Stop off at your local Dollar Store and pick up a packet of pony-tail ties: $1 for 500. I just got a pack of black ones for that price (TACTICAL, no less!). You put a pony-tail tie just ahead of the Rim of each cartridge before you chamber it. When the cartridge fires, the tie holds it back against the bolt-face, case-stretch is just about zero and any expansion is at the FRONT. Your brass is now fire-formed to YOUR chamber and it will last a LOT longer.
When you reload your casings, you neck-size them only, weigh your charges carefully and you are halfway to Match-grade ammo.
Just be sure to keep that ammo for THAT rifle.
One of the many VIRTUES of the Lee-Enfield rifle is that oversized Chamber. It was made that way as a reply to both the very poor quality control on some makes of ammunition during the First World War, and to the utterly appalling conditions of the War. If the Chamber was oversized enough, the rifle would WORK with any crap ammo, even if it was slathered in mud. P-14s were held a bit tighter but the chambers still were larger than necessary in a day and age of SAAMI-spec ammo (which is NOT the original Board of Ordnance spec) and no trenches in your back yard.
Using O-rings or pony-tail tis on your ammo (first firing only) and then neck-sizing only is a damned nuisance today BUT it helps your brass to last up to 15 times as long as it would if you just followed "the book" and full-length sized every time. The brass is HALF the cost of your ammo: no point wasting it!
Cartridge overall length on the .303 was 3.05 inches for ALL Marks of ammo.
P-'14 rifle is essentially a very solid Mauser with controlled feed. It should ALWAYS be loaded through the magazine: extractors are scarce. SMLE also should be loaded through the Magazine, just not quite as critical. Just watched a video of a girl pushing the rounds into an SMLE chamber and then closing the bolt; I cringed for the poor extractor!
What MAKE is your P-'14?
W = Winchester
RI = Remington, Ilion plant
RE = Remington Eddystone (Pennsylvania) plant
Hope this helps.