Just curious. Seems like a minor tooling modification to go from rimmed 7.92 x 57 to .303 as was done with the ZB vz 27 and Bren.
With the Besa, I think the round was chambered by being pushed forward out of the metal belt. That wouldn't have been possible with a rimmed case. You only get away with it in the Bren if the rounds are correctly loaded in the mag with each round being in front of the one above.
"The Czechs designed the ZB53 around the German 7.92 x 57 mm rimless cartridge and the British avoided the problems associated with a change of calibre, particularly from a rimless to a rimmed case, by producing their versions in the same calibre. " Besa Machine Guns
The BESA as an armament for the AFV was on borrowed time almost from the moment they started using them. Very early on they discoved that the fumes from the BESA, especially when fired on full auto - i.e. with the accelarator up, had a tendency to gas-up the fighting compartments and render the occupants unconscious. This was something that the Physiology Lab at Lulworth was tasked to work on in 42 and there was some resistance to the idea that this was indeed a problem. They resolved this particular issue by getting a very senior commander down to Lulworth, sticking him in a closed-down tank and letting him loose off as many belts as he liked. When he came round and found that they'd had to haul him out of the tank, he basically gave them the green light to investigate further and find a solution, whcih they eventually did do, but it involved lots of work on extractor fans and so forth. But essentially, whilst th BESA was a very good gun and was well liked by all who used it, it could prove hazardous to health in an unventilated tank and so once that was known it was on borrowed time. Of course other issues came into play when it came to standarisation but that early black mark also came into the decision making process.
Surely using any type of machine gun would cause similar problems (given the same rate of fire and propellent powder used in the ammunition) ? I can't imagine that it was only the BESA that was at fault.
Every single tank type that used a Besa, from the Light Tank MkVIC onwards, was subjected to gassing trials from 1938 onwards. These were originally undertaken at Lulworth (or occasionally Farnborough) by members of the Chemical Warfare Defence Establishment at Porton Down, though later on they were undertaken by the Medical Research Council at Lulworth. On some tanks the existing engine compartment fan was deemed sufficient to evacuate the fumes, on other tanks additional extractor fans were provided in the turret, and, where necessary, in the hull gunner's compartment. The reason the Besa was replaced with the slower, less accurate Browning was due to NATO standardisation, not fume extraction. The loading mechanism of the Besa was gas operated, whereas the Browning's was recoil operated. It was the fumes from the loading mechanism (Carbon Monoxide basically) that caused the problems, not the propellant.
Some files from TNA, which I have recently been wading through. To be honest I wasn't actually looking for this data but it sort-of came my way when looking for something else and when I saw this thread on the BESA I thought I'd offer it up to see if anyone was interested enough to ask for the references, to be fair I probably ought to have mentioned that I'd recently stumbled upon this stuff in TNA but then I rather expected a more civilised discussion than the one I find myself in! Now I've copied a load of files which contain this info so what I'm giving here is just a couple of snap-shots from 1941 - 1943 and it basically covers the beginning of what we now call OR, or Operational Research, i.e. the embedding of Scientists with the forward elements of the military in the belief that they can, and will, collate and interpret data that might escape the attention of those less trained in Scientific Research methodology. It was a bit of a hard slog to get the Army (and especially the RAMC) to view the possibility of 'embedded Scientists' as anything other than 'Tourists' who got in the way of the Army doing its job. But, by 1943 the Army has at last accepted the need for OR and most of this stuff is being absorbed under various AORG units so for Normandy and NW Europe we find the same kind of info under the AORG files. Most of this stuff is early to mid war and is concerned with events after Dunkirk and mostly against the background of the fighting in North Africa I haven't done any kind of in-depth analysis of this stuff, as I said earlier I more or less stumbled upon this whilst looking for something else but as I worked through the files I began to notice was that this info was spread across numerous, related, files some of which carry the same or similiar information whilst others bring something wholly new to the picture. This was not the only stuff in the files, lots of information on the development of clothing, (the string vest stuff is most interesting) goggles, gloves, boots, periscope prisms, casualty figures and how to prevent certain types of casualties, helmet designs, all-round vision cupola etc. etc. So, here it is, such as it is! As early as 1941 there were some confused reports about dangerous conditions in AFV and the need for greater ventilation, the document below, from the MRC Physio Lab at Lulworth, reflect this and is dated March 5th 1941. By June 12th 1941 they are beginning to hone in on the causes of the problem as being Carbon Monoxide and that it is coming from the guns in AFV's Also, in June 1941, because they had no quantitative data on the effects of Carbon Monoxide on the human body they began to conduct tests by exposing human subjects to various levels of CO for differing periods of time, and with different periods of clean oxygen in between each