published FPS??
- Thread starter Axis II
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Grumulkin
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Most of the time when I've chronographed loads they're within 100 fps of those published. Yea, that's not too precise I know.
jmorris
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I think they are likely pretty close using the particular rifle/pistol, case, primer, powder, bullet, OAL, in the environment they had that day.
Most chronographs are not as precise as you might think, you can fire a shot and have 3 different chronographs (even if they were all made by the same company) arranged so the single bullet passes through all the sensors at the same distance from the muzzle and you will get 3 different readings.
Not to mention "what the book says" is going to be an average from some number of different readings.
So, if it says 2000 fps it would be very, very unlikely to match that exactly.
You would likely have better luck picking the player number that will score the first points in the Super Bowl next year.
Most chronographs are not as precise as you might think, you can fire a shot and have 3 different chronographs (even if they were all made by the same company) arranged so the single bullet passes through all the sensors at the same distance from the muzzle and you will get 3 different readings.
Not to mention "what the book says" is going to be an average from some number of different readings.
So, if it says 2000 fps it would be very, very unlikely to match that exactly.
You would likely have better luck picking the player number that will score the first points in the Super Bowl next year.
Reloading manual listed velocities are results of the loads used in their equipment. Their barrels, their guns, their components, etc. I just use the manual's velocities as a comparison, as a rough idea, not an exact point to strive for...
From my experience, my data varies from the published manual data. If the barrel length is similar and the firearm type is similar, the difference will be less.
But in one case, my data matched the book values very closely. Sierra Bullets used a Colt Match Target AR-15 to establish there Service Rifle loads for 223 Remington. My Colt Match Target matched Sierra Bullets' velocity numbers almost exactly for the couple powders that I used and tested.
But, my Compass Lake Match Service Rifle AR-15 with a Frank White chamber would shoot the same ammunition at about 200 fps, about 8%, faster than the book numbers or my Colt numbers.
(Note, all three rifles have 20" barrels and no muzzle devices)
But in one case, my data matched the book values very closely. Sierra Bullets used a Colt Match Target AR-15 to establish there Service Rifle loads for 223 Remington. My Colt Match Target matched Sierra Bullets' velocity numbers almost exactly for the couple powders that I used and tested.
But, my Compass Lake Match Service Rifle AR-15 with a Frank White chamber would shoot the same ammunition at about 200 fps, about 8%, faster than the book numbers or my Colt numbers.
(Note, all three rifles have 20" barrels and no muzzle devices)
Sunray
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"...not using the same rifle they did?..." Not at all the same. Hodgdon used a 20" 1 in 38 twist barrel that was most likely on a universal receiver. The twist is rumoured to be the same, but manuals reflect conditions using the exact components of the day of the test only. A different powder lot can give different velocities. And the figures are averages.
Hodgdon's site shows 24.0 as the Max rifle load and gave 'em 1,778 fps.
Anyway, accuracy is more important.
Hodgdon's site shows 24.0 as the Max rifle load and gave 'em 1,778 fps.
Anyway, accuracy is more important.
splattergun
Member
It is accurate only for the gun they used to test the loads, which is not the same gun that you are using.
RecoilRob
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Also pay attention to the methods used to make the measurement because they DO matter. Some will talk 'muzzle velocity' but actually make the measurement at 10-15 feet because many chrono's don't like you shooting right up on them as the muzzle ejecta can mess with the screens seeing the bullet accurately. This can create false readings, so many move back to eliminate this from happening, then either report the velocity readings as tested or calculate what the MV would have been. This can make a bit of a difference and enough to matter sometimes.
The really big ones are in how the Military measures the velocity of their rifle rounds. This is measured 78 feet from the muzzle! http://www.ar15.com/content/page.html?id=434 I believe this is part of what causes people to argue about the 5.56 vs .223 being different in that the civilian entities test them a different way than the military so one will appear 'hotter' while it might actually have less pressure. So the published velocities will be exactly as they tested them...in the way they tested them. Will they be exactly the same as YOUR testing? No....almost no chance, but they should be pretty close and in the same ballpark and especially useful for watching trends meaning if their velocity starts to peak or get erratic...so will yours even though the actual numbers might be less.
The really big ones are in how the Military measures the velocity of their rifle rounds. This is measured 78 feet from the muzzle! http://www.ar15.com/content/page.html?id=434 I believe this is part of what causes people to argue about the 5.56 vs .223 being different in that the civilian entities test them a different way than the military so one will appear 'hotter' while it might actually have less pressure. So the published velocities will be exactly as they tested them...in the way they tested them. Will they be exactly the same as YOUR testing? No....almost no chance, but they should be pretty close and in the same ballpark and especially useful for watching trends meaning if their velocity starts to peak or get erratic...so will yours even though the actual numbers might be less.
There can be near 100 fps spread in average velocity numbers across several people who shoot the same rifle and ammo and chronograph setup when shot off their shoulders. We all don't hold rifles against us the same. Standard deviation numbers will also be different.
Handguns are no different.
Best test for standard deviation and extreme spread only is with a fixed barrel that doesn't move back while bullets go through them. Average velocity will be higher than when the gun is hand held.
Handguns are no different.
Best test for standard deviation and extreme spread only is with a fixed barrel that doesn't move back while bullets go through them. Average velocity will be higher than when the gun is hand held.
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The numbers you see published are the ones they got when they tested the ammo in their rifle. The internal dimensions vary slightly on every barrel; you could find your loads are very close, or 100fps or more slower. In rare cases your barrel may be slightly faster than the load data or factor ballistics show.
Barrel length is the biggest factor. Often with factory loads they test the loads with barrels longer than commonly used. Most 30-30's have 20" or shorter barrels, all the test data is from 24" barrels which very few shooters own. You see the same with revolvers. Most published magnum revolver loads are shown with 8" barrels while 4-6" are much more common. Semi-auto rounds are usually tested in more common 4-5" barrels and published data is usually much more realistic.
Most of the time, with most of my rifles I'm very close, actually right on the money when you factor in for barrel length. But I own one rifle that is consistently 60-90 fps slower. One rifle that is often 15-20 fps faster.
Barrel length is the biggest factor. Often with factory loads they test the loads with barrels longer than commonly used. Most 30-30's have 20" or shorter barrels, all the test data is from 24" barrels which very few shooters own. You see the same with revolvers. Most published magnum revolver loads are shown with 8" barrels while 4-6" are much more common. Semi-auto rounds are usually tested in more common 4-5" barrels and published data is usually much more realistic.
Most of the time, with most of my rifles I'm very close, actually right on the money when you factor in for barrel length. But I own one rifle that is consistently 60-90 fps slower. One rifle that is often 15-20 fps faster.
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