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Mk7 Ballistic Coefficient

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BJ72 View Drop Down
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    Posted: November 07 2019 at 12:59am
I apologize if this has been answered before but I can't seem to find a verified answer anywhere. I've been trying to find some sort of documented reference to the ballistic coefficient of standard 303 British Mk7 ammunition i.e 174grain flat base FMJ bullet with filler in tip etc. I know it's pie in the sky stuff unless you happen to have a stash of MK7 ammo or projectiles, it's more of a general interest thing.

I've found a number of claims on the net that seem to range from around .400 up to high .400's which seems way too high by my estimation/guess. The Sierra 180g SP is rated at .411 when doing over 2000 ft/s. I would've assumed the MK7 bullet would be something similar.

Since I couldn't find an answer, I did some playing around with my ballistics program. I used the following parameters:

Velocity of 2440 feet/second
Sights 1 inch above center of bore
Elevation of +3 inches at 100 yards
Elevation of 0 at 200 yards
BC - Unknown

The three inches above point of aim at 100 yards comes from the Zeroing of rifles, Technical School of Training REME, which says the no1 mk3 should be sighted to have a mean point of impact of 3 inches directly above point of aim at 100 yards when sighted for 200 yard zero. I'm assuming that's correct, I found it on the net Shocked

There were no technical equations done on my part, I just kept altering the BC value in my ballistics program until the 0 - 200 yards trajectory matched the above values.

The result was a BC of approximately .375.

I printed off a MOA table using the BC of .375 and I found it indicated an increase of 41.75 MOA would be required to go from a 200 yard zero to a 900 yard zero. I then pulled out my Central No4 range site which has the side plate graduated for 303 Mk7 ammo. Counting the clicks I found it moved up 42 MOA when adjusted from the 200 yard to 900 yard mark. That value is extremely close to what I found using my ballistics program, 41.75 compared to 42 moa.

Am I on the right path here or am I missing something. Would the BC be very close to .375 rather then some of the quite high values sometimes quoted? Does anyone actually have a documented reference to what the BC was supposed to be?

Thanks in advance, I hope I haven't bored you with my ramblings. It's my first question to you guys and gals since I joined the forum. My head is still spinning from some of the knowledge I've gained since joining. Wacko
My idea of gun control is hitting what I aim at and nothing else.
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britrifles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: November 18 2019 at 7:31am
I've got the Mk 7 bullet BC somewhere, I'll need to look it up.  I think its a bit higher than .375.  I also have the trajectory tables for the Mk 7 ammunition in the No. 4 rifle which could be used to back out the BC; which I have done on my Strelok ballistics program. The Mk 7 bullet is quite long for it's mass, only the cylindrical part of the core is lead, the nose core is aluminum, so I expect it to be higher than the 180 Sierra.  
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: November 18 2019 at 9:29am
I've heard of 0.467~0.468 from several sources, but its highly contested as you will see from this old thread. It IS a long (comparatively) bullet because of the internal construction. PPU 180 Gr & Mk VII ball.

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 BJ72 Quote  Post ReplyReply Direct Link To This Post Posted: November 19 2019 at 1:52am
Thanks for the link to the old thread Shamu. Folks obviously tried to work it out before me but it looks like they couldn't settle on a clear answer. If you ever find that info britrifles please let us know. If only someone would give us a big bucket full of Mk7 bullets we could all head to the range and work it out for ourselves LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: November 19 2019 at 6:47pm
I checked my Strelok program and the value I had for the Mk 7 bullet is 0.467.  This matches what Shamu had.  The Strelok predicted trajectory at a muzzle velocity of 2440 fps comes within 5 inches at 1000 yards when compared to the Elevation sight settings in the Parker Hale Service Rifle Score Book.  So I believe this is a good number.  

The 174 gr SMK ballistic coefficient is 0.499 at 2200 fps and above.

A word of caution in using the PH5C sights, the bullet impact moves approx 1.2 inches per “MOA” on the elevation scale, and this is accounted for in the Parker Hale Score Book “rises between ranges” data.  The scale is not in true MOA.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote BJ72 Quote  Post ReplyReply Direct Link To This Post Posted: November 20 2019 at 1:40am
Thanks britfires. It's very interesting what you mentioned about the PH5C sights. I realized today I kinda already had the answer to my question. I have a copy of "Accurising & Shooting Lee-Enfields" by Skennerton and Labudda. I found it contains elevation tables for both MkVI and MkVII ammunition. The book contains two elevation tables for MKVII ammo which had me scratching my head. That's until I read your reply and looked a bit closer. I noticed one is specifically listed under the heading of "No. 9c Aperture sight". The other table appears to be a generic table for MkVII ammunition. There's a big difference between the two. For instance the table for the 9c aperture sight lists an increase in elevation to go from a 200 yard zero to 900 yards of just 36 moa. The generic table for MkVII lists a required increase of 43.5 moa for the same 200 yard  to 900 yard zero. Clearly it makes a big difference which brand and make of range sight you're using when it comes to published elevation tables. Of course this all relies on us using actual MKVII ammo. I have a fair stash but unfortunately some of it is like shooting a matchlock, Click..fizz................Bang. Unhappy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: November 20 2019 at 8:58am
That's because of the infamous "Enfield Inch", it wasn't exactly an inch of movement, nor a half inch, at the target, with the SMLE & No4 because the angular movement had been calculated form the longer-barrelled Martinis & Long Lees.
This is the No9 sight. There were several versions on the basic design.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: November 20 2019 at 8:58am
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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