Does anyone have SCATP-7.62?


#1

I’m trying to find a copy of SCATP-7.62, the Army’s ammunition ballistic acceptance test methods. All I can find are mentions of it, and sites requiring payment to get a copy. Does anyone have it in digital form?

This is a site where it is for sale: global.ihs.com/doc_detail.cfm?d … y=00093162
There also seems to be a SCATP-5.56

“4.4.4. Accuracy.
-The test shall be conducted in accordance with
SCATP-5.56, except that the Mean Radius shall be recorded to the nearest
one-tenth of an inch.”


#2

Through a good friend at an undisclosed location, I have received a PDF copy of SCATP-5.56. Still no SCATP-7.62, but he tells me it is very much the same except for details. (SCATP = Small Caliber Ammunition Test Procedures).


#3

In case you want to know how accuracy requirements differ, the answer is:

For 5.56 mm M855 at 600 yd a standard deviation of 7.0 in is required.

For 7.62 mm M80 at 600 yd a mean radius (!) of 7.5 in (linked ammo) and 5.0 in (loaded in clips) is required.

Standard deviation and mean radius are not the same. Also 5.56 mm are fired in 3 groups of 90 shots and 7.62 mm “the old way” in 9 groups of 10 shots, if my information is correct. Adjusting for this difference, one gets:

Requirements for 7.62 mm M80 at 600 yd are equivalent to 6.3 in (linked) and 4.2 in (in clips) standard deviation.

The current versions of specifications 46931 and 71208 are limited distribution documents, but I doubt above requirements were changed. The specification for .30 AP M2, which is also limited now, was erroneously unlimited for some time. It showed that bureaucratic rules for the testing were blown up to unprecedented dimensions, but nothing of consequence was changed.

Edit: Multiply the standard deviation by 3 to get a typical extreme spread for a 5 shot group.
Edit2: The requirements are upper limits for passing acceptance. A manufacturer will try to achieve (in my view) not more than 80 percent of these figures in normal production to avoid lots being rejected due to bad luck.


#4

All Match ammunition had the same accuracy specs but virtually all of it was much better than the max allowed. Also, Match ammunition was usually tested using the best barrels picked from all of the test barrels available. The first lots of 7.62mm Match M118, for example, had a 600 yard mean radius average of a remarkable 1.82 inches. The best of the Cal .30 Match M72 averaged 2.0 inches. Some Match ammunition was also judged by other methods, such as Figure of Merit groups.

Some of the last Ballistic Testing data sheets for 7.62mm Match indicate that the old mean radius measurements were replaced by AES (Average Extreme Spread) at 600 yards for 100 shots from an M14 Rifle. That would be a more meaningful measure for Match ammunition. The data sheets for one lot of M852 manufactured in 1989 indicate an extreme spread of 8.6 inches.

Later M118LR data sheets measured both Average Extreme Horizontal Spread (AEHS) and Average Extreme Vertical Spread (AEVS). One 2008 lot measured 6.7 and 6.8 inches at 1000 yards, proving the long range advantage of the 175 grain SMK bullet.

BTW, the specs shown by JPeelen are for link pack and carton/clip pack. The link pack is what is normally considered Machine Gun ammunition although much of it was a lot better than the 7.5" and 6.3" max allowed.

Ray


#5

What I am looking for is methodology. There are all sorts of methods for some indicator of shot dispersion. I think the Nayy’s acceptance method for accuracy has the most merit. They simply fire five 10-shot groups at 300 yards in each of two SCATP-compliant test barrels (100 shots total). Each group must have an average extreme spread of no more than 3.5", with no single group greater than 4.5" for lot acceptance. This is what they require for the MK 262, MK 316, MK 318, and MK 319 rounds. They feel very strongly that no other dispersion measurement method (mean radius, circular probable error, radial standard deviation, “figure of merit”, mean horizontal and vertical spreads, etc.) is nearly as practical as the simple extreme spread. And it seems to work well for them. Typical average Extreme Spreads for five 10-shot groups virtually never exceed 2.5" at 300 yards (and sometimes go under 2"), and only rarely does any single 10-shot group exceed 4". They have never had a single lot of MK 262 fail acceptance.


#6

Dennis

It looks like the Navy way is very similar to what LC uses for the 7.62mm M188LR. But, I wonder why they chose 300 yards as the test distance. That really doesn’t tell you much since it’s not hard to develop accurate loads at short range. 1 MOA at 300 is fairly common out of many good quality hunting rifles with some brands of factory ammunition.

Ray


#7

" But, I wonder why they chose 300 yards as the test distance."

The Navy’s tests have indicated that the 600 yard ES MOA dispersion is close enough to the 300 yard ES MOA dispersion to be negligible, so 300 yards as an acceptance distance is fine with them. Black Hills loads the MK 262 (AA53: 5.56MM SPECIAL BALL, LONG RANGE MK 262 MOD 1), using Sierra 77 gr bullets, and lot acceptance test firing is done at Sierra’s 300 yard indoor range. Despite the use of two different test barrels, my analyses have indicated there is no statistically significant difference in ES grouping performance between the two barrels. Incidentally, their muzzle velocity requirements are very tight. I think the maximum difference between the average MV of all five 10-shot groups to the average MV of any single 10-shot group can be no more than 15 ft/sec. That probably also helps grouping performance. Keep in mind that this ammo is made for SEALs and Marines to shoot human varmints, not paper targets. Their priority is high-level performance consistency under a wide range of conditions, not one-hole groups.


