The Gewehr 43 is the first self-loading rifle in the game, and is the second unlock for the Assault class. Its in-game depiction is pretty much accurate and it is clip-loaded by default, but can be upgraded to allow the player to reload it by swapping out the magazines.
The Remington Model 8 inexplicably returns from Battlefield 1, presumably out of developer laziness. It is the first self-loading rifle unlocked for the Recon class, and is relegated to the role of a sniper rifle. Unlike other self-loading rifles in the game, the magazine cannot be extended, despite an extended mag version appearing in Battlefield 1. Of course, in real life, the Model 8 probably saw no use in World War II whatsoever, as it was never intended as a military weapon and was primarily only sold as a civilian hunting rifle in the US. The in-game description admits as much, which calls into question why this gun is featured in the game to begin with.
The M1A1 Carbine, the paratrooper variant of the M1, is featured in the game as the second self-loading rifle for the Assault class. It looks and functions like a real M1A1, although since there is no American faction on launch, it is strange that the M1A1 should be featured; especially since other iconic American weapons, like the M1 Garand and BAR, are absent.
The Model 1907 also returns from Battlefield 1; again I can only chalk this up to laziness. The gun is depicted as a fully-automatic assault rifle with a very high fire rate, in contrast with the slow-firing automatic version of the M1907 in Battlefield 1. The magazine by default has 16 rounds but can be upgraded with the long mag seen in the previous game.
Curiously, the in-game description claims this gun was used by French and British forces (I don't think it specifies when, but since this is a WWII game, I'll assume that's what the developers meant). While a relatively small order for M1907s was made by the French Air Force during World War I, which were allegedly fully-automatic models, these were retracted from service before 1918 and would have been long obsolete by World War II - I wonder, in fact, whether the French had not already sold off the majority of their models during the inter-war period. The British, on the other hand, are also claimed to have bought a small number to equip the RFC during the early stages of World War I, although I've never seen proof of this. If it's true, then the numbers must have been even less than the French, and these supposed guns must have been long retracted from service by World War II.
The Czech ZH-29 rifle is the second self-loader for the Recon class, again intended as a sniper rifle. It has a small 5-round magazine capacity that cannot be extended, despite the fact that larger magazine capacities for the gun exited in real life. By default, it's depicted as being clip-fed, but can be upgraded to allow the player to swap out the magazines like the Gewehr 43. The game notes that this gun was used by China in World War II and this is correct, but since China is not actually in the game, it's a bit of a strange inclusion. The Germans no doubt also fielded some models that were captured from the Czechs, and it is thought that they studied the gun in developing the revolutionary StG.44, but the number of German service ZH-29s was probably very low in reality.
An interesting note to mention here is that the British Expeditionary Force did, in fact, test a fully-automatic conversion of the ZH-29 in December 1939, while stationed in France. This gun was never adopted but indicates that there was some limited British interest in the weapon.
The Russel Turner conversion of the SMLE No.1 Mk.III rifle is featured in the game as the third self-loading rifle for the Assault class (since the M1907 is categorized as an assault rifle). For gameplay purposes, it's not as powerful as the regular Lee-Enfield, despite essentially being exactly the same gun. The inclusion of the Turner SMLE in the game was no doubt fueled entirely by the coverage of the weapon on Forgotten Weapons, as DICE are known fans of the series since they credited it in Battlefield 1. In real life, only a sole prototype was developed for Canadian Army tests, and it was rejected without any serious consideration for its adoption. It was never sent to London for inspection by the Ordnance Board, so was never even tested by the British.
Realistically, there are several better choices for automatic SMLE conversions. The Charlton conversion from New Zealand converted the Lee-Metford and Lee-Enfield rifles into fully-automatic support weapons, of which about 1,200 were made and issued to the New Zealand army. The British also expressed some interest in the South African-designed Rieder conversion, which was a detachable device that could convert the SMLE into a rapid-firing automatic rifle. Even the Howell conversion, which was featured in Battlefield 1, was briefly proposed as a weapon to equip the British Home Guard during World War II, although this proposal was denied. Ultimately there was never an official wartime requirement for a self-loading rifle in British service and as such none were adopted. Other automatic SMLEs of the period included the Francis and Ekins conversions, developed in 1943 and 1944 respectively.
