I have a Leen Enfield No.1 MkIII* with a modified barrel that can shoot high velocity cartridges. Is it save to use 'normal' cartridges? What's the advantage of HV-cartridges?
Assuming its still .303 calibre, there should be no issue shooting "normal" (I'm guessing you mean standard .303) cartridges. If its been modified for high velocity rounds, the barrel and chamber would have been strengthened to be able to survive the added force. A high velocity round uses more powder than a "normal" one. Because of this, there is more pressure exerted on the barrel and the chamber, and hence a greater force. A standard barrel would have issues standing up this added force, and after a few cycles it may even explode or be otherwise damaged. If it was modified for high velocity rounds (and you have successfully fired them), there should be no issue shooting less powerful ("normal") rounds through it. Maybe someone here can confirm this (maybe Ulrich). I don't have a Lee Enfield myself. As for the advantage of high-velocity rounds: A HV round uses more powder. This added powder accelerates the round faster, and produces a higher muzzle velocity by the time it leaves the barrel. This higher muzzle velocity leads to a much greater muzzle energy (a standard .303 is around 3.5 kJ), which in turn gives the round much more "kick", both in terms of penetrating power and damage. I believe hunters and long-range marksmen favor high velocity rounds.
There is no reason why a standard cartridge can't be fired in a strengthened barrel/action. There is one exception however: IF you reload and are loading the cartridge to extremely low levels then that could be dangerous. For some reason, some powder/cartridge combinations generate more sudden pressures with underloads than with max charges. Some powders have this trait and some don't. The above advice is for the 303 British military cartridge ONLY! If someone has rechambered the rifle for another round, say 7.62X51 (308 Win.), then I would be extremely careful.
Hi OP - was the rifle strengthened for HV rounds in your ownership? If not, might be worth letting a decent gun shop check the bolt headspace now if you're altering your normal firing routine with a lighter load. It's a cheap check-through.
Well, more information about the gun is necessary. The British switched to a new high velocity round, the Mark VII High Velocity "Spitzer" round in 1910, which had a muzzle velocity of some 2400 fps and a chamber pressure of 19.5 tons per square inch(as opposed to some 2000 fps and a chamber pressure of about 17.5 ton per square inch) Then, in 1938, they introduced the Mark VIIIZ round that had a muzzle velocity of 2550 fps and a chamber pressure of about 21 tons per square inch. The Mark VIIIZ round was designed for the Vickers machine gun, but could be fired from the Lee Enfield. I would believe that, without more knowledge of the gun, that it was for firing the Mark VII HV round. While capable of firing the "hotter" Mark VIIIZ round, barrel life would be approximately halved.
Try posting your question at Surplusrifle Forum • Index page in the Lee-Enfield forum. You will be asked as to how you know this is a "high velocity" barrel. As Takao posted, the Mark VII cartridge was the standard round for that rifle. If the rifle is marked as a No.1 Mk III*it is post WWI.
Normally if the HV marking was made by a armourer it should be save and you shouldn´t have any problems. But the best is to go at a forum like Old Schoolr mentioned or at milsurps.com
Thanks guys for your expertise. I can tell that my Lee Enfield is from 1944 made by Lithgow and on the barrel is marked 'HV'.
Than it is sure to fire the normal .303 rounds from S&B or PRVI or whatelse. Critical are only the ones from the WW1.
