Hodgdon's methods for measuring velocities in their loading data

[Lennie]

I just thought this was good information to share:

Until you understand, it may be confusing to test your handloads on a chronograph and find the velocity is not what you expected based upon the reload data. There are a number of reasons for this. We will attempt to clarify this mystery with the following:

• Hodgdon reloading data is fired from Industry-Standard Test Barrels
  The test barrel is a precision piece of ballistic equipment. To yield the greatest consistency in data, the test barrel has very precise chamber dimensions and bore dimensions. Your firearm, although a finely crafted machine, is built on a production line where tolerances and tooling wear occur. Not only do different gun types vary in dimensions and tolerances, but even two of the exact same gun model can show dramatic differences in velocity produced.
• Test barrels generally do not have cylinder gaps
  If you are a revolver shooter, the cylinder gap will cause your velocity measurement to be lower than the reload data due to gas loss in the gap.
• Test barrels have a fixed length
  In centerfire rifles, the test barrels are all 24-inches long. Your 26-inch varmint rifle will shoot higher velocity, and your 18-inch carbine AR-15 will show lower velocity.
• Velocity measuring screens are set at an exact distance apart (10 feet) with the center of the screens exactly 15 feet from the muzzle
  Few handload type chronographs have the screens separated apart more than a couple of feet. Generally, at the range, chronograph distance from the muzzle of the gun is not fixed or exact.
• Muzzle flash and blast can impact the recorded velocity
  Ballistic labs generally protect the screens from muzzle flash and blast.

This does not mean your chronograph setup for measuring handloads is not useful. Just be aware of these factors and establish what level your particular setup is at. One way to help establish where your test setup is shooting is to fire some factory loads and compare your results to the factory published numbers

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[red442joe]

Tagged

Joe

 

[orygun]

The first thing I discovered when I got a Chrono was that my ammo was slow.
Barrel length plays a huge part in that and it's more of a difference that I'd expected.
The second thing I noticed was that I could beat factory ammo velocity in some rounds, but matching the consistency (SD, ES) was difficult.

 

[Mikej]

Interesting. I don't have a chrono so have no idea where my loads fall. I don't think I care, for MY purposes anyway. What I think is more important is pressure. Too bad we don't have a way to measure that for ourselves.

 

[orygun]

Interesting. I don't have a chrono so have no idea where my loads fall. I don't think I care, for MY purposes anyway. What I think is more important is pressure. Too bad we don't have a way to measure that for ourselves.

In a backhanded manner a chrono will help with understanding pressures when used in conjunction with info gathered from reliable sources.
Also, I think that there's a piezo style that's available, but have no clue as to it's price.

edit to add,

Rifle Barrel Chamber Pressure Testing Hardware & Software | Pressure Trace

Measure ACTUAL rifle chamber pressure for each shot, barrel harmonics, rise time, time to muzzle exit and OBT barrel timing.

www.shootingsoftware.com

 

[arrowshooter]

Great info Lenny. My brother-in-law was always chasing the "data" until this sunk in. If I may, I would like to add to your first point that the age/round count of a barrel comes with an increase in tolerances that effects FPS. Case in point: My 2020 Winchester XPR 30.06 shoots the exact same load as my 1936 Winchester Model 54 30.06 almost 200 FPS faster. Even after tweaking the "bump" and COAL it was still 60 FPS faster with 1.5 gr less powder.

 

[oremike]

I have this discussion quite often, there is no industry standard for harvesting the data. They use a closed breach test fixture and I use off the shelf firearms. If you look in some different load books you will find some use actual guns to gather their data. I was just looking at the Lyman pistol and revolver load book for 45 Colt and they list using both a 71/2" Blackhawk and a Universal receiver to gather the data but they don't say how long the barrel on the closed breach test fixture was or differentiate what loads were gathered by what method.

 

[orygun]

I have this discussion quite often, there is no industry standard for harvesting the data. They use a closed breach test fixture and I use off the shelf firearms. If you look in some different load books you will find some use actual guns to gather their data. I was just looking at the Lyman pistol and revolver load book for 45 Colt and they list using both a 71/2" Blackhawk and a Universal receiver to gather the data but they don't say how long the barrel on the closed breach test fixture was or differentiate what loads were gathered by what method.

In another thread recently something just like this was brought up. One of the bullet companies had originally tested with a bolt action rifle. Through several editions the load data stayed the same. At one point they changed from the rifle to a test barrel. The maximum loads were instantly reduced by a couple of grains.

Everything is different. Every gun, every bullet, everything.