exposure. In this way they built up a reliable picture of the effects of CO on the human body. The fact that they were doing this in 1941 shows that they had already identified the problem very early on and it is also evident from the files that the main offender in this regards was the BESA, although the 6 pdr also came in for some criticism. They went as far as taking regular blood samples to ascertain the length of time CO remained in the blood stream, and they noted that... "It must be emphasized that the concentrations of carbon monoxide used in these experiments can only be tolerated for very short periods. Even 0.10% carbon monoxide may prove fatal if breathed for several hours." So, in a closed down tank, in a hull-down position, without adequate ventilation, the risk of a fatality from just firing a BESA was a real possibility! Finally, the test subjects for these experiments were the two scientists working on the project, they couldn't get enough traction with the army to do this work so they experimented on themselves! By January 6th, 1942, they were lamenting the Army's reluctance to make the necessary changes to the ventilation systems in AFV's to alleviate this problem, especially in the new Tank designs for the Churchill and the Cromwell. And by January 19th, 1943, they still don't feel that they have convinced the powers to be, although they are finally getting some tractions on the problem. Note the point they make that (The BESA Machine Gun is an outstanding offender in this respect). Note also on the second page of this report that they make a strong comparison between the BESA and the .30 Cal Browning (which replaced the BESA in the post-war period). January 29th, 1943, and again on February 1st, more info on the difficulty of getting this problem recognised and acted upon So, all of this is what I am basing my comments on and it should be noted that one of the over-riding concerns here was the the need to have a locked down tank in the event of a CW attack. Early in the war it was still a major concern that that the Germans would once again deploy some form of Chemical Warfare and it was considered that the most likely place for them to do this was the open plains of North Africa. Any failure of charging units, or extractor fans, in those conditions would mean that the use of BESA, and the 6 pounder, had the real potential of becoming a serious threat to the AFV crew. Furthermore, the data from North Africa had suggested that the wearing of CW equipment (i.e gas capes and Gas masks) inside in a locked-down AFV would result in swift and rapid dehydration which could also be fatal for a tank crew. All of this is referenced several times in all these files. Finally, the tanks with the real problem in regards to venting gases from the guns were the new designs of the Churchill and the Cromwell and the various Scientists and committees were getting very vexed about the fact that these tanks, if not modified, could prove quite hazardous to the well-being of their crews once they were being used in anger; and their failure to get any kind of traction with DTD over a two year period really began to worry them. There is tons of this stuff in the files and I'd be here all week if I was to sort it all out and post it all here and to be honest just don't have the time for that. So, I'm afraid, sonny, if anyone is talking horseshit around here it is you and in reflection you haven't actually said anything that markedly disagrees with what I said. You just came on strong and tried to make it sound that you knew what you were talking about and that I did not. Very odd behavious given that, in effect, all you did was repeat what I had said. For the record, if you want to disagree with someone the accepted way to do this is to start off with something along the lines of "Well I'm not sure I agree with your opinion on this, my understanding of this would suggest...."... It's called politeness, decent behaviour, good form, or whatever you want, and it is the accepted method of opening polite debate / discourse. What you don't do is act aggressively and pretend that you and you alone hold the unknowable truth on all matters! When you behave in this manner you become the very reason that the ignore button was invented! Something I fully intened to make use of in the next few minutes because, ultimately, I have no need of people like you!
Well, if you'd posted that lot in the first place, I wouldn't have had a go. I get a bit annoyed with the old "everyone involved in British tank development was an idiot/small-minded/incompetent" line that your original post was meant to convey. And it was complete nonsense. It was recognised that the Besa would represent a contamination risk before it was ever fitted in a tank, and tests were undertaken from the very start. You can find the early tests in the National Archives in the WO 189 (Porton Down) series in the National Archives. Examples below: WO 189/1173 Contamination of air in tank trials with ZB 53 Machine Gun 1939 WO 189/1864 Contamination of air in tank trials with ZB 53 Machine Gun 1938 WO 189/1872 Contamination of air in tank trials with ZB 53 Machine Gun 1938 WO 189/1873 Contamination of air in tank trials with ZB 53 Machine Gun 1938 WO 189/1874 Contamination of air in tank trials with ZB 53 Machine Gun 1938 WO 189/4414 Contamination of air in tank trials with ZB 53 Machine Gun 1937 WO 189/4429 Contamination of air in tank trials with ZB 53 Machine Gun 1937 WO 189/4433 Contamination of air in tank trials with ZB 53 Machine Gun 1937 If you would like copies of these files, I would be delighted to provide you with them. That the MRC was more concerned about the issue than the Army, and wanted more comprehensive solutions is certainly interesting, but it doesn't mean that the Army did not previously know about it.
