As for your tank's 50 mm, is it similar to ballistic performance of https://en.wikipedia.org/wiki/5_cm_KwK_38
without the over-engineered gun breech and is the US Army consider the belief of the tank destroyer doctrine of the late 30s to early 40s as a viable strategy against enemy tanks and not the proper doctrine of the multi-role tank tactics of the post WW2 years?
As I actually carried it forward from the time of Mr. McKinley's Navy, the gun which is the basis used has the following characteristics:
Designed in 1894
Produced M1894 5 cm/40 - 1895
..............M1894A 5 cm/50 - 1913
Weight: 240 kilograms (530 lb)
Length: 2 meters (6 ft 7 in)
Barrel length: 1.83 m (6 ft 0 in) for the 40 caliber
Shell: Fixed QF
Shell weight 1.75 kg (3.9 lb) which gives it, its nickname "the 4 pounder"
Caliber/(bore diameter): 5 cm (~2.0 in)
Breech: Wedge block type
Elevation: on naval carriage -5° to +20°. in army use, varies by
Traverse: 360° on pedestal mount
Rate of fire: 10 rpm
Muzzle velocity: 656 m/s (2,150 ft/s)
Maximum firing range: 6.2 km (3.9 mi) at +20° for 40 caliber model
Now it is based on a Driggs Seabury naval gun
that started its life out as an anti-torpedo boat gun. It was never intended to be used in the anti-armor role, either afloat or ashore. It has a high explosive shell as a standard base issue shell. That is usually the shell that a breech loading gun of this era is designed around. That practice (with rare exceptions like the Rheinmetal 12 cm tank gun one finds on most western tanks these days) remains standard practice to the present. One designs the base shell, then one designs the gun/howitzer around it. It, the 5 cm/40/50 will acquire a tank-busting shell as the US gains more experience with this kind of vehicle, but even then a tank is properly expected to use high explosive shells most of the time. It should be noted that this did not come out of thin air, that this use is so, for the way tanks are used in 1925-31 (Paraguay War) and by Poland and Russia against each other, is known to the American army. The main ammunition needed, the Americans see, is high explosive shell to deal with infantry and machine guns. This, despite J.F.C. Fuller and Liddell Hart is not going to change much through and up to the mid 1950s. Tanks spend most of their time fighting infantry
For HE 50 mm ammo, they should have an elongate shell for higher explosive yield insert into regular shell cartridges and training of firing them when supporting infantry or develop HEAT and/or HESH shells. Or rely on the self-propelled AFVs to do infantry support.
How is that supposed to happen again? The American army (1928-1931) thanks to Patrick Hurley has one (1) experimental motorized regiment. It is not going to have a full division, nor is it going to do things, British. The American army hates things British. The Americans are influenced by France
. The "fact" that the US Army has a lot of armored cars in the motorized regiment is more a function of the "police function" the army has than due to any battlefield doctrine. Congress funds those cars because they recognize that the "red menace" and racial tensions which produces vigilantism
needs a quick reaction force to stamp out the riots. The army simply uses the armored cars in the RTL (and in the AU) to outfit some cavalry troops. This shows up in the experimental motorized regiment.
For next generation US tanks, they must accept a high-velocity 75 mm similar to the https://en.wikipedia.org/wiki/7.5_cm_KwK_40
or a 76 mm variant similar to https://en.wikipedia.org/wiki/76_mm_gun_M1
because the Germans use their high-velocity 75mm when they encounter the T-34s and the KV-1s and that should apply to the US Army if they encounter more heavily armoured future conflicted European tanks in 1940s and beyond. The
M4 Sherman of the RTL was an adequate tank for late 1930s but they nerf the 75 mm gun for infantry support and could attack only tanks like the Panzer MK. 3 and MK. 4 equivalents.
It is too early to think about PZKW II's III's and IVs. The AU, objectively, has to make sense. The Americans, RTL or AU, are more concerned about Vickers 6 tonnes they may face in Mexico, or Japanese Type 87s and Type 89s (armed with a decent 4 pounder 47 mm/40 gun) they might fight in the Pacific in 1931. In the AU the Americans develop from the T-3 (1927) a tank of their own to match the contemporary threats they expect to meet.
As for machine guns, the Browning Model 1917 will be made because the US military didn't like the Vicker Maxim variant and used them as substitute to supplant the existing US Maxim model stockpile and return them or scrapped them when WW1 ended.
The American army RTL spend a boatload of money before WW II they do not have
to replace the Browning .30 because they do not like it.
^1 The Maxim as well as the Browning are used in WW II. Just depends on what is in the National Guard armory and who is issued what, where and when. WW II is, in the RTL, a come as you are war. The Americans are certainly using Lewis guns and even Hotchkiss guns in the Philippines. Later they standardize on Brownings, RTL, because that Is all they have
and can make in their government arsenals. Post WW II, they try again to develop a new machine gun. Why? They, still, do not like the heavy cumbersome Browning medium machine gun
that they use in Korea. The weapon is hard to move on a mobile battlefield; which is what the American army now expects. It gets hot (even the water cooled versions) and suffers cookoff. It is despised on Guadalcanal when it replaces the Johnson LMG (Marines) and it is disliked in Korea.
