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Handloaders Need a Chronograph

scott338lm72

Not so long ago, chronographs were expensive, finicky things rarely seen on public shooting ranges. Now inexpensive chronographs are readily available, offering ballistic insights that would have been impossible only a few years ago. For the handloader, they should be considered indispensable tools for making accurate ammunition.

Velocity Deviations

Internal ballistics studies variables and how they interact within the pressure/time curve. Our ballistics lab does everything possible to control these variables. Data is developed using test barrels in universal receivers. Each chamber is held to minimum SAAMI specifications and barrels are manufactured specifically to conform to testing standards. Cartridge brass is calibrated for pressure off-set by lot and unfired cases are used for testing to avoid pressure changes caused by work-hardened brass. The powder is loaded on laboratory-grade scales in a room that is controlled for temperature and humidity. The velocity we get is accurate, on that test day. Variables beyond our control mean that the same combinations fired on another day may vary slightly, as the barrel’s throat erodes or ambient conditions change.

Here is fact that all handloaders need to accept: Your results will vary.

The average handloader with a pound of powder they purchased a year ago and kept in the basement, using range brass they found and full-length resized, will develop different pressure and velocity than the test barrels in their controlled environment. This isn’t bad; it is simply a result of the many variables that are part of internal ballistics. If the shooter’s barrel length is different than the tested barrel, accurately predicting velocity becomes virtually impossible.

One of our most common customer service questions is tied to velocity changes associated with barrel lengths The questions usually look like this: “I see you shot your data in a 24″ barrel. How much velocity will I gain in my 28″ barrel?” They are hoping that a simple mathematical formula exists to calculate velocity change by barrel length. It does not. A chronograph is the only tool that can accurately answer a question regarding your rifle’s velocity using a given load. It is useful information to have.

Using that information, a shooter with a chronograph can use a bullet’s velocity and ballistic co-efficient to make very good trajectory estimates over long distances. The same is true for the various scope reticles that offer aiming points for given ranges. All of these systems use the bullet’s velocity as a primary variable for predicting bullet impact. If you are going to invest in these tools, get a chronograph, too. It will make them work better.

Using a Chronograph to predict pressure

Variations in chambering, powder condition or handloading techniques can result in pressures and velocities outside of what has been predicted in our lab. A chronograph is best tool to explain the discrepancy.

labchrony72

Velocity and pressure go hand-in-hand, which is why Western Powders includes pressure data along with its maximum loads. Armed with a chronograph, the handloader can compare a firearm’s actual velocity to the published data. Loads that exceed the maximum velocity, within a given barrel length, probably also exceed SAAMI or CIP pressure limits. The inverse is also true, with lower velocity equaling lower pressures.

Automatic pistols are common culprits when it comes to lower than anticipated pressures using a published load. When a load proves to be anemic in an auto-pistol, a chronograph can be used to look for lower than anticipated velocity. There can be a number of answers for velocity loss. Generous chambers, long throating or powder that may have been stored improperly are just a few. The chronograph in this case gives the handloader license to increase the charge weight, knowing that they are most likely under pressure if they are under velocity.

On the other extreme are shooters who live for velocity above everything else. Attributing their much higher velocities to custom chambers in rifles built by demi-gods, they produce astonishing velocities “without visible pressure signs.” They tend to ignore the pressure/velocity correlation; failing to see that an increase in one means an increase in the other if other major variables are held constant. In this case, the visible pressure sign is a bullet that screamed out of the barrel 200 feet-per-second faster than the lab’s maximum tested load. The load is over pressure and the chronograph has told the tale.

Shotchony72

An entry-level chronograph costs about as much as a good powder measure or electronic scale. Like these other tools, they should be considered an integral component for accurate handloading. Just keep the bullet between the sky screens and remember that velocity and pressure hold the secrets to good accuracy.