While MkVIIIz is a popular topic...

I entered into a discussion elsewhere about the statement that MkVIIIz was banned from use in rifles because they blew up and started the world turning backwards (or some such tripe)
There was references to a wiki post that said MkVIIIz was 10% hotter than MkVII, had a MV of 2550fps. I looked up Mr Edwards' section in the "Lee Enfield" to see that by his notes, MkVIIIz actually had less NC in it than MkVIIz, but had the same MV at 2440fps. (top of page 594)

I did some digging and found this in the hope of getting to the bottom of the stories once and for all.... Please, all discussion and any more official documentation welcome to (hopefully) put this to bed...

From Armourers Updates 1943

Attachment 71026

Attachment 71025

I read this as saying that the use of MkVIIIz caused accelerated wear due to the difference in the shape of the projectile base causing a concentrated heat area up the boat tail out to the barrel, rather than the base of the FB projectile meeting the barrel at a tangent.... this effected already partly worn MkVII barrels more than new barrels.
The last bit says to me that MkVIIIz can be used in rifles under the same circumstances as stated for using in the LMG (Bren) and that being where less muzzle flash may be desirable on night ops.

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Originally Posted by Son

. . . I read this as saying that the use of MkVIIIz caused accelerated wear due to the difference in the shape of the projectile base causing a concentrated heat area up the boat tail out to the barrel, rather than the base of the FB projectile meeting the barrel at a tangent . . .

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This seems not in agreement with the statement in the last paragraph of section 4 in the displayed document:

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"* Although the use of Mark VII and kindred types of cordite loaded, flat base bulleted, ammunition reduces Mark VIIIz barrel life, the reverse is not the case." (emphasis added).

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What actually may to be implied is that the accelerated erosion from cordite Mk VII ammunition can render barrels too worn to perform well with the shorter bearing surface inherent with boattail bullets of the same weight, a result easily attributable to greater opportunity for yaw in the worn throat.

https://www.milsurps.com/images/impo.../2unulu9-1.jpg
Simplified sketch showing how boattails have a greater propensity for yaw in worn throats than flat base bullets.

Numerous tests over the years have demonstrated the popular idea that boattail projectiles hasten barrel wear is based more on imagination than fact. The article below summarizes some of the test results.

https://www.milsurps.com/images/impo.../35b6rkm-1.jpg

I have just finished a book on an Australian MG battalion based in New Guinea 42-44 they conducted a test on barrel wear and using a Vickers when they had @16,000+- the barrel was considered shot out as they could not guarantee the beaten zone for long range would not be a threat to the troops if the fire was to be close in support. From memory they may have used VIIIz they had 23,000 rounds for the test

[QUOTE=Son;35886
...snip...
I read this as saying that the use of MkVIIIz caused accelerated wear due to the difference in the shape of the projectile base causing a concentrated heat area up the boat tail out to the barrel, rather than the base of the FB projectile meeting the barrel at a tangent.... this effected already partly worn MkVII barrels more than new barrels.
...snip....[/QUOTE]

What your documents quite clearly say is that CORDITE propellant results in premature wear and firing even a few rounds of CORDITE ammunition results in a barrel whose accuracy life span is unpredictable and therefore restricted from overhead fire.

MK8z isn't the problem, mk7,6, tracer and AP (commonly CORDITE propellant) ect are the problem.

This is an excellent discussion, months ago, I had conducted some informal research into this Mark 7 vs Mark 8 "machine gun" ammunition being loaded hotter and damaging Lee Enfield rifles. I had read that Mark 8 "Vickers" ammunition was prohibited from use in rifles in a variety of places including Love and Duty, a memoir style book about the PPCLI in Korea, made reference. I took it as gospel until more recently I discovered that a large lot of IVI surplus once fired brass all featured 2008 headstamps and Mark 8Z markings, clearly from issue to the Canadian Rangers.

