"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!

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