Correctional Officer Training and Education: Does Temperature Affect Bullet Point of Impact?

Sierra Bullets are some of the most accurate bullets available today.

Recently, Sierra Bullets put out an informational publication concerning the topic of temperature effects on bullet trajectory. This topic has been in the mainstream lexicon of precision shooters, hunters, and target shooters for decades. Opinions on the matter range from tem…
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Muzzle velocity is NOT a constant! It varies considerable due to a host of factors. In order to successfully engage targets at long range it is CRUCIAL that you be able to predict account for your MVV (muzzle velocity variation). This is the entrance key into effectively setting your ballistics tables. Whether you will be using ballistic software in the field, ballistic cards, or using a calc form to come up with your firing solutions, this information is key to getting your ballistic data arranged in a way that will be effective across various bore conditions and multiple ammunition temperature ranges.

Below is the link to the Ammo Temp MV Curve TABLES by TiborasaurusRex:

https://docs.google.com/file/d/0Bzvx3RuRX1QTNzBkV3R2UE14WDA/edit?usp=sharing

DOWNLOAD THE CURRENT VERSION by hitting the downward pointing arrow at the top left of the page and OPEN or SAVE the document so you can use it.

Video DETAILED NOTES:

Muzzle Velocity Variation (MVV)

A. Bore/projectile Dynamics and MVV
1. Bore wear – Gas escaping around the projectile decreases chamber pressure and can lower MV
2. Fowling – An increase in bore resistance to projectile movement before peak pressure increases the pressure developed within the barrel and can cause MVV.
3. Coppering
a) Slight coppering resulting from firing a small sample of rounds at higher charges tends to increase muzzle velocity.
b) Erratic velocity performance is a result of excessive coppering whereby the resistance of the bore to projectile movement is affected.
4. Bore Temperature – Variations in bore resistance can be caused by temperature differences between the inner and outer surfaces of the barrel.
5. Projectile Temperature
6. Barrel Memory – Originally observed in field artillery — According to the FM 6-40: Tube Memory is a physical phenomenon of the cannon tube tending to react to the firing stress in the same manner for each round, even after changing charges. It seems to “remember” the muzzle velocity of the last charge fired. For example, if a fire mission with charge 6 M4A2 is followed by a fire mission with charge 4 M4A2, the muzzle velocity of the first round of charge 4 may be unpredictably higher. The inverse is also true.

B. Rifle manufacturing tolerances and MVV
1. Chamber dimensions
a) headspace
b) bolt lockup
c) chamber size
C. Ammunition Inconsistencies and MVV
1. Minimizing Ammunition Inconsistencies that increase MVV
a) Factory Ammo — buy premium quality match grade ammo
b) Reloading — you control quality and can custom developed loads
D. Ammunition Temperature and MVV
1. Propellant Burn Rate Changes with Temperature

Ammunition Burn Rate Curve
1. Setting up and Ammunition Burn Rate Conversion Chart
2. Causes of Ammo Temperature Changes
a. Ambient Air Temp
b. Sunlight
c. Chamber Temperature
(1) cold bore shot
(2) hot bore shots
– cycling ammo in chamber
3. Dealing with Ammunition Temp Issues
a. Use Ammo Burn Rate Conversion Chart
b. Ammo Storage – The temperature of cartridges in sealed containers remains somewhat insulated from differences in ambient air temperature. Once a cartridge has been unpacked, its temperature more rapidly approaches the air temperature. The time and type of exposure to the weather results in temperature variations from round to round and the shooter must be aware of this.

These precautions will allow propellant and projectile temperatures to approach the air temperature at a uniform rate throughout the firing unit.

4. Also, copper jacket lubricity changes with temp, as does brass case and the lead bullet core plasticity — all can affect MV.

All the music in this video was created by TiborasaurusRex, an unsigned artist.

Song Title: Wadi Watir
Music and Lyrics by: TiborasaurusRex
Instrumentation and Vocals by: TiborasaurusRex
Recorded by: TiborasaurusRex

The ammo temperature muzzle velocity calculator was created on Microsoft Excel by TiborasaurusRex using burn rate data obtained from the “Ammunition Burn Rate Conversion Chart” figure in a book titled: “The Complete .50-Caliber Sniper Course Hard Target Interdiction” by Dean Michaelis, pages 175 and 176. ISBN 1-58160-068-2 http://www.paladin-press.com

To review these various concepts in more detail, also see the US Army FM 6-40

Weapon featured in thumbnail image is a Remington 700 SA equipped with an Applied Weapons Technologies chassis system – full review coming soon.
More info: http://www.appliedweaponstech.com/page/products
Video Rating: / 5

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