Lee Enfield bore size after slugging

Hi all,

:surrender:
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?

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!

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Originally Posted by 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 caliber guns we use a bore-micrometer. No such thing available for small-arms though so we're left with 10th best!

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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.

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

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Originally Posted by Bindi2

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

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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?:banghead:

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.

https://www.milsurps.com/images/impo.../2i27bmf-1.jpg

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.

https://www.milsurps.com/images/impo.../30iudqc-1.jpg
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".

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.

Thanks Guys, All of you have been very insightful. :thup:

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?

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.

Very informative thread - Sticky?

Two votes for a sticky....

The problem that arises with this is that - and you'll have to forgive my less than patronising almost to the point of insulting view, so sorry before I go on........... for the average enthusiastic amateur, bless 'em, is that you get the '.......all the gear and no idea syndrome'. You know......... full set of gauges and all the tools and all the......... you get the idea....... When all you need to know is that the rifle is accurate. And when the accuracy starts to drop off, THEN you start to investigate, starting with the bleedin' obvious.

Here's an example...... During the era of the No4, we had all manner of bore and body gauges. In fact, the Chief Examiner had a whole inspection tray full of them plus the others for this that and the other. So a good accurate No4T for example would come in with what looked like an area of corrosion or pitting or whatever that was proving a bit tough to scrub out - only to find that the XY gauge would enter more than Z". So on that basis alone, the rifle would have the barrel changed - and when that happened, maybe it couldn't CHS and so it'd be ZF'd. We've all seen barrels as bald as a badgers ars........, er....... bottom or shining like a sewer pipe and wonder how the xxxx the bullets get out of the end. And we've all seen almost new L96's that are simply incapable of grouping

Those days are GONE.............. Now, the criteria is 'does the GO gauge run freely?' If so, 'does it pass the accuracy test?'. If it does, then that's the end of the matter. But for a sniper rifle, we let the final arbitrator be the sniper. I suggest that this is the criteria you stick to.

I could be wrong of course

All true Peter but reloaders can be a puckered cheek bunch when it comes to finding the "perfect load".

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Originally Posted by Peter Laidler

The problem that arises with this is that - and you'll have to forgive my less than patronising almost to the point of insulting view, so sorry before I go on........... for the average enthusiastic amateur, bless 'em, is that you get the '.......all the gear and no idea syndrome'. You know......... full set of gauges and all the tools and all the......... you get the idea....... When all you need to know is that the rifle is accurate. And when the accuracy starts to drop off, THEN you start to investigate, starting with the bleedin' obvious.

Here's an example...... During the era of the No4, we had all manner of bore and body gauges. In fact, the Chief Examiner had a whole inspection tray full of them plus the others for this that and the other. So a good accurate No4T for example would come in with what looked like an area of corrosion or pitting or whatever that was proving a bit tough to scrub out - only to find that the XY gauge would enter more than Z". So on that basis alone, the rifle would have the barrel changed - and when that happened, maybe it couldn't CHS and so it'd be ZF'd. We've all seen barrels as bald as a badgers ars........, er....... bottom or shining like a sewer pipe and wonder how the xxxx the bullets get out of the end. And we've all seen almost new L96's that are simply incapable of grouping

Those days are GONE.............. Now, the criteria is 'does the GO gauge run freely?' If so, 'does it pass the accuracy test?'. If it does, then that's the end of the matter. But for a sniper rifle, we let the final arbitrator be the sniper. I suggest that this is the criteria you stick to.

I could be wrong of course

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Peter,

I'm not sure why your so scorned? If amatures want to be more proficiant isn't the best way to ask questions?
Sure if you know nothing about firearms and all you want to do is shoot them then your statement is very true.
What if you want to be more than "All the gear and no idea" Shooter? Should we all just not ask any questions and leave it up to people like yourself to discuss the in's and out's of guns. Sounds like you have 'tall poppy syndrome'
Your 'In My day' Speel provided nothing to the thread and I appologise in advance if I come across rude.

