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I've been reading and thinking about auto-loading firearms lately and it seems that they fall into two categories: open bolt and closed bolt. And, closed bolt seems to be the preferred mode of operation in the civilian market. My question is, what difference does it make one way or another? Is one more accurate, less susceptible to fouling, what? I know there are lots of military buffs and collectors here, as well as many class III owners. Why one way or the other? Thanks, Jason "Chance favors the prepared mind." | ||
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An open bolt, as I understand it, uses less parts and is simpler in operation than a closed bolt. The Thompson SMG started it's life as a closed bolt, retarded blowback weapon, and by WW2 was a much simpler and cheaper to produce firearm firing from an open bolt. The greasegun also fired from an open bolt, and was much cheaper still. An open bolt does expose the action, chamber, etc to dirt, etc, and the forward motion of the bolt jars the weapon effecting aim, initially- this gets overlooked because accuracy is not a first concern with an SMG, due to the nature of the weapons, I suppose. The greasegun had an ejection port cover to keep dirt out of the action. It boils down to simplicity and cost effectiveness, it seems. I think a greasegun cost less than ten bucks to manufacture. | |||
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Not necessarily preferred, just legaly the way to go. There was so much hoopala about how easy the MACs, TECs and other open bolt guns were to convert to full auto, that they were essentially "ruled" out of production by the BATF&E. As far as accurate fire, a open bolt is harder to shoot to a fine degree of accuracy because of the mass moving while you are holding a sight picture. It applies itself better to spray and pray type of shooting. Open bolt is cheaper to manufacture. No fireing pin, per say, no hammer, fewer parts. I am not too sure about that statement about the Thompson beginning life as a closed bolt. As per Phil Sharpe's description and my limited hands on experience 40 yrs ago: "As in other machine guns, the Thompson "cocks" by drawing the bolt to the rear where it catches through the engagement of the sear with a notch milled in the under surface. The somewhat heavy trigger-pull (10 pounds) disengages the sear, the bolt springs forward scooping a cartridge from the magazine, and firing it as it rams it home in the chamber. The heavy bolt, flying forward, gives a noticable mechanical recoil, similar to that experienced in releasing the lock-back slide of the .45 automatic pistol while empty. This mechanical recoil, while slight, seems to be the only noticeable "jump,, to the sub-machine gun in slow fire. With the Compensator there is even a marked tendency to pull slightly away from a shooter, so there is little danger of bruising the cheek in rapid shoulder fire." http://www.saf.org/LawReviews/PSharpe1.html Thaine "Begging hands and bleeding hearts will always cry out for more..." Ayn Rand "Life may not be the party we hoped for, but while we are here, we might as well dance" Jeanne C. Stein | |||
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I assumed due to this locking system that the original Thompsons fired from a closed bolt- but that isn't necessarily the case as it could remain locked even if it fired from an open bolt. what you cite above are the facts, as Sharpe states the open bolt outright. | |||
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If you are suppressing, closed bolt is the way to go. Also, compared to a open bolt, the closed is quieter and more accurate. "There are creatures here that cannot even be found in books, and I have killed them all......" | |||
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open bolt is for full auto submachine guns, the bolt is heavy , has a fixed firing pin , very simple trigger not much more than a lever that catches and releases the bolt, the shear weight of the bolt may be the delayed blowback, also the open bolt helps prevetn cook offs. these are not desined for semi auto. even if they have the feature of a disconnector and selector switch when the bolt lurches forward no way you can hold the gun steady for target shooting.these would be macs , uzi, grease ect. the police use mp5, they fire off closed bolt delayed roller system that would allow you to aim your shot on semi, as far as silencers go a full auto mac firing 1100 rpm wouldnt draw much attention ( noise wise) on a crowded street they are about as noisy as an air gun maybe quieter If your gonna be dumb, you gotta be tuff. | |||
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M-60? | |||
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As I see it, the primary advantage of open-bolt designs is in preventing "cook-offs". If there is no cartridge in the chamber, it is pretty hard to have it heat sufficiently from a hot barrel/chamber to fire. With an open bolt design, the cartridge is not chambered until about the same instant it is fired. Hence no open bolt cook-offs. Preventing Cook-Off CAN be a major design problem in closed bolt guns subjected to sustained fire use. Then it may become dificult or impossible to halt firing until the ammo supply is exhausted or otherwise interrupted. My country gal's just a moonshiner's daughter, but I love her still. | |||
