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Low Velocity vs High Velocity gun...


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#1 GrandsonofAMarine

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Posted 12 April 2009 - 02:34 PM

What exactly is the difference outside of the obvious increase in velocity. I was reading about the Sturmgeschütz III and the article was talking aobut how its' 75mm went from a low velocity to a high velocity weapon. Does that mean its barrel was lengthened? I read that the longer the barrel the greater the velocity of the shell.

Is this correct? Excuse my ignorance as I have just started to read more in depth about weaponary.


#2 brndirt1

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Posted 12 April 2009 - 03:04 PM

What exactly is the difference outside of the obvious increase in velocity. I was reading about the Sturmgeschütz III and the article was talking aobut how its' 75mm went from a low velocity to a high velocity weapon. Does that mean its barrel was lengthened? I read that the longer the barrel the greater the velocity of the shell.

Is this correct? Excuse my ignorance as I have just started to read more in depth about weaponary.


That is one of those "yes and no" questions, where the answer is both. Yes, the length of the barrel is directly related to the velocity of the projectile. But, no it isn't JUST the barrel length.

When the propellent charge is increase, the barrel has to be lengthened so that the charge can burn in the confines of the tube, and not after the projectile has left the muzzle. Too little charge in a longer barrel may just as easily slightly slow the projectile as it would have quit expanding before the projectile left the end of the tube, and friction could (in theory) begin to effect the speed in a negative.

Here is something interesting which I just saw demonstrated the other day on a program on "bullets". If you hold a bullet (sans charge), with a device which releases it when the trigger of a rifle sitting next to it is pulled, and the bullet in the rifle is the same weight as the bullet in the holder, and there is nothing in the way to stop the powered bullet; they will both hit the ground at the same time.

Gravity, while not too evident a force on a bullet in flight, acts on both items at the same force rate. Very much like the experiment on the moon when that astronaut dropped a feather and a hammer to demonstrate that Galileo had it right. Both the feather and the hammer arrived at the surface of the moon at the same moment.
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Happy Trails,
Clint.

#3 razin

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Posted 12 April 2009 - 06:18 PM

GrandsonofAMarine

It depends what purpose the weapon is for. Anti-aircraft guns and Anti-tank gun require a high velocity for diferent reasons, the Anti-aircaft gun needs a high velocity to reach high altitude, the anti-tank gun requires high velocity to have sufficient energy to penetrate the target. Therefore the famous 88mm gun Flak18 could put an explosive shell to 9900metres or put a 9.5kg shell through a 105mm plate at 30° inclination at 1000metres.

You may also see the term L/48 L/70 etc this describes the length of the barrel as a ratio of the bore hence a 75mm L/70 gun will be 5.25metres long this refers to the length of the rifled part of the barrel so the length of chamber and breach need to be added as an overall length.

The L/70 length guns such as the Panther and Tiger 2 and US 3inch Naval gun have very high velocity with large propelling charges, however there is a cost, the high velocity barrel wears out faster, to the effect that some barrels have only 200 round life expectancy and many Anti-aircraft guns have quick change barrels or inner barrels to overcome this. For example the 40mm Bofors gun barrel is replaceable and later 88mm A/A guns had a removeable inner tube.

Shorter guns have value for other purposes the U.S. 75mm M3 gun as fitted to the Sherman was not a great anti-tank weapon because of its chamber size and length of barrel, however it was a superb weapon for High explosive shell fire with consistant accuracy, low barrel wear and ability to fire for long periods without problem

There can also be problems at extreme range with the accuracy of long barreled guns (sometimes called dispersion) this is very complex and can depend on many diverse factors, however it is sometimes found that altering the length of the barrel can improve accuracy, an example of this is the French developed the 75mm gun of the Panther Post War and found that by shortening it to 62calibre the accuracy improved at its maximum range, albeit with a slightly reduced armour piecing capability. However the similar length British 17pdr was less accurate at the same range.

So it is like much else in weapons technology improving one parameter may effect others the important thing is to get a balance.

~Steve
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#4 GrandsonofAMarine

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Posted 13 April 2009 - 12:13 AM

Wow. You guys really know what you are talking. Thanks a lot.

#5 mac_bolan00

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Posted 13 April 2009 - 11:47 AM

high rate of fire and a long time for the barrel to overheat is what i want.

#6 Thompson Tony

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Posted 14 April 2009 - 01:06 AM

Thats what the did with the Thompson. They took the .45 caliber bullet and slowed down so it would have more of a punch.
War is like tying your shoe, sometimes you win, sometimes you don't.

#7 brndirt1

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Posted 14 April 2009 - 01:19 AM

Thats what the did with the Thompson. They took the .45 caliber bullet and slowed down so it would have more of a punch.


Please explain this statement of yours. Gen. Thompson took the existing .45 ACP round, and designed a weapon around it. The same ACP round as used in the M1911 travels at a higher muzzle velocity as it exits the Thompson.

The company did slow down the Rate of Fire for the Thompson, at the military's request, but the speed of the bullet remained the same out of the Thompson even at the rather sedate 600 rpm (rounds per minute). The original Thompson fired at about 1100 rpms.

I'll post the numbers if you like.
Happy Trails,
Clint.

