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Pressures, .50 caliber rifles, strength of materials, PART 1

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Pressures, .50 caliber rifles, strength of materials, PART 1

Old 03-11-2006, 07:46 AM
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Nontypical Buck
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Default Pressures, .50 caliber rifles, strength of materials, PART 1

I earlier said that alot of powerful, effective deer killing loads could be operated under 10,000 psi. As a starting point, I would like to explain why and how that is possible, because for many, it may seem to be very anemic pressure for a hunting rifle. Lets consider a centerfire rifle first, say a 25-06. Loads for the 25-06 need to operate at peak pressures less than 51,000 psi and for 100 grain bullet, the muzzle energy is in the neighborhood of 2300 ft.lbs. Now the pressure impresses force on the bullet by the following equation

Force = Pressure (lb/sq in.) * Area of bore (sq. in.)

So at peak pressure, the force is:

Force = 51000 * (PI*.25^2)/4 = 2503 lbs. force

Now lets calculate the pressure required to generate the same force in .50 caliber. The big difference in pressure will come about by the dramatic increase in cross sectional bore area. Since area increases by the square of the bore diameter, doubling the bore size actually quadruples the cross sectional bore area. So lets calculate the pressure required to impress 2503 lbs force on a .50 cal projectile.

Pressure (psi)= Force (lbs force) / bore area (sq in.)

Pressure = 2503 / ((PI*.5^2)/4)= 12,750 psi

Are you surpised? Now think about a few things. The 25-06 isn't particularly efficient at delivering muzzle energy. With a 3200 fps MV, there is alot of friction in the bore. Also its going so fast that the time in which the breech gases have to accelerate the bullet is considerably shorter than in your muzzleloader. So you should see by now. That very, very, effective devastating deer, elk, and grizzly hunting loads can be loaded into your muzzleloader for a fraction of the risk, (and monetary cost), of a three pellet "magnum" load.

In my next, post i will discuss the strength of materials and how pressure translate into stresses within your barrels.

Happy Hunting, Phil

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Old 03-11-2006, 09:57 AM
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1

Taking the concept one step further would be a cannon. I built one of these when I was in high school. Used a 4" steel bar that was about 24" long. Bored a 2" hole in it. No rifling. Made a mold for casting a 1.9" lead ball. I would expect the pressures, even with a 1/4 can of black powder, were quite low.

However, the trend toward smaller bullets at higher velocities and pressures in undeniable. Mainly for long range trajectory and, to a lesser, degree, recoil I'm personally thinking about hunting with a 200 grain Shockwave in 2006. This .40 caliber bullet has a high BC and is going over 2300 comfortably; and could represent an honest 250 yard load. I like the big lead conicals but they start dropping off pretty fast beyond 150 yards.
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Old 03-11-2006, 10:14 AM
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1

ORIGINAL: Roskoe

Taking the concept one step further would be a cannon. I built one of these when I was in high school. Used a 4" steel bar that was about 24" long. Bored a 2" hole in it. No rifling. Made a mold for casting a 1.9" lead ball. I would expect the pressures, even with a 1/4 can of black powder, were quite low.

However, the trend toward smaller bullets at higher velocities and pressures in undeniable. Mainly for long range trajectory and, to a lesser, degree, recoil I'm personally thinking about hunting with a 200 grain Shockwave in 2006. This .40 caliber bullet has a high BC and is going over 2300 comfortably; and could represent an honest 250 yard load. I like the big lead conicals but they start dropping off pretty fast beyond 150 yards.
Right, and I understand the need for the load you use. I also live in Colorado and if I used my ML in regular rifle Elk season, I would probably use a load just like the one you are using. I expect to draw antlered elk for statewide ML season this year and hope to call my elk close enough for a big lead conical.

Allow me to say this. I am not worried about you, sabotloader, and others who are very experienced with MLers. This is really for the benefit of individuals who have been frightened from using their Spanish barrelled rifles and people who have children who are not experienced with MLers.I am hoping to givethem an understanding which will give them some level of confidence that the Muzzleloader they purchase can be enjoyed and hunted with safely.

Happy Hunting, Phil
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Old 03-11-2006, 07:33 PM
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1

Pglasgow

Allow me to say this. I am not worried about you, sabotloader, and others who are very experienced with MLers.
I for one am interested in the development of this thread, in fact if I didn't have such a fond feeling for my Firebolt - I would offer it for any tests that you or Roskoe, as a gunsmith, might want to conduct with it. Actually they are so darn cheap we ought to take up a collection buy one for one of you guys- let you get behind a dirt wall and see what the thing will take. But I do not know what that would prove, because we are probably not qualified to make such a test. Well, I do not have the qualifications for it to mean anything other than myself....

looking forward to more information....


