Lee Enfields and Boat Tailed Bullets

[David TS]

Pray tell where you get it "cheap"

All things being relative, I meant cheap at £61/100 (basically Krank's price, ordered from my local RFD), as opposed to the £100/100 Sako and Remington .308 factory deer loads I buy

[Brian Dick]

Good deal David. I'll bet that rifle visited me last year before heading back to the UK! There's some more on the way too so you guys over there save up some Quid and get one when they're available. Enjoy 'em while you can.

[Bruce_in_Oz]

Notes on boat-tailed bullets from Gale McMillan (McMillan Barrels):

“If you consider the way a boat tail bullet is made you will understand that it is an impossibility for the tail of the bullet to be inline with the body. If the tail is formed in the upper punch it will always be off by half the amount of the clearance between the punch and die. If it is made in the lower punch it will be a wider tolerance since there is more clearance in the lower punch. With the tail of the bullet being off center by at least 1/2 a ten thousandth of an inch, this keeps the bullet from flying true.”
“That is the reason you don't see them used in competition (Bench Rest, that is). We will hear a loud cry from long range shooters and all I can say is the ability to lay on ones belly and shoot 1/10 moa is an impossibility so they can get away with using them since the error factor is still smaller than the shooters ability. There was a remark made above about a flat base shooting better in a factory barrel and I will change that and say any barrel! My favorite saying is the records speak for its self. Show me a national benchrest record shot with a boat tail bullet. One thing that clouds the issue is that no high power match bullets are made with a flat base so they can only be compared with custom match bullets made with flat bases of which there are few.”
“I will say that the small amount of loss of accuracy is off set by the ability to overcome conditions due to decreased flight time at ranges of 600 and beyond.”

I will dig out some more of my notes on the subject shortly. There is a lot of interesting stuff about the Mk7 vs the Mk8 projectile, rifling dimensions and exterior ballistics buried on one of my hard drives.

[Laufer]

Aren't 2-groove bores a major factor? This seems to be the main problem in BT topics at Surplusrifle, Gunboards etc.

Bought two Longbranch rifles (my first) last winter. The previous #4 is an ROF (F), which has more grooves.
Using new Prvi Partizan 174 SP BTs in both LBs, one made some really bad "keyhole" slashes from 100 yards, but the other made clean, round holes.

My Fazak. with its four or five grooves has never made any keyholes, and has used a good bit more of the exact same factory ammo, plus reloads with 147-grain bullets (38 gr. IMR 4064 powder).

Both LB bores are equally bright and both appear to have equally good rifling, but with my bore light, it is very difficult to determine what the difference might be-never mind how to check the 'leade' etc.

[Bruce_in_Oz]

Some observations on bullets:

Whilst a bullet is traveling at supersonic speed, the air turbulence at the base of the bullet is a somewhat less important factor in drag than the shock wave at the point. However, during the trans-sonic phase, the base turbulence becomes significant as the airflow becomes laminar. During subsonic flight, smooth, stable laminar airflow is essential to maintaining stability and minimizing velocity loss. This is where boat tails come into serious play.

A down side to boat-tailed bullets is to be encountered at the point of starting the bullet in the rifling. Because of the reduced parallel bearing surfaces on the bullet, starting alignment is more critical. Couple this with “oversized” groove dimensions and a “generously” throated chamber and there will be trouble.

A quick look at the development of the .303 Service cartridge is instructive. Up to and including the MkVI version, the .303 was loaded with flat based, round nosed bullets. (The MkII hollow-point was a bit of a creative deviation.) After the Germans introduced their spitzer (pointed) bullet in the early years of the 20th century, almost everybody followed suit. The MkVII .303 cartridge was the British response. The designers had to keep the same overall length of bullet and cartridge as the 215grain MkVI for several reasons. A shorter projectile would have required radical re-engineering of the feed mechanisms of automatic weapons chambered for the MkVI and previous cartridges. As it turned out, the magazines on the Lee Enfield Rifles had to be redesigned, especially around the front lips, to achieve greater reliability of feed with the new ammo. Rear sights were also adjusted.

Thus the 174grain MkVII has an aluminium filler element at the tip of the core. Had the core been solid lead, there would have been less ballistic improvement over the MkVI it replaced. (Muzzle velocities: MkVI – 2060fps, MkVII – 2440fps.) This filler also contributed further to the rearward shift of the centre of gravity of the bullet. This and the bullet length meant that the 1:10” twist had to be retained; how convenient!