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Somewhwere, sometime in my dim and distant past I have read that some one had an automatic weapon that fired from an open bolt in full auto mode and from a closed bolt in semi-auto mode. Am I dreaming or does [did?] such a beastie exist?????? Also, the Browning designed BAR fired from an open bolt in both the semi and full auto modes yet was an exceptionally accurate rifle. I've had very little experience with the BAR, only fired a few mags through it and never in semi-auto mode so can't speak from first hand experience. And someone, perhaps Gevarm?, made a 22 rimfire semi-auto that fired from an open bolt. Anyone recall any of this or have comments on same? Lord, give me patience 'cuz if you give me strength I'll need bail money!! 'TrapperP' | |||
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The Fallschirmjäger Gewehr 42 , designed by Herr STANGE(Sp?) works open bolt for full auto to help cooling and closed bolt for semi to get more accuracy. The BAR is one of the most stable LMG but its weight makes it a PITA to carry it whole day. The GEVARM fired open bolt. HTH | |||
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I thought the BAR was a couple of pounds lighter than the M60 - at least that is how I recall it. Only fault I ever heard with the BAR was those damnable 20rd magazines vs anything that was belt or box fed. And back again with one I left off and out of the prior post: What about the BREN - I have always heard very good things about this weapon but have never had an opportunity to fire or observe it. Anyone have first hand knowledge of this piece? Lord, give me patience 'cuz if you give me strength I'll need bail money!! 'TrapperP' | |||
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Reliable, accurate and comfortable to shoot both in .303 or .308. easy magazine change on the top. | |||
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let me clarify an eariler post, open bolt is best for full auto mode on submachine guns, has a lot less moving parts no hammer , the firing pin is welded or machined into the bolt face barrels dont have to tilt ect. a SUB machine gun fires pistol bullets and usually has a very heavy bolt. this is different than a machine pistol like a glock 18. i dont see any reason why any machine gun couldnt be made to fire from an open bolt on auto and fire semi from a closed bolt it just depends how complicated you want to make the guns trigger ,disconnector and firing pin. stens, uzi, macs, grease guns are not much more than a tube or box with a spring, bolt, magazine and barrel best bet is go to the library find a Janes book or some other small arms book If your gonna be dumb, you gotta be tuff. | |||
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The TSMG was never a closed bolt weapon. The 1921 and 1928 guns as well as the M1 and M1A were all open bolt. The semi auto versions made in West Hurley, NY were because the ATF required a closed bolt design. Full auto weapons can be designed either open or closed bolt. They are often designed open bolt so as to improve cooling AND to reduce the tendency to "cook off" a round in a hot chamber after heavy use. Mike -------------- DRSS, Womper's Club, NRA Life Member/Charter Member NRA Golden Eagles ... Knifemaker, http://www.mstarling.com | |||
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how did the schmeisser (spelling) operate? open/closed? just curious. | |||
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MP-38 and MP-40 were both open bolt ... as were the Sten, Sterling, and Uzi. Mike -------------- DRSS, Womper's Club, NRA Life Member/Charter Member NRA Golden Eagles ... Knifemaker, http://www.mstarling.com | |||
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I was lucky enough to go thru a foreign weapons course offered by the military for law enforcement several years ago. It was a two week course and we were able to handle and shoot every military weapon from 1891 to present. If my memory serves me correct, the only two closed bolt auto weapons we fired were the MP 5 and the U.S. Reising. All the belt fed machine guns were open bolt guns. Other postings were correct, being the main reson for open bolt mechanisms were to prevent cook offs. Most sub machine guns due to limited magazine capacity cook offs are not a problem and until the HK MP 5, reliability was the guiding reson for open bolt, that and cost, simplisity, ease of maintainence. Swift, Silent, & Friendly | |||
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You weren't able to fire the US 30 carbine in the M2 version?? Full auto, fires from a closed bolt and a joy to shoot! Lord, give me patience 'cuz if you give me strength I'll need bail money!! 'TrapperP' | |||
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Nope, no M-2 carbine, BUT, I did get to shoot a Czech M-62 Skorpion in 7.65 caliber with suppressor! One thing I did see,the older open bolt sub guns were the only ones that didn't "break" during the week we fired them. As for the "assault" type weapons, MP-44, AK's, M-16's, no malfunctions or broken parts and we fired thousands of rounds of ammo thru them. Swift, Silent, & Friendly | |||
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Not all open bolt guns have a fixed or welded in place firing pin. Example: The Thompson again, it has moveable firing pin with spring and a little triangular block, described as a hammer, is on a pivot and as the bolt slams home this hammer hits the receiver wall, pivots and hits the firing pin. Joe | |||