That sparked the question in my mind, if the Rangers have been shooting it for all these years and rifles haven't exploded, there must be something else to the Mark 7 vs Mark 8 discussion that isn't around chamber pressure. I made some private speculative conclusions about an order in the spirit of preserving "good" MG ammunition for the guns and to keep regular riflemen from wasting a precious MG asset, which became a soldier's urban legend. The "should" not fire in a rifle evolved to "shall never" fire in a rifle, because it's loaded "too hot" and will blow up / damage the rifle.

Much in the same spirit that the belief still circulates in the Canadian Infantry Corp: "You aren't allowed to sharpen your bayonet because of the Geneva convention." which is a bastardization of the Hague conventions, Section IV.3 and a 1973 report from the International Red Cross on "Weapons that may Cause Unnecessary Suffering or have Indiscriminate Effects". Neither of those documents mention bayonets, misinterpretation becomes fact, but bayonets continue to be issued with sharpening stones. I think this may be a similar case.

I do not have access to official documents, and can only regurgitate the possible misinformation of the internet, so I won't have a lot of facts to add here. However I will look for the references from Love and Duty for the interest of the forum.

The Rangers use No4MKI's do they not? It is fine to shoot MK8Z in a No4 but not in a NoIMKIII SMLE. I have personally seen a SMLE that someone ignored the advice of others to not shoot MK8Z in it and it did indeed over time stretch the action.

I gotta say, I tried some Mk.8 in my No.5, recoil was horrible and the bolt became very tight after a few rounds.
Took a bit of work to repair the sprung action and resecure the charger bridge.
So these days I steer clear of the stuff(although I will admit that when I fired the stuff, it was a red hot day and the ammo had been cooking for awhile) it was bloody good brass though, still using the cases.

MUffet,

I used some, Kynoch, and it seemed to go alright here in the frozen North.
Have a bit of PPU I think it is. actually didn't notice much difference in my old Ishy. no sticky bolt or anything. Forget the date on that rifle now, but not a late production.

The SMLE that had the stretched action never had a sticky bolt. After about 4-6 competitions of using PPU MK8Z it started spraying rounds into big groups. Upon inspection it was found the action had stretched.

There has been a prodigious quantity of Jugo/Serbian "NNY" (PPU) Mk8 ball sprayed downrange here in Queensland alone over the last decade or so.

Reasons for its popularity?

No Mk7, Z or otherwise, to be found ANYWHERE in commercial quantities.

Reliable ignition.

Acceptable grouping from existing barrels.

That said, a Lee Enfield barrel already eroded by seventy-plus years of Mk7, will potentially have "issues" if fed a steady diet of Mk8. The gas-bleed around the boat-tail at ignition will just keep chewing out the already generous throat/ leade region.

As has also been mentioned before, swapping out an "under-performing" barrel on a Bren or Vickers is child's play compared to re-barreling a SMLE or No4.

In my mind, the obvious choice would be Mk7Z; the "magic" (flat-based) bullet driven by much cooler burning NC propellant. Most of the world's production of 7Z apparently got sprayed out of Browning aircraft guns, (less muzzle flash), or "carelessly" dropped into deep water post WW2.

Mk8 was ONLY introduced to extend the useful range of said Bren and Vickers guns, (extra distance is GOOD on the two-way rifle range), NOT to supply "match-grade" ammo to the basic foot-sloggers.

Actions stretching? We had this discussion some time (and tome....) ago regarding L1A1's. How does a rifle action stretch? Put a bolt and nut between a slab of steel, tighten the nut up and the bolt will stretch - if you over tighten it! Because it has exceeded the limits of its mechanical elasticity. This action doesn't happen with a rifle as you have to stretch something between two (or several) points. The bullet passes through the bore and the rifle recoils. The bolt is under tremendous compression and the body might measurably twist and warp and then resume its shape. But it isn't subject to tension.

Many things happen to rifle bodies but 'stretching' ain't one of them!

