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Mk VII & Mk VIII (Z) ball ammo (long)

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    Posted: August 20 2013 at 6:25am
.303 British, Mk VII ball & the “bore-killing, hot Mk8Z”

So, here I was somewhat bored, surfing the various Enfield forums & I got to wonder about some ammo I had acquired. It was headstamped as Prvi Partizan (“nny-85” headstamped) Mk8Z in .303 British. This is the “bore killing uber hot machine gun ammo, never to be used in rifles”. What was this stuff in reality?

Being me, I pulled down a couple of dinged up rounds & did some testing & guess what I found? There’s more than one kind of “Mk8Z” & it differs quite a bit by country/manufacturer. A bit more research & I worked out that a lot of us are actually making & shooting modernized Mk8Z-type ammo & our bores are doing just fine.

OK, let’s start at the beginning. What’s “real Mk VII” in detail?

In 1910 the British "War Office", part of the "Ministry of Defense", “sealed” the design & nomenclature of British Mk VII service ball ammunition. “Sealed,” means no changes, ever the spec is cast in stone & can’t be un-done, or modified without some serious pre-planning. It’ll probably become a new Model, Mark, or at the least get a (*) added to denote it’s different from “regular issue stuff”.

Such was the case with the MkVII (or Mk 7, after 1945) ball ammo. It was a 174 Gr FMJ flat-based bullet with a “tenite, (cellulose plastic)” fiber or aluminum internal core at the front & a lead core behind that. B.C. was 0.467. Propellant was charge weight that could vary from 35 to 38 grains, averaging 36.5 grains of “Cordite”, (the standard 58% Nitro-glycerin, 37% Nitro-cellulose and 5% Mineral Jelly) propellant of most British ammunition. Muzzle velocity was 2440 FPS & pressure was 52,900 PSI. (Current SAAMI specs are lower at 49,000 PSI, but that was yet to come, as were modern measuring techniques for pressure). 45000CUP was the actual measurement used at the time. There was a card disc over the propellant used as an anti-ablation shield to reduce flame-cutting erosion of the bore.

So. What’s different about a MkVII(7) or Mk VIII(8), or Mk8(z) round, designed for use in the Vickers machine gun for long range shooting?

A few things actually & there are several variants on the basic Mk8 Mk8(Z) design. It was never “sealed” like the Mk VII(7) was, so changes were easy.

The biggest difference was the bullet. The ballistically inefficient Mk VII round with its drag inducing flat base was replaced by a couple of different boat tail designs. Boat tails reduce drag, increase the BC of the bullet & allow it to fly on a flatter trajectory, increasing the effective range over a similar flat base one. The Mk 8 bullet was a 175~190-grain boat tailed, streamlined, steel jacketed bullet. Initially the boat tail was not full diameter but “stepped” with a flat annular base with the boat tail starting at a slightly reduced diameter. This was done in an attempt to stop rifling erosion, resulting in blow by & reduced accuracy. Because of its design the Mk 8 bullet was found to have a different issue, stiffness. Compared to the relatively soft Mk 7 it didn’t obdurate as well, so conforming to the rifling, particularly in worn, or cordite-eroded 2-groove barrels, was less efficient. At that point the stepped boat tail was dropped in favor of a “normal” full diameter boat tail design.

Slightly more “neonite”** propellant was added, giving a muzzle velocity of 2550 ft/s (780 m/s) and somewhat better ballistics. Chamber pressure was higher, at 40,000–42,000 lbf/in² (about 280 MPa). These were the “Hotter, Vickers machine gun only” ammunition that started the whole debate off. Neonite** incidentally is NOT cordite, nor a derivative of it. The closest current propellant to it is IMR 3031, a nitro-cellulose powder!

But there wasn’t anywhere near the standardization that existed with Mk VII ammo because of the “sealed changes” in design!

So is ALL Mk8Z a bore killer, or are there variations that are less damaging?

Some surprising things I’ve discovered about Mk8Z ammo. It varied way, way more than thought, look at these pull down figures!

