I recently bought a alpha chrony. After reading the instructions and loading up my favorite .308 round, I headed to the range. After 40 rounds or so I was a little disappointed because after all of my hard work in case prep, bullet weight sorting and meticulously measuring powder down to the tenth of a grain, the velocity of each round varied sometimes 60 fps. Is this normal? what would be an exceptable spread and what could I do differently?
- Thread starter Derrekc
- Start date
Re: Chrony spread
You need to find a load that works well with the harmonics of your particular barrel. If the charge weight isn't what your rifle wants, how meticulous you are is pretty irrelevant.
You need to do a ladder test first paying attention to the SD and ES numbers of the strings on your chronograph. A lot of guys look at group sizes first. I look at the numbers first. A swollen group is probably more the shooter than the rifle and ammo and since groups with low ES/SD numbers tend to shoot consistently that's usually going to be your most accurate load also.
Look for single digit SD numbers and an ES of 30 or less for a nice accurate load.
Rich
You need to find a load that works well with the harmonics of your particular barrel. If the charge weight isn't what your rifle wants, how meticulous you are is pretty irrelevant.
You need to do a ladder test first paying attention to the SD and ES numbers of the strings on your chronograph. A lot of guys look at group sizes first. I look at the numbers first. A swollen group is probably more the shooter than the rifle and ammo and since groups with low ES/SD numbers tend to shoot consistently that's usually going to be your most accurate load also.
Look for single digit SD numbers and an ES of 30 or less for a nice accurate load.
Rich
Re: Chrony spread
I've mentioned this before, but I changed from a Shooting Chrony to a CED M2 and my ES/SD numbers came way down (more consistent measurements from the CED).
May not work in your case though and if this is your first time reloading you may have to work on making your process repeatable/consistent before judging the results.
I've mentioned this before, but I changed from a Shooting Chrony to a CED M2 and my ES/SD numbers came way down (more consistent measurements from the CED).
May not work in your case though and if this is your first time reloading you may have to work on making your process repeatable/consistent before judging the results.
Re: Chrony spread
"...meticulously measuring powder down to the tenth of a grain,"
Well, you're collecting data, now you need to analyalise it. First thing is, you now know that precisely weighted charges don't automatically equal precisely consistant speeds, right? So...what matters? It's burn rate of the load!
Obtaining a consistant burn rate of any powder demands the peak pressure be in the right range, neither too low nor too high, AND that the bullet jump be right to insure the needed ingniton resistance. So, vary both your charge level - and maybe try a different powder - and OAL until you get the E.S. down.
Actually, for most purposes, a 60 fps spread isn't all that bad. For reasons we don't understand it's uncommon for best accuracy to occur with the lowest E.S. load.
"...meticulously measuring powder down to the tenth of a grain,"
Well, you're collecting data, now you need to analyalise it. First thing is, you now know that precisely weighted charges don't automatically equal precisely consistant speeds, right? So...what matters? It's burn rate of the load!
Obtaining a consistant burn rate of any powder demands the peak pressure be in the right range, neither too low nor too high, AND that the bullet jump be right to insure the needed ingniton resistance. So, vary both your charge level - and maybe try a different powder - and OAL until you get the E.S. down.
Actually, for most purposes, a 60 fps spread isn't all that bad. For reasons we don't understand it's uncommon for best accuracy to occur with the lowest E.S. load.
Re: Chrony spread
"...meticulously measuring powder down to the tenth of a grain,"
Well, you're collecting data, that's good. Now you need to analyalise it; first thing is, you now know that precisely weighted charges don't automatically equal precisely consistant speeds, right? So...what matters? It's the burn rate of the load!
Obtaining a consistant burn rate of any powder demands the peak pressure be in the right range, neither too low nor too high, AND that the bullet jump be right to insure the needed ingniton resistance. So, vary both your charge level and maybe try a different powder or primer and OAL until you get the E.S. down.
Actually, for most purposes, a 60 fps spread isn't all that bad. For reasons we don't understand, it's uncommon for best accuracy to occur with the lowest E.S. load.
"...meticulously measuring powder down to the tenth of a grain,"
Well, you're collecting data, that's good. Now you need to analyalise it; first thing is, you now know that precisely weighted charges don't automatically equal precisely consistant speeds, right? So...what matters? It's the burn rate of the load!
Obtaining a consistant burn rate of any powder demands the peak pressure be in the right range, neither too low nor too high, AND that the bullet jump be right to insure the needed ingniton resistance. So, vary both your charge level and maybe try a different powder or primer and OAL until you get the E.S. down.
Actually, for most purposes, a 60 fps spread isn't all that bad. For reasons we don't understand, it's uncommon for best accuracy to occur with the lowest E.S. load.
Re: Chrony spread
The .308 is an easy round to load for, tell us what rifle, and what bullet and powder you are trying to use.
