Ammo Seeking References for Dahlgren Half-Charges (Myth?)

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Aug 14, 2019
Multiple websites have had some variation of three things:
1) A Dahlgren gun exploding in testing somewhere between 1860 and 1861 causing half-charges to be implemented
2) This restriction being repealed in 1864
3) The Commander of USS Monitor believing that full charges would have allowed Monitor to sink the Virginia
Thus far, however, I have been unable to find any sources for this information and was wondering whether or not anybody can supply documentation
Additionally, this PDF claims that half-charges are a persistent myth and cites military documents
Any help is appreciated
 
The period-appropriate handbook for the guns of the USN states that Dahlgren XI" guns have a 15lb charge (as the full charge) and no 20lb charge.
The 1864 handbook adds the 20lb charge.

There was never a 30lb charge authorized at any time. 15lbs is not "half", it's a full charge.
 
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This is the 1860 table for service charges for naval guns. You'll note that the XI" gun has a larger charge than the X", which has a larger charge than the IX", which in turn has a larger charge than the 8".



The NYT in 1862 states:


The 11-inch guns of the Monitor were designed chiefly for shells, which were computed to leave with a velocity of at least 1,250 to 1,300 feet. In the action, shot were used with an initial velocity of 1,120 feet. But since that, the same class of gun has been ascertained to be capable of throwing solid shot of 169 pounds, with a charge of 30 pounds, giving an initial velocity of 1,400 feet.

(the "action" in question is Monitor-Merrimack)

The reason I quote this is not the figures, but the timing - the ability to fire with 30 lb charges is "since that".
 
I'll need to dig back to find this, but it is my understanding that there was concern about concussion in the Monitor's turret, as opposed to any real fear of a Dahlgren bursting (to my knowledge, no Dahlgren smoothbore ever burst in service-- just in testing, when they kept adding charge till they found the point at which it would burst) so the commander may have been advised not to overcharge his guns; but yes, Saphroneth is quite right, the 15-pound charge was in fact the standard charge at that time.

I'm not clear on when the idea occurred that the Monitor was on "half-charges," but I suspect it was postwar recollection, when somebody may have said something like "later, we could use more, but then we couldn't" or something of that nature, and it went from there. I certainly always believed it for years, right up until the myth was exploded (ha!) on this forum during a discussion.
 
One thing I will note is that, IIRC, there was a kind of "at own risk" footnote that you could fire the 11" with a 30lbs charge if the gun was new. Dahlgren said a new gun could take it, but the Navy disagreed, so they basically made it a case of "don't blame us if you die".

I have to wonder if the "half charge" idea came about after it was revealed that the Virginia was mostly firing shell as she'd depleted her shot the previous day - a kind of "yeah, well, we had one hand behind our back as well".


The other possibility that I'm wondering about is that Monitor shipped ten experimental wrought iron shot - the first used in the USN IIRC. They hadn't been gauged, however, and would have been incredibly dangerous to fire so they weren't used. (Of the ten wrought iron shot, it was later found that four were too large and would have burst the gun if fired - and post hoc calculations have suggested they wouldn't have pierced Virginia even with 20lbs charge at point blank range. The other six were fired by Winnebago and Chickasaw against the CSS Tennessee, to no penetrative effect.)
Something like "we had shot on board that we didn't fire because they might burst the gun" may have become corrupted in memory into "we didn't fire at full charge because we might burst the gun".
 
I have to wonder if the "half charge" idea came about after it was revealed that the Virginia was mostly firing shell as she'd depleted her shot the previous day - a kind of "yeah, well, we had one hand behind our back as well".

If that wasn't the origin of the idea, it was quickly picked up to be that.

In reality, the Monitor missed a number of chances through less-then-spectacular gunnery-- most likely due to the sheer exhaustion of the crew, many of whom had gotten little or no sleep since leaving New York a couple of days previously. The Virginia's officers were concerned that the Monitor might find Virginia's waterline, since the latter was riding high after shooting a lot of weight off in the previous day's battle and the edge of her casemate armor was perilously close to the surface. But in the event, the Monitor seems to have been content to simply pound on the Confederate ship's casemate armor.
 
If that wasn't the origin of the idea, it was quickly picked up to be that.

In reality, the Monitor missed a number of chances through less-then-spectacular gunnery-- most likely due to the sheer exhaustion of the crew, many of whom had gotten little or no sleep since leaving New York a couple of days previously. The Virginia's officers were concerned that the Monitor might find Virginia's waterline, since the latter was riding high after shooting a lot of weight off in the previous day's battle and the edge of her casemate armor was perilously close to the surface. But in the event, the Monitor seems to have been content to simply pound on the Confederate ship's casemate armor.
probably because the range was too short to depress the guns for a "sinking" shot.
 