As for the .50 Browning HMG, it maybe created or the https://en.wikipedia.org/wiki/Hotchkiss ... achine_gun
wins the design contest and for LMGs or the real GPMGs, the https://en.wikipedia.org/wiki/Hotchkiss ... achine_gun
with a proper metallic strip ammo belt feed system or an AU BAR design.
??? The Browning .50 cal is effective for what it is originally supposed to do. It is scaled up from the .30 machine gun as the medium AAA machine gun and as a truck/tank killer that General Pershing requests. Later Browning and his successors after he dies evolves it (out of necessity) as an aircraft borne weapon; but as such an aircraft weapon, it is not the RTL history purpose for which Browning weapon develops it.
The BAR needs a lot of work and it will not end up as expected, either. (See below about the Belgian MAG.) The Colt made BAR stovepipes. It, (European version), is heavily modified by FN to produce the MAG; a rather good belt fed machine gun (1950). The Hotchkiss, is in the here and now, that uses Obrice's gas operated cyclic. it makes for a good but awkward base of fire fixed position machine gun, excellent for trench warfare. The RTL advantage it has over the American Browning medium machine gun in .30'; a recoil operated machine gun of similar purpose, is that Benet (USN) and Mercie (French engineer and co-gun maker) figure out the quick change barrel method in 1902 RTL. In this AU, that solution happens in Connecticut and not at all at St. Etienne. The RTL 1897 Hotchkiss air cooled weapon is also the RTL granddad of the Nambu Type 3, Type 1, and the Type 03 machine guns. None of these Japanese machine guns have the quick change barrel, because Colonel Nambu can not figure it out. Won't matter anyway, because in this AU, the Japanese, like the French do not obtain the Hotchkiss. They are stuck with Maxims. (Good luck with that.) The US Hotchkiss in the AU is based on the post WW I French Hotchkiss export model (1924) which will be used RTL in the Paraguay War. All up, it weighs a hefty 40 kg weapon.
As for WW II, the US should have tooled up for the T23E1^2 that it developes at great expense. Ruger knows what he is doing. The best RTL competitor, the Johnson LMG has serious problems; mainly it being jam prone in deserts and not very ergonomically friendly with that awkward magazine arrangement. The US rejects the T-23 because it has to be milled from block steel. The Americans want a stamped metal machine gun like the Browning. It is "cheaper" to make a gun that way. Sure that stamped sheet metal process makes industrial sense if you have two equally effective machine guns, one milled and one stamped. However, this is not the RTL case, here. (Colt has quality control issues.) How many G.I.s die, clearing feed jams in a Browning 30 cal (John Basilone being one) or die while they try to carry that dead paper weight across ground on their shoulder, because it can not be assault fired at the walk/run like a Bren or a modern SAW?
The T23E1 can be used that way, like a SAW.
^1 The history about John Browning's genius is mostly true. But
like most "popular' histories, the details matter. His guns work well for what they are meant to do. If one understands that the M1919 is intended to solve WW I problems (trench warfare) one realizes that the machine gun, while a good trench weapon, is not the right solution for the kind of "colonial" wars the Americans expect to fight. The Americans are not stupid. They see what is going on in Europe. They see what their own gun designers do. Thompson's "trench broom" is a step in the correct direction. But the problem is controlled automatic fire from a man carried weapon that one uses on the run. The BAR is the first American attempt at a solution. The Thompson is the second.
What is the problem? Wrong bullet. The candidate bullets in use: 7.5 mm (French) 7.92 (German) and (7.7) (British) or the US and Russian
Remington (7.62) are all wrong. The only solution in sight is either the 6.5 mm Schoenauer or the 6.5 mm Mauser. Pedersen, a prima donna, actually develops a special bullet for his rifle. (7x51mm). That seems a reasonable solution. Macarthur (see him above) kills the rifle (correct decision) but also decides to stay with the 30.06 (7.62 mm, the wrong decision.). Nothing in the AU can fix that outcome unless the US adopts the 7 mm (Spanish Mauser) and sticks with that "right" decision.
^2 During WW II, the American army learned a lot about what happens when one tries to take a precision piece of machinery based on the MSL system (metric) and tries to reverse engineer it to FSG (Imperial English system of measurement) tech. It does not work. The British simply adopt (French) metric tools to make BESA (Czech) machine guns according to BRNO drawings and use the German 7.92 bullet. Smart? It depends on what one accepts as an acceptable logistics nightmare. The American army hires GM (should have hired FORD Canada) to make an American clone of the stamped metal process German designed and used MG-42. Should be simple, but headspace errors (millimeters to 1/1000ths of an inch) and the wrong bullet (30.06 is powerful, too powerful for the German weapon as 7.92mm designed since the bullet blows the weapon apart; there are other errors built in; such as the roller bearing arm indexer geometry.), anyway, the point is that measure errors matter. The US should have gritted its teeth and used its superior but expensive milling technology and built the Ruger.