#8

Dennis

Interesting findings by the Navy. As a long time competition shooter, my experience, and that of most everyone I shoot with, is just the opposite. Group sizes do not increase proportionally with distance. Even going from 100 to 200 yards, and much more so as the distance increases. If only it were so.

But, if 300 yard groups satisfy the Navy requirements, that is what they should use.

BTW, competition shooters also strive for consistency under a wide range of conditions. One-hole groups make for good sea stories but not much else. I believe you are thinking of point-blank Benchrest shooters who usually shoot tiny dots. When the targets are moved to 200 yards and beyond, the dots are soon replaced by groups.

Ray


#9

I don’t think there are any 600 yard indoor ranges (at least in the US), and I have understood that Sierra’s is the only currently existing 300 yard indoor range. That’s also important if you are trying to eliminate wind as a factor in judging pure ammunition performance. Here is an interesting story about a 325 yard indoor range which used to be in Houston: angelfire.com/ma3/max357/houston.html

One important factor in achieving the best grouping performance is matching the overall cartridge length to the chamber to allow the optimum “Jump” of the bullet into the rifling. That’s not really possible for military applications, because military ammunition must work satisfactorily in many different weapons. The Navy did a lot of work to determine the best bullet profile for the MK 262 to minimize the relationship between bullet jump and grouping, and the 77 grain Sierra was the result. They originally wanted to use a “Very Low Drag” (VLD) bullet, but found that they were very sensitive to bullet jump. The other advancement was the development of a propellant which produces consistent ballistic performance which is largely immune to temperature changes over a wide range. I do not know what that propellant is.

In my personal experience with both Army and Navy ammunition development capabilities, I’ll choose the Navy every time.


#10

Gentlemen, I do not share your trust in the extreme spread. From the 10 shots, only 2 have an effect on the result. The data of the remaining 8 shots is effectively ignored. This introduces an element of chance into the ES sizes. Mean radius and standard deviation use the information from all shots.

If you shoot a large number of groups from the same ammunition lot (let the computer do it, because no private person has the resources), the ES sizes you find are spread over a very wide range. You get a lot of ES too small (considering the true dispersion in this ammo lot) and a lot of ES which are too large.

Mean radius and standard deviation values are much closer together, better reflecting the actual dispersion of the lot.

Based on ES, good lots will be rejected, and -much worse- bad lots have a greater chance to be accepted.

I think, those in the U.S. adopting the mean radius for acceptance tests more than a century ago, knew what they were doing.


#11

We are really getting far astray from cartridge collecting and possibly testing the patience of the Moderators. So, let me get this last comment of mine in real quick.

In truth, none of the methods are perfect. The ES measurement is dependent on two shots, and often, very dependent on a single shot. Mean radius gives more information but it’s the result of averaging and so it is possible for two groups with the same mean radius to vary considerably in ES.

What is missing from all measuring methods is the shape of the group. We are all familiar with the proverbial 4 and 1 or 9 and 1, the curse levied on all shooters. Only the human eye and brain can evaluate group shapes. To paraphrase JPeelen, we don’t want to reject good lots and/or accept bad lots, something that can happen when we rely strictly on the numbers.

JMHO

Ray


#12

“If you shoot a large number of groups from the same ammunition lot (let the computer do it, because no private person has the resources), the ES sizes you find are spread over a very wide range.”

I’ve done extensive computer grouping simulations. You can actually get very good consistency in extreme spreads by averaging the ESs measured from multiple groups if you use enough groups. The numbers of groups depends upon the number of shots per group. For example, the Navy’s practice of using 5 groups of 10 shots each will produce a mean ES with a standard deviation of approximately 5%. For two such 5 X 10 groups (which is actually what the Navy uses), the SD is somewhat lower than 5%. Regarding mean radius (MR), it is very closely related to ES if large numbers of shots are fired, and the relationship approaches MR = .25 X ES. For individual groups of small numbers of shots, the relationship between ES and MR can indeed be all over the place, the ratio typically being between 0.3 to 0.4 (or more). And I have substantiated these findings by actual test firing.

I have found that even single groups of 30 shots or more will produce very consistent values of ES and MR, also with very low SDs, typically 10% or less. And this information can very readily be translated into another measure, which I call the Mean Circle of Maximum Dispersion (MSMR), which can be determined fairly precisely with as few as 30 shots. The MSMR is the diameter of a circle which encompasses, theoretically, an infinite number of shots fired under identical conditions. Additionally, it has the benefit of allowing good estimates of the diameter which will contain various percentages of shots. An example is that for a large number of shots, 50% of them will be contained within a circle described by the MR. And as far as I am concerned, that’s about the only usefulness of the MR.

I have also discovered that the use of 3-shot groups is essentially worthless in understanding anything about grouping, as the average distribution of ESs of 3-shot groups is typically about 9:1 (least to most). Therefore, if you like using 3-shot groups, you’d better shoot lots of them and average the results. It’s actually statistically better to fire large numbers of 2-shot groups, e.g., 15 2-shot groups is will give more consistent results (lower SD) than 10 3-shot groups. I consider firing at least 5 groups of six shots (or perhaps six groups of 5 shots) to be about the minimum required to produce reliable grouping data. The NRA uses 5 groups of 5 shots for their accuracy evaluations, and that is also fairly efficient. If you want to depend on MR s a measurement, you cannot depend upon just measurements from one group, as it is far too variable between individual groups. You need to add together every distance between the shot and the group centroid for every group fired - not simply averaging the MR of each group.