In doing a quick check, I found 2 references, in "A Brief Sketch of the First Monitor and It's Inventor", and in "The Monitor Boys: The Crew of the Unions First Ironclad" regarding a directive to use half-charges, due to the fact that the guns had not been completely tested and they did not want to risk of bursting a gun in the turret, which would have destroyed the ship.

However, later tests showed these fears to be unfounded.
 
It wasn't that the guns hadn't been tested-- they were actually guns that had already been in service aboard another vessel (name began with an M but can't fully remember it off the top of my head); it was the firing within the turret that some people were skittish about.
 
It wasn't that the guns hadn't been tested-- they were actually guns that had already been in service aboard another vessel (name began with an M but can't fully remember it off the top of my head); it was the firing within the turret that some people were skittish about.
My understanding is that they were Dahlgren XI guns 27 and 28, formerly on the Dacotah (which was rearmed to use a 10" gun and a 100-pounder rifle, so quite conceivably they just grabbed whatever was to hand..)

In doing a quick check, I found 2 references, in "A Brief Sketch of the First Monitor and It's Inventor", and in "The Monitor Boys: The Crew of the Unions First Ironclad" regarding a directive to use half-charges, due to the fact that the guns had not been completely tested and they did not want to risk of bursting a gun in the turret, which would have destroyed the ship.

Given the only charges ever authorized for the 11" gun, half-charges would mean 10-lb or even 7.5-lb, and I suspect they didn't even carry the latter as a bag. Possibly not the former either.
Note that the table I posted above lists Dahlgren gun cartridges as conical, so you need specially made bags (or ar least that's my understanding).
 
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My understanding is that they were Dahlgren XI guns 27 and 28, formerly on the Dacotah (which was rearmed to use a 10" gun and a 100-pounder rifle, so quite conceivably they just grabbed whatever was to hand..)



Given the only charges ever authorized for the 11" gun, half-charges would mean 10-lb or even 7.5-lb, and I suspect they didn't even carry the latter as a bag. Possibly not the former either.
Note that the table I posted above lists Dahlgren gun cartridges as conical, so you need specially made bags (or ar least that's my understanding).
I'm curious as to why the charge bags were conical, unless the breech end of the chamber was the same shape. The loaders would have had to make sure the bags were the right way round.
 
I'm curious as to why the charge bags were conical, unless the breech end of the chamber was the same shape. The loaders would have had to make sure the bags were the right way round.
It looks like it was:

pc08a.png



(From the Ordnance Instructions of the US Navy, the version at Gutenberg.)

Presumably this was considered to have some impact on preventing the breech blowing out, by avoiding sharp corners? Certainly the instructions repeatedly mention how the conical chamber affects the care of the gun.

(The same source gives specific and distinct dimensions for all authorized Dahlgren gun powder bags. It doesn't give dimensions for the 30 pound Dahlgren charge, which it says "May" be used against ironclads* but does not specifically authorize; it looks like a case of "theoretically possible but if you do it you'd better come home successful, because if you blow out the gun we'll blame you posthumously.")

* which only tends to concord with the idea that it was an overload charge worked out after ironclads became A Thing


I'm starting to wonder if 30 lbs was ever used in action, even after it became a charge that they thought the gun could take.
 
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Saph is right. Also, if you "double bag" then the first bag will push the second bag out of the barrel.

If you look at the chamber, the ignition is in the centre. The burn will spread from there, and prettymuch everything behind the hole will burn in the barrel. However, powder in front of the hole will start to be accelerated down the barrel before it ignites. This is a problem even with a single bag. With a second bag, the whole bag is accelerated down the barrel and at some point the bag may burn through at the second bag start burning. Note that the bags were designed to retain the burn for as long as possible, in order to maximise the amount of powder that burns.

No 30 lb charge was ever used in action, nor can I find details of construction. I have found the proof charge (25 lbs) used a few times (4) with steel shot, which is heavier. Mostly, once authorised the gun captains used the 20 lb charge against ironclads though.
 
I'm starting to wonder if 30 lbs was ever used in action, even after it became a charge that they thought the gun could take.

Not certain, but the story is that James W. A. Nicholson, skipper of the Manhattan, overcharged his XV-inchers to 60 pounds at Mobile Bay at least once in an attempt to penetrate the Tennessee's armor (which very nearly succeeded). I don't know what the corresponding "normal" service charge for the XV-inch was, though.
 
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