Meplat dia vs BC

[RockyMtnMT]

I have been following the controversy regarding melting tips on tipped bullets. It brings to mind the question of how much difference does meplat dia. make when it comes to bc of a bullet. In our manufacturing we have been very conscious keeping the hollow pt as small as possible and still function in terminal performance, in order to keep bc as high as possible. From the manufacturing side, the smaller the hole the more problematic. Larger drills are much less susceptible to breaking. Larger holes initiate expansion at lower vel better.

So how much difference does 1mm, 2mm, 3mm hole size make? As bullet dia becomes bigger does it make less difference?

The good news is our bullets don't have tips so they can't melt. At this point in time we will continue to concentrate on 1mm hollow points.

Steve

 

[Beng]

Brian Litz published a formular to approximate the bc of G7 shaped projectiles in "Applied Ballistics for Long Range Hunting". You could use that formular as a starting point to quantify the impact of different meplat diameters. Maybe crossreference measured bcs against the calculation to check for accuracy.

 

[HammerB1]

We have no problem testing or coming up with a bc. The question is, how does the meplat dia affect bc? Is there a big difference between a 1mm and a 2mm meplat diameter? I would only assume the smaller the better bc?

 

[Darkker]

It doesn't make much difference.
Read Harold Vaughn, Rifle Accuracy Facts.

 

[Bravo 4]

Going off of memory but from past reading of accurateshooter.com/benchrest.com/6mmbr.com trimming the meplat will slightly reduce BC and bullet pointing gives a slight increase. Or have I been reading that all wrong?

 

[rcoody]

Going off of memory but from past reading of accurateshooter.com/benchrest.com/6mmbr.com trimming the meplat will slightly reduce BC and bullet pointing gives a slight increase. Or have I been reading that all wrong?

that is my conclusion from my reading. Is it worth it for you? You will have to decide.

trimming meplats and then pointing is the best of both worlds.

berger says don't mess with theirs. From what I have read they have the most consistent.

I slightly trim my hunting VLD's just to ensure they are open for proper expansion.

One thing is if you start messing with them then your ballistic app is going to be off. You have to establish what your real BC is and plug it in.

http://www.accurateshooter.com/gear-reviews/whidden-bullet-pointing-die/

 

[Beng]

The equation entered in a spreadsheet allows you to enter different values for meplat diameters and compare the results. The exponents of the different factors might tell you how important the individual factors are.

ps: The meplat diameter in calibers and not in absolute length is the factor, caliber does make a difference. Afair Litz used .30 cal and .224 cal as examples for the influence of meplat diameter against caliber in one of the books, I don't remember which.

 

[Deleted member 46119]

The equation entered in a spreadsheet allows you to enter different values for meplat diameters and compare the results. The exponents of the different factors might tell you how important the individual factors are.

ps: The meplat diameter in calibers and not in absolute length is the factor, caliber does make a difference. Afair Litz used .30 cal and .224 cal as examples for the influence of meplat diameter against caliber in one of the books, I don't remember which.

Any chance you could save and share the spreadsheet.

Biggest reason I ask: Not sure where by book is.

 

[Deleted member 46119]

It doesn't make much difference.
Read Harold Vaughn, Rifle Accuracy Facts.

Incase you have never considered this: Just because it's in a book does not make it correct.

Physics contradicts you statement. I can't speak to the book because I don't have it.

 

[Deleted member 46119]

that is my conclusion from my reading. Is it worth it for you? You will have to decide.

trimming meplats and then pointing is the best of both worlds.

berger says don't mess with theirs. From what I have read they have the most consistent.

I slightly trim my hunting VLD's just to ensure they are open for proper expansion.

One thing is if you start messing with them then your ballistic app is going to be off. You have to establish what your real BC is and plug it in.

Whidden Bullet Pointing Die within AccurateShooter.com

I am using the Whidden trimmer with the Hoover tipper. Works for me.

 

[Bravo 4]

I slightly trim my hunting VLD's just to ensure they are open for proper expansion.

Yep, or you might run into this and not realize it. This is worse case scenario, not good for expansion:

 

[elkaholic]

I do not have any EXACT data, but from my bullet making over the years, I can tell you that it is quite significant between a bullet with say a .060" meplat and a sharp point on the same bullet. If memory serves me, it was 10-15 points in a .308". Litzs' data should show what it actually is.......Rich

 

[Darkker]

1) Incase you have never considered this: Just because it's in a book does not make it correct.
2) Physics contradicts you statement. I can't speak to the book because I don't have it.

1 - Yes, Just because a former powder tech for General Dynamics(Emary) finally gets the toys everyone else has used, doesn't suddenly make him a genius with bullets either; even if he writes it down in a book.

2- No, not so much. This topic aside, you really should read his book; very good stuff!

Now lets run some calcs:
Horn-head loves to talk in the white paper about the 300 WM, Well lets use some over-loads.

Elevation - 850 feet
Air temp - 55 deg. F
Humidity - 35%
ICAO Std
Zero - 100 yards
Wind - 10mph
Angle - 90 deg
Baro - 29.92 "
Units in Mils
No spin drift / Coriolis
Muzzle Velocity - 3,100 fps

208gr "Melty"-max, Litz tested G7 of 0.324
100 - U-0, R 0.1 mil Vel - 2952.7
1,000 - U- 6.4, R1.5 Vel - 1796.9

212gr ELD-X. Hornady claimed G7 of 0.336
100 - U-0, R-0.1 Vel - 2957.8
1,000 - U- 6.3, R- 1.4 Vel - 1837.0



So what do we see? 0.1 mil difference, which if you talk to the PRS boys; 0.1 - 0.2 mils is typical gain from tipping bullets.
So what does this mean? Here is what I see.

There is no PRACTICAL difference for anyone EXCEPT the worlds greatest shooters. At 1,000 I argue that that tight is even repeatable for them. There is in fact a difference, just not anything practical. And Vaughn's work showed this already. The tip DOES affect the BC, but again, it isn't a significant amount compared to what the Ogive and Tail angle contribute. For a more recent example of this, look at the original 168gr SMK that tumbled at Camp Perry long ago. That had a CG/CP issue going against it, BUT it was the 13 deg. tail angle that did it in. That tail angle gave it a super-swinging-sexy BC. As Dr. McCoy's work showed, that ain't going to cut the mustard when it comes time to cross trans-sonic.

Now why there is no difference is where you can pick your poison:
Now is the tip ACTUALLY melting? I have NFC. But when using Litz's G7 number, which is the appropriate measurement of this type of bullet; we can conclude one of the following:
1 - It IS melting, but is irrelevant.
2 - it ISN'T melting, and is irrelevant.

My tinfoil-hat view is: Hornady quickly realized that their use of a single inflated G1, isn't appropriate. They noticed "something was wrong". Was it a melty tip? Don't know, but as we now know, it doesn't matter.
This whole Tip-Gate nonsense is a stab at who they now see as an easy target, Nosler. As Litz has shown many times, Nosler is the worst offender when it comes to inflating G1 numbers. They also have a highly sought-after Crap-U-Bond Long Range bullet. What better way to stick a knife in their side, and disguise the 30% price hike for a slight redesign?