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Old 03-11-2006, 07:50 PM
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1

First let me say I am not an engineer, nor am I
a metel fatique specialist. I do however understand
FORCE/MASS/PRESSURE. I also own a 45cal with
the dreaded barrell. So keep me posted, I'm
never too old to learn. I do understand that
their are some who need close scrunity when
handling any ML. Most of these folks have no
idea of what really happens when they load
prime & touch off their ML. Just my 2-cents
Danny

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Old 03-11-2006, 07:57 PM
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1


Force = Pressure (lb/sq in.) * Area of bore (sq. in.)

So at peak pressure, the force is:

Force = 51000 * (PI*.25^2)/4 = 2503 lbs. force

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Pressure (psi)= Force (lbs force) / bore area (sq in.)

Pressure = 2503 / ((PI*.5^2)/4)= 12,750 psi
With the top formula are you assuming a 100 gr bullet weight? If that's so since you used the 2503 then you have a 50 cal shooting a 100 gr bullet for that pressure. As you increase bullet weight the pressures go up. You'd be better off comparing something with a reasonable bullet weight. The minimum I'd use would be 240 gr. Your pressures will be higher than you think. Of course this doesn't take into account the differences between plastic (saboted bullets) and a copper jacketed lead bullet or bore conditions. The smoother the barrel the more velocity your pressure will give you. And plastic saboted bullets don't generate the friction of a copper jacketedbullet which would translate to slightly lower back pressure/increased velocity for the same bore. If your comparing the Copper jacketed bullet to a lead conical that doesn't equate right either. The lead will use some of the pressure to swell into the rifling. This is why comparing saboted bullets of equal weight the lead bullet will be somewhat slower. 100-200 FPS depending on bullet weight.

In reality formulas really don't tell you anything but theoreticals. The only way to know for sure is to use a test barrel specifically designed to test pressure. Strain gauges won't even give you accurate data. You can use them as a comparison tool but their use in muzzleloaders is shaky at best.
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Old 03-11-2006, 08:03 PM
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1

Wolfhound76

Patrick, I have read this term a couple of times now "strain gauge" I think I have the concept but I can not picture the physical apparatus and how it might be hooked up... Could you explain further to me?... and this is an honest question...

thanks mike
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Old 03-11-2006, 08:04 PM
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1

I guess I will be following this thread with interest too, it is one thing to understand what is going on in a rifle when you fire it, and quite another to be willing to take the time necessary to put it all into terms that some one with out the education or 40 or 50 years experience can understand.
I say good for you. Lee
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Old 03-11-2006, 08:34 PM
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Nontypical Buck
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1

ORIGINAL: AQUATECH

First let me say I am not an engineer, nor am I
a metel fatique specialist. I do however understand
FORCE/MASS/PRESSURE. I also own a 45cal with
the dreaded barrell. So keep me posted, I'm
never too old to learn. I do understand that
their are some who need close scrunity when
handling any ML. Most of these folks have no
idea of what really happens when they load
prime & touch off their ML. Just my 2-cents
Hey Danny,

It is important to know that with 45 cal., your pressures are going to be higher for an equal charge of powder and equal weight of projectile than in a .50 cal. Roughly, not exactly mind you, 66% higher. There are good reasons for this. Because the bore area is smaller, the pressure must rise above .50 cal pressure in order to accelerate a bullet at the same rate of accelleration as it does in 50 cal. In a .50 cal, because of the greater bore area, the breach volume expands faster than it does in .45cal, meaning that, pressures will build longer and won't drop as fast from the peak as they do in a 50 cal. That said .45 cal, because of the smaller bore, for the same pressure, will stress the barrel less, given the same wall thickness. I'll get into this in more detail in my next thread, its just a fancy way of saying that a .45 barrel with the same or thicker wall thickness can carry more pressure in the bore while stressing the barrel less than .50 cal.

There will be alot more on this subject Danny.

Happy Hunting, Phil
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Old 03-11-2006, 08:36 PM
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Default RE: Pressures, .50 caliber rifles, strength of materials, PART 1

ORIGINAL: sabotloader

Wolfhound76

Patrick, I have read this term a couple of times now "strain gauge" I think I have the concept but I can not picture the physical apparatus and how it might be hooked up... Could you explain further to me?... and this is an honest question...

thanks mike
This is my understanding so if sombody noticesI'm wrong on something speak up.

A strain gauge is nothing more than electrodes placed on the barrel that are connected to a computer. They measure the flex of the metal. The problem is that you have to know exactly what alloy your barrel is and you have to place them in a certain place (over the bullet I believe). With muzzleloaders having no case a powder increase/decrease changes the place they have to be and and if they're not placed exactly right can give you false readings. Also I believe you have to calibrate them with a known load. It's just software and the electrode aparatus.

There's also another way to estimate pressure that relies on software and a chronograph. You imput the velocity, bullet etc. and it spits out a pressure graph. It's not that accurate either and can be off by a few thousandPSI if all the variables aren't right.Plus I don't think there's a version for muzzleloaders with all the extra variables we deal with so there's an error factor built in.

The only way to know for sure is a test barrel. And even that will be off because of variances in the bores. It's still by far the best way to do it.
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