Mark VIIIz Spec - bullet 175~190 grns +-2 grns, propellant 37 to 40 grains “neonite”** . Velocity 2,360~2,550 fps.
Spennymoor 1941 - Bullet 175.0 grns, prop.38.0 grns
RG 1944 - bullet 176 grns, prop. 36.5 grns
Spennymoor 1944 - bullet 174.5 grns, prop. 37.5 grns
Spennymoor Ballistic Standard 1944 - bullet 174 grns, prop 36.5 grns
RG 1945 - bullet 174.5 grns, prop.36.75 grns
RG 1948 - bullet 177 grns, prop 37.0 grns
IVI 1985 - bullet 175 grns, prop 37.5 grns
(The ballistics of the IVI Mark 8z was arranged to be between the Mark 7 and Mark 8z suitable for the No.4 rifle with 300 yard battle sight).

I weighed & measured the COAL of a S/A "R1M3Z ~ A80" (which is Mk VII spec, including the filler-tipped 174 Gr bullet), & the "nny-85" ball round, heres the results for loaded, unfired rounds:
R1M3Z
Length = 3.0285"
Weight = 408.7 Gr.
Powder charge was 39.6 Gr of a stick powder similar in appearance to IMR 4895, but there’s no way to tell what exactly it was. The bullet was a FMJ FB 174 grain MKVII.

nhy-85 Mk8Z
Length = 3.053"
Weight = 405.5 Gr
Powder charge was 38.4 Gr of a stick powder similar in appearance to IMR 4895, but there’s no way to tell what exactly it was either. The bullet was a boat tailed 190 gr FMJ.

Now for the big surprise! The Prvi Partizan MkVIII(z) variant is slower than South African R1M3Z. It also has less recoil (big surprise there.)
Chronograph results.
R1M3Z 174Gr ball
Average = 2525
Low = 2497
High = 2592

Prvi Mk8Z 190 Gr ball BT
Average = 2359
Low = 2335
High = 2359
(All velocities instrumental @ 10' from a standard No4 Mk2 barrel).

The SA R1M3Z is about on the ball for weight. Military .303 weights are 174gr bullet, 195 gr case and about 35-40 gr prop. With 38gr prop and a 190 gr bullet it suggests the PPU has a case of about 177 gr.

For comparison purposes, case weights & thickness vary a lot so its misleading to just weigh a loaded round to see whats insde it:
empty (fired case) weights
S/A R1M3Z = 201.4 Gr
nny = 178.2 Gr
R-P commercial = 160.9gr
PPU = 173.3gr
HXP = 186.7
RG-50 = 185.7 Gr.
(This is actual British-made Mk VII ball, so I include it as a reference for weights.)

So all Mk8Z is not created equal at all!

Bullets can vary in weight, velocities likewise & several different propellants are used. The reason cited for the “Machine gun only” restriction was because of the combined effects of cordite erosion (amazing as there was no cordite in them) & boat tail bullet shape & construction. Not one cause, but a combination of things. Flame temperature, bullet construction & bullet shape all combining to have a negative & damaging effect. Where does that leave us today? There have been improvments in powders, better designs of bullets & so on. Can we make, or use something with the better performance of the “Long Range Mk VIII(z)” or are we stuck with the Mk VII including it’s flat base limitations?

Well whats a”regular, average, normal” Mk8(z)?
Using the widely varying components & velocities of the different versions of the round, somewhere between a 175gr & a 190 gr FMJ BT with a BC of between 0.470 0.485 & bullet doing somewhere between 2550FPS at the muzzle & 2359 FPS at 10 feet with somewhere below 42000PSI of chamber pressure.

Heres my suggestion. We not only can do a better MKVII(z) but we have been dong it for quite a while with a great deal of success & no horrible barrel damage.

How ?

Use the Hornady .311” 174 gr Matchking, or the similar Hornady #3131 .3150" 174 Gr FMJ-BT!

Propel it with 41.6 gr of IMR 4895 for 2450 FPS, or 43.0 gr of .IMR 4320, for 2470. None of these exceed the lower SAAMI pressures of 49,000 PSI. & The Sierra Match King’s BC of 0.499 & better construction will allow full upset for full obduration of the bore completely eliminating the blow by problems of the old Mk VIII bullets, while gaining the trajectory because of its better design & boat tailed shape. The lower flame temps of modern powders should help as well. In fact they have been doing just that at matches for years, we simply didn’t recognize it!

