SMLE barrel index?

[Steve H. in N.Y.]

I've installed three or four SMLE barrels now and each time I've had to redo it several times until I was satisfied with the sight alignment. Seems I'd put it together and everything would look straight & perpendicular but half an hour later I would look again and decide that the barrel was over or under-rotated and the sights tilted just a couple of degrees, then it's back to square one. Peter has described using the backsight pivot axis and front sight protector to align things on the No.4 rifle and I'm wondering if there is a similar accurate method that will work for an SMLE.

Information

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[Brian Dick]

You need to use a protractor aligning the Knox and rear sight base with the flat on the body behind the charger bridge. I try to check all three reference points and use my eye too with the front sight because they aren't always perfectly aligned. It's a bit of a black art with the SMLE unless you have the original tools. I suspect it still may have been even with the correct tools! I have a real RSAF barrel vice but I don't have the breeching gauge so I have to improvise a bit.

[browningautorifle]

I have to improvise a bit

Do you use an angle meter like I have to with the M1 Rifle?

[Brian Dick]

Pretty much. I use a protractor. I should get a digital but my old one has had good results so far. The reading must be the same across the back of the receiver/body, Knox and rear sight base. Then a visual on the front sight base/blade for good measure.

[browningautorifle]

I have the magnetic one with a needle. It's so easy to read if it's one degree here then it's one degree there...and so on... Sure made things easier.

[Brian Dick]

That's exactly what I use. To be honest, I doubt the digitals are that much better. Much like laser bore sighters which are really no better than mechanical collimators in my experience.

[Peter Laidler]

Personally, I would avoid the nocks form like the plague. The Bridge Charger guide flat is as good a horizontal datum as anything (there are other things but.....). And the backsight leaf, when it is lifted to vertical is as good as square as it gets. Go from there. Looking/gauging from the rear, when the backsight leaf is square to the bridge, the barrel is square to the body. And that's all you are concerned with

You COULD do something similar using a ground steel bar in vee blocks across the backsight leaf axis holes in a similar fashion to that of the No4 in reverse. But no real Armourer I know ever relied on the nocks form as a measure of correctness. It's a bit like breeching up an SA80 barrel using the so called breeching-up lines.

[Steve H. in N.Y.]

Thanks everyone for the advice. I do have access to a precision protractor at work and I'll experiment with that. A trip to the optometrist is probably in order, too.

[Bruce_in_Oz]

From; “Specification S. A. 462 P, 14 dec 1939

Paragraph 12 (i):

“(i) Barrel with body (breeched up), - The barrel will be submitted for view assembled to the body, the latter being examined for browning and for polishing of the bullet lead. The barrel must be well bedded down into the body. The barrel will then be gripped in a breeching-up vice, and the position of the flat on the barrel gauged from the body. The breeching-up will be tested by means of a hand-operated spring wrench, which, when pulled to completely depress the spring, should not unscrew the body. A pull of about 30-lbs. applied 12-inches from the axis of the movable arm of the wrench being required to move it, and about 55-lbs. to completely compress the spring; the axis of the movable arm being 2,32-inches from the axis of the body. The position of the flat on the barrel will again be gauged, and the barrel and body spun.”

End of excerpt.

Never having seen the tools specified in the text, I can only surmise that the “trick” is to wind in the barrel until it “lines up” with the receiver AND the rear of the threaded tenon is firmly bedded against the inner breech ring (just like a Mauser 98).

THEN the test is to see if it unscrews under a specified amount of torque.

[Peter Laidler]

That's an interesting extract BinO. It SOUNDS like an early version of or an adapted variant of an old 'springy-bar' torque wrench. Or certainly something that relies on a spring/springy loading.

Anyone out there remember the old 'spring bar' type torque wrenches that we used to use into the 60's? You know......, the sort where an arm attached to the handle aligns with a readout on a scale attached to.......... anyway......... I still have an old one and took it to the calibration bay at the big workshop. It attracted a but of attention but passed the 4x calibration steps. But unfortunately, I ALSO got a condemnation certificate for it which I felt obliged to take to the Tech Storeman who took the certificate and handed me a brand new Snap-On torque wrench! Built loads of trouble free engines with the old one and the new one just sits unused in my tool box!

While we're on the subject........ The underside of the body side frames under the magazine well are reputed to be exactly square/horizontal to the verticality of the body. Maybe these could be used as a datum instead of the top surface of the bridge charger guide.