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First SMGs did not have fixed pin and inspired others. http://www.securityarms.com/forums/showthread.php?t=5 | |||
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The french AAT 52 also known as ANF1 uses a delayed opening system, is very accurate, reliable and a dream to carry in both LMG or HMG version. | |||
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Military Arm. corp. produced the MAC-12 which i belive was the fastes sub @ 1350 RPM in the 380. hell the 45 was close to 1100 if i remember. they were/ are unbelivably quick. dont even sound like gunfire. just a "braaaaaap". | |||
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"A dream to carry?" Are we speaking to the same weapon? I'm looking at a 10kg weapon with light barrel and bipod or a 23kg weapon with tripod and heav barrel????? And if you know, is there a weight difference between the AAT-52 in 7.5 French vs the AAT F-1 in 7.62 NATO? I've never seen or used one of these but have heard they really come into their own in heavy, continuous sustained fire - any comments here? Delayed blowback, Q/C barrel, fluted chamber - any relation to any previous designs? Lord, give me patience 'cuz if you give me strength I'll need bail money!! 'TrapperP' | |||
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 I have often carried the LMG version during basic training and ROTC both in 7.5 or 7.62 with the French Forces in Germany. I found more comfortable to carry the AA52 combat ready with its carrying sling than carrying the FSA MAS 49/56 combat ready. I never carried the tripod LOL and extra ammo. Since it is a delayed opening system, the chamber needs to be fluted to float the brass and help the primary extraction of the fired case. this was designed around 1945 but adoption came much later. An AA52 on steroids was made for .50 BMG round but never adopted. The AA52 is a very accurate weapons, shooting 2 or 3 rounds bursts inside an A4 size target at 200 meters is incredibly easy ( at least for me, always loved the LMGs) this is my favorite LMG  | |||
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Some answer there, about the french developments. https://forums.accuratereloading.com/eve/forums/a/tpc/f/7811043/m/363105656 | |||
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If I remember correctly, the AAT 52 was described in Small Arms of the World as being prone to headspace problems resulting in case separations. Had a resultingly bad reputation in the field. (Just a remembrance from the time I read a lot about this stuff.) Mike -------------- DRSS, Womper's Club, NRA Life Member/Charter Member NRA Golden Eagles ... Knifemaker, http://www.mstarling.com | |||
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Never heard of headspace problems. There were some case separation with the switch to 7.62 NATO due to ammo in worn out barrels when using certain aging lots of laquered steel cases. | |||
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Edmond, I'm directing most of this at you. Finally was able to break out my copy of W. H. B. Smith's "Small Arms of the World" but was not able to find the reference to the caliber controversy in the development of the Fallschirmjäger Gewehr 42 so we'll have to pass on that point for now. Did find the reference to the Gw 42 bolt being derived and developed from that of US Lewis gun. And I did find a reference to the French 30 Carbine and find it was called the 1949 MAC. What can you tell us about this one? I know that 'M AS' is acronym for "Manufacturer d'Armes de St. Etienne" - is the 'C' in 'M AC' for "Chatellerault?" The article states the weapon was never adopted but as I stated I saw some French Marines armed with them, somewhere around 1964? And finally, I found a reference to the French having made an adapter for the AAT 52 allowing it to be used on the US M2 tripod. Can you shed any light on why the AAT 52 was in development for so long before being adopted? I find this a bit odd - or do we smell 'politics' at play here? Again, this is a most interesting thread and an intriging subject. "Vive La Belle France, Lebel y Poilu" trapperP | |||
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adoption of new weapons after WW2 was delayed because France was rearming heavily to counter the Soviets. France is a founder of NATO. The war in Indochina was a burden on ffrance budget and the stock were full of french , american, english and german weapons. The .30 carbine weapon was a kind of HK as developed by AME in 1946. I'll post link to pictures on Security Arms http://securityarms.com/all.html | |||
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Not really because a cook off takes up to a minute to happen in an overheated chamber as I noticed when purposely doing tests with worn out barrels I had to change. It is always possible to eject the chambered round and keep the bolt assy at the rear until fire is resumed. | |||