So far you haven't provided any uselfull information to this thread so I wonder now...Who is it that has all the gear and no idea?

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Originally Posted by Mal Enfield

I'm not sure why your so scorned? If amatures want to be more proficiant isn't the best way to ask questions?

Your 'In My day' Speel provided nothing to the thread and I appologise in advance if I come across rude.

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I don't think Peter is scorned here at all. Most of us hold our breath and read his posts carefully. There's wisdom to be had. If you don't get what he's saying then read again. He's telling you not to worry about your barrel size and just get on with it. I'm a reloader. I've probably loaded more ammo than most will ever see. I got past the anal part of reloading years ago and have very successful loads for accuracy.

Among folks who give out sound advice on firearms, there are those who have education, those with practical experience, those with intelligence, and a very few with plenty of all three. One of these few, Peter Laidler, is giving you the best advice I've seen on this thread. While others have tried to help fix your measurement technique, he has pointed out that your efforts are misdirected - specifically that measuring the barrel's dimensions is pretty pointless when compared to a practical accuracy test.

In general, bore and groove sizes are meaningful only to advanced handloaders who may select the size of their (cast) bullets in an attempt to fit them to the individual barrel. It this doesn't describe your situation, you're expending thought and effort for no practical result.

Sorry if you feel like that Mal, but as I say fairly often on the forum, the place I learned about straight talking and no mincing of words was in Australia! And to be fair, I did apologise even before I continued. You're right, someone did ask the Q. so I answered as best, truthfully and above all, as honestly as I could. That said, it's not all '....in my day.....' although 'in my day.....' second best was never good enough. I actually SAY that in my day, in the 60's, we did do all this stuff. And to be honest, it was a load of crap compared to currrent thinking. The CURRENT way is to just VIEW the barrel for straightness (better than any 'GAUGE, testing straightness of bore believe me.....), see that the calibrated bore gauge runs and accuracy test it on our test range. There's nothing 'in my day.....' about that. It's just good plain bleedin obvious to me!

And JUST to prove my point, I'll ask you how we do our current megga accurate sniper rifles (both sorts.....) Yep, you got it in one. View the barrels on the rollers, dry the bore, run the gauge through ensuring that it drops on its own weight and then accuracy test. Passes all of that and he gets it back!

Peter Laidler
Pete the Pom.
Australian Army 1967-70

I have been blunt on this forum but I get warned for it. You can talk about scrapping a barrel for how it shoots but you are missing one element that you admit to knowing nothing about and that is reloading. Just because a rifle shoots poorly with the military ball load does not mean it will not shoot well with other ammo expecially handloads. And I don't mean highly developed handloads. I mean ordinary handloads put together with care, using an appropriate bullet and powder. That is, no experimenting beyond the first 20 loads. And so what if I do burn up 50 or 100 rounds if I save a barrel for another 1000 rounds? Your barrels get a little gauging, a little run out check, an accuracy check and you throw them in the trash if they fail?

Quote:

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Originally Posted by Peter Laidler

Sorry if you feel like that Mal, but as I say fairly often on the forum, the place I learned about straight talking and no mincing of words was in Australia! And to be fair, I did apologise even before I continued. You're right, someone did ask the Q. so I answered as best, truthfully and above all, as honestly as I could. That said, it's not all '....in my day.....' although 'in my day.....' second best was never good enough. I actually SAY that in my day, in the 60's, we did do all this stuff. And to be honest, it was a load of crap compared to currrent thinking. The CURRENT way is to just VIEW the barrel for straightness (better than any 'GAUGE, testing straightness of bore believe me.....), see that the calibrated bore gauge runs and accuracy test it on our test range. There's nothing 'in my day.....' about that. It's just good plain bleedin obvious to me!

And JUST to prove my point, I'll ask you how we do our current megga accurate sniper rifles (both sorts.....) Yep, you got it in one. View the barrels on the rollers, dry the bore, run the gauge through ensuring that it drops on its own weight and then accuracy test. Passes all of that and he gets it back!