The Selbstlader 1916 is yet another carry-over from Battlefield 1, and is the fourth self-loading rifle for the Assault class. It is more or less exactly the same as its iteration from the previous game. In real life, only about 1,000 Selbstlader carbines were produced for the German Air Force during World War I and were quickly discarded after 1916, when machine guns rendered aircraft rifles obsolete. These rifles were never re-introduced into German service and as such were never used during World War II, except possibly issued to reserves during the latter stages of the war, when the Germans began to fall short of weapons and re-introduced many old and antiquated guns into emergency service. Even then, it is unlikely that any Selbstladers were used in combat.
The Volkssturmgewehr strangely appears in two iterations in the game. The first, called the "Sturmgewehr 1-5" and unlocked for the Assault class by default, is fully-automatic and is modeled off of the MP508 variant of the gun, which featured an angled stock and foregrip. The second, which is the last unlock for the Assault class, is a semi-automatic model known as the "Gewehr 1-5", modeled off of the regular version of the gun, the MP507. Why the developers chose to put the gun in the game twice is a very odd decision and I can only assume it is their attempt to bolster the otherwise shallow "Assault rifle" category. In real life, the Volkssturmgewehr was developed very late in the war as an emergency measure and issued only to Volkssturm units in 1945. Perhaps the developers should have reserved this weapon for the game's last update, given that it is an extremely late-war weapon.
The in-game depiction is somewhat unreliable for a number of reasons. Firstly, the 1-5 designation that the game uses is derived from a popular misdesignation of the Volkssturmgewehr - the so-called VG 1-5. This name arose from confusion between the Gustloff model and a separate series of five other rifles intended for the Volkssturm, known as the 1-5 series. As mentioned, the real designation for the Gustloff gun was MP507.
Secondly, the authenticity of the fully-automatic version can be called into question. There is a recurrent claim that automatic, assault rifle versions of the gun existed, although practically every surviving example is semi-automatic and there is no real record of a full-auto version. While I cannot dismiss the existence of such a variant outright, I suspect the rumors of this alleged assault rifle arose from a misunderstanding of the name - "Volkssturmgewehr" does not mean "People's Assault Rifle", as is commonly stipulated, but actually means "Rifle for the Volkssturm", which does not imply any fully-automatic capability.
Thirdly, the existence of the MP508 version is also rather speculative. While there may well be records of such a version, it seems likely that it was only ever planned as never actually produced, since there are no surviving examples and only sketches to attest for its apparent existence.
The StG.44 appears in the game as the third assault rifle for the Assault class. It looks and functions faithfully to the real-life version of the gun, but can be fitted with a fictional folding stock. The existence of a folding stock "paratrooper" variant of the StG.44 has been rumored and depicted by some sources, but no such gun actually ever existed.
The first SMG in the game, unlocked to all players by default. The in-game model is the Sten Mk.II and it's pretty much depicted accurately, except for its appearance in the singleplayer in which is used by British Commandos in Norway in 1940. The Sten wasn't developed until 1941 and the Mk.II version first saw combat use during the Dieppe Raid in August 1942.
The Suomi KP/-31 is the second SMG in the game and is curiously featured despite there being no Finnish faction. The Waffen-SS acquired small quantities of Suomis on the Eastern Front, but very insignificant numbers since the Finnish were pretty much reluctant to export arms during the war - nothing to do with moral objections, just the fact that they could barely spare any, as the strain on their wartime produce was very demanding. In-game, the KP/-31 can be upgraded with a 50-round casket magazine, but the commonly-used 71-round drum is absent.
The MP40 is the third SMG unlock and it is basically the exact same gun you've seen in every other WW2 shooter ever. The only thing I will say about this is that since the majority of the base game is set in 1940, the MP38 would actually be a more realistic choice, but seeing as DLC is going to bring plenty of maps set at later dates, going with the MP40 was probably the right decision.
The MP28 is the fourth SMG, and acts as a successor to the MP18 from Battlefield 1. The MP28 has a very odd quirk in the game; in first-person view, the player character holds the gun by the magazine underhanded, rather than overhanded as typically depicted in video games. The only reason I can suggest for this is that the developers wanted the gun to have a distinguishing "feature" that would make it easily identifiable from the similar-looking MP34. In reality, it would be ill-advised to hold the gun by the magazine, as this could cause stoppages.
