Gun Trivia for Fun & Useful Facts
(some for the novice & some for the experts)

Barney@GunShowroom.com 

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Here's how the gauge of a shotgun is determined.  You can likely impress some pretty good gun people with this one. 

The gauge of a shotgun barrel was originally determined by the number of identically-sized lead balls that have the same diameter as the bore, and weigh one pound.  Example: Let's say the bore of a 20 gauge is .6 of an inch.  It would take 20, six tenths of an inch lead balls, to weigh 1 pound.  Using the same numbers, if one were to build a gun with a bore of .675 it would take 16 lead balls that size to weigh 1 pound--- thus a 16 gauge.   Oops !! - what about a 410? Truth is a 410 is not actually a gauge.  It is a caliber...  .410 inches bore.  Applying the math to this would make a 410 shotgun actually a 67 gauge.... so next time you go to buy your 410 shells ask for some 67 gauge shells and see what happens :-).  

If you want to play with this (lots of time on your hands) here is some of the math.

• Formula for volume of a sphere is  (4/3) *( pie [3.1416]) * (R cubed). 
• "R" is radius or 1/2 the diameter which in this case would represent the bore of a shotgun.
• Approx. 2.4 cubic inches of lead weighs one pound.

If you want to quickly calculate the volume of a sphere here is a site --   VOLUME OF A SPHERE

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Caliber is the U.S. (English) measurement in inches of the diameter of the bullet.  A 45 caliber firearm shoots a bullet that has a diameter of .45 inches.   It can also be the gun's bore measured in inches.  

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Here's what I've been told and it, so far, seems to be the best answer.  At one time caliber was a measurement of the case diameter instead of the bullet diameter as it is now.   So a 38 firearm is actually a 357 caliber by today's measurements.  The bullet casing is .38 inches but the bullet is .357 inches.   The 38 was so popular as a standard for pistols that when the caliber measurement  changed from casing to bullet diameter, the 38 just stayed a 38 instead of changing it's name to a 357.  Then the 357 magnum came out and has gained a following and renown of it's own.  

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The "second trigger" (a small trigger on the big trigger) is a safety.  If the firearm is dropped or hit on the trigger it can't fire unless the "small trigger" is depressed. 

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A ported barrel is one which has holes of some type at the end of the barrel on the top.  These holes allow exhaust gasses to vent upwards through the holes rather than going out the end of the barrel.  By exhausting through the holes the barrel end of the gun has less rise when fired allowing the shooter to stay on target better than with a non-ported barrel.  

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What caliber is a 9MM?  Millimeter is the same measurement as caliber except it is expressed in metric.  Here's the magic number - 1 inch equals 24.5 millimeters.   Setting up the ratio of 1 inch is to 24.5 millimeters as "X" is to 9MM the answers is    ..367 caliber.   Just slightly (.01inches) larger than the 357 or 38. 

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A bullet that is traveling at 3000 FPS is going 2045 MPH.   Here are the numbers:

• 5280 feet per mile

• 60 seconds in a minute

• 60 minutes in an hour

So --- 3000 FPS x 60 seconds x 60 minutes / 5280 feet = 2045 Miles per hour.   WOW -  now I see that's fast ! 

What about a 45 that goes about 900 FPS?  =   614 MPH 

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What is "Shot String"?   This is a  measurement used with shotgun shells.  When a shell is fired the shot string is the distance between the shot pellet out front and the shot pellet in the rear.   The distance between the first pellet to hit a target and the last pellet hitting the target.   Shot String measures how far your shot load is "strung out" which has a bearing on the impact of the load.  Your "pattern" is the measurement of the horizontal distance between the two outermost pellets.  Using the values of  "shot string" and "pattern" allows a shooter to select the right shell for the type of shooting he/she is going to do. 

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Ballistic Coefficient (BC) is basically a measure of how streamlined a bullet is.  Ballistic Coefficient in plain words is a measure of air drag. The higher the number the less drag, and the more efficiently the bullet cuts through the air.  The bigger the BC number the better.

BC is what determines trajectory and wind drift, other factors (velocity among them) being equal. BC changes with the shape of the bullet and the speed at which the bullet is traveling, while sectional density does not. Spitzer, which means pointed, is a more efficient shape than a round nose or a flat point. At the other end of the bullet, a boat tail (or tapered heel) reduces drag compared to a flat base. Both increase the BC of a bullet.

To illustrate the practical difference between these three styles of bullets, let's use Hornady's trajectory figures for the 100 grain 6mm bullets.  Starting all three bullets at a muzzle velocity of 3100 fps from a scoped 6mm rifle zeroed at 300 yards, the trajectories are as follows.

There is a pretty big difference in trajectory between the round nose bullet and the two pointed bullets, making it obvious why it is folly to choose a round nose bullet for long range shooting with a high velocity rifle like a 6mm Remington or .243 Winchester. Also notice the big difference in BC between the round nose bullet (.216) and the spire point bullet (.357).

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What is twist rate?  First let's talk about rifling.  Rifling consists of grooves cut or formed in a spiral nature, lengthwise down the barrel of a firearm.  Rifling is placed in the barrels of firearms to impart a spin on the bullets.  Twist is the amount of turns the rifling has to spin the bullet.  Expressed in terms of the number of revolutions per inch of barrel length, this ratio is commonly expressed by designations such as 1:10, 1/10 or 1 in 10 twist, the 1 represents 1 twist, the 10 represents inches of barrel length.

What does the twist rate do:
 The rate of twist determines the optimum bullet weight for a given caliber and speed of the bullet by applying the proper spin on the bullet to prevent the bullet form yawing and pitching.

 How do you know what's right
A good rule of thumb is that the heavier and longer a bullet is, the faster the twist rate needs to be.  A lighter shorter bullet needs a slower twist rate to give proper bullet spin.

 Exception to the rule:
 Over stabilization of bullets can occur when larger heavier bullets are fired at very high velocities.

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What does the "06" mean in a 30-06 round. Here's the best answer I've found.  Of course the 30 is for .30 caliber.... the "06", so I'm told, stands for the year the round was introduced.  If this is true the 30-06 round first appeared in 1906.  If you know something different let me know.