"Tapered barrels"

[Bruce_in_Oz]

Regarding “tapering” in Lee Enfield barrels:

I just dug out my copies of the ORIGINAL specifications for the Mk1 SMLE (13July 1903 and the Mk lll (with cutoff) (14 December 1938.

Nowhere, in either document can I find a DIRECT reference to “tapering” in the bore.

HOWEVER, paragraphs 10 to 19 (inclusive) of the 1903 document contain an eye-watering amount of detail on exactly how the barrel is to be viewed, inspected and gauged at each stage of manufacture.

At “fine boring”, the bore was to accept a 0.302” gauge and reject a 0.3045.After rifling, it gets interesting: At the breech end; 0.3025” “accept”, 0.3045” “reject”. Muzzle end; 0.3025” “accept”, 0.306” “reject”.

Then it gets confusing! And I quote from paragraph 12:“The depth of the rifling is to be gauged with wing plugs receiving and rejecting. At the breech ed the stems of the plugs to be .3025 inch, .303, .3035 inch .304 inch, receiving and rejecting. At the muzzle end, .3025 inch, .303 inch, .3025 inch and .304 inch, receiving and rejecting.

Down in paragraph 18, it states:“The bore must take a .3025 inch plug, and reject a .3045 inch plug at the breech; at the muzzle it must take a .304 inch plug, and reject a .306” plug from 13 to 15 inches from the muzzle.

Now, the barrel “blank” is described as a forging. This is because it started out as a piece of parallel-steel bar with a diameter smaller than the finished “Knox Form”. The “chamber end was heated and then dropped (this is the forging bit) numerous time to bump the steel to a required diameter. This would also change the crystal structure in the steel a bit; perhaps to be better at withstanding the radial shock of firing. Either that or it was cheaper to do a bit of forging on a certain sized bar than to spend hours hacking a ton of swarf off a fat, parallel blank. Remember; all this stuff was made on fairly basic machines, driven by overhead belts powered by steam; no fancy CNC machining centres, let alone carbide or ceramic tooling in sight.

The “taper” allowance MAY be an inevitable result of the manufacturing processes, especially the “lapping”.

However, on pages 93-94 of Major Reynolds book, it says this:“The 1000 rifles (Mk 1 SMLEs) that had been made for troop trials all had barrels with a diameter as nearly as possible to .303 in., and were lapped out to .304 in. for 14 in. from the muzzle end; the grooves being tapered as laid down in the specifications. 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 combination that was considered to be the cause of bad shooting. Recovered bullets showed that they had not expanded in the grooved beyond .3155 in, The groove toleration at the muzzle was .3155 in accepting and .3205 in. 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 bullets, but they did not do so when the breech was to the low diameter and the muzzle to the high. The consequence was that the bullet was apt to leave the bore when not properly centred, and give sideways hits on the targets. The superintendent suggested that the remedy was to leave the grooves as they were, giving the desired extra velocity and, he believed, lessening the barrel vibrations, and making the bore parallel throughout. The velocity lost by doing away with the lapping would be small, and manufacture would be simplified. It was in the lapping process that the mischief crept in, and accuracy was often impaired by bell-mouthing the muzzles.”

Any other research or thoughts out there? Get yer beanie-copters and anoraks out!

Information

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[mgarrno4]

Hi Bruce , great read how does thes specs compare to the NO4 Mk1 rifles thanks

[Bruce_in_Oz]

That's a good question.

I have never seen a No.4 equivalent of the documents I have for the No1 series.

Any lucky campers out there?

[muffett.2008]

I remember commenting on a post about 'reverse tapered barrels' my thoughts on that was that it was a furphy.
The argument I used to counter it was the blowby and inaccuracy one.
But I am always open to facts when provided.





'

[jmoore]

The argument I used to counter it was the blowby and inaccuracy one.

Those very logical arguments are what make it's existence so intriguing! Never made a lick of sense to me, but it seems to have been given quite the try.

[muffett.2008]

I guess without experimentation, we'd still be living in caves.

[Bruce_in_Oz]

There is a key section in the text I posted:

"Recovered bullets showed that they had not expanded in the grooves beyond .3155 in,................"

What that says to me is that all the experts were expecting the jacketed bullets to expand into the grooves like the tried and true Minie ball of their recent past.

Given the relatively high hardness of the nickel-based jacket material used, this was always going to be a big ask. Certainly there would be some outward displacement into the grooves caused by the other 50% of the surface area being compressed by the lands. Something was definitely going on as shown by the measurement of .3155" compared to the "unfired" .311" diameter. These projectiles were NOT light-jacketed "varmint" bullets. Somewhere in the cupboard is a Mk6 projectile dug out of the stop-butts of a 300yd range in the late 1970s. It has almost no impact deformation of the jacket apart from a very slight distortion at the nose. The rifling marks (5 groove) are quite visible. I did measure its diameter once, but can't remember the result.

Quite a few Mk7 bullets were also dug from the same butts. These were ALWAYS distorted to greater or lesser degree. Some had bent at right-angles and partly lost the core, whilst others were curved like a banana but flattened sideways at the same time. Some had broken up, with the core separated from the jacket.

I remember being told as a kid that .303 bullets on the battlefield just drilled neat holes in people. That may have been somewhat true for the old Mk6, but I have my doubts about Mk7. With the Mk7 bullet being constructed "base heavy" and with a two-piece core, it is almost inevitable that it would become wildly unstable as it transitioned from air to "unfortunate" soldier.

What was just as interesting was that, on that same range, there were also a lot of spent projectiles from 7.62 NATO rounds. These were also generally quite distorted. The most common form was a bullet that was quite bent. This would indicate that, at the very least, the bullets were seriously destabilised on impact and the "heavier" base end had rotated forward to thus make the bullet travel sideways in the earth of the stop-butt. Sometimes this bending had been sufficient to rupture the jacket at the "natural" weak-point: the cannelure. Many were notice to be almost snapped in two at the cannelure.