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TrapperP, The BAR weighs in about 16.5 to 18 pounds depending upon whether or not you have stripped off the bipod and carry handle. It ONLY fires from an open bolt. The original and the A1 versions both fired single shot or full rate, while the A2 is full rate and rate reduced. They have firing pins and "hammers", I won't get any more specific than that. The BREN is a fine LMG, but I prefer the BAR. The BREN weighs around 24 pounds (about the same as an M60 +/- a pound ). The advantage of the top feed (magazine on top) means that it can only be fired by right handed shooters IF you desire to use the sights. The BREN also fires from an open bolt in both single shot and full rate (the BREN is selective fire). The BREN also has a fire pin and "hammer". Both the BREN and BAR fire from a locked breech, there is NO delayed blow back! When firing from the bipod on the open bolt issue is mute, IMHO, with regard to accuracy. I hope that answers some questions regarding those two weapons platforms. With regard to the original question of the post. In SMG the open bolt is utilized for cost effectiveness and safety (elimination of cook offs). In machine guns the open bolt is utilized for safety (elimination of cook offs). By the way, cook offs aren't typically instanteous. It typically takes a "considerable" amount of time for the round to fire, at which point the muzzle of the weapon may not be pointed in a "safe" direction any longer. So cook offs aren't typically a big deal with regard to guns running full auto themselves. Runaways are a different phenomena and can be very scary. The runaway is typically the result of a mechanical failure in the feeding/firing mechanism. Hope this was helpful. | |||
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Scott: Some of what you say I knew, some I did not. The one glaring fault I see with both the BREN and the BAR is the same as the M14 - the 20 or 30 rd magazine. I know with the M14 you packed 4 20rd clips plus one in the rifle giving you one hundred rds and that is not a lot of ammo, even in semi-auto mode. I can only imagine how quickly you could burn it off with the BAR or the BREN. Stoner tried and addressed this by using the 100 rd box or belt, right or left feed with his M63 LMG. Quite a weapon but one with some major problems. As for the runaways, I have never seen that with anything except the M60. We were taught to grab and twist the belt to stop the gun - the only time I personally ever had this happen we just let her run the belt through. Something in the bolt had broken but I don't recall what if I even ever knew what broke. Strange to let off and she keeps on chugging! Guaranteed to get your attention. And back to a statement I made in an earlier post - the little 30 carbine beats all I have ever fired when you consider it chambers a round, locks with a rotating bolt, fires, rotates, extracts, ejects and then repeats all this very, very quickly - say some 850-900 RPM! An amazing little weapon - too bad it was not developed with a little better cartridge thatn the 7.62X33 as it would have been a true assualt rifle. Lord, give me patience 'cuz if you give me strength I'll need bail money!! 'TrapperP' | |||
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TrapperP, I did not mean to insult your intelligence or anything, and I figured much of my comments were already well understood. | |||
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ScottS; Please - I hope I said or wrote nothing to make you think I was insulted by what you said. I have enjoyed this exchange immensely and I have learned a lot. This is as close as we can come to a face-to-face encounter and as the old Confederate sargent said in some movie (I can't recall which) "Some of the things I seen ain't in the book." Well, some of the things posted here are not to be found in the book but a lot of them I truly believe. For instance, I listened to a Korean Conflict era Marine speak of the bitter cold they faced and the problems they had - mentioned they had all sorts of frozen weapons until somebody came up with the idea of using Vitalis hair tonic on the weapons to lube them. The stuff didn't freeze and the guns kept on working. Amazing or what? And please, keep on posting. We may well disagree on a point but our frame of reference may well be different, i.e., my points from hot and humid jungle may different from yours of hot, dry and dusty - so there. Tell me what you know and tell me why, we'll sort it out. I'll even buy a round when it's my shout. Lord, give me patience 'cuz if you give me strength I'll need bail money!! 'TrapperP' | |||
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Trapper, I forgot to post the link about the little thing in .30 Carbine http://securityarms.com/20010315/galleryfiles/2100/2128.htm | |||
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In my early Army career, we were still using the M1 and the B.A.R. Despite being heavier, and the bipod, I was still able to hit distant point targets much better and more frequently with the M1 than with the B.A.R. The reason was that massive bolt and gas system slamming shut then the round going off so much later threw my aim off. If I had acquired more extensive experience with a flintlock, I might have been able to "hold through" better, waiting for that damn B.A.R. to fire.... I have since been told that those rifles were worn out, and that originally their lock time was not nearly so slow. I don't know, but I generally shoot better with a closed-bolt weapon! "Bitte, trinks du nicht das Wasser. Dahin haben die Kuhen gesheissen." | |||
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The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Military & Military Surplus Automatic: Open bolt Vs. Closed Bolt
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