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The 1952 Hall report “redux”   Small Arms <20mm

Started 4-Aug by EmericD; 1637 views.
EmericD

From: EmericD

4-Aug

With the realization that the NGSW program is simply the “light rifle program done right”, how long before the return of the Small Calibre High Velocity (SCHV) trend?

The “Hall report” or BRL-MR-593, clearly defines the objectives of the SCHV concept, i.e. increasing the “overall expected number of kills” by a factor 2.5 between 0 and 600 m, compared with the Garand M1 system firing the .30 M2 ammo.

This report could be found here :

https://apps.dtic.mil/sti/pdfs/AD0377335.pdf

This increase of the “expected number of kills” was achieved by combining 3 factors:

-           A better hit probability at all range due to more favourable exterior ballistic properties of the round,

-           A similar wounding capacity at short range, and a still good wounding capacity at long range,

-           A great increase of the number of round carried due to ammo & rifle weight reduction.

The weight of the system used as reference was 15.0 lbs (6.71 kg) and included the M1 rifle (9.6 lbs; 4.36 kg) and 96 rds of .30 M2 ball ammo (0.057 lbs without clip; 25.9 g per round).

Among the various .21”, .24”, .27” and .30” ammo studied in BRL-MR-593, the most promising one was the short range .21” (6/10th the M1 powder load, for 32 gr or 2.07 g of powder).

-           The hit probability was equivalent or better than the .30 M2 up to 650 yards and still >85% of the .30 M2 up to 1000 yards,

-           The terminal effectiveness was equivalent or better than the .30 M2 up to 400 yards and still >88% of the .30 M2 up to 1000 yards,

-           The ammo & rifle were light enough to carry 224 rounds of ammo instead of 96 (2.33 more).

This “.21 BR” (expected weight of 12.6 g per round) was supposed to launch a 52 gr bullet at a muzzle velocity of 3485 fps (1063 m/s; 1900 J of ME) from a 4.0 kg rifle.

The C6 value of 0.18 reported in BRL-MR-593 is not supported by both the shape factor of the M2 bullet and the results presented in the report, so after some crosschecking it was determined that a C7 of 0.142 was a much better value.

The terminal ballistics of those SCHV were investigated using a .220 Swift rifle using a 60 gr bullet launched at 3660 fps (1116 m/s; 2400 J of Muzzle Energy so this round was much more powerful than the proposed round) and positive results were achieved for impact velocities above 1800 fps.

As this report was one of the major step towards the acceptance of the M16 rifle and the M193 round, it could be interesting to evaluate the performance of current “Small Calibre, High Velocity” systems using the same methodology presented in the Hall report.

Hit probability in BRL-MR-593 was computed using the following hypothesis:

(1) A standard deviation of range estimation of 20% of the range to the target.

(2) A standard deviation of cross wind estimation of 3 miles per hour.

(3) A standard deviation of aiming and ballistic error of 0.6 mils for all ranges.

(4) A target 3-1/2 ft. high and 1 ft. vide.

Unfortunately, it seems that there is a mismatch between those hypothesis and the published hit probabilities.

Using the AB Analytics software and this set of hypothesis (and an extreme spread of 4 times the standard deviation for 2.4 mils or 8.25 MoA) produces a hit probability much lower than reported in BRL-MR-593 (for example 70% vs. 78% at 200 m; 36% vs. 51% at 300 m; 14% vs. 30% at 400 m).

Reducing the range standard deviation from 20% to 10% allowed to reproduce the hit probabilities found in the BRL-MR-593 report.

