Mk VII & Mk VIII (Z) ball ammo (long) |
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Shamu
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Posted: August 20 2013 at 6:25am |
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.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 |
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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303Guy
Senior Member Joined: July 10 2012 Location: Auckland Status: Offline Points: 495 |
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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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303Guy
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Shamu
Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 17603 |
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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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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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LE Owner
Senior Member Joined: December 04 2009 Status: Offline Points: 1047 |
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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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Shamu
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"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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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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LE Owner
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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.
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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Shamu
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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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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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LE Owner
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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
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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Canuck
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I just bought a box of 20 .303 INCH BALL MK8Z CDN made by IVI lot# IVI87H02.01A. After reading everything above I still have to ask if this ammunition is safe to shoot in any of my #4/#5 rifles? The vendor at the gun show mentioned this ammunition will have higher recoil so be prepared to feel a difference from regular ammunition.
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Castles made of sand slip into the sea.....eventually
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Online Points: 6539 |
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Interesting old post. I have some IVI Mk 8z and have shot it thru my Long Branch No. 4. I have the chrono results, I’ll dig that up and add to this post. IIRC, it did chrono around 2500 fps, but did not notice increased recoil. My own 174 gr Sierra MarchKing loads at the time were at a similar velocity.
I’m fairly certain that this ammo was loaded for the Canadian Ranger No. 4 rifles. Some others on the forum should know. |
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englishman_ca
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Correct, manufactured in Quebec for the Canadian Rangers' No.4 rifles. The brass is Boxer primed. Good stuff for reloading.
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. Look to your front, mark your target when it comes! |
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Canuck
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Thank you gentlemen!
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Castles made of sand slip into the sea.....eventually
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infantry919
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i bought
500 RDS WWII BRITISH VICKERS MG .303 AMMO ON BELTS, can i fire this through my British 1955 Enfield rifle. |
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Online Points: 6539 |
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Officially, it was only allowed “in emergency” situations. The Mk 8 loads were slightly higher pressure than Mk 7. I don’t think Cordite was used, what is the headstamp on the case head?
I’d put it away for collecting.
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The Armourer
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Goosic
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You have a very desirable weapon there with the 1955 made No4Mk2 infantry919. This is my opinion and mine alone. As The Armourer has shown you, the accuracy will be outstanding, right up to moment the barrel has lost all of its integrity. You might have spent a good sum of money on the ammunition but, you would be better off displaying the ammunition still on the belts as britrifles suggested. Was your rifle still mummy wrapped when you purchased it? If not, ask yourself the question. How many rounds of ammunition have been through it from its previous caretakers until you acquired it? The given or projected barrel life is ten thousand rounds for the MG but is also a standard for the No4 rifles. 500 rounds seem like such a small number is comparison to 10,000 does it not? That leaves you with 9500 rounds of whatever standardized 303B ammunition you have chosen, if in fact the rifle has never been used until you came into possession of it. Here the rub. One of those previous caretakers could have been a competitive rifleman with the CMP as an example. That person could very easily go through 200 rounds in one week of shooting. If he or she managed 200 round a week for one year, it has just had 10,400 rounds through it before you even had a chance to fire it. If the above scenario was true then, your rifle is already over the suggested barrel life and would be deemed unsafe from an armourers or gunsmith perspective. If on the otherhand your rifle was unfired,(minus the initial test firing from the factory,) when you recieved it and your are a casual shooter who will maybe see a chance of getting less than 500 rounds down range in a six month period, then maybe treat yourself to one belt. Just like a good sipping whisky, keep it in moderations.
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