Well, here you go;

Major EGB Reynolds includes original spec drawings, etc in his great book on the Lee-Enfield rifle.

"Enfield" .303 dimensions as introduced:

Bore; .303
Groove; .0065 {each}
Total Groove depth; .316

After 1896 and starting with the Mark 1 Carbine, "Enfield" .303 dimensions;

Groove; .005
Total Groove depth; .313

Later, w/ the introduction of the SMLE MKI, dimensions get even cloudier, w/;

Groove at breech; .005 deep
Groove at muzzle; .0065 deep

Now, to be precise, this is spec fo the 5-groove Enfield rifling form with offset lands/grooves. So it applies forces to the bullet differently than does even-grooved 4- or 6-groove rifling forms. But regardless, and as demonstrated with many service rifles, the supposed ".312" groove depth is not the "standard" many believe it to be. Also, remember, other rifling forms were used at various times during Lee production; 4, 6, and even 2 groove barrels being produced in the many thousands each.

See the discussion {p.77} on worn barrels, too... w/ scrap spec being based on BORE wear as it should be.

Now, jump to p.92 and we find;

"1. Bullets made to the high diameter {.312} gave better results than those made to the low limit {.310}.
2. Barrels made to the low limit of BORE diameter shot better than those to the high diameter limit."

Emphasis on BORE, mine.

And............................

On page 93-94, we see. Hold on to your hats;

"When deciding on the manufacturing tolerances of the Short rifle, the bore tolerance laid down was similar to that for the Long rifle, i.e. z.02 in. The breech could be .3025 in. to .3045 in., and the muzzle .304 in. to .306 in. It was this coimbination that was considered to be the cause of bad shooting. Recovered bullets showed that they had not expanded in the grooves beyond .3155 in. The groove toleration at the muzzle was .3155 accepting and .3205 rejecting. With this large diameter the bullet was loose in the grooves. It was considered that this would not have been harmful if the LANDS had supported the bullet, but they did not do so when the breech was to the low diameter and the muzzle to the high."

LANDS emphasis, mine.

Goes on and on, and but you fellows who are unhappy with .315 groove barrels might look elsewhere for the cause of bad shooting in your rifles.

Check lands {BORE}, and by all means stocking up.

Reynolds had more experience with the Lee .303's than all of us combined. And I'm almost embarassed to say my experience at short and longer ranges shooting the .303's absolutely confirms what he says. Mine is nothing compared to his, but I cannot argue with him.

If I was Ruger, I'd refuse to rebarrel a .315 barrel. It is w/in spec by any standard of .303 production history, and falls outside only as a dimension for custom barrels.

Again, my No4MkI* Canucks regularly placed 5 shots inside 6 inches at 429 yards on the ranch range here in "normal" weather conditions. They more or less one-holed similar groups at 100. These guns sported .315 barrels and we were shooting various surplus and handloaded ammunition. Don't blame ".315 Groove" barrels for troublesome shooting. Ain't so.