The MKVIII cartridge was developed as extended range machine gun ammunition. The boat-tailed bullet did not require a nose filler as the weight removed from the tail (as a result of the boat tail form) enabled the overall length of the bullet to remain the same as for the MkVI and MkVII bullets. Thus the weapon mechanisms stayed the same, only the firing tables had to be rewritten. Changing to a granular nitrocellulose propellant also made a difference.

Essentially, boat tailed bullets were developed to extend the effective range of machine guns, not to provide increased accuracy in rifles.

[Thunderbox]

The MkVIII bullet was not actually designed as a military bullet at all - it was in fact the last iteration of the "303 magnum" long-range match target ammunition project run by a Bisley/Kynoch/BSA committee between the wars. By 1929 they were using a 9o stepped boat-tail "streamliner" bullet in the match round, and this round (the committee had also reverted to the .303 case by then) was more or less adopted as the MkVIIIz military round in 1938.

[Bruce_in_Oz]

And another thing:

The rear end of a boat-tailed bullet spends relatively more time "exiting" the muzzle than a flat based one and so there is more time for the bullet to be disturbed. A good, even crown will ensure that the gas flow over the bullet is even. ANY bullet eccentricity (as per McMillan's notes) will have an effect, even with a "perfect" crown. Given the condition of a 70 year-old barrel with a crown cut under wartime conditions and attacked by cord wear and erosion, it's a miracle that we can even hit the backstops, let alone the bullseye with some of these rifles.

The 11 degree, so called "Bench Rest", crown used on many match barrels is promoted as having a good interface with the boundary of the shock wave from the escaping gases, (so the theory goes), and so minimizes turbulence. I have cut both square and 11 degree crowns on quite few barrels. I suspect that the real key is the accuracy of the machining, especially the finish on the very ends of the lands. if the run-out of the lands into the crown face is not perfectly symmetrical, the gas flow will also be non-symmetrical. The result will be yaw and subsequent precession, resulting in enlarged groups.

We are talking differences in the nano-second range when discussing the transit of the base of a bullet moving at almost 2,500ft/sec. However, given the forces involved, it appears to be significant.

And then there is the fact that a cartridge containing a bullet of different shape and weight, driven by a propellant with a different burn rate and resultant pressure curve MUST produce vibration and stress patterns quite different from those created by the Mk7 cartridge for which the rifle was regulated.

[Son]

And then there is the fact that a cartridge containing a bullet of different shape and weight, driven by a propellant with a different burn rate and resultant pressure curve MUST produce vibration and stress patterns quite different from those created by the Mk7 cartridge for which the rifle was regulated.

Well said, Bruce! Fellow shooters often used to ask me why I push my handloads (usually 174gn HPBT Matchkings) at the MkVII spec. I had given up trying to explain that the standard rifle with a light barrel and to an even greater extent, the snipers and "range pattern" No1's with H barrels were set up for best performance with MkVII ball. I proved a few "light loads" (whimpy little 150gn'ers) even though giving less felt recoil, and at their best, were actually less accurate than my MkVII equivalents. Not to mention the advantage of the rifle's sight graduations being true!


On the topic of boattails vs flat base, I considered the smaller variation in projectile weights of the well made Sierra's compared to two or three others at the time, would help more with longer range accuracy than any (usually unperceivable anyway) inaccuracy caused by the boattail itself. With the exception of the Taipan 170gn HP (which were very hard to get) The Sierra was the best pill for the job (in the hands of a middle of the road B grader anyway)

Thankyou for your insight here, Bruce. Perhaps your posts can be stuck together to form a MKL entry on the topic?

Here's a magic picture taken by a mate of EFD 3 Band at the instant of projectile exiting the barrel. The colourfull smoke goes far to illustrate the forces of the gas escaping around the projectile. Mr Bannerman kept a copy of the pic for his lesson on intermediate ballistics...

[Peter Laidler]

Was that Scobie Bannerman by any chance Son? An old instructor at Bandiana. Give him my regards although he never actually taught me as I was already been an apprentice

[Son]

Was that Scobie Bannerman by any chance Son? An old instructor at Bandiana. Give him my regards although he never actually taught me as I was already been an apprentice

That's the man. The one and only... Will do, at next opportunity.

Did you strike him over there or here?