#8 PzJgr

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Posted 14 April 2009 - 01:34 AM

The StuG III was designed as an infantry support weapon, thus it had the low velocity short barrel L/24. A longer gun with better characteristics was what was needed and a version of the Stug III was developed, relatively quickly, with the long barrelled Stuk 40. Vehicles armed with the new gun received the following designations:

Stug 40 Ausf F 40/L43
Stug 40 Ausf F/8 40/L48
Stug 40 Ausf G 40/L48
Stug 40 Ausf G 40/L48 with Saukopf mantlet.

The designation "Stug III" was used until the war but the number '40' was intended merely to indicate that the vehicle carried the longer Sturmkanone 40.

Not detracting from the thread but expanding on your Stug example since Stugs Rule!:salute:

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#9 Thompson Tony

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Posted 14 April 2009 - 01:54 AM

Please explain this statement of yours. Gen. Thompson took the existing .45 ACP round, and designed a weapon around it. The same ACP round as used in the M1911 travels at a higher muzzle velocity as it exits the Thompson.

The company did slow down the Rate of Fire for the Thompson, at the military's request, but the speed of the bullet remained the same out of the Thompson even at the rather sedate 600 rpm (rounds per minute). The original Thompson fired at about 1100 rpms.

I'll post the numbers if you like.


i thought they slowed down the bullet to increas lethality and give it more of a punch the the 1911
War is like tying your shoe, sometimes you win, sometimes you don't.

#10 lwd

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Posted 14 April 2009 - 01:06 PM

i thought they slowed down the bullet to increas lethality and give it more of a punch the the 1911


Slowing a bullet down decreases its KE and momentum thus its leathality and "punch". The rare exceptions are HEAT rounds (especially early ones) and some other obscure armor projectile interaction cases.

#11 razin

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Posted 14 April 2009 - 01:53 PM

Thompson Tony
thought they slowed down the bullet to increas lethality and give it more of a punch the the 1911


No all the 45cal SMGs had a muzzle velocity of approximately 920f.p.s as opposed to the 45cal pistols and revolers of 830f.p.s

This is because the SMgs have a barrel length between 8" (M3) and 11"(Reising M50). whereas the revolers have a barrel length of 5.52 and the M911 5".

As Brndirt1 in Post#2said

"the barrel has to be lengthened so that the charge can burn in the confines of the tube"


As the propelant is burnt up it allows a more pressure to build up propelling the bullet at higher speed- and therefore better killing power (marginally) or longer range and greater accuracy. It also cut down the muzzle flash that is noticable when firing a pistol. The shorter barreled M3 series were later equiped with a flash supressor as they to had a flash dueto unconsumed propellant.

Slowing the bullet down does not improve lethality unless you are talking about using hollow points etc. If you need proof of this go try shooting a grizzly with a Welbley .455 revoler, very heavy bullet, low 600f.p.s muzzle velocity, no stopping power at all- second thoughts stay home the Grizzly should be eating nuts and berries not people.

~steve

Edited by razin, 14 April 2009 - 05:44 PM.
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#12 brndirt1

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Posted 14 April 2009 - 02:36 PM

i thought they slowed down the bullet to increas lethality and give it more of a punch the the 1911


Here is that data, there are tests which show the .45 ACP through the 10.5" barrel in the Thompson to be quite impressive (for a heavy pistol round).

That said, here is a portion of an interesting report (Philip B. Sharpe review of the M1928A1 Thompson from 1929):

"This .45 automatic pistol cartridge, in the arm designed for it (1911 pistol), delivers about 810 foot per seconds velocity. In the 10 1/2-inch barreled Thompson it delivers about 925 f.p.s. Tests indicate that accuracy and penetration is quite respectable, even at the longer ranges. A single shot two feet from the muzzle, using the 230 grain bullet, tested on 3/4-inch yellow pine boards spaced one inch apart, ran through 6 3/4 boards. At 100 yards it would plow through six boards; at 200 yards through 5 1/4; at 300 yards, 4 1/2; at the 400 mark through four boards, and at 500 yards it could still stumble through 3 3/4 boards sufficient to cause very unpleasant sensations in the body of a recipient." [Page 1107]


The original "Thompson gun" had about a 1100 rounds per minute rate of fire. The US military wouldn’t even consider the thing until the rate was reduced. Originally it could empty it’s 100 round drum in under 4 seconds without jamming! The Thompson people made the bolt heavier, and the return spring stiffer, and "slowed it down" to about 600 to 700 rpms (rounds per minute), but it still threw out it's very heavy bullet,very rapidly, and with its Cutts suppesor with very little barrel climb.

I also have the tests from the early 1900s where the .45 pistol round was picked after the Army tested it against live animals and human cadavers in Chicago. General Thompson was in on that testing as well, along with a Dr. LeGrande. The one at a stockyard (hundreds of live cows and horses), and the cadavers at an undisclosed area.

Originally John Browning designed his pistol which was going to become the 1911 with a slightly lower bullet weight, but the Army demanded the 230 grains, so he obliged and increased it from 200, his original bullet weight. But this was of course years before the first "Tommy gun" was even produced. The bullet weights for both the Thompson SMG and the 1911 .45 ACP are/were identical in military loadings.

Edited by brndirt1, 14 April 2009 - 02:45 PM.
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Happy Trails,
Clint.




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