**”Neonite” is a nitrocellulose propellant, as referenced in both 1920's "Dictionary of Explosives" as well as the 1944 edition of the "Textbook of Ammunition".
Neonite loaded ammunition, both pistol and machinegun, is listed with the 'z' designation, the chopped cordite loads for pistol ammunition being clearly differentiated from it.

http://www.archive.org/stream/dictionaryofexpl00marsrich/dictionaryofexpl00marsrich_djvu.txt
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 303Guy Quote  Post ReplyReply Direct Link To This Post Posted: August 20 2013 at 12:57pm
That's interesting, thanks.  Have you come across the South African R2M2 head stamped ammunition?  Muzzle velocity of 780 m/s (2550 fps), a copper jacket, aluminium insert and I don't recall it being boat tail.  It was loaded with cordite - the cordite was ribbed longitudinally and hollow and it did wear my barrel!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: August 20 2013 at 10:09pm
Never found such a beast, sorry.
The only Cordite I've ever seen looked like dirty angel hair pasta, long thin solid sticks.

Incidentally there is now a controversy (surprise!) about how the charge was set up for standard Mk VII ball. One camp swears by a specific grain weight, the other says that, due to variations in manufacture each batch of Cordite was measured by length to get a specific performance & then that exact same length was the load used, weight varying a bit, but performance being standardized.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: August 25 2013 at 6:32am
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Prvi Mk8Z 190 Gr ball BT
Average = 2359
Low = 2335
High = 2359
(All velocities instrumental @ 10' from a standard No4 Mk2 barrel).
Ammunition matching that description was the subject of a warning years ago. The warning stated this ammo could spring the action of an SMLE and that it had shattered a No.4 bolt head.
 
I have some FN long range MG loads that have a very unusual bullet. The boatail portion is long and extreme the base is tiny in comparasion . The ogive looks sort of fat, it would fill out a throat with little slack.
 
As for why they restricted Mk8z ammo to the MG, they found that when the average No.4 rifle had been fired with as few as 200 rounds of MkVII ammo using cordite that the throat was burned out enough that the boat tail Mk8 bullets would keyhole.
 
Major E G B Reynolds ran tests to determine what was going on when due to disrupted supply lines the Tommy in the field often had to use delinked Mk8z ammo till sufficient supplies of MkVII could be obtained.
If used only with M8z or MkVIIz there was no keyholing problem.
Machine gun barrels were separately  marked for use with NC or Cordite ammo only.
 
Flame temperature of NC propellants is much lower than that of Cordite. Some will tell you different but that's because Cordite temperatures are usually listed in degrees Kelvin. Also Cordite can't be mixed with common flash suppressants, muzzle blasts from automatic weapons using cordite are more easily spotted and easy to tell apart from other weapons in battle.
The Germans once wiped out a company of central European ( Hungarian) Fascist conscripts they had armed with captured British weapons when German artillery observers saw the cordite flashes and mistook them for British troops.
Late in WW2 orders were cut to use Mk8z ammo in the BREN Gun during night operations.
 
 
For best results with boat tail bullets major diameter bore sizes must be close to bullet diameter. That's seldom the case with Lee Enfield barrels.
 
Chamber pressures for Mk8z in Copper Units is more like 48,000 CUP.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: August 26 2013 at 8:57pm
"Ammunition matching that description was the subject of a warning years ago. The warning stated this ammo could spring the action of an SMLE and that it had shattered a No.4 bolt head."
Do you have a link or more information on on that?
 
Was it a bad batch, or what, from everything I discovered this isnt a "hot" load at all. Its actually got les propellant than the 174 Gr round & seems to be withing SAAMI specs for ammo from reloading tables I've checked with! (Its not posssible to really tell though as we dont know the exact powder used.)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: August 27 2013 at 5:18am
Originally posted by Shamu Shamu wrote:

"Ammunition matching that description was the subject of a warning years ago. The warning stated this ammo could spring the action of an SMLE and that it had shattered a No.4 bolt head."
Do you have a link or more information on on that?
 
