A meplat is either the frontal flat surface of a flat nosed slug, or the frontal area of a hollowpoint slug after it has expanded. Hollowpoints seek to create the biggest meplats of them all when they don't fragment (soft lead isn't prone to fragment) exposing and maintaining a large frontal face.
Those BuffaloBore guys know their stuff, and judging from their firearm ammo offerings, they subcscribe to the exact same philosophy on meplats that I lean towards.
Though their application of the same philosophy is very different, as they are using it to evaluate the slugs performance in FIREARMS. With airguns the same DV principles hold true, though we have the added factors of our use of soft lead, and lower velocities to consider, and contend with.
Their handgun hunting loads all appear to be using the same killing power formula that I also feel is proving to be very accurate, and they score right where the originator of the DV (Displacement Velocity) Formula recommends they should for best performance on big game animals (around 105-130). His name is Veral Smith, and he came up with the formula after killing around 800 North American big game animals, about half of those with revolvers using all sorts of different bullet designs, and also bases it on the hundreds of reports he receives on the performance of his cast bullet designs.
To tell you the truth, Veral Smith, the originator of the meplat/velocity based DV Formula that I refer to so much, and also owner of Lead Bullet Technologies (LBT) also invented the exact bullet on almost (save one or two) every single cast bullet the above linked BuffaloBore.com offers for big game hunting, and those slugs are loaded to velocities in accordance with his recommendations. All the LBT/LFN/WFN ones.
The formula is meplat size times velocity divided by 4, and the resulting number best for North American big game is around 105-125. Airguns have a hard time getting there or even close but they can and have done it.
There are obvious factors to be considered when comparing the performance of a slug in airguns as opposed to it's performance in firearms. The firearms guys can lose performance with excessive velocity and/or meplat size in both accuracy and killing power, as there is a fine line between optimum killing power, and "to much destruction").
They are taking shots on game with firearms at much longer distances than the distance most of my shots on game will be with an air rifle. There are several other examples of the differences between them that I won't go into here.
It states in Buffalobore's article, that very large meplats CAN(read "not necessarily") reduce accuracy at short range: short range is generally accepted in firearms terms to be about 50-100 yards. The benefits of the LFN are both 1)achieve higher accuracy than the larger meplat WFN design out past 50-100 yards, and 2)to reduce excessive killing power in very hot loads.
Unlike firearms, for a bigbore airgun excellent accuracy at 50 yards is a plenty good-enough test for a hunting load, as that is towards the long-end of my "extended bow range" (as people often call it) for hunting.
Airguns don't have the velocity to spare that many firearms do to tailor the DV. They struggle to obtain the velocity necessary to make a slug effective as it is, so reducing the velocity is detrimental.
To increase the DV of an airgun slug, the only options are 1)higher velocity with a certain size of meplat, or 2)a bigger meplat at any given velocity.
With a firearm you can tailor the DV of the slug by reducing/increasing velocity, or meplat size to avoid any overkill effect on game, and maintain accuracy.
Considering a big game airgun used to hunt within around a 50-65 yard maximum, should a WFN be as accurate as a LFN within 50 yards, the larger meplat of the WFN is the better slug for hunting.
Thus far, I have noticed big differences at airgun velocities between the terminal affects of a .32 meplat (a pretty decent sized meplat, about what a LFN is in .45) and a .36 meplat (BIG meplat, about what a .45 WFN meplat measures). Especially when comparing them to very small meplats such as the MaxiBall.
Testing done on a fresh goat carcass to determine wound channel and likleiness to produce a blood trail (best test I have found to date) showed the big .36 meplat to perform noticeably better than the still acceptable .32.
The tiny meplat of the MaxiBall penciled thru the game, enabling the entry and exit wounds to close up on themselves. It was determined the .36 meplat made for a much higher probability of a bloodtrail, as the holes were larger and cleaner. In this particular test gun (300+fpe) with these two slug designs, the accuracy advantage of the .32 meplat slug was determined to be enough of a factor to continue using it in lieu of the .36 meplat.
This is why I replied to the question above, that I wanted the biggest meplats that can be shot accurately for hunting big game. If I want to shoot paper or silhouettes at longer ranges I would just load the most accurate slug at long ranges and disregard meplat altogether. Meplat won't serve much purpose when doing that type of shooting other than possibly reducing any risk of ricochet, and punching very neat, easily measured holes in paper.
Airguns are also dealing with very low velocities with the same wight projectile when compared to the centerfire rifles. It seems more difficult to drastically deform the lead of a flat nosed slug/round nose slug at these low velocities we see. If it isn't a HP design, and doesn't hit heavy bone (I don't aim for heavy bone save a hog skull), it may be less likely to change course to the degree a slug going 1250-1350fps would.....who knows?
if you can get a .457 260grain WFN (the meplat of the WFN profile is caliber minus.09......45-.09=.36 Meplat) to shoot accurately at 900-950fps you have a very respectable DV of about 80 or 85. That's solidly in the territory of the original .45Colt round.
With the modded 2tube 909 I have, I struggle to achieve a DV of 60-70 using 205grain slugs that are a little lighter than I'd like to consider of a standard weight for "all" big game, but big enough for any deer within 50 yards if I get my heart/lung shot. I expect them to run some.
This is what Veral has to say about the DV scoring....
"My displacement velocity formula is: Velocity times meplat width in thousandths of an inch divided by 4. Ideal DV range for big game is 100 to 125, 130 at the very max for fastest kills. At 100, wound diameter will average about 1 inch, at 125 it will be around 1 1/4 inch. If the wound diameter is 1 1/2 inch or larger in diameter the animal will normally run like it's tail is afire for 50 to 150 yards before expiring, though the shot is centered in the vitals. Yes even with a 4 inch diameter exit wound on a deer. Many will drop instantly with large wounds, if nerve shock anchors them, but many will run violently because blood flow is slowed by too large a wound.
If wound diameter is 3/4 inch, about 85 DV, kills can be instant if well placed but some run can be expected. With a 70 DV, wounds will be about 1/2 to 5/8 inch. VERY deadly if well placed in the vitals, but some run is quite certain." Veral Smith
I want to add to this an explanation of why to high a DV score lowers killing power: This brings into play the principles of the bodies clotting reaction in response to wounding.
When suffering a slice from a razorblade, there is profuse and constant bleeding, as the body considers keeping the wound clean, and free of infection the top priority.
When a large portion of a limb is damaged by, say, a shark attack, the body shuts down blood circulation to that area. In this case, the body clearly knows that blood loss at that scale is the immediate threat to life.
The DV principle sees the best way of achieving a large permanent wound channel is to score about 105-125 which is the "sweet spot" or "fine line" that enables the permanent wound channel to bleed profusely without clotting.
Wound channels much larger than this will activate what are called "platelets" in the bodies system, which are the blood clotting agents. So the reasoning is that any part of the wound that is too large is risking the activation of these platelets.
Flat nose slugs penetrate very well while maintaining a straight path (stability), producing long consistent wound channels that make a nice leak going both directions fairly quickly, and they do so very reliably.
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