Grease groove in WWII .303 bullets important or not ?

[Bruce_in_Oz]

The 1879 Remington Lee, in .45-70 has the "second locking lug", opposite the big one on the right side of the bolt body, just like later Lee Enfields.

Lee's slightly later 1885 pattern is likewise equipped and has a number of features, some carried over from another earlier Lee, the 1882, that went on to feature on the Lee Metford and subsequent derivatives.

[browningautorifle]

Jim, are you saying "Yes, it's beeswax" and "No, it's not for lube it's for a sealant."
Am I following you right?
In which case, it's not an argument of tar vs. beeswax, it's an argument of lube vs. sealant. Right?

That's right...

[green]

That's right...

Glad to see that you agree that the bullet in the op would have had beeswax in the cannelure.

[browningautorifle]

the bullet in the op would have had beeswax

That's not quite where this thing went. Nor was it what was said. Don't put words in my mouth. Nor will I argue with you about it.

[Sunray]

"...to get more velocity and keep pressure down..." Grease doesn't do any of that. It's just a sealer. And that particular ammo is ancient. That's cordite. Not that it'll affect the bullet in any way.
"...middle of the bolt on the receiver bridge..." That long thing on the side of the bolt body is the locking lug. Bolt, Stripped | Gun Parts Corp.
"... groove dia. is around .314..." That'd be a nearly shot out barrel with a groove diameter of .314". And .3095" is not the bullet diameter. .311" is.

[CINDERS]

Line diagram explaining how the Lee-Enfield bolt locking lugs engage in the receiver

[Bruce_in_Oz]

.303 is the nominal BORE diameter, just like .30" is the nominal BORE diameter of the .30-06.

The ancient Russian Mosin Nagant was called the "Three Line Rifle". Why?

Because a "Line" is an ancient Russian unit of measure that just happens to be pretty much exactly one tenth of an inch. Thus, a .30 Cal. BUT the GROOVE diameters is where it gets messy or interesting, as you prefer.

As per OFFICIAL specifications and drawings, specifically Drawing A. 658, derived from Spec. S.A.I.D 13186, .303 barrels on the SMLE / No1 Mk 111*, had a closely defined BORE diameter of .301" to .304". However, the depth of the rifling, which was cut by multiple passes of a single-tooth cutter, could run from 0.005" to 0.008" in depth, from that nominal bore size.

Therefore, if you had a gauged and accepted blank that measured MAX .304" that went to rifling, it could end up with a groove diameter of 0.320" and STILL be within "tolerances.

The trick was that the bore AND groove had to be VERY consistent, from end to end.

EXCEPT in the early SMLEs where a whole regime of "creative' lapping went on to supposedly "taper" the bore diameter OUTWARDS towards the muzzle to try to achieve "long" Lee Enfield velocities with Mk6 ammo. All of that nonsense was supposed to have gone out the window with the advent of Mk7 ammo.

HOWEVER I have several "New, in bag" Lithgow HEAVY barrels that clearly (by measurement) have been factory-lapped at the muzzle to the point that there is a tiny, but measurable "belling" of the bore.

With a solidly-constructed bullet like the cupro-nickel-jacketed Mk6, there was NO way that the bullet was ever going to fully "blow-out" to a groove diameter of .320". With the lighter-jacketed, higher-velocity Mk. 7, there MAY have been some "setting up" of the base of the bullet, but it was still essentially a "bore-rider".

[Daan Kemp]

To take Bruce's post one unrelated step further. If the bullet 'rides the bore' and doesn't upset much being jacketed, there is some blow past in the grooves? Thus explaining why military 303 bullets are flat base and boat tail bullets don't work that well - longer bearing surface allows more consistency in the blow past?

[bombdoc]

The substance in the cannelure of UK SAA is either bitumen or luting and the purpose is to seal the case. The cannelure also serves to lock the core into the jacket. Lubrication is not required on a metal patched bullet. Lubrication is really only required in black powder guns to control fouling. It's use has been extended to lead bulleted smokeless projectiles as it does assist in controlling leading..

UK/Commonwealth Luting is green and looks like greengage jam to those of a certain age and background. It is used on a wide range of ammunition to seal threaded joints such as fuzes and primers. It has to be formulated to be free of contaminants which might react with the other components of the ammunition. It is issued in handy 2lb tins; the majority being used for jolly japes by the Ammo Techs..

[bombdoc]

To take Bruce's post one unrelated step further. If the bullet 'rides the bore' and doesn't upset much being jacketed, there is some blow past in the grooves? Thus explaining why military 303 bullets are flat base and boat tail bullets don't work that well - longer bearing surface allows more consistency in the blow past?

Nope.. the copper in a jacket is foil thick and the bullet upsets into the bore if it is set up properly. There is always some blow past on ignition until the projectile seats in the commencement of the rifling. You get an effect something like a sink plug settling in a full basin with the water rushing past the edges.. the gas flow is at its maximum at this point which can strip material off the bullet and erode the bore. This is why rifles wear from the breech forward, and the source of leading/coppering/nickeling.. the metal gets sprayed down the barrel and then gets ironed into the bore by the projectile..

Boat tailing has very little effect in the bore.. in fact boat tailing is only of use at the very end of the trajectory when the velocity drops below sonic. At this point the boat tail reduces the drag and extends the range of the projectile.. for a .303 this is well over 1000m so I would not worry about it.