Terminal effectiveness needed a little more work, but using the mathematical model used by the US Army at this time gives good results:

P(I⁄H)= 1-e^[(-a(M.V^(3/2)-b))^n]

The coefficient “b” was based on the minimal ballistic combination needed to produce a severe wound and for simplicity was kept constant regardless of bullet diameter. The coefficients “a” and “n” were determined using the curves for the .30”; .27”; .24”; .21” found in BRL-MR-593, and also for a stable .14” bullet in order to keep coherent hypothesis.

            a          b          n

.30       0.357    0.125    0.631

.28       0.405    0.125    0.629

.27       0.433    0.125    0.624

.26       0.465    0.125    0.617

.25       0.499    0.125    0.608

.24       0.537    0.125    0.596

.22       0.621    0.125    0.565

.21       0.668    0.125    0.545

.20       0.717    0.125    0.524

.18       0.826    0.125    0.473

.17       0.885    0.125    0.444

.14       1.080    0.125    0.343

The .28”; .26”; .25”; .22”; .20”; .18” and .17” coefficients were interpolated from the previous results, and for the .18” diameter compared with data collected during the evaluation of 4.6x30 mm and 4.6x36 mm rounds, with very good agreement.

The 3 metrics used in BRL-MR-593 were:

  • Relative hit probability compared with the .30 M2 round,
  • Relative terminal effectiveness compared with the .30 M2 round,
  • Relative single shot effectiveness, defined by the product of the hit probability and the terminal effectiveness,
  • And finally the number of “stowed kills”, defined by the product of the relati
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  • Edited 04 August 2020 14:35  by  EmericD
autogun

From: autogun

4-Aug

Very interesting, Emeric. I look forward to the number-crunching fest!

QuintusO

From: QuintusO

4-Aug

I see you've caught up to where I was in 2015!

stancrist

From: stancrist

4-Aug

EmericD said:

Hum, that’s not a really good start for the 5.56 mm, as there is a significant gap between the hit probability of the proposed SCHV and its realization. Relative single shot effectiveness (figure 2) is not good either, and at range longer than 300 m the 5.56 mm is really dragging behind the .30 M2, delivering only 40-60% of its “single shot effectiveness”, when the envisioned .21” 6/10 was as good (or even better) as the “full power” .30” round.

Which is a good example of why I dislike using theoretical calculations instead of empirical testing.

In theory, theory and reality are the same.  In reality, they too often are not.

EmericD said:

But if the single-shot effectiveness of the 5.56 mm was far from what was planned, at least the M193 was as light as anticipated and a combat load of 224 rounds was a possibility… Unfortunately, this was also a failure, as the 20 rounds magazine and the very low cook-off limit of the M16A1 didn’t initially allowed such combat load.

You're kidding, right?  It was quite common for riflemen to carry combat loads of 300+ rounds in 20-rd mags.

Below:  US Army rifleman in Vietnam, with twenty-two loaded 20-rd magazines.  That's a total of 440 rounds!

Vietnam Equipment page 3

  • Edited 04 August 2020 12:59  by  stancrist
Farmplinker

From: Farmplinker

4-Aug

There's a commenter at the Commander Salamander blog who was happy when he got to Vietnam and his platoon sergeant told him, "Standard load out is 22 mags. We carry 27 in this platoon".

SCHVPapist

From: SCHVPapist

4-Aug

Out of curiosity, where are you getting the 600m figure from? Neither Hall nor Hitchman set 650yd/600m as their goal - Hall states 

"From this it might be concluded that a rifle that is more effective at ranges up to 500 yds. should be favored over one that is more effective at ranges greater than 500 yds."
 

and 

"Furthermore, if it were necessary for a soldier with the M-1 to carry the rounds required for the same expected number of kills at 500 yd, as a soldier with 15 lbs. of Cal. .21 6/10 charge rifle and ammunition, it would be necessary for him to carry 10 lbs. more ammunition or a total load of 25 lbs."

Would you mind sharing more of your methodology? I would be very eager to explore it at length - to be truthfully honest, the fact that your method grants more stowed kills to the M1 Carbine than the M16A1 at 300m immediately produces an immense amount of suspicion for your data - .30 Carbine is both heavier per round and has the ballistics of a lumpy potato. 

Lastly, I suggest you look into the 1965 SAWS 1 trial. The data and methods there may prove a useful line of further research for you.

QuintusO

From: QuintusO

4-Aug

the fact that your method grants more stowed kills to the M1 Carbine than the M16A1 at 300m

I'm getting suppression index flashbacks.

