- Member since
February 2003
- From: Panama City, Florida, Hurricane Alley
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Posted by berny13
on Wednesday, August 13, 2003 11:34 AM
Originally posted by J-Hulk
Also, maybe the longer barrel allows the pressure on the projectile to increase more than it would with a shorter barrel.
I don't see how. Once the gas reaches its max pressure, it will still push the projectile out of the barrel, but I will not increase its velocity. A projectile going through a barrel reaches its max velocity inside the barrel, after the gas pressure reaches its max pressure. The longer a barrel, the less pressure at the end of the barrel where the projectile exits. Anything after that is for stabilization. The more stable a projectile, the less the wobble and tumbling, resulting in more range and accuracy.
The same reason you can spit a spitball farther through a straw than just out of your mouth.
Ptooey! Higher velocity!
True. But here you are talking about volume. There is less volume in a straw, more pressure and stability. Using just your mouth you have more volume, less pressure and stability.
Berny
Phormer Phantom Phixer 
On the bench
TF-102A Delta Dagger, 32nd FIS, 54-1370, 1/48 scale. Monogram Pro Modeler with C&H conversion.
Revell F-4E Phantom II 33rd TFW, 58th TFS, 69-260, 1/32 scale.
Tamiya F-4D Phantom II, 13th TFS, 66-8711, 1/32 scale. F-4 Phantom Group Build.
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- Member since
February 2003
- From: Tochigi, Japan
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Posted by J-Hulk
on Wednesday, August 13, 2003 12:43 PM
Maybe a bad analogy.
Truth is, I have no idea!
But in practice it seems that the longer barreled guns are the higher velocity weapons.
Any other theories as to why? Is it simply the longer barrel that somehow increases velocity, or is the shell itself beefed up to chuck a projectile more forcefully out of a longer tube at higher velocity in order to take advantage of the better range and accuracy? I'm thinking of the Tiger I and Tiger II 88mm cannons and ammunition here.
~Brian
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- Member since
May 2003
- From: USA, GA
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Posted by erush
on Wednesday, August 13, 2003 1:12 PM
Both of you are right on the basics.
A projectile fired by a powder charge is propelled by the gas from the burning powder. The maximum pressure of that volume of gas will develope at a certain point in a long enough barrel and after that the projectile does indeed begin to slow down due to friction.
Now, all calibers and powder charges have a different barrel length where that maximum pressure is reached. This can only be truely found by testing and will change with different powder charges and projectile weights. This will give you the maximum muzzle velocity for a round.
Then effective range of a projectile is determined by the mass of the projectile and the velocity that it leaves the barrel. The heavier and faster it is, the more enrgy it will carry downrange.
That's the basics, you also have to get into chamber pressures and coeificient of friction on the projectiles and that's why you see so much about handloading amongst firearms enthusiests.
As for the length of the barrel effecting accuracy, it does only to a point. Once the bullet reaches the maximum spin rate (in a rifled barrel) beyond that accuracy is effected more by the barrel itself in how much flex and vibration occures while the projectile travels down it. (Heavy barrel rifles ((thicker walled)) are generally more accurate). Also a thin walled barrel with warp more from the heat if fired too fast.
As for smoothbore cannons accuracy again is determined by the barrel vibration etc. but also the projectile itself being a stable design that maintains the stability after it leaves the bore or in modern cases, finned projectiles that maintain the stability.
* deep breath * ![Tongue [:P]](/FSM/CS/emoticons/icon_smile_tongue.gif)
hope that down and dirty helps some.
Eric
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- Member since
May 2003
- From: USA, GA
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Posted by erush
on Wednesday, August 13, 2003 1:24 PM
BTW, The to answer the length of the Tiger 88 barrel lengths. Yes it was due to the round requiring a longer barrel to maximize the potential of velocity for the round. Basically the bigger the diameter and bigger the powder charge the longer barrel you'll need up to a point. It's a weird science and still usually takes test fireing to get the best results. you can get close on paper with most ballistics but only close.
Also on the Sherman the short barrel cannon probably did not have the velocity or the accuracy of the long barrel version. I think that barrel was too short to be worth anything, but that's just my opinion. I've not seen any ballistic data for either one.
Eric
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- Member since
February 2003
- From: Panama City, Florida, Hurricane Alley
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Posted by berny13
on Thursday, August 14, 2003 8:13 PM
erush. I can fully understand what you are saying. The book states that both tanks used the same ammo. In my way ot thinking that would give the long barrel a disadvantage. Ammo wasn't specfically developed for the long barrel until early '45.
The book shows that the long barrel version would fire so the round would arc up and fall down on the top of an enemy tank, instead of shooting directly at the side or front. I don't know if this was because of the thicker armor of the German tanks or to compensate for the lack of penetrating power of the 76 MM cannon.
Berny
Phormer Phantom Phixer
On the bench
TF-102A Delta Dagger, 32nd FIS, 54-1370, 1/48 scale. Monogram Pro Modeler with C&H conversion.
Revell F-4E Phantom II 33rd TFW, 58th TFS, 69-260, 1/32 scale.
Tamiya F-4D Phantom II, 13th TFS, 66-8711, 1/32 scale. F-4 Phantom Group Build.
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- Member since
May 2003
- From: USA, GA
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Posted by erush
on Thursday, August 14, 2003 8:33 PM
I can see that Berny. If the round was designed specifically for the short barrel cannon then the longer barrel could actually shoot the round slower. This would require a greater arc to the ballistics of the projectile to shoot the same distance at a slower speed.
Eric
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