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Author Topic: Meplats  (Read 380 times)

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Offline G Dog

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Meplats
« on: August 03, 2018, 02:51:17 PM »
First, how to determine the meplat? Is it a percentage relative to the widest diameter of the bullet proper or is it a percentage of the base of the ogive?



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Offline Omnivore

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Re: Meplats
« Reply #1 on: August 03, 2018, 04:38:15 PM »
Hi G Dog;

Do you mean, "how do you determine the ideal meplat for theoretical best accuracy?"  The literal answer to your literal question is, "you measure it with calipers".  Otherwise I have no idea, but I was once told by Rodwha that it was a percentage of the bullet's major diameter.

I’ve concerned myself more with length-for-weight because powder capacity has been the issue for hunting bullets (kinetic energy), and therefore a very wide meplat is called for (the Accurate molds 45-225L or 45-200S being two cases in point) for that reason and also because, all else being equal, a wide meplat inflicts more trauma to the target.

Also, the wadcutter bullet has been a long-standing “match/target” bullet, and they have a meplat equal to the bullet's major diameter.  If a wide meplat were an accuracy destroyer then I don’t believe the wadcutter would ever have been a popular target competition bullet.

To contrast the above point, I’ve also heard that the issue of having a overly wide meplat doesn’t begin to manifest itself until shooting distances exceed the 50 yard mark or thereabouts, and so it would be important to first determine the use of the bullet, assuming any of this is a real issue.

That's all just heresay and circumstantial though.  For one thing you cannot change meplat diameter without changing either the bullet's length or its weight, or its center of gravity, or all three, so it is impossible to isolate meplat diameter from those other, possibly accuracy-changing, factors. (It'll also alter the drag coeficient and have possible large effects on sonic speed-transition buffeting).

Does anyone have empirical evidence relevant to this question?
« Last Edit: August 03, 2018, 04:49:01 PM by Omnivore »
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Offline AntiqueSledMan

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Re: Meplats
« Reply #2 on: August 04, 2018, 04:32:24 AM »
Hello G Dog,

Copied from the Mountain Mold's page,

Meplat  refers to the flat nose (and for now, flat noses are the only kind I make).   It is expressed as a percentage of bullet diameter.   For example, a 0.300" meplat on a 0.432" bullet would be 70%.   A 70% meplat is similar to what some call a "Long Flat Nose" except now you can make the nose as long or as short as you like.   An 80% meplat is similar to what some call a "Wide Flat Nose".   Bigger meplats punch bigger holes in the target, but may not feed in some guns and may be more difficult to stabilize, just depending on the gun and the load and the range.   Smaller meplats are more likely to be accurate but are less effective on game.   A 70% meplat is a great compromise, usually accurate yet adequate on game.


Hope this helps, AntiqueSledMan.

Offline rodwha

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Re: Meplats
« Reply #3 on: August 04, 2018, 03:41:46 PM »
Here’s a link to something enlightening on wide meplats:

https://www.ballisticstudies.com/Knowledgebase/The+Effects+Of+The+Meplat+On+Terminal+Ballistics.html

As to the percentage of meplat to caliber, my understanding is that something around 78% was found to be as large as one wanted to go for longer range (~100 yds+?) shooting as it can become unstable in flight, but also unstable in penetration where it can be seen to veer off at an angle.

I’ve sent some bullets I designed before I read of this that measure about 83% and a fellow who competes with these was interested in seeing how they do at 50 yds. Unfortunately he lives in Alaska and has very limited time with the weather on top of his schedule so I’m waiting to hear how they chronograph (he uses the same type of guns and powders) as I weighed my more accurate charges for my NMA (~33 grns 3F Olde E) and ROA (~38 grns 3F Olde E). I’m no pistolero so 50 yds would be quite the stretch for me even if I placed my pistol and myself in a vice!

However another fellow who is friends with the man who runs LBT bullets claims meplats over 78% are quite effective and he designs them into his bullets. Not sure if velocity is the key or range, or what for the discrepancy.

As expansion cannot be counted on a wide meplat for hunting, much like Omnivore pointed out, is of importance were one to want these to hunt with. They should create a larger than caliber permanent wound track whereas a ball seems to create slightly smaller than caliber holes. And of course there’s the greater mass for better penetration, especially if bone is struck. Also as a bullet has greater width driving bands, along with the additional weight/mass, these increase the pressures which in turn creates a greater velocity. Omnivore has seen in one instance that the same powder charge pushed a 180 (IIRC) bullet faster than a ball.

« Last Edit: August 04, 2018, 03:46:32 PM by rodwha »
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Offline rodwha

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Re: Meplats
« Reply #4 on: August 04, 2018, 08:49:00 PM »
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Offline Omnivore

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Re: Meplats
« Reply #5 on: August 21, 2018, 04:11:33 PM »
The Accurate Molds 45-200S and 45-225L that I use both have a 78% meplat (meplat diameter is 78% of bullet's major diameter) but of course they're different bullets with different ogive radii and different lengths and weights.  Also, of course, they may be fired from the "same model" gun but with radically different rifling twists (~16" to ~30"), radically different barrel diameters (about 2", to about 18" for the Remington Carbine) and at radically different velocities using different powders with different pressure curves, and with different amounts of different lubes, or wads, etc.

Those two bullets both shoot quite well at 30 yards, and marginally OK at 50 yards, and are essentially worthless at 100 yards with the loads I've tried so far.  BUT they'll knock the snot out of our Northwest White Tailed Deer within the accuracy range.

Also; the issue of expansion has been altered since I've been experimenting with hollopoint bullets in percussion revolvers.  You now know how to use a "normal" or relatively narrow meplat hollopoint bullet, and possibly (who really knows?) have the best of all features.

I have that other mold, which was made for the 45 ACP or Colt cartridge and received the hollowpointmold.com inset bar conversion.  It has a quite small meplat but thus hollowpointed, and "heeled", and driven with maximum charges from the Colt Walker or 18" Remington Carbine it will expand up to the point of marginal fragmentation in water jugs.

And again; a wide meplat means a shorter-for-weight (compact) bullet leaving more room for powder.  Narrow meplat with a correspondingly long nose means a long-for-weight bullet leaving less room for powder.  So what are our goals here and are we nit-picking on one issue of relative unimportance when there are other considerations which might be more important?

Also; in regard to accuracy, it must be stressed again that one of the all-time most popular match/target bullets for a revolver is the wadcutter, having a 100% meplat.
But whoso looketh into the perfect law of liberty, and continueth therein, he being not a forgetful hearer, but a doer of the work, this man shall be blessed in his deed.   James 1:25 (KJV)

So speak ye, and so do, as they that shall be judged by the law of liberty.   James 2:12. (KJV)