Bullets - Shells - Ammo - Reloading

[Whitlock]

Glenn and I were in the gun store today. The shelfs were empty four pistols in the cabinet. The store owner told us that Glock is about 100,000 guns behind
Do you think that American citizens are arming themselves or what

[MountainDon]

I have used a friend's reloading equipment for some time. My son and I have been talking about getting our own equipment. What's a good make/model? A kit with everything except the disposables and maybe the caliber specific dies?

[peternap]

I have used a friend's reloading equipment for some time. My son and I have been talking about getting our own equipment. What's a good make/model? A kit with everything except the disposables and maybe the caliber specific dies?

This is the press you want Don:
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=513567

RCBS makes a kit with the Rock Chucker. That press will do any and all single stage reloading you will ever need. 

For shotgun shells, I've used the original of this for 40 years (The same machine):
http://www.ballisticproducts.com/prodinfo.asp?number=1308447%20%20%2012&variation=

[MountainDon]

Thank you Peter. I have been looking at that RCBS at Midway    ; hadn't got to thinking about the shotgun yet. 

I've been told the 505 scale is very good.   ?

[NM_Shooter]

Hmmm... my browser ate my reply!

I have had a few scales, and the 505 is my favorite.  If I recall correctly, it has agate bearing surfaces.  Don't store the scale with the beam on the scale.

Once you get a scale, get a bunch of small objects like paper clip, dime, bb's, etc, and weigh them.  Note their weights and put them in an envelope for storage.  If you ever wonder if your scale has drifted out of calibration or gotten damaged or whatever, pull out those references and check them.  You can also buy check weights if you want a more expensive way to check your scale.

I have found that I get much more accurate and repeatable results if when I measure, I tap the scale pan to let it swing gently. 

The 505 is also a nice scale in that the magnetic damper uses a copper sheet instead of aluminum.

[NM_Shooter]

BTW... I once started to wonder about how those scales actually work.  It took me an overnight sleep to figure it out.  Here's the question...

If you have a perfectly theoretical balance beam,  it will balance perfectly when the two moments exactly equal one another.  But if one side weighs more than the other side just a little, that heavy side will collapse all the way down.

With a scale, if you are just a little bit off, the heavy side will go down maybe just a little bit.  Many scales have a graduated pointer to help in measuring. 

If one side is heavier than the other at the initial balance point, how is it possible that the reloading scale (a practical scale vs a theoretical one) can find equilibrium and not keep moving until it hits a mechanical stop?

Any guesses?    

[John_C]

The center of gravity is below the pivot.

As the lighter side rises, the lever arm on that side increases and the lever arm of the heavy side decreases.  Soon the moments of the two sides are equal.


Things that make you go hmmmmm

[NM_Shooter]

Nope... both sides are proportionally affected the same... by the cosine of the angle.  The weight dish places a point load on the beam that stays in the same location.

This would also work if the load was above the pivot point of the beam.   

[peternap]

I have several scales and I keep using my 40+ year old Lyman. It is a near duplicate of the 505 and hasn't let me down yet.

Don, you'll find you use the scale very little if you have a GOOD dispenser. Use the scale to set it up and weigh every 10th charge.....unless you are loading maximum loads. Carefully weigh each one using the same routine each time.

[John_C]

I was running out the door when I posted earlier and don't think I explained it well.  But if the pivot was below the CG it wouldn't work.

It can be considered as one load with a single CG as shown above or as two loads each having a moment arm from the pivot.   I can draw it the second way as well. 

[NM_Shooter]

place a square stick on top of your finger and balance it.  Put a small weight on top of the stick on one end.  The stick will rotate slightly and will come to equilibrium even though the center of mass of the stick and weight are above the fulcrum. 

Now do the same with a razor blade for a balancing point instead of your finger.  The slight change in mass on the end will make the stick rotate much more, and quite possibly cause the whole thing to topple off.  The CG / CM and initial fulcrum point have not changed, yet the stick rotates much more.

Why do you suppose that is?    

[MountainDon]

I'm trying to imagine what's going on without getting our balance beam scale out of wherever it is. 

Maybe I need to sleep on it?

[John_C]

The CG of the loaded beam essentially form a pendulum beneath the pivot.

When you balance a stick on your finger (or anything mushy) the pivot point can move a little. The load is spread out and a small change would be accommodated.

You can balance a stick on top of a razor blade but if the cg is above the pivot an imbalance will not be corrected by a small rotation of the beam (stick).

[John_C]

Here is a drawing with the CG above the pivot.  Any loading that moves the CG from directly above the pivot will disturb the balance and in this case as the beam rotates counterclockwise the moment arm between the load and the CG increases.  Exactly the opposite of our beam scale example.



You seem to be saying that a beam balance behaves the same whether the CG is above or below the pivot and that's not the case.

[NM_Shooter]

Hmmm... you've got me thinking.  So here's the question.. why does it find equilibrium for some point other than theta = 90deg?   I believe that if you replace your pivot point with a roller bearing, the system becomes grossly imbalanced.  Consider the force diagram for this:



Unless the beam in the model can not be represented as a line..
Are you saying that the shift of the mass of the beam itself (the small wedge of the beam under the fulcrum point) is solely responsible for the new equilibrium?

[John_C]

In your example once out of equilibrium the beam would not stabilize. 


Here is a diagram of what I tried to verbalize in my first post.  You took it to mean that I said the CG of one side or the other had moved...not at all

The CG stays the same but the moment arm changes as the CG rotates around the pivot point.  The moment of each side is dependent on it's horizontal distance from the pivot.

If one side is slightly heavier it will rotate in a direction shortening the moment arm.  The moment arm of the lighter side becomes somewhat longer.  The beam will "pendulum" until the two moments are equal.

[NM_Shooter]

If you replace the pivot point on your model with a roller bearing... what happens?

Yes... in my diagram equilibrium won't occur.  That was my point.  But in practice equilibrium occurs.  Why does my force balance model not fit the actual beam?  Is it because the beam can not be modeled as a single line?  That might be it.

I had though that the reason for equilibrium was that the fulcrum point is not perfect... it has a radius.  As the beam shifts down, the moment arm on the downhill side shortens as the fulcrum point rolls towards it.  (the finger and stick example)

However, in looking at my balance in the garage, the fulcrum point is above the center of the beam itself, which is what you noted above.  I think that if we use either your first or third drawings, when the beam shifts, a larger portion of the mass of the beam is displaced which is below the pivot point. So the thing is stable at some theta angle.  If we use your drawing #2, the majority of the mass of the beam is above the pivot point and the beam would topple.  Is that right?

Another night's sleep wasted!

-f-

[John_C]

Is it because the beam can not be modeled as a single line?

BINGO

Here is a drawing showing (more or less) the change in the moment arm as the beam rotates from horizontal (gray beam) to 30˚

Changing the pivot from a point, which is what it is in a good beam balance, to a finger or a roller bearing just muddies the issue.

The pendulum drawing #1 is probably the easiest to understand.