The QF 4.5 Inch Gun

[Emma]

The game currently only has guns in calibers of nice whole numbers, which is fine in my eyes. However, if I want to simulate gun calibers of uneven numbers, such as the famous British QF 4.5 inch guns, which were a great success and have been used for a long time, do I go up, or down on the gun caliber?

The Royal Navy seems to be loving guns that have uneven calibers...such as the 4.5 inch, the 4.7 inch, the 5.25 inch, the 5.5 inch, the 7.5 inch, the 9.2 inch, and lastly the 13.5 inch.

Do I round up, or do I round down on the inches to try to find the closest match in game?

Perhaps it varies depending on the specific gun model? What are your thoughts? Thanks

[director]

I'd recommend a 4" +1 as a reasonable fit.

I do not know for certain but I suspect those guns (the 4.5 inch, the 4.7 inch, the 5.25 inch, the 5.5 inch, the 7.5 inch, the 9.2 inch, and lastly the 13.5) were actually metric, rendered over to the nearest fraction of an inch. This gets done to the guns of other nations when they are rendered from metric to inches - 4.!", 5.9", 6.1" and so forth.

I get frustrated when they refer to guns by the weight of the projectile - IE the 6-pounder - but that is mostly for army weapons.

[rodentnavy]

Jun 15, 2021 14:28:18 GMT -6 director said:

I'd recommend a 4" +1 as a reasonable fit.

I do not know for certain but I suspect those guns (the 4.5 inch, the 4.7 inch, the 5.25 inch, the 5.5 inch, the 7.5 inch, the 9.2 inch, and lastly the 13.5) were actually metric, rendered over to the nearest fraction of an inch. This gets done to the guns of other nations when they are rendered from metric to inches - 4.!", 5.9", 6.1" and so forth.

I get frustrated when they refer to guns by the weight of the projectile - IE the 6-pounder - but that is mostly for army weapons.

If I am trying to emulate 6 pounders (57mm) I go with the in  game 2 inch gun though its shell weight is more like a primitive 3" from RL.  4.5" DP, 4.7" LA, 5.25" DP and 5.5" LA are all treated as 5 inch DP or low angle guns accordingly.  7.5" guns are treat as in game 7 inch because shell weight in closer than in game or rl 8inch.  Likewise 13.5inch guns firing the light weight shell get rendered as 13inch and the heavyweight shell version 14inch, the considered 16.5" guns for the G3s prior to going with a 16"*  I tend to emulate using the in game 17inch, those tend to get used sparingly as they are not nearly as dominating in long range fire in RTW2 as they were in RTW1

*(oddly enough those and the ones actually fitted to the Nelson class might be better represented as 15 inch guns in game as the British took on board some very odd German ideas concerning high velocity light weight shells for naval rifles)

[nimrod]

I would say generally round down at .5; above .5 I would round up. This mostly has to do with shell weights as RodentNavy noted. If the gun is firing a heavy for caliber shell, than I would consider rounding up to better reflect rate of fire and penetration; or adjust the rounded down gun's quality upward if gun weight / ROF are concerns as would be the case for lighter ships. 

I would agree with director in general. I'll add that (mostly prior to the WNT) some nations would report shell diameter, others would report the distance between the bores rifling and others would report the maximum bore size as being bottom of grove to bottom of grove. Once you have treaties in play between countries, than their are established maximum bore diameters and generally agreed upon ways of measuring... That doesn't mean that some weird reporting / dis-information didn't occur prior to and during WWII.

I believe the Japanese, Italians, British and Russians were the primary culprits on reporting barrel diameters (be it grove to grove or lands to lands) rather than shell diameters; but I could be wrong here. To give an example, Navy Weapons states the following for a couple of Japanese shells:
"36 cm Capped Type 91 AP Projectile
Actually 14" (35.56 cm). Also for Cap Head for 15.5 cm design."

"20 cm Uncapped Type 91 AP Projectile
Actually 8" (20.32 cm). Also for 15.5 cm design."

www.bevfitchett.us/forensic-ballistics/info-lav.html states the following: "In Great Britain the size of the gauge or bore is actually measured at a point 9 inches from the breech, as laid down by the Proof Act and Rules. In rifled arms the size is denoted by the actual diameter of the bore across the lands, that is by the smallest possible diameter of the bore " A quick example from small arms; the USA reports shell diameter such that a USA 7.62 cartridge uses a .308" diameter bullet. The British .303 round uses a .311" diameter bullet, as the .303 refers to the rifling to rifling measurement. The Russian 7.62 rifle rounds like the British use .311-.313" diameter bullets.

[charliezulu]

The 4.5" wasn't a metric calibre, just the British being British (it's around 11.4 cm iirc?), and like the 5.25" I'm pretty sure it was just the British throwing every DP gun at the wall to see what stuck. The 4.7" is properly 12 cm, but the historical choice of 12 cm much prior was supposedly due to it being close to the traditional 12 pdr muzzle-loader. The 5.5" was also a metric gun (14 cm), which arose in a few places because 14 cm shells are significantly easier to handle than 15 cm/6" shells. I'm pretty sure the 9.2" gun was just Britain being Britain, as was the 13.5" (although in the latter case, they tried to continue the pattern with 15", 16.5", and 18").