Well there's no arguing with you. It went out of headspace and no other bolt head would bring it back into headspace. So I guess you know what would have happened as I have no Idea.

The hardening in the locking lug recesses is probably worn out. That has nothing to do with stretching. The bolt will set back causing excessive headspace. I think it's mythology that the Mk.VIIIz cartridge has more pressure. The only difference is the 175 grain boat tail projectile as opposed to the 174 grain flat base projectile in the Mk.VII/VIIz.

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Originally Posted by Bruce_in_Oz

Mk8 was ONLY introduced to extend the useful range of said Bren and Vickers guns, (extra distance is GOOD on the two-way rifle range), NOT to supply "match-grade" ammo to the basic foot-sloggers.

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Exactly the case and it falls exactly in line with my experience and expertise in the theory of machine gun fire, it appears that ballistic experimentation nearing the later part of the First World War discovered that a BT bullet was more stable in the far ranges of direct and indirect MG fire. This is still practiced today with a variety of guns, mounts and sighting systems to ranges of 1,300 (approx tracer burnout) to +1,800m, the summary was that the FB bullet would deliver a beaten zone that was somewhat unpredictable, lacking density and the cone of fire was less than useful at extreme ranges. Whereas the BT bullet is more stable in flight at extreme ranges, not so much way to increase absolute range, but as a way to increase effectiveness of the weapons system at the beyond shoulder fired, direct fire distances.

At those ranges the MG would be used as an area weapon, usually in a grouping of several guns to deny ground and restrict movement, long bursts were used to saturate the ground with incoming projectiles.

In the most basic of terms a BT bullet at extreme ranges would deliver a smaller extreme spread of the "grouping" and deliver a more consistent beaten zone.

Sorry if I appear to have rattled you a bit Martin, but no offence meant at all. And I don't mind or feel threatened if you want to argue the point but mechanics and physics isn't on your side. I only came onto this (and ONLY this) site because I was asked to comment on something a few years ago. I say it as I find it and as it is from an Armourers perspective, and as an engineer to boot. There are many myths surrounding small arms especially from the old and the bold that have been passed down from generation to generation. Here's a few examples: The Sten will go off and kill everyone nearby if you drop it - it won't(?). The Bren is deadly accurate. It's not, it's crap. Rifles stretch........... I'm not alone here either. And the straightest talkers are the Australian contingent!

PS I was the last Vickers MMG trained Armourer left in the UK Military which gave the UK MoD an opening to use our remaining guns

Hi Peter, I'm not rattled but there is no point in arguing about it because I know you know your stuff. I had the same thing hapen to a SMLE in 303-25 that I loaded too hot. But as I said I have no Idea thats why I am here.
Cheers.

Bodies stretch, alright. In the "good old days", Oz rifle club armourers had spare ones just for such occasions.

A classic example is the fate of the Lithgow experimental 7.62 NATO carbines built on SMLE actions in the mid-1950s.

The remains of those I have seen are DEFINITELY "distorted". The right-side rail, being the thinnest piece in cross-section was visibly stretched and the body effectively bent. HOWEVER, NONE were reported to have "failed catastrophically", i.e. (blown up). Bodging the mag well to accommodate an FAL mag probably didn't help, either.

The poor old things were originally made from a simple Carbon-Steel alloy, as per the original early 20th Century recipe, and as opposed to the No4 which employed a different brew.

The locking shoulder / recess were "spot-hardened" using pointy carbon electrodes to raise the temperature followed by a quench etc. If you look closely at a near-mint Oz SMLE, you will see small, circular patches of discolouring on the exterior of the body, just behind the locking shoulders.

The use of oiled, proof-rounds for "stress testing" probably didn't help either.

These shoulders also WEAR quite rapidly once this surface-hardened skin gets too thin. Then you will also start to see "set-back" marks, mainly on the nice, big RHS one. By that time, your bolt body, if original, will probably be getting a bit tired too.