So it is generally agreed that the BAR was inferior to the BREN, the MG 34 and the MG42. Some rather unproven claims are then made as to its comparability to MGs of other nations
Lets look at some of those other nations and for comparison I chose the French M-29
For the French Fusil-mitrailleur Modele 1924 M29, no one has stepped forward to claim that they have ever used it, so the comments being made, including mine are speculative at best, most likely heavily biased, and further likely to be plain wrong
The operational reports that I have seen suggest it to be measurably superior to the BAR. The FM 24/29 was the standard squad weapon of the French infantry and cavalry at the start of WWII. After the French surrender in World War II, the Germans captured large quantities of this weapon, which they used operationally until the end of the war. I have not found any significant reports from that quarter that the type suffered any significant problems.
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The most significant appraisal of the type that I have been able to find is dated 1943. From 1943 on, as the French army was re-equipped and reorganized in North Africa with Allied support, the FM 24/29 was kept in service. The Free French forces which at certain points had used the BAR, submitted reports stating that overall the French weapon was considered measurably superior to the Browning Automatic Rifle and more reliable. It is significant that the French weapon had five more rounds capacity and the ability for aimed single shot fire, something the BAR apparently lacked. Barrel changing arrangements were considered superior in the French weapon
A measure of the overall success of the FM 24/29 was that it remained the workhorse in the Indochina war, and continued to serve as a front line weapon until the 1960's when it was replaced by the AA52. Nevertheless it was still in use with National Gendarmerie regional brigades until 2006.
Heavy duty versions of the MG were accepted in 1931, in which the barrel was strengthened to extend its life. The fortress version also included a rather unique barrel cooling system. I don't know too much information on the fortress version, but the French claimed it was capable of sustained fire for many hours. There is no way of verifying that really.
The BAR was not really capable of single shot sustained fire. It is debateable as to whether this was a disadvantage at all, but my personal opinion is that it was, not so much from a technical point of view but more a psychological one. Since WWI the US army has placed greater emphasis on firepower over aimed fire. In situations where th ere are no logistic constraints, this thirst for ammunition is probably not a significant issue, but in situations where the amount of ammunition is limited (which is often) it definitely is a problem. You have to make every shot count in those situations.
To be fair in 1931 (I think) a rate rducer began to be installed in which I have read it was possible to fire the weapon at two rofs.
The weapon had difficulty in penetrating the export market. As might be expected it was adopted in central and and sth america more or less without question. In Europe it was built under licence by the Belgians and used also by the Dutch, the Poles and the swedes. It was used second hand by the yugoslav partisans. It was foisted upon the free french, whio as indicated above disliked it. After Belgium was overrun, the factory fell into german hands. I cant find any evidence of the type being produced under German occupation, though im happy to listen if anyone has useful information on this.
The BAR was not without its critics even in US service. The US army recognised its principal limitation in the continuous fire configuration. This criticism is well documented in the US army historical records. In an attempt to overcome the BAR's limited continuous-fire capability, U.S. Army combat divisions increasingly began to specify two BAR fire teams per squad, following the practice of the U.S. Marine Corps. One team would typically provide covering fire until a magazine was empty, whereupon the second team would open fire, thus allowing the first team to reload. In the Pacific, the BAR was often employed at the point or tail of a patrol or infantry column, where its firepower could help break contact on a jungle trail in the event of ambush.
After combat experience showed the benefits of maximizing portable automatic firepower in squad-size formations, the U.S. Marine Corps began to increase the number of BARs in its combat divisions, from 513 per division in 1943 to 867 per division in 1945. A thirteen-man squad was developed, consisting of three four-man fire teams, with one BAR per fire team, or three BARs per squad. Instead of supporting the M1 riflemen in the attack, Marine tactical doctrine was focused around the BAR, with riflemen supporting and protecting the BAR gunner.
Despite the improvements in the M1918A2, the BAR there are many US army reports describing the type as a difficult weapon to master with its open bolt and strong recoil spring, requiring additional range practice and training to hit targets accurately without flinching. Again I sense the overweaning US view that accuracy was secondary. As a squad light machine gun, the BAR's effectiveness was mixed, since its thin, non-quick-change barrel and small magazine capacity, coupled with more difficult reload abilities, greatly limited its firepower comparison to genuine light machine guns such as the British Bren, or the M29. Most sources I have read suggest even the Japanese type 96 was superior in the support gun role.
The weapon's rate-reducer mechanism, introduced from 1931, was a delicately balanced spring-and-weight system described by one Ordnance sergeant as a "Rube Goldberg" device (a deliberately complex contraption in which a series of devices that perform simple tasks are linked together to produce a domino effect in which activating one device triggers the next device in the sequence). The rate reducer came in for a lot of criticism in the US army, and operationally it did cause a high rate of malfunctions when not regularly cleaned.
The bipod and buttstock rest (monopod), which contributed so much to the M1918A2's accuracy when firing prone on the rifle range, proved far less valuable under actual field combat conditions. The stock rest was dropped from production in 1942, while the M1918A2's bipod and flash hider were often discarded by individual soldiers and Marines to save weight and improve portability. With these modifications, the BAR effectively reverted to its original role as a portable, shoulder-fired automatic rifle.
Due to production demands, war priorities, subcontractor issues, and material shortages, demand for the M1918A2 frequently exceeded supply, and as late as 1945 some Army units were sent into combat still carrying older, unmodified M1918 weapons.
After a period of service, ordnance personnel frequently began to receive BARs with inoperable or malfunctioning recoil buffer mechanisms. This was eventually traced to the soldier's common practice of cleaning the BAR in a vertical position with the butt of the weapon on the ground, allowing cleaning fluid and burned powder to collect in the recoil buffer mechanism. Additionally, the BAR's gas cylinder was never changed to stainless steel. Consequently, the gas cylinder frequently rusted solid from the use of corrosive-primer. M2 service ammunition in a humid environment when not stripped and cleaned on a daily basis contributed to this problem. In summary the type suffered a thin-diameter, fixed barrel that quickly overheated, limited magazine capacity, complex field-strip/cleaning procedure, unreliable recoil buffer mechanism, a gas cylinder assembly made of corrosion-prone metals, and many small internal parts. Despite all this, it has to be said that the BAR proved rugged and reliable enough when regularly field-stripped and cleaned.