Ballistics gurus, can you help me out?

[shawn1172]

I'm trying to find out what the muzzle velocity would be in my .44 magnum Marlin 1894. I'm using Hornady 200gr. XTP in it. Their website lists mv at 1500 fps but their test barrel is 7.5". What would it be out of the 20" barrel on my Marlin?

And another question, does anyone know the BC for Federal's 180gr. .308 Powershok? I can't find it on their website and I'm trying to get a drop chart for it with a 100 yard zero. Federal gives a drop chart but it only goes to 300 yards with a 100 zero so I was going to use the calculator on Hornady's site but need to have the BC for that.

Thanks!

[knitepoet]

Would have to know what powder to figure the MV between a 7.5 and 20" barrel.

there are programs that is you have the 100 and 200 yard velocities, they will figure the bullet's BC. Though with just published velocities, it's not going to be very close.
Best way to find out is actually shooting at distance and recording your drop.

You can figure the bullets BC and figure APPROXIMATE trajectory here though
http://www.jbmballistics.com/ballist...culators.shtml

it's all online, no downloads of anything required. Though you'll have to scroll down to get to the BC calculator

[shawn1172]

Thanks Knite. I don't know the powder since this isn't homeloads, just store bought ammo. I have both a revolver and rifle in .44 mag and was trying to figure the best distance to zero. Hornady's calculator tells me that if I zero the revolver at 25y it will be 0.4 high at 50y, 0.4 low at 75y and 2.6 low at 100. I was going to zero both of them at 25 until it occured to me that the mv will be different for the rifle due to the longer barrel so the above trajectory won't apply. I guess I'll just zero it at 50y and check it's POI at 100. I doubt it will be different enough to be of any concern regarding minute of deer. So basically, as I often do, I'm just overthinking the matter.
As for the BC for the .308 round- I just wanted to find out the drop at distances beyond 300. I wouldn't try to shoot beyond that hunting but would like to know the drop anyway so I can try to get some practice at longer distances and be able to adjust accordingly so my rounds aren't hitting some unknown point in the dirt. Federal's site gives drop charts for longer distances but only with a 200y zero and I want to stay with 100.

[shawn1172]

I just checked the Winchester site to look up the same weight/design bullet from them. They give drops out to 400 with a 100 zero. Their 200 and 300 drops are pretty close to Federal's (4.6 and 16.6 win vs 4.9 and 17.3 fed) so their 37.5 drop at 400 will give me an approximation anyway.

[Pegasus]

The Federal website gives a drop chart to 500 yards with a 200 yard zero; look at the drop box under "Long Range".

The JBM calculators require you to have beginning and ending velocities, or time of flight (better have a good stop watch and fast reflexes.)

The bullet drag and twist calculator will require you to pull one bullet and measure it well, then enter the measurements in the form.

[Spk]

I'm trying to find out what the muzzle velocity would be in my .44 magnum Marlin 1894. I'm using Hornady 200gr. XTP in it. Their website lists mv at 1500 fps but their test barrel is 7.5". What would it be out of the 20" barrel on my Marlin?

Here's a start:
http://ballisticsbytheinch.com/44mag.html

Surprisingly, over the range of loads tested (165 gr. -- 240 gr.) there seems to be only about a 5-10 percent increase in velocities from 7-8 (in) to 18 (in).

If I were to guess and give Hornady a 5-10% increase in velocity for the longer barrel then I might expect to see velocities around 1575-1650 f/s. (this is a guess only though)
http://www.hornady.com/store/44-Mag-200-gr-XTP/

I would probably expect to see better performance from their LEVERevolution® line of ammo in a lever gun.
http://www.hornady.com/store/44-Mag-...EVERevolution/

And another question, does anyone know the BC for Federal's 180gr. .308 Powershok? I can't find it on their website and I'm trying to get a drop chart for it with a 100 yard zero. Federal gives a drop chart but it only goes to 300 yards with a 100 zero so I was going to use the calculator on Hornady's site but need to have the BC for that.

Thanks!

Use a BC of .390 (G1 drag model) and your numbers should be very close.