Was it a bad batch, or what, from everything I discovered this isnt a "hot" load at all. Its actually got les propellant than the 174 Gr round & seems to be withing SAAMI specs for ammo from reloading tables I've checked with! (Its not posssible to really tell though as we dont know the exact powder used.)
 
If the warning is still up its supposed to be in the Q&A section of the Gunwriters website, IIRC the site is based in Finnland, at least the majority of there subject matter deals with weapons used by Finnland. They have good detailed information on other military rifles as well, mostly those used in Finnland during wartime or post WW2 hunting and target rifles.
 
I'll see if I can find a link for you.
 
They said at the time the ammo might have been intended for use in Vickers or Maxim guns in northern climes and the warmer weather in Australia boosted the chamber pressures.
 
I also ran across an old warning on Privi .303 cases dating from when they first exported ammo to the U S A. The first batch had very soft cases that caused some problems.
This was in a list of ammunition recalls, I'd been looking for an old recall of Federal .30-30 ammo due to soft primer cups.
I've no doubt they ironed out all the bugs long ago, but the lighter cases you measured may not be up to snuff for warm reloads, if they are from an earlier batch.
Come to think of it the problems leading to the safety warning may have been due to the cases being too soft for the load rather than a hot load per se'.
 
PS
Main reason I remembered the warning is that some supposed experts adamantly denied that Privi ever loaded any .303 ammo with bullets heavier than 175 grains. Good to see that someone else has run across this extra heavy bullet ammunition.
 
 
Here's the article in full.
Quote
 
NOTES & COMMENTS OF VISITORS

he!!o Gunwriters,

Further to Yugoslav rifles and ammunition, a lot of Yugoslav ammunition was imported to Australia at one time, mainly .303 British, 8 x 57mm German, 7.62 x 39mm and .223 (5.56mm). (We used to have a huge number of .303 No.1 MkIII SMLE rifles here before our restrictive gun laws -- We still have a large number of them but you don't see them in public any more. There were several problems with this beautiful, shiny Yugoslav ammo:

The .303 British:

This ammunition was marked PPU or PPYU MKVIIZ & MKVIIIZ. It lived up to it's marking. (Late WWII British MKVIIIZ was a high powered round using nitrocellulose powder, not cordite and it was designed for machine gun use in Vickers and .303 Brownings, not rifles.) The Yugoslav projectile was heavier than a standard .303 British, 190 or 198 grains boat-tail (I think) instead of 174 grains and the powder load was VERY hot.

I think the problem may have been twofold, the powder was developed and tested in a cold climate, and my guess is the load was higher because it was originally intended for military export use and the probably wanted it to drive tired old .303 Browning Machineguns, Vickers and BRENs in their export markets in third world Africa.

In a .303 SMLE No1 MKIII it would stretch the action if used too often. It was OK in a good .303 No.4 action, but I have seen it blow an extractor out of a .303 No.4 which was a bit worn and loose.

The 7.92 x 57 mm ammo seemed OK, but most K98 actions are very strong anyway.

The .223 was a REAL problem, it was not made to standard US SAAMI specifications and it had an extremely hot load. It was OK in some bolt actions but it destroyed automatics. One problem was the primer cups were too brittle and they'd perforate when used in a Ruger Mini-14 or an M16. Bulged heads, split cases, loose primers and bulged barrels all happened. I have seen a full-auto 5.56 mm SMG disintegrate while using this ammo.

A problem which you probably wouldn't get too often where you are is that ammunition is very temperature dependant. In Australia if you leave ammunition in the sun on a hot day, breech pressures can go off the scale and accuracy will suffer markedly.

Similarly, ammunition designed for the tropics may not cycle a weapon in the arctic or may not ignite powder correctly under extreme cold, causing low powered rounds and short feeds, particularly in 9mm.


Anyway, that's all on Yugo ammo. Stay away from them. Their rifles are good. (Their Simonov variant, AK variants, their K 98s and their 'Dragunov') but stay away from their ammo, it's far, far too hot.

As for the Serbs releasing weapons, I think that's unlikely, unfortunately they're all far to busy using them on each other and with the promiscuous way they fire them there won't be an unworn barrel left in the area.