EmericD

From: EmericD

4-Aug

SCHVPapist said:

Would you mind sharing more of your methodology? I would be very eager to explore it at length - to be truthfully honest, the fact that your method grants more stowed kills to the M1 Carbine than the M16A1 at 300m immediately produces an immense amount of suspicion for your data - .30 Carbine is both heavier per round and has the ballistics of a lumpy potato. 

It's not "my" methodology, it's written in the report!

Due to the fact that wound ballistic data are lacking on the caliber .30 carbine, this gun was not shown in the curves of this report. However, estimates on the wound ballistics by the author show that at 300 yds. the single shot effectiveness is approximately one-half that of the standard M-1 rifle. This is due to the low muzzle velocity (1970 fps)* Since the carbine is quite light it would take 240 rounds to bring the total weight of gun and ammunition to 15 lbs. Therefore the overall effectiveness is high at very close ranges but falls off rapidly for increasing ranges so that it is the least effective for all the guns for ranges greater than 300 yds.

But to be fair, if I compute the results for the M1 carbine, I don't reach the "one half single shot effectiveness" written in the report (by a large factor). I've kept this 0.5 factor because that was their evaluation, and their comment was based on this evaluation.

Now, if you want to do the computation, it's pretty easy.

Use AB Analytics (or any other software that you want) to compute the hit probability of your favorite round using the hypothesis given above (you just need the MV and a BC), then use the bullet weight, diameter and impact velocity to compute the probability to inflict a severe wound (I'd put all the needed coefficients in the first post), and multiply the two to compute the "single shot effectiveness".

Then multiply this "single shot effectiveness" by the combat load to compute the "stowed kills".

Divide all those values by the respective value achieved with the .30 M2 to obtain the relative value.

EmericD

From: EmericD

4-Aug

You're kidding, right?  It was quite common for riflemen to carry combat loads of 300+ rounds in 20-rd mags.

Below:  US Army rifleman in Vietnam, with twenty-two loaded 20-rd magazines.  That's a total of 440 rounds!

Is that the combat load as "issued"? (or just something carried "because I could"?)

Carrying 440 rounds for a rifle with a cook-off limit of 120 rounds (full auto) or 140 rounds (semi-auto) seems to be a recipe for disaster...

EmericD

From: EmericD

4-Aug

SCHVPapist said:

Out of curiosity, where are you getting the 600m figure from? Neither Hall nor Hitchman set 650yd/600m as their goal - Hall states  "From this it might be concluded that a rifle that is more effective at ranges up to 500 yds. should be favored over one that is more effective at ranges greater than 500 yds."   and  "Furthermore, if it were necessary for a soldier with the M-1 to carry the rounds required for the same expected number of kills at 500 yd, as a soldier with 15 lbs. of Cal. .21 6/10 charge rifle and ammunition, it would be necessary for him to carry 10 lbs. more ammunition or a total load of 25 lbs."

Also in the same report:

An interesting comparison is made in the ability to penetrate 10 gauge (.137") cold r-.1-led sheet steel. The experimental Cal.e.220 round gave complete penetration at 500 yds. (or 1800 ft/sec velocity) and partial penetration at 600 yds. (or 1600 ft/sec). A Cal.*.30 Ball M1-2 round will completely penetrate the same 10 gauge steel at 625 yds. (or 1i00 ft/sec) and partially penetrate at 725 yds. If, however, the Cal. .22 was made with a 7.0 Cal. tangent ogive (so as to give it the same form factor as the Cal. .30), the range at which the velocity would drop below 1800 ft/sec would be 700 yds. or approximately equal to the Cal. .30. This is not unreasonable when it is considered that the value of MV4/ 3 /A, where M is the bullet mass, V the striking velocity, and A the maximum diametrical area, is practically the same at these velocities for both the Cal. .30 and .22.

Terminal ballistics up to 700 yards were at least one of their concern.

More globally, there are some indications that they wanted the same level of performance as the .30 M2, but in a lighter package.

As a sidenote (just to show the gap between the envisioned .21" calibre and the real stuff), during the NATO trial, the M193 used as reference was capable of defeating 50% of the time the 10 gauge plate at a distance of only 291 m (320 yards)...

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