Question rearding T104E1


#1

The T104E2 was the early designation of the 7.62 NATO M59 boattailed bullet.
The T104E1 was flat based and weighed only 140 gr.

In the Royal Armouries at Leeds I found firing table information for both. This would be most interesting for the old question of the real effect of a boattail on bullet drag PROVIDED the T104E1 has the same ogive radius as the T104E2.

Does anyone know the ogive radius of the T104E1 from a reliable source?


#2

No, the T11 bullet loaded in the T104E1 had a 7-caliber tangent ogive, while the M59/T104E2 had a 10-caliber secant ogive.

One can see the difference here. More info here and here.

Please do post the firing tables, though!


#3

Yes, I would also like to see the tables.

Even if the two bullets had the same ogive, the ballistic tables would be more of a reflection of the Ballistic Coefficient (BC), rather than simply the boattail vs flat base. Factors other than BT and FB could affect the BC more so than the shape of the base.

Ray


#4

Tau, thanks a lot for the prompt response to the point and especially the first link with the photo. Really great (Ray Meketa) photo! Pity that T11 has only the run of the mill 7 calibre ogive.

Ray, I know that ballistic coefficients would be different. :-) But if base shape were the only difference, the effect of different weights could easily be stripped from the data. Reliable data that allows to see the real effect of boattails is very, very rare. Nobody doubts the effects of boattails at very long ranges, especially at subsonic speeds. But what about rifle shooting at 600 to 800 meters (or yards)? I am willing to clutch on any straw for data. That triggered my question.

I have to retype the firing tables from my notes to be able to post them. Will do it one of the next days. Being BC fans, you will be pleased to see the BC changing with range. G6 for T104E1 and G7 for T104E2.


#5

Here are the firing tables:
column 1 distance (muzzle to 2000 yards)
column 2 and 3: T104E1 ballistic coefficient (G6) and velocity
column 4 and 5: T104E2 ballistic coefficient (G7) and velocity
Data based on the US Standard Metro atmosphere (not ICAO)

yd C6_ fps C7 _fps
0000 0.194 2846 0.208 2837
0100 0.194 2588 0.208 2617
0200 0.194 2332 0.208 2407
0300 0.195 2087 0.209 2208
0400 0.197 1857 0.210 2022
0500 0.198 1640 0.210 1842
0600 0.199 1441 0.210 1670
0700 0.195 1230 0.210 1505
0800 0.191 1071 0.210 1347
0900 0.187 0977 0.210 1200
1000 0.182 0892 0.210 1077
1200 0.176 0757 0.207 0973
1400 0.171 0635 0.204 0894
1600 0.166 0526 0.200 0821
1800 0.161 0424 0.196 0753
2000 0.156 0335 0.192 0686

There is no additional data on the sheets (originator, date etc.). The sheets are from an envelope that contains eexchange of letters between Frankford Arsenal and the Office of Chief of Ordnance.


#6

I thought the effect of having a boattail on a bullet was fairly well understood. It will reduce base drag at all speeds, but base drag becomes a much higher percentage of the complete drag model at subsonic speeds.

I’ve got that right, haven’t I?


#7

Here’s a good paper on the subject.


#8

Tau,
first, thank you for the link to the paper on the subject.
I neatly illustrates the problem as I see it: a lot of words and no factual data. Nobody doubts that boattails do reduce drag significantly in the transonic and subsonic regions. But the days of long range machine gun fire are long gone.

Nevertheless, 7.62 NATO and 5.56 NATO have boattail bullets. Practically every Match bullet (sole exception Lapua G490) has a boattail. So I would like to know (preferably in reliable numbers) what the real world advantage of these bullet shapes compared to flat base is at typical rifle distances, which are supersonic to the target. We simply do not have such data as far as I now. My provocative statement has been that Match bullets only have a boattail because it looks so much cooler than a flat base.

As I wrote, currently the only reliable source are G7 and G8 drag models, which are based on the same bullet projectile shape with/without boattail. But these were obtained with 76 mm projectiles (at Shoeburyness) and 40 mm projectiles (at Woolwich). We know from experiments that differences in drag of 10 percent between an artillery projectile and its scale model in 12.7 mm do occur. The difference between G7 and G8 is of the same order, so we cannot be sure that G7/G8 reflect the real difference for rifle projectiles. This is why I am trying erverything to lay my hand on any data that can shed light on this question.

A word regarding “at all speeds”: G7/G8 show clearly that above Mach 2.9 drag is identical up to about Mach 4, where the boattailed again has an extremely small advantage. But these are speeds well above rifle velocities.

This is one disadvantage of seeing ballistics from the BC viewpoint: subtleties of air drag are totally submerged in the fixation on BC.


#9

There are a lot of old myths regarding boattailed bullets that are being laid to rest. One that I’m personally familiar with concerns Match bullets. Conventional thinking used to tell us that BT bullets were only needed at long distances and that they should not be used at the shorter distances because they are not as accurate as FB bullets. It was only a few years ago that Benchrest shooters started to ignore this thinking and results from actual competition have proven the conventional wisdom wrong. Many world class Benchrest shooters now use BT bullets at the point-blank yardages (100 & 200 yds) and FB bullets at the mid and long range distances (600 & 1000 yds). I have done both. Several years ago I shot a world record group at 600 yards using a 6PPC and a 68 grain FB bullet. Everyone back then said it could not be done but my target (and others) proved them wrong. My best shooting buddy shot a PPC with 65 grain FB bullets in an F-Class match at 800 yards and cleaned the target. He was still centered at 1000 yards although the holes started becoming oval shaped. With a bigger case and more velocity, even they probably would have rounded out.

Never say “never”, and always avoid the word “always”.

Just sayin’.

Ray


#10

Speedy Gonzalez, a mentor of mine, mostly uses FB bullets in his .223 and 6mm PPC guns. I’ve got a few bullets I made on his press somewhere around here…


#11

Yeah, I know Speedy, I used to shoot with him back in the 90s in Texas, New Mexico, and Arizona. He’s old school. (That’s good) I still have some of his old wildcat cartridges from the old days.

I didn’t mean to imply that all Benchrest shooters buck convention. Some do and have had good results. There are other myths that have been exposed in recent years, not just bullets. Most Benchrest shooters are like most other competitors - they get stuck in a routine and have a hard time changing anything in fear that they will get their butts kicked. OTOH, world class shooters have nothing to prove because they’ve been there and done that. They are the ones not afraid to try new stuff. Or, like me. What did I have to lose? I can’t finish any lower than last. ;-)

Ray


#12

Oh, I was just providing supporting evidence for what you were saying Ray.

Speedy knows everybody in the industry, it seems. I was very lucky to study under him (though not so lucky as others who got one or two years full time with him).