With the 100 yard zero you can expect drops of about [ @ 400 yards (-39.2") and @ 500 yards (-72.5")]

JMHO

[Eturn]

General rule of thumb is between ten and twenty ft.sec per inch. But only out to a point. So depending on the powder, you can actually see a lower velocity because of drag in the barrel once the expanding gasses have found equilibrium. If you are using a very fast burning powder then it will find equilibrium faster.

Sorry for the edit. Out of my 24" barrel running the same bullet with 9.6 gr of titegroup I have chronoed mine at 2130 ft.sec. Which equates to almost 40 ft.sec per inch. Like I said, rule of thumb.

[JasonMPD]

General rule of thumb is between ten and twenty ft.sec per inch. But only out to a point. So depending on the powder, you can actually see a lower velocity because of drag in the barrel once the expanding gasses have found equilibrium. If you are using a very fast burning powder then it will find equilibrium faster.

"Equilibrium"? No...

The barrel of a gun is a pressure vessel. Equilibrium is ONLY reached when the bullet leaves the barrel and the expanding gases escape the muzzle and pressure inside the barrel returns to atmosphere. As long as there is still substantial pressure behind the bullet (there will be) then the bullet will continue to accelerate until it reaches the muzzle. What can happen is that the pressure drops dramatically after the bullet reaches a certain point in the barrel, but then you will just receive no appreciable gains in velocity.

If that barrel was 60" long, then you might get a bullet stuck in the barrel.

[Eturn]

Eventually the friction of the barrel will overcome the force of the expanding gasses. The point when friction equals force from expanding gasses is equilibrium. How soon that happens depends on many factors. One of which is the burn rate of the powder.

[shawn1172]

Use a BC of .390 (G1 drag model) and your numbers should be very close.

That's the ticket! The drop that gives me at 200 is off of Fed's by 0.1 and is the same at 300 so it should be good to go. Thanks!

[Pegasus]

Eventually the friction of the barrel will overcome the force of the expanding gasses. The point when friction equals force from expanding gasses is equilibrium. How soon that happens depends on many factors. One of which is the burn rate of the powder.

The principle of operation of smokeless powder is that when it burns it turns into a gas that is about 1000 times the volume of the unburned powder under standard temperature and pressure (STP). The powder is manufactured in such a way that it burns much faster and is consumed much more completely when it is confined, in other words when it burns under pressure.

Now through formulation and coating, various powders have different burn rates. Some will burn very quickly and others will burn more slowly, but the identical amounts of powder will generally produce identical amounts of gas, about 1000 times the volume of the powder.

So, whether it takes .01 seconds to burn 40 grains of powder or it takes .015 seconds to burn the same amount, the resulting amount of gas is the same in the barrel. What is different is that the faster powder will burn completely very quickly, while the bullet is still close to the case or maybe even in the case, whereas the slower powder will take a little longer to burn as the bullet is moving down the barrel a little bit and as the bullet moves the volume of the bore increases.

What generates muzzle velocity is the amount of gas produced by the burning powder and that amount is directly proportional to the amount of powder used. The more powder you burn, the faster the bullet goes until it exists the bore. Now, I said "directly proportional," and that's not quite right, burning powder creates energy and pushing the bullet is one of the uses of that energy. Energy is also used to create heat, noise and not all of the powder is consumed. So at the top end, adding more powder does not seem to translate directly to the expected velocity increase. But that's another story.

The reason we use "fast powder" in a pistol is because we do not have a lot of it and we need to accelerate the bullet very quickly because the barrel is short and the gas does not have a long time to push the bullet.

The reason we use "slow powder" in a magnum rifle with a long barrel, is because we use a LOT of powder and if it all burned at the rate of a "fast powder" we would have incredible pressures while the bullet is still in the case or barely out of it. By spreading out the generation of gas over a (short) period of time, we get all the powder to burn and thus get our full load of gas, and we keep the peak pressure to sane levels.

All that to say is that for the purposes of the discussion here how fast we get our full amount of gas is not a factor in determining when bullet friction overcomes the pressure of the gas behind the bullet, provided we start with the same amount of powder.

[Eturn]

That does make sense. But there is just something in the back of my mind that is telling me Im missing something. I need more coffee.