An Odd Characteristic of the SMLE

[gwahlert]

Can anyone coomment on this observation from an old Aussie sniper from Korean War:

"As the rifle bolt on the .303 is locked at the rear, there would be a crossover of shots at between 900 and 1200 yds. This was an odd characteristic of the Lee Enfield. It meant that the rounds would impact to the left or right of the aiming point. … Rifle was zeroed at 300 yds" He was firing the No.1 HT.

Was this a well known aspect of the SMLE?

Cheers

Glenn

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[Thunderbox]

Its hard to understand what he is describing. Does he mean that there is a lateral spread in the group, between 900 & 1200 yards?

If so, thats not a known general characteristic of No1 rifles. Maybe the HT mount itself is flexing, and the error simply amplified by distance? Normal No1s have both sights on the barrel and grouping is not particularly affected by what goes on behind the chamber.

No1s are highly individualistic; they made over 4 million of them , but they're all different.....

[Bruce_in_Oz]

Shooting a SMLE, with or without the primitive optics of the old Patt 18 scope, at 1200 yards would be an exercise in optimism. I would think that targets at that range would be at least "Jeep" sized.

900 is certainly do-able, as it was and still is, one of the more "challenging" distances for "full-bore" shooting.

I gather that what the writer means by "crossover", is lateral dispersion.

Do any (still-youthfull) Bren or Vicker drivers have any similar experiences?

As I have mentioned before, the actual path of a bullet is rarely a perfectly smooth parabola. The miniscule variations in jacket and core construction mean that bullets are unlikely to spin around their actual dimensional centre-line. Then there is the equally miniscule variations caused to the airflow by the fact that the bullet is, in fact, spinning at several hundred thousand revs per minute. Take into account variations in air density, humidity, ammo temperature, barrel temperature and it starts to get interesting.

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

SO, what may be happening is that the bullet is spun at least fast enough to achieve stability at any practical temperature and air density on the face of the planet. The trick is that as the range increases, "linear" velocity decreases. The outrageous initial rotational velocity means that the (over) stabilised bullet tries to stay aligned with the 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 has a brief struggle with rotational inertia and the the bullet, already "precessing" (describing a tiny spiral motion AROUND the actual "trajectory) jumps randomly until the aerodynamics haul it back into line.

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 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 it travels down-range.

Mk7 bullets are only spun at their speed becaise of their length. The bullet is within a whisker of the same length as the heavier, round-nosed Mk6 that preceeded 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 this maintenance of length was to not require that every .303 weapon be re-built to reliably feed a shorter projectile.

[Peter Laidler]

Once the bullet has left the bore, then it's on its way, under its own steam and whatever happened in the rifle has ended. Thereafter will have no effect on it (I may have said that slightly incorrectly..............). If it does go left or right or up or down, then it does so due to other influences.

You know my experiences with the old and bold and their versions of events relating to small arms...........

[RJW NZ]

never heard this one in regards smle's as a rule, except when hunting with cheap rifles and home made scope installation on LE s.

My simple minded 2 cents, inflated ones with little value, if this was my sporterised enfield hunting rifle with a cheap scope on it, and the shots showed a cross over, the simple thing I'd look at is that the scope is not parallel to the bore in the yaw axis, and intersects the line of sight/shot at a particular range. If the scope were zeroed for that range it would shoot eg left at shorter ranges and shoot right if one raised it a couple of hundred yards. I'm not sure if Hts all had scopes but that would be my first approach.

I think the comment that it was zeroed for 300 yards is a mental diversion, this is about the scope being parallel to the bore, or not, not the range drum zero.

[Patrick Chadwick]

the simple thing I'd look at is that the scope is not parallel to the bore in the yaw axis, and intersects the line of sight/shot at a particular range.

Add my 2 cents to that. It is a well-established (but often overlooked) performance inhibitor on the Mosin-Nagant sniper rifles, where people have often retrofitted PU scopes without realizing that the scope axis needs to be accurately above the bore axis in the vertical plane.

[Bruce_in_Oz]

The phenomenon of lateral deviation of bullets has been known for quite a while.

That's why the old Lee Enfields ("Long Toms") had "issues" with sighting in the early days. Issuing a new "mark" of ammo every year or so wouldn't have helped at all.

Note that from early days, SMLEs had their front sight bases offset from dead-centre by a noticeable amount. (I am not in "The Crypt" as I type this and the exact offset escapes me. The "ears" on the nosecap are similarly offset so that the sight picture is not too "wonky".

The bullets had lateral drift in still air and thus compensation had to be built in. This was achieved by offsetting the "nominal" centre line of the front sight assembly.

[Patrick Chadwick]

As the rifle bolt on the .303 is locked at the rear, there would be a crossover of shots at between 900 and 1200 yds.

I see no connection between the rear locking and any recurving of the sideways drift in the air - but I await enlightenment. As Peter has delicately hinted, once the bullet is in the air it has no "memory" of being fired from an Enfield or anything else. What it has are solely the ballistic characteristics of its form, plus the velocity, spin, yaw etc imparted on firing. Which may also be influenced by the deformation of the system on firing. But once the bullet has left the barrel, it is hard to imagine that a bullet thinks "OMG, I was fired from an Enfield and now I'm past 900 yards, time to start curving back!"

The phenomenon of a bullet fired from a rifled barrel drifting one way or the other, depending on the direction of twist, has been know since blackpowder days. This results from the attitude of the bullet in flight, not the locking lugs in the system that fired it, and hence will increase in a non-linear fashion with distance, depending also on the tractabiity i.e. the way the attitude of the bullet alters during the curve of the trajectory.

Take a look at the Buffington sights on a Trapdoor, and you can see that the backsight leaf is angled very slightly to compensate for this effect. Which is the same effect as used by spin bowlers to make the ball curve in the air. Surely every Aussie knows that, unless they live a highly secluded existence and have never heard of Shane Warne!

[Paul S.]

My only thought here is to wonder if a lateral crossover at long distance could be caused by wind drift with winds down range being significantly different than anticipated, and the rear locking of the bolt theory was just barrack room speculation becoming gossip becoming gospel. Thoughts?

[Peter Laidler]

One of the many good things about a forum is that you can air all sorts of ideas and ask all sorts of questions and nobody really gives two hoots. Even if to others they might seem silly, daft or just plain stupid, you'll always get answers. In classrooms, I always say that there's no daft, silly or stupid questions - just questions that deserve answers

But it is better to ask and discuss these things here (or in the class) than to go full steam ahead and publish them. That way, the readers KNOW that you're daft, silly or just plain stupid