Peter Laidler
Pete the Pom.
Australian Army 1967-70

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Originally Posted by ireload2

Your barrels get a little gauging, a little run out check, an accuracy check and you throw them in the trash if they fail?

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Yes, quite rightly too!
Peter is writing about the military environment, where the user does not normally make up his own reloads. The rifle must produce satisfactory results with "off the shelf" ammo. Maybe snipers are permitted to select ammo, but surely not the non-specialist troops. As private persons we may indulge in spending a great deal of time and material on experimentation to our heart's content, but if we were to cost that in proper commercial terms, then in many cases a new in-spec barrel would be cheaper and faster.

Of course, we are also babying along many ancient weapons for which there is quite simply no replacement barrel available. Or the original bullets, let alone ammo. Can anyone point me to a source of a new original-spec barrel for an Egyptian Rolling Block? I doubt it. I am one who indulges in the above-mentioned entertaining activity of individually-tuned reloading, and successfully shoots with battered old smoke poles that may look ghastly on the outside, but work - sometimes after a lot of faffing about. But loading long, fat flat-base bullets as far as possible out of the case in an attempt to overcome worn throats and bores - "to save a barrel for another 1000 rounds" - is not a solution for a professional soldier. In such cases, Peter and his colleagues would rightly say "bin it". We are, however precisely we may go about it, still really entertaining ourselves with "boys toys", not being dumped in the back of nowhere in a situation in which lives may depend on the equipment functioning flawlessly without any fussing and fiddling.

Which was, for instance, the doom of the Ross rifle in WW1. Considered by many, at the time, to be a better target rifle than the Lee Enfield No.1, it was apparently plagued by malfunctions in the mud and muck of battle, dumped by many soldiers as soon as they found a SMLE. Which would still work with ammo that had been dropped in the mud, stepped on, picked up and wiped down on the battledress trousers, and popped into the magazine without checking for the last 0.001" of seating depth, the special bullet, the ideal powder etc. etc. It just plain worked. And thoughtless reloaders ever since have been griping about its tendency to split reloaded cases if they are fully-sized. But that's another story...

Reloading is for hobbyists, not soldiers.

The above point is correct...I've loaded ammo to the highest degree with pulled 147 ball for .308. I was careful to only use bullets that weighed correct. Not up or down. I weighed 600 bullets and came up with 55 that were correct. I carefully loaded them to match spec and shot them, they could only do about 4 inches at 100...I then tried a few hunting rounds I loaded and they were all on top of each other. Loaded the same, but the bullets made the difference. That was when I understood our ball ammo wasn't quite what it might be...

Point of the story is, try something other than factory ball for accuracy before you give up.

The fun thing about all of this is the number of variables at play, every time you squeeze the trigger.

However, before we start;

1. The throating: To the end, SMLE barrels carried over the long throat necessary to accommodate the old Mk6 “torpedos”.
2. The internal dimensions of the barrel: As noted previously, as per the specifications on the original drawings, the BORE spec was tightly controlled around the nominal .303” figure. However, GROOVE diameter could run out to .320 and STILL be in spec.

So, we have a bullet that is smaller in diameter than the possible groove diameter; thus what we potentially have is what is called in modern parlance, a “bore-rider”. Yes, the bullets DO certainly engage the rifling, as can easily be seen by the fact that recovered projectiles are clearly engraved with the five lands and the fact that you generally hit your target (or at least give it a nasty fright).

HOWEVER, it is a bit more “interesting” than that.

Upon ignition, the bullet is bashed forward into the start of the rifling. With any luck, this engagement of bullet and rifling will be concentric.

Now, if your bullet of choice is like the classic Mk7, the slightly concave, flat, but open base WILL expand slightly to provide some improvement to the gas-seal.

If, however, you have chosen unwisely and taken the boat-tailed “pill”, things are a little different. The short cone of the boat-tail directs a much greater proportion of the super-heated gas AROUND the sides of the bullet. Now, if the bullet were a close fit to the nominal GROOVE diameter, this would be a lesser problem. HOWEVER, given the difference between the GROOVE diameter and the actual BULLET diameter, there will be gas “leakage” and thus gas CUTTING of the throat and leade.

