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RML Cannon of 7"

An occasional update of progress on my next artillery model.

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Buffer01/03/2021 19:40:06
306 forum posts
138 photos


I thought I would start a thread on the latest piece of artillery I am hoping to model. Progress will be a bit slow I'm afraid as I have quite a few distractions at the moment, however I'm hoping that putting this on here will encourage me to pull my finger out and get on.

For any enthusiasts it will actually be a Mark 4 barrel. The carriage will be a Garrison Casemate or Dwarf sat on top of a Dwarf A Pivot Slide. Its going to be about 1:12 scale so the barrel will be about 12" long as that is about as large as I can handle in my lathe.

At the moment I am slowly producing a CAD model of it so I can get a few bits cut such as the carriage side plates.

I hope at least one of you might find this interesting. Thanks.

gun carriage assembly

Edited By Buffer on 01/03/2021 19:43:06

Mick B102/03/2021 11:43:16
2044 forum posts
117 photos

Not at all sure of this, but from Wikipedia only the 7-inch 7-ton RML seems to have reached Mk.IV, and then only as a drawing as far as I can see - there don't seem to be any surviving examples.

A digital library in Victoria, Oz seems to have a handbook available.

I've found these guns a rather obscure area of ballistic history.

I've never properly understood why they had such massive reinforces ("coils" ) around the chambers. Were they expecting massive pressure peaks from the black powder propellants? Seems a bit OTT in view of the 1300 -1600 ft./sec. MVs, even allowing for the additional mass of Palliser projectiles over roundshot.

Edited By Mick B1 on 02/03/2021 11:43:54

SillyOldDuffer02/03/2021 16:47:44
7675 forum posts
1693 photos

Posted by Mick B1 on 02/03/2021 11:43:16:


I've found these guns a rather obscure area of ballistic history.

I've never properly understood why they had such massive reinforces ("coils" ) around the chambers. Were they expecting massive pressure peaks from the black powder propellants? Seems a bit OTT in view of the 1300 -1600 ft./sec. MVs, ...


They are fascinating. The massive bottle shaped reinforces were indeed due to Black Powder. Gunpowder has many shortcomings as a propellant; the chemical reaction produces a lot of solid material that damages the bore, gives away the gun's position, and blinds the gunner who can't see through his own smoke. It also burns too quickly, producing excessive pressure at the breech, and the effect gets worse as the gun gets bigger.

Various things were tried to slow the burn down, such as using partly charcoaled wood, compressing the powder into large pellets, which could be as big as a fist, and shaping them to slow down the rate of combustion. One of my old books mentions a lady watching a salute at Portsmouth catching a fizzing pellet in her stacked up hair-do. Seems these guns sprayed burning pellets about like a shot-gun.

The efficiency of modern guns owes as much to chemistry as it does improved steels and design. Unlike gunpowder smokeless powders can be adjusted to burn at the optimum rate needed to accelerate a projectile up the barrel without over-stressing it. Artillery became much slimmer - thin walled barrels and no need for bottle reinforcing at the breech.

Didn't happen overnight. Propellant problems destroyed several French, British, Italian, and American battleships. Bulk smokeless powder is prone to spontaneous combustion unless carefully made from pure materials, stored in temperature managed magazines, tested regularly and with and rigorous observation of best before dates. Harbour accidents took the Iéna and the Liberté at Toulon, HMS Vanguard and HMS Bulwark in the UK, the Italian dreadnought Leonardo da Vinci, and probably the USS Maine, and the USS Iowa turret explosion in 1989.

Maine before and after pics from Wikipedia:

Many more ships were lost in action due to inadequate protection of the magazines, notably the British battlecruisers at Jutland and HMS Hood in WW2. Cordite packed an extra wallop, but it proved more likely to go bang by accident than the relatively weedy propellants used by other powers!

Lots more info here.


Mick B102/03/2021 18:43:42
2044 forum posts
117 photos

Nevertheless, Dave, the black powder Express big-game rifles were capable of similar or slightly higher velocities, with similarly overweight conical projectiles as compared to round ball, but without grotesque reinforcement.

The measures involving granule size and form could have some effect in combating severely degressive burning - in fact early 303 rifle rounds used a longitudinally perforated moulded pellet of BP, although the change to nitro propellants such as Cordite was always planned.