[aeson]

Jun 15, 2021 15:21:45 GMT -6 charliezulu said:

I'm pretty sure the 9.2" gun was just Britain being Britain, as was the 13.5" (although in the latter case, they tried to continue the pattern with 15", 16.5", and 18").

The British 7.5" and 9.2" guns fit fairly well into the doubling-weight pattern of many of the common British gun calibers of the late 19th and early 20th Centuries - you have the 3-, 6-, and 12-pdr guns, obviously, and then the early 4" guns were designed for 25 lb shells, the 4.7" and 5" guns fired roughly 50 lb shells, the 6" guns fired roughly 100 lb shells, the 7.5" guns fired roughly 200 lb shells, the 9.2" guns fired roughly 400 lb shells, and the 12" guns fired roughly 800 lb shells. The 13.5" gun is arguably more of an oddity than the 9.2" gun is, as it looks like something of a half-step whether you're looking for round-number diameters or doubling shell weights at each size step.

[charliezulu]

The first 9.2"s had shell weights of around 380 lbs, so the choice of that specific calibre as opposed to, say, 9.4" was what I couldn't figure out.

[tbr]

And then there is the ongstanding German preference for an 88mm calibre vice the usual 3inch/75mm used by other nations. The missing half inch level between gun calibres has the more influence the lower the calibre.

[okonu]

The British used more 88mm than the Germans - the 25pdr of WW2 fame is 88mm.

[tbr]

Jun 16, 2021 17:17:19 GMT -6 okonu said:

The British used more 88mm than the Germans - the 25pdr of WW2 fame is 88mm.

That is WW2. The 88mm use in the German Navy goes back to decades before WW1. The Kaiserliche Marine and Reichsmarine never used "3inch" guns, the Kriegsmarine had some as war booty and a very few 7,5cm FlaK (as in two dozenb) of German production, everything else in that size/weight/shell weight range was 8,8cm. Only the Bundesmarine introduced the 3inch/76mm OTO Melara as a standard gun, and relatively late in the 1980's.

www.navweaps.com/Weapons/WNGER_Main.php#Smaller_Caliber_and_Anti-Aircraft_Guns

[raider13i]

Jun 15, 2021 23:04:50 GMT -6 aeson said:

Jun 15, 2021 15:21:45 GMT -6 charliezulu said:

I'm pretty sure the 9.2" gun was just Britain being Britain, as was the 13.5" (although in the latter case, they tried to continue the pattern with 15", 16.5", and 18").

The British 7.5" and 9.2" guns fit fairly well into the doubling-weight pattern of many of the common British gun calibers of the late 19th and early 20th Centuries - you have the 3-, 6-, and 12-pdr guns, obviously, and then the early 4" guns were designed for 25 lb shells, the 4.7" and 5" guns fired roughly 50 lb shells, the 6" guns fired roughly 100 lb shells, the 7.5" guns fired roughly 200 lb shells, the 9.2" guns fired roughly 400 lb shells, and the 12" guns fired roughly 800 lb shells. The 13.5" gun is arguably more of an oddity than the 9.2" gun is, as it looks like something of a half-step whether you're looking for round-number diameters or doubling shell weights at each size step.

The British 4.5 Inch Calibre is actually 4.45 inch decreed by the Admiralty in the 1930s to known henceforth as 4.5 inch even to this day.

I believe but I far from certain that it was to do with inaccurate burn rate of propellant of the era and by increasing the size slightly they could get a more consistent burn along with long standing traditions revolving around weight of shot.

It could be as simple as because they had 1 too many pink gins when they signed the contract.

[wlbjork]

I know that on land - especially during WW2 - there were a number of weapons systems that were actually the same calibre but had to use different ammunition. These were labelled as different calibres to make it harder to supply the wrong sized ammunition.

Don't think that any navies had quite the same problem, fortunately.

[aeson]

Jul 7, 2021 1:43:09 GMT -6 wlbjork said:

Don't think that any navies had quite the same problem, fortunately.

The Colorados to my understanding could not use the same type of 16" ammunition as the newer North Carolinas, South Dakotas, and Iowas as the newer ammunition was too large for the older battleships' shell handling systems; likewise for Arkansas and the Alaskas with 12" ammunition. I would not be surprised if something similar could be true for the 5"/54s and the 5"/38s as the navweaps pages indicate that the shells for the 5"/54 were about 14 pounds heavier than those for the 5"/38s.

Other navies have had similar issues - for example Britain had a number of predreadnought battleships armed with 12"/25, 12"/35, and 12"/40 guns, which all used different types of ammunition, and the same was also true for the 13.5"/45-armed dreadnoughts and the 13.5"/30-armed predreadnoughts that were still in service in the First World War.