The choice to include the MP28 was no doubt spurred by a desire to re-use the MP18 model from the last game, and while the MP28 was used in some capacity during World War II, it was primarily fielded by German police, Gestapo, and Waffen-SS units rather than the Wehrmacht. The in-game description also claims that the MP28 was used by China and Japan; while some MP28s might have found their way to China, the gun adopted by Japan was the SIG MP20, which predated the MP28 by eight years. China was also a known buyer of the SIG gun, which calls into question whether supposed MP28s seen in South East Asia during the period were actually misidentified MP20s.
The EMP appears in the game as the fifth SMG, and there's not a whole lot to say as the in-game depiction is more or less accurate. The version in the game is the MP35 model, identifiable by its simplified fixed rear sight and safety latch in front of the cocking slot. This gun, like the MP28, was primarily used by German security forces during WW2 and was not formally adopted by the Wehrmacht. It was popular with the Waffen-SS and was also in use with the Vichy French Carlingue forces.
The game describes the gun as having been used during the Spanish Civil War, which is true to an extent. Actually, the earlier MP34 model, without the safety latch and with a tangent rear sight, was the version donated en masse to Franco's forces as part of Nazi Germany's support for the Spanish Nationalist rebels. The Republican government managed to acquire about 3,000 MP35 models from Poland during the war, but almost all of these ended up being confiscated by the French when the remainders of the Republican forces fled Spain after Franco's victory in 1939. Thus, the French acquired a large quantity of MP35s without having to pay a penny to Germany, and these were the same guns used by Vichy France during the World War II.
The S1-100 is the sixth SMG in the game, and is referred to by the Austrian Army designation, MP34. By default it feeds from a 20-round magazine, but can be upgraded with an extended mag. This is an interesting addition to the game, but a rather unnecessary one, as there are already three other German SMGs available. In real life, the S1-100 was adopted by Austria in 1934, and produced under license at Steyr on behalf of the Austrian Army. Due to the costs inherent in manufacturing the weapon, it was never produced in huge numbers, so during World War II it would have been a relatively uncommon sight. When Germany annexed Austria in 1938, the Austrian Army was absorbed into the Wehrmacht and thus Austria's entire military arsenal was appropriated by the Germans. This included all their MP34s. It was probably retained in some numbers by Austrian units of the Wehrmacht, but a portion also went to the Waffen-SS. The SS had at least different three SMGs in their service called the MP34, so this probably led to some logistical issues.
The seventh and final SMG in the game is the Thompson, depicted as the M1928A1 model. The version in the game has a smooth M1 barrel rather than the actual finned M1928 barrel. The M1928A1 was a "transitional" model built during the war for the British and US militaries, and was soon supplanted by the cheaper M1 and M1A1 models. The M1928A1 seems to have been chosen for the game as a compromise weapon that could be used by both British and American troops (the latter of which are not yet featured in the game but are bound to be added with a future update), as it did see service with both, whereas the M1A1 was primarily only by the Americans.
The Auto-5 returns from Battlefield 1 and is the first shotgun available for the Support class. Like in the previous game, it is named the 12g Automatic, probably to avoid using the Browning name for some reason (it wouldn't be a copyright infringement, but they're probably playing it safe anyway). Auto-5 shotguns probably saw some limited service by American troops in World War II, but to my knowledge were never formally adopted by any country. Although DICE have been insistent since Battlefield 1942 that the Auto-5 was used by British forces across both world wars, it was actually only adopted by the British Army after World War II, during the Malayan Emergency in the 1950s. The British designation was L32A1.
The Sauer Model 30 "Luftwaffe Drilling" triple-barreled shotgun appears in the game as the second and final shotgun available, with more to be added in future updates no doubt. It can fire two 12-gauge shots and one rifle round, like the real-life version of the gun, although in reality the rifle was intended only for hunting small game, as the gun was issued not as a combat weapon but a survival measure for stranded Luftwaffe pilots who had been shot down. Thus, the in-game depiction of it as a German combat shotgun is inaccurate, as the Germans never issued any shotguns in World War II. It is often said that this is due to their insistence that using shotguns for combat constituted a war crime; while the German Army held this attitude in late World War I, I do not think they made such protests during World War II - rather, the reason they didn't issue such weapons was likely down to their limited usefulness. Only the Americans were really sold on the idea of combat shotguns, and no other army formalized the use of them.