If the bullet construction has less than PERFECT concentricity of both the jacket thickness and core insertion, its centre of mass will not be coincident with the notional aerodynamic centre. Inside the barrel it will tend to spin around a centreline somewhere between that of the bore and of its own mass.
Once the bullet gets to the muzzle, things start to get interesting. The “pointy end” passes the muzzle without any drama, BUT as the rear of the bullet exits, things get exciting.

A flat based bullet exiting a perfectly cut crown will cause the propellant gases to erupt in a “perfect circle” around the base of the bullet. At this precise time, these gases will not just flow sideways at “ludicrous speed”, but being a fluid (with mass), rush FORWARD, past the bullet, thus potentially affecting its stability to some degree.

In the case of a boat-tailed bullet, this gas “blow-by” takes place over a comparatively longer time AND acts on the wedge-shaped boat-tail. Thus, there is potentially more scope for destabilisation. This is on top of the fact that boat-tailed bullets have, for a given mass, a shorter bearing surface than a flat-based bullet, so their initial alignment in the bore is more “fraught”.

What happens next is that after the bullet clears the muzzle, the tiny (one hopes) difference between the actual centre of mass, the aerodynamic centre line and the ACTUAL rotational axis come into come into conflict. In a vacuum, the bullet would rapidly settle down to spin on its centre of mass, regardless of shape. Once you add the real-world annoyance of the air we breathe, it gets more complicated.

Aerodynamics come into play rather unsubtly. Oh, and then there is GRAVITY.

At launch, the bullet, if supersonic, forms a compression cone at the front and another, smaller shock cone at the rear. These are the principal sources of drag in supersonic flight.

Under the influence of Gravity and Drag, the bullet is losing speed and altitude from the moment it leaves the muzzle. The trajectory is pretty much a parabola.

However, all is not (generally) perfect. The previously mentioned precession caused by tiny discrepancies between the various “centres” now comes into play. The bullet is NOT traveling on a “perfect” parabola, but rather, precessing (spiraling around this nominal flight path). The “size” of these spirals is a part of the explanation of “groups” vs “one-holers”. Given that a “typical” rifle bullet is spinning at several hundred thousand revs per minute, it is a miracle of engineering that they hold together at all.

Finally, consider that whilst the rotational velocity does NOT decrease very much as the bullet goes downrange. LINEAR velocity does.

Now comes the fun part.

We now have a bullet spun fast enough to achieve stability at any practical temperature and air density on the face of the planet. Due to drag, as the range increases, "linear" velocity decreases. The outrageous initial rotational velocity does not decrease much at all, and thus, the spinning bullet tries to stay aligned with the original line of departure at the muzzle. What this means is that, at SEVERAL intervals along the "parabolic" trajectory, the pointy end will no longer be exactly aligned at a tangent to the curved trajectory.

Eventually, aerodynamics wins a brief struggle with rotational inertia and the bullet, already "precessing" jumps back into line (more or less).

The new "stable state" is very likely to NOT be exactly on the original trajectory: it could be to either side of it. The more "excessive" the rotational stability, the longer it will take to re-stabilise.

If your barrel was elevated 15 degrees to land bullets at some particular range, then the bullet will try to keep pointing at 15 degrees, until such time as the aerodynamics overcome it. If this happens in tiny increments at short intervals, the relative grouping deviations will be small. If your bullet is OVER stabilised, the corrections will be fewer and MUCH bigger as you travel down-range.

Mk7 bullets are only spun at their speed because of their length. The bullet is within a whisker of the same length as the heavier, round-nosed Mk6 that preceded it. The higher muzzle velocity of the Mk7 means, of course, a correspondingly higher rotational velocity, and thus a completely different set of down-range dynamics. I suspect that sticking with this “traditional” length was deliberate and meant that there was no urgent requirement to re-engineer EVERY .303 weapon in the inventory to reliably feed a shorter projectile.

(Anorak back in closet)…………