Posted: 5/28/2009 8:46:32 AM EDT
What is that eccentric cylindrical bulge in the main barrel?
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It's called a "bore evacuator" here in the U.S., or a "fume extractor" over in europe. It functions to vent the gasses from the propellents from the main gun round out toward the muzzle as opposed to back inside the turret.
ETA: When you remove the "bore evacuator" (made of a composite material) for cleaning (part of "after ops" PMCS subsequent to firing the main gun), you'll see holes located evenly around the barrel under the BE-can't remember how many (four?). A mechanical engineer explained to me once that some the gasses from the round vented through the holes in the barrel into the BE chamber, and as the projectile exits the muzzle, the gasses vent toward the path of least resistence (the muzzle, since the breach is still closed at that instant) because the chamber has higher air pressure than the ambient air around it. In his words, it operated on the "high-low" pressure system. Whether that's the correct explanation or not, I don't know but it seemed reasonable at the time. |
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Bore Evacuator.
It uses the vacuum of the round passing through the barrel to pull out most of the noxious fumes after firing, expelling them out via the muzzle end, so the crew doesn't choke to death. It's not 100% effective, but is far better than the alternative. Posted Via AR15.Com Mobile |
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What they said.
Most all modern tank guns have them, not just the M1. The last tank I'm aware of that doesn't is the T-54, and it's one of the relatively few differences between the T-54 and T-55. The British Scorpion light tank's 76mm gun also doesn't have one, and that's the reason they got rid of all the Scorpions. IIRC the fumes would suffocate the crew if they were operating buttoned up - which is something they need to do to work in a chem environment. -K |
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I don't know about the M1-series, but the M60A1 I served on with the 105mm main gun, the bore evacuator got real filthy when firing the main gun....a spanner wrench loosened a locking nut, then the crew could unscrew it & remove it by sliding it over the muzzle. Posted Via AR15.Com Mobile |
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Quoted:
What they said. Most all modern tank guns have them, not just the M1. The last tank I'm aware of that doesn't is the T-54, and it's one of the relatively few differences between the T-54 and T-55. The British Scorpion light tank's 76mm gun also doesn't have one, and that's the reason they got rid of all the Scorpions. IIRC the fumes would suffocate the crew if they were operating buttoned up - which is something they need to do to work in a chem environment. -K The French LeClerc doesn't use a bore evacuator system. |
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Quoted:
It's called a "bore evacuator" here in the U.S., or a "fume extractor" over in europe. It functions to vent the gasses from the propellents from the main gun round out toward the muzzle as opposed to back inside the turret. ETA: When you remove the "bore evacuator" (made of a composite material) for cleaning (part of "after ops" PMCS subsequent to firing the main gun), you'll see holes located evenly around the barrel under the BE-can't remember how many (four?). A mechanical engineer explained to me once that some the gasses from the round vented through the holes in the barrel into the BE chamber, and as the projectile exits the muzzle, the gasses vent toward the path of least resistence (the muzzle, since the breach is still closed at that instant) because the chamber has higher air pressure than the ambient air around it. In his words, it operated on the "high-low" pressure system. Whether that's the correct explanation or not, I don't know but it seemed reasonable at the time. Heard the same thing. This might not be true, but seeing as the M1 was designed to fight in nuclear scenarios, the bore evacuator also keeps fallout from entering the turret. |
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Quoted:
It's called a "bore evacuator" here in the U.S., or a "fume extractor" over in europe. It functions to vent the gasses from the propellents from the main gun round out toward the muzzle as opposed to back inside the turret. ETA: When you remove the "bore evacuator" (made of a composite material) for cleaning (part of "after ops" PMCS subsequent to firing the main gun), you'll see holes located evenly around the barrel under the BE-can't remember how many (four?). A mechanical engineer explained to me once that some the gasses from the round vented through the holes in the barrel into the BE chamber, and as the projectile exits the muzzle, the gasses vent toward the path of least resistence (the muzzle, since the breach is still closed at that instant) because the chamber has higher air pressure than the ambient air around it. In his words, it operated on the "high-low" pressure system. Whether that's the correct