Truth is the 7.62mm Nagant is a very good long range sniping calibre with good ammunition. (Some of the old Soviet Bloc ammunition is terrible!)

I've done very good shooting with a Russian 7.62mm Nagant Sniper despite the terrible stock and single stage trigger. Mine was mint new condition and it had a lapped and air-gauged barrel courtesy of the Soviets.

If you reload with care and use .303 British projectiles (They're the perfect size, .311") it will shoot one MOA all day.

Regards,

Sherro. (Australia).




 
 
Seems the author developed a very low opinion of Yugoslavian manufacture ammunition.
From the content and the fact that this archive is for pre 1999 correspondence I suspect the author is speaking of a problem of early 90's or late 80's. Australia eased up on gun ownership restrictions in most jurisdictions long ago.
The article seems to have been written during the UN Bosnia intervention or slightly before. 
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Thats interesting. Funnily enough the case weights weren't what I was expecting when I started the project. My original intent was to work out what was really what by actual test instead of repeated 3rd or 4th hand info.
 
I remember some complaints about "soft rims deformimng" on .308 Prvi, mainly in fairly violent semi-auto guns though. But I don't recall anything about .303.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LE Owner Quote  Post ReplyReply Direct Link To This Post Posted: August 27 2013 at 6:14am
Originally posted by Shamu Shamu wrote:

Thats interesting. Funnily enough the case weights weren't what I was expecting when I started the project. My original intent was to work out what was really what by actual test instead of repeated 3rd or 4th hand info.
 
I remember some complaints about "soft rims deformimng" on .308 Prvi, mainly in fairly violent semi-auto guns though. But I don't recall anything about .303.
 
An FN FAL can tear the rim off a .308 case if the powder charge is a slow building double base charge. The Garand has problems with some loads that use heavy bullets and double base powders, mostly bent op rods.
 
With a heavy bullet and slow powder the gas port pressure peaks too soon, and the action tries to open before the bullet clears the muzzle and pressure drops in the case. The case wall grips the chamber wall like a tie rod end grips its tapered hole. The rims of Winchester .308 long range match loads were badly deformed by an FAL I used for awhile. To prevent bulged or split cases you had to turn the gas regulator down as far as it would go and still cycle.
 
Like as not since the defective Privi ammo came from Yugoslavia during its post Soviet break down they would not have sold off ammo that passed military QC inspections.
 
 
PS
Quote
Was it a bad batch, or what, from everything I discovered this isnt a "hot" load at all. Its actually got les propellant than the 174 Gr round & seems to be withing SAAMI specs for ammo from reloading tables I've checked with! (Its not posssible to really tell though as we dont know the exact powder used.)
Remember you are dealing with a much heavier bullet and unknown powder. Heavy bullet loads can be expected to have a lower muzzle velocity than the standard bullet weight loads even with less powder, and may generate higher pressures to get that velocity.
The load sounds fairly stout, few 7.62 Long range MG loads ever used a bullet of 190-196 gr. Some .308 long range target loads have used the Lapua 190 gr bullet. 220 gr .308 boat tail match bullets are available, but I've seen no tables or data for these.
 
Older .303 loads , up to MkVI, used bullets heavier than that, but at a much lower velocity.
 
If the cartridge uses a thick laquer or asphaltum neck sealant these can harden with age and cause increased pull strength with resulting higher chamber pressures.
 
A thick case neck wall can cause increased pull strength, and so can a fat ogive profile that crowds the origin of rifling. Both improve long range accuracy in an MG bore, but may cause problems in a rifle chamber. Build up of hardened carbon fouling in the chamber neck causes the same problem with standard rifle cartridges.
I made a scrapper out of brass tubing to clear away hardened fouling. It came away in thin streamers that resembled the material of old laquer based records. In fact degraded smokeless powders were recycled and used to make some of the old style records, as well as furniture finish and water proof wood glues.
That sort of fouling is extremely hard to get out, its tightly compressed and won't soak up solvents.
Hard to see as well since chamber pressure irons it onto the chamber neck walls and leaves a slick shiny surface.
 
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