Also tell us what you intend to do with the load.
I would be happy with 30 fps spread on a 10 shot group.
SScott
The .308 is an easy round to load for, tell us what rifle, and what bullet and powder you are trying to use.
Also tell us what you intend to do with the load.
I would be happy with 30 fps spread on a 10 shot group.
SScott
Re: Chrony spread
An interesting article regarding Chrono's, SD and ES. May have been read by many, maybe not. Just someone else's perspective that may help you. Here's the link : http://riflemansjournal.blogspot.com/2010/07/statistics-for-rifle-shooters.html
An interesting article regarding Chrono's, SD and ES. May have been read by many, maybe not. Just someone else's perspective that may help you. Here's the link : http://riflemansjournal.blogspot.com/2010/07/statistics-for-rifle-shooters.html
Re: Chrony spread
here are my latest results
the rifle is nothing special
store bought remington 700p in .308
my main goal was be to become a better shooter, have fun and get out of the house
im didnt include the extreme spread and standard deviation because i didnt stick with a particular powder charge
thanks for your suggestions and comments, im learning a lot.
<span style="text-decoration: underline">Cartridge Load Report</span>
Firearm: Rem 700p .308
<span style="text-decoration: underline">Conditions</span>
Date:9-11-11
Pressure:29.90
Location:Sun Valley
Altitude:1540
Temp:72.1F
Wind/Dirc:3.5@340deg
Humidity:37.8
Target Dirc:261deg
Target Dist:100Yards
<span style="text-decoration: underline">Cartridge Information</span>
Case:Win
Case Trim Lengh:2.005
Primer:WLR
Base to Ogive:2.345
Bullet:175 gr sie hpbt match
Powder:Benchmark
BC:.496@ 2800-1800fps
<span style="text-decoration: underline">GRS.Vel. ft/s</span>
37.5 2435
37.5 2383
37.5 2365
38 2438
38 2375
38 2410
38.5 2539
38.5 2447
38.5 2458
39 2470
39 2514
39 2486
39.5 2530
39.5 2535
39.5 2517
40 2558
40 2550
40 2570
40.5 2587
40.5 2582
40.5 2584
41 2582
41 2547
41 2567
41.5 2537
41.5 2562
41.5 2603
42 2634
42 2633
42 2634
42.5 2615
42.5 2640
42.5 2635
43 2611
43 2668
43 2698
43.5 2727
43.5 2718
43.5 2682
44 2743
here are my latest results
the rifle is nothing special
store bought remington 700p in .308
my main goal was be to become a better shooter, have fun and get out of the house
im didnt include the extreme spread and standard deviation because i didnt stick with a particular powder charge
thanks for your suggestions and comments, im learning a lot.
<span style="text-decoration: underline">Cartridge Load Report</span>
Firearm: Rem 700p .308
<span style="text-decoration: underline">Conditions</span>
Date:9-11-11
Pressure:29.90
Location:Sun Valley
Altitude:1540
Temp:72.1F
Wind/Dirc:3.5@340deg
Humidity:37.8
Target Dirc:261deg
Target Dist:100Yards
<span style="text-decoration: underline">Cartridge Information</span>
Case:Win
Case Trim Lengh:2.005
Primer:WLR
Base to Ogive:2.345
Bullet:175 gr sie hpbt match
Powder:Benchmark
BC:.496@ 2800-1800fps
<span style="text-decoration: underline">GRS.Vel. ft/s</span>
37.5 2435
37.5 2383
37.5 2365
38 2438
38 2375
38 2410
38.5 2539
38.5 2447
38.5 2458
39 2470
39 2514
39 2486
39.5 2530
39.5 2535
39.5 2517
40 2558
40 2550
40 2570
40.5 2587
40.5 2582
40.5 2584
41 2582
41 2547
41 2567
41.5 2537
41.5 2562
41.5 2603
42 2634
42 2633
42 2634
42.5 2615
42.5 2640
42.5 2635
43 2611
43 2668
43 2698
43.5 2727
43.5 2718
43.5 2682
44 2743
Re: Chrony spread
alot of that data makes sense, but some doesn't quite make sense... you are going up in powder but gettig speeds below the previous step. I also have had lots of head scratching data on carefully loaded handloads. I found if I push back the chron to a good 15 ft away, no closer, I get better data, and with the light directly overhead is best too. I try to have the bullet pass overhead about 4" or so.
This is with a CED chron... after much trial and error this is what works for me with this unit.
alot of that data makes sense, but some doesn't quite make sense... you are going up in powder but gettig speeds below the previous step. I also have had lots of head scratching data on carefully loaded handloads. I found if I push back the chron to a good 15 ft away, no closer, I get better data, and with the light directly overhead is best too. I try to have the bullet pass overhead about 4" or so.
This is with a CED chron... after much trial and error this is what works for me with this unit.