explanation or not, I don't know but it seemed reasonable at the time. Heard the same thing. This might not be true, but seeing as the M1 was designed to fight in nuclear scenarios, the bore evacuator also keeps fallout from entering the turret. Either way, the residual gasses from firing a round are considerable once the breach drops and extracts and ejects the "stub base" in the confined space of a turret that may or may not be "buttoned up". It's not too bad when the hatches are opened, but with the hatches closed the NBC overpressure system sure as hell makes a considerable difference. In an NBC enviornment, the NBC overpressure system, combined with a round loaded in the main gun, should be sufficient against contaminaion even with the breach opened for a few seconds after firing until a fresh round could be loaded. |
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It is similar to the gas port in your AR barrel. And, the gas port hole under the bore evacuator isn't very large either. I'm thinking they are around .25 of an inch or so, I've cleaned them with Q-tips on many occasions. They are at about a 45 degree angle back toward the turret, IIRC. I'll have to dig out my data from "gun tube technology" form Mike Golf School (no, I didn't attend it, but I used to scavage as many of the lesson plans as I could). |
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Quoted:
Quoted:
What they said. Most all modern tank guns have them, not just the M1. The last tank I'm aware of that doesn't is the T-54, and it's one of the relatively few differences between the T-54 and T-55. The British Scorpion light tank's 76mm gun also doesn't have one, and that's the reason they got rid of all the Scorpions. IIRC the fumes would suffocate the crew if they were operating buttoned up - which is something they need to do to work in a chem environment. -K The French LeClerc doesn't use a bore evacuator system. Isnt the Leclerc on an auto-loading breach? |
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It is similar to the gas port in your AR barrel. And, the gas port hole under the bore evacuator isn't very large either. I'm thinking they are around .25 of an inch or so, I've cleaned them with Q-tips on many occasions. They are at about a 45 degree angle back toward the turret, IIRC. I'll have to dig out my data from "gun tube technology" form Mike Golf School (no, I didn't attend it, but I used to scavage as many of the lesson plans as I could). It has been a long time.  I just remember that they're small, compared to the size of the main gun. Also, they improved the bore evacuator from the M1 to the M1A1 by making it much easier to remove. As Silverstate was talking about a spanner wrench, I think the BE on the M1A1 was removed via a single allen screw. 
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[-K The French LeClerc doesn't use a bore evacuator system. Is that because they never fire their gun? 
[/quote] Ahh, the words "French" and "tanks" come up and the hilarity ensues lol. The French don't seem to be into the whole "bore evacutuator" thing...Neither the AMX 30, the Israeli "Isherman" (that used a modified French designed 105mm main gun on an M4 Sherman) or any of the experimental AMX series like the AMX 40 ever had a BE. I believe they use an "excavating fan" inside the turret to deal with the fumes. I could be wrong, but that's how I recall it. The last time French tanks were used in combat was Desert Storm, I believe-somebody correct me if I'm wrong. I don't know if they were involved in any main-gun engagements or not. |
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It is most definatly a "bore evacuator". and it does exacly as described above. I was a TC on a USMC M1A1 for 6 of my 10 years in the "suck". Just like the M60's bore evacuator it is removed with a spanner wrench and has 2 large "O" rings that keep it sealed. IIRC there are 4 very small ports for the gasses to vent into the evacuator. If you youtube a video of the tank firing you will see that when the main gun comes back into battery that there is a puff of smoke that comes out. Those are the gasses that were in the evacuator being "pulled" out.
That area inside the evacuator doesnt get to dirty and is fairly easy to clean in comparison to the M60. One thing I had my crew do at every PMCS was to pull the evacuator and give the area on the gun tube a good thin layer of greese. Made cleaning it a breaze. the other difference is the propellants used in the 120mm burn alot cleaner than the 105mm. You definately want to make sure you take care of this piece though. ifit gets to dirty it can cause a flare back inside the turret of the tank like i found out when I was gunning on tank table VIII one time. Scared the shit out of me but the halon supression system put it out before I even realized what was happening. After it set in, thats when I almost shit my CVC suit. But I have to tell you, the smell of nitro cellulose injected J2 triple base propellant is one of the most beautiful smells in the world right after cooking off a round
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