I'd welcome other solutions but for myself I've come to 2 alternatives:-

a) the difficulty and expense of manufacturing big naval gun barrels of >20 calibre length, and mounting these in ships, caused designers to accept high pressures in order to provide high accelerations to achieve desired velocities in such short barrels,


b) the behaviour of propellants and resulting gases in large calibres with heavy projectiles was incompletely understood, and designers played very safe.

Edited By Mick B1 on 02/03/2021 18:44:41

Buffer05/03/2021 10:30:33
306 forum posts
138 photos


I have a book from 1860s on rifled artillery manufacture and they say the reason for the greater strain on a rifled gun is because of the following which are quotes from the book. "The greater weight and length of the projectile increases the friction and inertia". "The opposition is greatly augmented if the projectile is constrained to travel through the bore in a spiral". "Round shot yields promptly to the impulse of the powder gas (to which it presents half its surface) and bounds freely forward through the bore almost unimpeded by friction, while the strain of the gun is immensely relieved by the comparatively great windage. Also the inertia and friction of a projectile increase with weight in a cubic ratio, whilst the surface of the chamber and the base of the projectile increase as the square ratio, it follows that the larger the charge and the weightier the projectile the harder and stronger must be the barrel".

I've also got a photo of a gun in New Zealand which claims to be a mark 4 but it could I suppose be the similar looking 2. Anyway here's the progress so far.


Roderick Jenkins05/03/2021 11:10:41
2129 forum posts
586 photos

I found this video of the largest black powder gun on Malta very interesting, including description of the steam/hydraulic systems used to reload.



Buffer10/03/2021 16:46:45
306 forum posts
138 photos

Rod that's the 100 ton gun, there is another in Gibraltar.

Quick update, I have made a bit more progress on the slide. I thought there wasn't many bits in one of these but that was a mistake.


Ian Lee17/10/2021 22:23:51
53 forum posts

My son has just started making one of these 7INCH Gguns. He is short of some details. Do you have any Breach block details please or is yours a muzzle loader.

Buffer18/10/2021 08:35:04
306 forum posts
138 photos

It's a muzzle loader. But let me know what gun it is as I may have a drawing.

Samsaranda18/10/2021 09:19:04
1244 forum posts
5 photos

Rod, the gun at fort Rinella in Malta is very impressive, I saw it a few years ago when they opened the fort as an attraction, since then the re-enactment society concerned with preserving the gun now fire it on occasions using a black powder charge which I am told is well worth witnessing. Malta is full of historical venues and worth visiting but you need to remember the island is unique and has its own ethos, only understood by those who have been there, I first went to Malta in the 70’s when serving in the Air Force, been back many times on holiday and love the place, the people are great. Dave W

Ian Lee18/10/2021 21:44:06
53 forum posts

The gun is the RBL 7 inch 110 pounder screw breach loader in service from 1861 until around 1900, weight was 83cwt, HMS Warrior in Portsmouth Harbour has at least 2 of the guns on show.


Buffer19/10/2021 00:12:27
306 forum posts
138 photos

If you do a Google search of ' constructure of ordnance 1877' the first item my phone shows is treatise of construction ....1877. This has many drawings and details of that gun and its breech block. It's a free ebook for you to download.


Edited By Buffer on 19/10/2021 00:20:39

Alan Charleston19/10/2021 06:19:53
122 forum posts
21 photos

Hi Buffer,

The gun in NZ has an interesting story behind it. It was originally bought out to protect Auckland during the Russian scare of the 1870s. The Russians never got this far - they were stopped by the Japanese so the gun was never used.

During the second World War it was thought to present the Japanese (not our friends this time) with a tasty target for their bombers so it was buried to protect the surrounding area.

I believe it was in the 60s that it was dug up and some bright spark thought it would be a good idea to mount it on a traffic island near central Auckland where a main road split into two with the barrel near the front of the island facing the traffic. During the 1970s there were a number of accidents where people ran into it with their cars and the gun's original purpose of killing people was finally realised.


Alan C.

Ian Lee19/10/2021 15:05:58
53 forum posts

Thank for your assistance, I have download the book.


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