Lee Enfield bore size after slugging

[Mal Enfield]

Hi all,


I'm a little confused...

I have recently bought a Long Branch LE and on purchase was told it had a new barrel. I was skeptical but bought it any way.

I got it home and slugged the barrel. Using my Kinchrome calipers the slug measured out at .303...hmmm I thought they were .311 - .312... so I re-slugged a second time and the result .303 again. I measured a round from remmington for their .303 British SP and that measured in at .3045

So my assumption is that the new barrel is a recent production and milled with new technology to get it to exact .303?

I thought that most new barrels were spec'd to mil-spec at .311?

Any thoughts?

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Peter Laidler]

The trouble with slugging a bore is that by default, you will only ever get the smallest diameter that it passes on its way out! That's why on large calibre guns we use a bore-micrometer. No such thing available for small-arms though so we're left with 10th best!

[Mal Enfield]

The trouble with slugging a bore is that by default, you will only ever get the smallest diameter that it passes on its way out! That's why on large caliber guns we use a bore-micrometer. No such thing available for small-arms though so we're left with 10th best!

Ah of course! (Light Bulb!) That might explain why it was so easy to push the slug through the bore. the first 3-5 inches needed a tap with a hammer but the rest I could easily do by hand.

Is it safe to say that if the muzzle has a tight diameter of .303 the barrel is relatively new? I'm just trying to identify the approximate condition of the barrel.

[Bindi2]

I would be looking down the bore with a borescope to see why the first bit is tighter than the rest.

[Mal Enfield]

I would be looking down the bore with a borescope to see why the first bit is tighter than the rest.

I've had a good look down the barrel and it all looks good. nice and smooth and shiny.
I bought the rifle from a reputable firearms dealer so am pretty confident the bore is good. Just want to get an understanding of why the barrel is the way it is.
If 95% of the bore is .311-.312 and the last 5% is .303 (Muzzle end) is that normal for a new barrel? or should it all be the same caliber? Considering the projectile is a shy over .3045 it should squeeze out the muzzle nicely... right?

[Parashooter]

It's highly likely you've stripped your bore slug and are therefore seeing only the bore diameter, rather than both bore and groove. Does the slug show clear impressions of the lands like the one at the end of this photo montage? If not, try a different technique and/or raw slug configuration, perhaps as shown here.



How many rifling grooves does your barrel have? If it's an odd number, like 5, then you need to use special technique or tools to get a useful reading.


Measure across the "corners" (red line) for a reasonably accurate reading on odd-grooved rifling.

As for the Remington bullet that measured .3045", were you measuring a loaded bullet just ahead of the case mouth? That might not give you the major diameter, which can normally be measured only after removing the bullet from the case. If you did measure a pulled bullet and found it was that small at it's largest point (usually the back end), then you should recalibrate your caliper and be sure you're employing it correctly. It would be extremely unusual to find a factory .303 British projectile with a major diameter less than .310".

[Bruce_in_Oz]

The numbers can be murky:

In the SMLE drawing (A.658), barrel inner dimensions read thus:

Diameter of Bore: 0.301" (low), 0.304" (high).
Depth of rifling: 0.005" to 0.008"

Thus, if you have a "MAX" bored barrel (0.304”), the total groove DIAMETER can run out to 0.320", which is a little larger than the presumed 0.312" "max".

A "minimum" barrel would work out at 0.301" / 0.311"

This generous range of sizes is also the reason for NOT using boat-tails, especially "solid-based" (sporting) ones in any quantity in original Lee-Enfield barrels. IF you are lucky enough to have a MINT example that runs to absolute minimum spec, ......maybe......

Note also that early SMLE barrels were also taper-lapped; the diameter of the bore INCREASING towards the muzzle. The theory was that if the bullet could run "more freely" as it accelerated, the shorter barrel of the SMLE could ALMOST match the muzzle velocity of the longer Lee Enfield Rifles. All of this caper was done when the very HARD Mk6 bullet was the latest technology.

The later and MUCH better solution, brought about by the advent of the German 7.92 x 57 "Spitzer" loading, was to change to a lighter, pointy bullet: the mighty Mk7.

[Mal Enfield]

Thanks Guys, All of you have been very insightful.

Parashooter, I'll try again with the slug as I think I have stripped out the slugg because I can't see the groves. And the remmington projectile was measured just before the neck of the casing so that's definitely why I'm getting a small reading.

I'll re-slug again later today and let you know the outcome.

PS It's a two groove barrel if that makes any difference?

[Mal Enfield]

Ok, so my measuring was off by the looks of it.

Firstly I was measuring the 'lands' and that was giving me .3045

Measuring the grooves from the corners gave me a reading of .311 (Corner) to.313 (Just off the corner), that was measuring two different slugs and they both gave similar readings.

So thanks guys now I have a definitive answer to my bore size.

[Gnr527]

Very informative thread - Sticky?