. This, of course, reduces the space for propellant. A racy "VLD" boat-tail will add a bit to the stern as well.

Regarding fuel for these beasties, what was the powder used in Mk7Z? For that matter, what did FN use in their very nice post WW2 Mk7 ball ammo?

And all of the foregoing assumes a barrel in very good condition, especially at the throat The throat is somewhat important, as it it how the bullet is introduced into the rifling.

I occasionally drag my Swiss K-11 out to the range for fun. It shoots well with "proper" GP-11 ammo, but that stuff is like hen's teeth around here. So, I fiddled around with various recipes and endes up using a Hornady A-Max. Before settling on these A-Max loads, I ran up a batch of Sierra Match-Kings with good results. A fellow enthusiast asked if he could try some of these Sierra-bulletted loads in his K-31. Instant drama: The bolt would not close and the round would not extract. Dodgy load? Nope! The K-31 is throated EXCLUSIVELY for the GP-11 bullet, whereas my old K-11 is throated rather generously for the older round-nosed bullet; somewhat akin to the .303 Mk6.

Eventually we cleared the K-31 and did some more homework. The GP-11 bullet has a SECANT ogive whereas the Sierras hava a TANGENT ogive. The K-31 has a very short throat to make the most of the shape of the GP-11 bullet. The Swiss rifles also have VERY tight bore and groove specs, my K-11 groove diameter mikes out at .3075".