L39 & L42 Barrels - An open offer to forum members

[Peter Laidler]

Regarding the remaining tolerances and material...... Maybe Ensci can give us the exact material spec that I couldn't get when I was writing about it. But it was certainly a good quality material and cut like a dream. As for the breech thread spec, then without any doubt, this will be a bog standard BSI (British Standard) 1" 12 (or is it 14?) TPI whitworth 55 degree form to the same BSI tolerances. I'll gauge a few barrels up to get a ball park chamber depth with a 1.635 CHS gauge.

The machinist/barrel maker could experiment a bit by 7.62mm chambering a few scrap No4 barrels. (He only needs to chamber ream as far as the 7.62mm neck and there's sufficient meat in a .303" chamber to form a 7.62mm neck sufficient to make a few depth calculations.......).

The muzzle crown is what it is. The foresight block band is a different matter. The early ones that were not accepted for service use had the bog standard No4 foresight block band but the service standard had a larger diameter, But this varied wildly ( I mean wildly in engineering terms.......) The bored out L42 block band wasn't available as a spare part because of this. If you needed to replace it, the rifle was sentenced to a Field Workshop and an existing No4 block band was machined to suit and re-sweated on

To be honest, with a barrel blank of sufficient length and diameter and a decent set of drawings, anyone half decent turner with a decent lathe could turn one up - or down - in a few hours

Information

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[Bruce_in_Oz]

Standard No4 barrel data:

Thread is 1.001" x 14TPI Whitworth (55deg.) form. (NOTE SMLE and Martini thread is 49deg. 40min included angle, NOT 55 and DEFINITELY NOT 60deg.)
Crests flattened to min 0.996" dia.
Pitch dia. 0.9553"; 0.9523" min.
Max allowable eccentricity of thread to bore: 0.004" (radial) or, 0.008" "clock" (diameter) reading.

VERY IMPORTANT:
Headspace on the L-42 is different!!

As per page 111 of the excellent book on the No4 T and variants, by some chap called Laidler (and Skennerton):

GO gauge is 1.628"
NO GO gauge is 1.635"

These are different from the sort of gauges that you whack into an L1A1 or M-14, let alone .308" Win gauges.

From p.110 of said tome: The material is EN 19AT steel.

[bigduke6]

BSI (British Standard) 1" 12 (or is it 14?)

Must be a sign of the Alzheimer's setting in ? 14 TPI ,

To be honest, with a barrel blank of sufficient length and diameter and a decent set of drawings, anyone half decent turner with a decent lathe could turn one up - or down - in a few hours

The important thing is a Taper turning attachment, one of these and your in business, but to be honest, most barrel blank suppliers will contour any blank for little cost and I know Lothar Walther charge approx $65, 41 pounds (pound sign not working on laptop) for the ammount of time setting everthing up, and your own time on the machine etc, more cost effective to let them do the contour including the Tenion, the finish is excellent, so you will have a blank with correct contour and a machined tenion ready for the thread and chamber.

Most expensive part is the Chamber, If you buy your own reamer easy enough to do, Think in the USA you can rent them? that leaves the thread, no need to worry about the thread start, just machine thread and add knox form on completion of the final CHS.

One cheaper way of doing it, is to look out for any old target rifles based on the No4 action, plenty still about with hammer forged barrels, still may need to make a spacer etc for correct CHS and still need a reamer.

[jmoore]

The important thing is a Taper turning attachment, one of these and your in business, but to be honest, most barrel blank suppliers will contour any blank for little cost and I know Lothar Walther charge approx $65, 41 pounds (pound sign not working on laptop) for the ammount of time setting everthing up, and your own time on the machine etc, more cost effective to let them do the contour including the Tenion, the finish is excellent, so you will have a blank with correct contour and a machined tenion ready for the thread and chamber.

Talked "ftf" with a Lothar Walther man today (purely by chance). He indicated that doing a barrel complete with the hammer forged "scale" finish would likely be very cost prohibitive for a short run, as the set up is far more involved than doing a net near shape with a finish turn. Oh, well...