Miniature Practice Bombs & Spotting Charges (formerly "A big cartridge & other Navy things"

Thisis something I got from my Dad, (WWII Navy), and it is way outside of my area of interest, (since I was a Ground Pounding, Mud Puppy, LRP). It looks like there was never a [non-threaded] primer installed, it is steel [magnetic] 8 7/8" long, 2 7/16" across the rim, 1 3/4" dia mouth.

And then there are these. Not quite “cartridges”, but odd Navy Things.
Aluminum, (or at least non-magnetic), 2.45 pounds, 8 1/8" long, 2" wide on the front end. The opening is slightly recessed in front, .937" dia., and .850" dia. between the fins, no threads.
There are raised numbers on them:
170133-B-1 with a small “U(anchor)S” just above the ‘B-1’

The recesses at the top are 1.5" dai., roughly .6" deep, with these marks in one recess on each:


Top item appears to me to be a shortened 40mm MK III L60 Bofors case cut off below the shoulder. Normal L60 case length is 311mm.

Primer would be pressed in.

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Is this a clearing cartridge?

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Since it appears to be a ‘virgin’ casing showing no sign of having been loaded, much less fired…

Pete: Why would the shell have been cut down?

EOD: Would a “clearing cartridge” be something used simply to make sure the bore was clear of debris?

Jack, “clearing cartridges” or “clearing charges” are used to shoot out stuck projectiles.
Means when a cartridge had a missing propellant load and fired the projectile into the rifling just with it’s primer and or priming charge the projectile has to be removed somehow.
Then a shortened case is used (to avoid obstruction by the projectile base when inserting it) and the stuck projectile is “cleared”.

Most common ones I noticed to exist were for the 20x110RR Oerlikon.
Maybe because when a primer failed the whole cartridge got rammed and the projectile may have been pused into the rifling (as per the API breech system). Upon extraction then the case came loose and the projectile remained and had to be cleared.
So my my thought. Maybe some 20mm Oerlikon operators can tell?

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Is it possible that the two “odd Navy things” are minesweeper floats?

The two objects are practice bombs which were made in several different configurations to match specific size bombs. Material used may vary with Mark/Mod or maybe just reflecting wartime substitutions with less critical material.
A spotting cartridge (shotshell marker type) was inserted in the nose to prove flash/smoke on impact.

The 40mm case Mark 3 is a short version which I believe was used exclusively for blank/saluting charges.

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The Mk. 3 case started as a regular length case but was cutdown to be used as a blank in saluting cannons. They are still in service and used with cartridges converted/loaded in 1997-98 by Milan Army Ammunition Plant (from WW2 cases).

What I would really like to see is a 105 mm clearing cartridge for the AC-130E/H/U guns.



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John, thank you for that, I have been looking at that recess in the nose for years, with no inkling of usage, thinking they look like a bomb, but were too small.
Since these are so light, what type of bomb would they represent, and at what timeframe? The only thing I can imagine is them being dropped from a biplane.

Any idea what type of “spotting cartridge” would have been used?
A 10 ga. shotshell is too small, as the rim slips cleanly into the opening until it reachs the shoulder at appx. 1.589".
The 10 ga. rim is .922" diameter, and the openings are .933"~.937" diameter.

Jack, these were used much later. At least in WW2 and I think after.

The basic model was the Mk 19 if I recall it right.
And there is a few modifications over the years. Several differences in the fin sections.

Thanks for the proper direction to search, you guys are the best!

"a. Description. Miniature practice bombs (MPB) MK5 Mods 2 and 3 (figs . 2—55 and 2—56, and table 2—46), the MPB AN—MK23 Mod 1, and MP B MK43 Mod 1 are similar in physical appearance, but differ basically in the metal used to cast the body. Bomb MK5 1s manufactured from zinc alloy and weighs the least of the three bombs.
Bomb AN—MK23 is made of cast iron. Bomb MK43 is manufactured from cast lead and is the heaviest of the three bombs. The cast body has a bore throughout its transverse axis which houses a signal and firing-pin assembly. Four fins are cast integrally with the bomb body.
b. Use. Miniature practice bomb MK5 is used for bombing practice on armored-deck target boats.
Bomb AN—MK23 is authorized for all bombing practice except that involving armored-deck target boats. MPB MK43 is used for low altitude, horizontal or dive bombing and on armored-deck target boats.
Bombs MK5, AN—MK23, and MK43 are used with the MK4 signal. These bombs also are 2—76 used with the MK5 signal which contains a fluorescein dye and is actuated by impact on water. When the MK5 signal is installed, the firing pin assembly is not used. Special containers are utilized by aircraft to carry and release these bombs.
c. Functioning . The firing pin assembly fires the signal which expels a large puff of smoke rearward through the base of the bomb .
Over-all length…8.25 inches Body
Diameter…2.18 inches Fin
Dimension…2.5 inches
Weight…AN-Mk 23 -3 lb. + 2 oz
Signal…AN-Mk 4,
Reference: OP 1280, Aircraft Bombs, February 1945;
TM 9-1325-200, Bombs and Bomb Components, April 1966

So, a Very Long 10 ga. shell with a firing pin assembly held in with a cotter pin!

I have 3 Signals for these Practice Bombs. One seems to be shortened.
The paper case is salmon coloured. Headstamp is:
No WINCHESTER 10 NUBLACK made in USA. 153mm long.
The aluminium case Mk 4 Mod 3 has no headstamp. Filled by NF 8-48. 152.7mm long.
The short case has an alloy wad and loaded by EDI 0569. 127mm long.
You can see the red dye stain inside the long fired case.

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Here some random material on these:

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Here an excerpt from TM 9-1980, Bombs for Aircraft,1942


And here what OP 1280, Aircraft Bombs, 1955 is saying about:

Any chance you might want to part with the fired case?

No, I want to keep the case as it has all the print intact. I even have a NPE with no case print.
These are hard to find and I would prefer to keep them here in Australia since we cannot import or possibly send items overseas without causing lots of hassles. Must be some in USA. Ron.

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Here’s my photos

long shiny (green case mouth) very hard to read markings

odd “primer” on right lower one

very hard to make out the case markings on this one (no h/s)

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That is VERY cool!
Any chance you have an odd duplicate you might be able to part with?

Not overly uncommon at cartridge shows…especially SLICS