Explosive Ordnance / GICHD_Ukraine_Guide_2022

[kz11gr]

Here

https://www.gichd.org/fileadmin/uploads/gichd/Publications/GICHD_Ukraine_Guide_2022_Second_Edition_web.pdf

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[AMMOTECHXT]

One thing I learned about the M557 fuze - I know it is old - there was a handling and movement constraint on it, NOT TO BE ROLLED IN EXCESS OF 6 MPH, AS IT MAY ARM. For anyone coming into contact with the M557 - please keep this in mind.

 

[Eggburt1969]

One thing I learned about the M557 fuze - I know it is old - there was a handling and movement constraint on it, NOT TO BE ROLLED IN EXCESS OF 6 MPH, AS IT MAY ARM. For anyone coming into contact with the M557 - please keep this in mind.

I find that very hard to believe, where did this fact come from?

The M557 is stated in technical reference data to require at least 32 g (≈314 m/s², ≈1,030 ft/s²) of linear (axial) acceleration initially, and then a spin (rotational) rate of at least 33 revs per second (RPS) to fully arm. Its minimum non-arm spin level stated to be 16 RPS.

A quick fact check...

1 mile = 63,360 inches
6 miles = 380,160 inches
M577 maximum diameter = ≈61.3 mm = ≈2.413 inches
M577 maximum radius = ≈192.6 mm = ≈7.583 inches

6 mph = 380,160 inches per hour = ≈106 inches per second (i.e. 380,160 / 60 / 60)

As the fuze has a diameter of ≈2.413 inches, to cover the ≈106 inches (per second) it would have to rotate ≈14 times per second (i.e. 106 / 2.413). As such it does not even reach the minimum non-arm level of 16 RPS at 6 mph.

Also simply rotating the M557 along the ground only provides the second arming criteria, spin, it does not provide the first, axial acceleration.

 

[AMMOTECHXT]

Thanks for your reply. The information was in A & ER Vol 3, Pam 41, the Part relating to inspection points spacific to a Nature. It would have been supplied by the CILSA / DLSA sponsor for that nature when it was first introduced into British Land Service and, since it was American, I presume the information must have been supplied by the Americans. That was the info available to British army ammunition technical staff in the 1970s and 1980s. I don't think it was in LUMAT - Limitations in the Use of Missiles and Ammunition at Training - as that was a publication first produced in the (mid?) 1980s. What was the technical reference available to you? A & ER did not include the type of information you provide in your post, otherwise we perhaps could have worked out that for ourselves. Perhaps the publication sponsor did not think the technicians would need such detail.

I presume the fourth point of your quick fact check relates to the circumference rather than the radius of the fuze and that you meant to state M557 rather than M577? If the figures you provide relate to the M557 then it is a shame we did not have that information as there would have been no need for a handling and movement constraint.

Granted that most fuzes in British service have for a long time needed at least two forces to be fully armed. In 1991 I was witness to a fire involving British WP ammunition. After an hour or so it became pretty spectacular, with items lobbed out and lazily spiralling back to earth, often with an explosion or detonation on impact. Those fuzed items also needed at least two forces to be fully armed. I know that 120 mm Tank and 81 mm Mortar rounds were involved although the cause of the fire was believed to be a No 80 Grenade with filling that had melted in the heat. Although cam nets had been indented for, weeks earlier, unfortunately they had not arrived by the time of the fire.

 

[Eggburt1969]

Thanks for your reply. The information was in A & ER Vol 3, Pam 41, the Part relating to inspection points spacific to a Nature. It would have been supplied by the CILSA / DLSA sponsor for that nature when it was first introduced into British Land Service and, since it was American, I presume the information must have been supplied by the Americans. That was the info available to British army ammunition technical staff in the 1970s and 1980s. I don't think it was in LUMAT - Limitations in the Use of Missiles and Ammunition at Training - as that was a publication first produced in the (mid?) 1980s. What was the technical reference available to you? A & ER did not include the type of information you provide in your post, otherwise we perhaps could have worked out that for ourselves. Perhaps the publication sponsor did not think the technicians would need such detail.

I presume the fourth point of your quick fact check relates to the circumference rather than the radius of the fuze and that you meant to state M557 rather than M577? If the figures you provide relate to the M557 then it is a shame we did not have that information as there would have been no need for a handling and movement constraint.

Granted that most fuzes in British service have for a long time needed at least two forces to be fully armed. In 1991 I was witness to a fire involving British WP ammunition. After an hour or so it became pretty spectacular, with items lobbed out and lazily spiralling back to earth, often with an explosion or detonation on impact. Those fuzed items also needed at least two forces to be fully armed. I know that 120 mm Tank and 81 mm Mortar rounds were involved although the cause of the fire was believed to be a No 80 Grenade with filling that had melted in the heat. Although cam nets had been indented for, weeks earlier, unfortunately they had not arrived by the time of the fire.

I'm going by US data in various official manuals and booklets.

Yeah, typos I can't correct now... they should have said.

M557 maximum diameter = ≈61.3 mm = ≈2.413 inches
M557 maximum circumference = ≈192.6 mm = ≈7.583 inches

Maybe they meant rolling of the projectiles at greater than 6 mph? Problem is, the larger the projectile the less it has to rotate (around its circumference) to cover the distance (106 inches in this case) in the time period. As such the projectile's rotational (spin) rate would be even lower: a 105 mm (≈4.13") only ≈8.2 RPS, and a 155 mm (≈6.10") only ≈5.6 RPS.

I don't really have access of a physical M557 to double check the internals to see where the set-back and rotational arming elements are. There might be an inert one in the office. I'll have a look on Wednesday.