I'm chronying my loads out of my 7wsm and getting large velocity spreads (anywhere from 30-50fps on a group). I'm loading with an RCBS throw, trickler and their rangemaster digital scale. The scale was like $250 so I would think it would be fairly accurate. I'm trickling to every .1 of a grain, the most accurate I could possibly be measuring. I'm seating my berger 168 vlds with a forster ultra bench rest seater. The only thing I haven't started doing yet is turning necks and deburring the inside of my flash hole. I believe this velocity spread is affecting my groups. Please help!
Velocity Spread
- Thread starter matthewpauls
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I trickle my powder by throwing .1 under the required charge then dropping in single grains till I achieve the required number.That way I know the charges are about as consistant as I can get. 44.5 for example,can be anywhere up to 6-8 actual grains of varget different and still read the same thing on the chargemaster.I have been getting up to about 15 fps difference in mine but the average is about 6-9 fps difference.Hope that helps!
sundance1972
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- duncan b.c.
Just a thought, but are you letting the barrel cool completely between shots?
If not, the heat from the barrel/chamber may be warming up the next loaded round which can cause variances with temp sensitive powders
If not, the heat from the barrel/chamber may be warming up the next loaded round which can cause variances with temp sensitive powders
Got Juice?
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30 FPS is acceptable within standard deviation. As stated earlier, throwing .1 gr less then manually adding will probably tighten up the speeds to 30FPS. I do not believe it is possible to get much better than that unless you start micing each cartridge individually and trimming accordingly, and truing the flash hole of the primer.
Except for long ranges ( more than 300 yards) a load with a higher SD may sometimes shoot the smallest groups but as ranges increase the velocity variations will string out the groups. So unless the load is for long range I go for the most accurate load and worry less about moderate extreme spreads. Just my 2 cents
This load is for 1000 yards so it does need to have a smaller velocity spread. I do trickle up to my final weight and I do for the most part cool between loads. I am currently loading IMR 4350. Is this powder possibly bad for that? Or is it still something else. Could all of that just be the flash hole?
I have found that the chony is usually far less accurate than the scale.
Setting up the chrony in the perfect way yields far better results.
For me. I pinch individual kernels onto my acculab Vicon 123 scale, a 400$ scale that I trust so I know my loads are consistent.
The last time at the range this week I set up my chrony and was getting some variation, about +/- 30 fps, which is about average for a chrony.
But I readjusted the chrony, being very careful to line it up perfectly both with my bbl/target, but also how far from the bench, made sure it was level, and at the right height.
Then I shot 5 rounds and my extreme spread was a whopping 2fps!!! That was also the best group I have ever shot lol.
When it comes to a lot of velocity variation in some of my shooting, I lean more on blaming the chony than I do my reloads.
You are using a good combo so I would look at improving your chrony set up before making any extreme changes to your powder pouring techniques.
Setting up the chrony in the perfect way yields far better results.
For me. I pinch individual kernels onto my acculab Vicon 123 scale, a 400$ scale that I trust so I know my loads are consistent.
The last time at the range this week I set up my chrony and was getting some variation, about +/- 30 fps, which is about average for a chrony.
But I readjusted the chrony, being very careful to line it up perfectly both with my bbl/target, but also how far from the bench, made sure it was level, and at the right height.
Then I shot 5 rounds and my extreme spread was a whopping 2fps!!! That was also the best group I have ever shot lol.
When it comes to a lot of velocity variation in some of my shooting, I lean more on blaming the chony than I do my reloads.
You are using a good combo so I would look at improving your chrony set up before making any extreme changes to your powder pouring techniques.
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thanks for that. Ya you know it's been seeming to me that the cheaper chronies are just that, and when fine tuning might cause more frustration than anything. Mine is an F1 from shooting chrony. any real good recomendations, or is there still anyone that thinks I could improve somewhere else?
Use a beam scale for a double check.
I use the RCBS Chargemaster and then double check on a beam scale. I know that the chargemaster usually throws a bit lighter than what my beam scale reads (2-4 kernels light) so I just trickle a few kernels of powder in to top up the load.
I chronied last night and got an Extreme Spread of 14fps over 15 rounds with a Standard Deviation of 4.
I use the RCBS Chargemaster and then double check on a beam scale. I know that the chargemaster usually throws a bit lighter than what my beam scale reads (2-4 kernels light) so I just trickle a few kernels of powder in to top up the load.
I chronied last night and got an Extreme Spread of 14fps over 15 rounds with a Standard Deviation of 4.
I weight sort my Lapua brass into 1 grain lots (ie. 126.0-126.9), clean the necks up to about 80%, uniform primer pockets, trim to same length, and deburr the flash holes. Beyond that there is only one thing left to do but I don't have enough spare time to devote to separating cases by internal volume.
*Rant mode.
You guys sure have a lot more faith in your chronographs than I do. There's 3 of us that have been playing with ours lately, and there is a consistant 200 (sometimes 300) fps discrepency between them, when they aren't dropping shots or coming up with totally random numbers. Why I should believe the extreme spread when I can't trust the individual shots? I've watched another experienced shooter gradually gain 300 fps over an hour or so with premium factory loads in an HS Precision rifle, before dropping back to the quoted velocity. Real precise instruments we're packing.
I'm down to shooting 500 yard groups and selecting loads based on the least vertical spread before shooting again at my longest available range. I also just take the measured drops at 3, 5 and 650 yards and back-calculate a velocity to make the program say the same thing as the targets.
You guys sure have a lot more faith in your chronographs than I do. There's 3 of us that have been playing with ours lately, and there is a consistant 200 (sometimes 300) fps discrepency between them, when they aren't dropping shots or coming up with totally random numbers. Why I should believe the extreme spread when I can't trust the individual shots? I've watched another experienced shooter gradually gain 300 fps over an hour or so with premium factory loads in an HS Precision rifle, before dropping back to the quoted velocity. Real precise instruments we're packing.
I'm down to shooting 500 yard groups and selecting loads based on the least vertical spread before shooting again at my longest available range. I also just take the measured drops at 3, 5 and 650 yards and back-calculate a velocity to make the program say the same thing as the targets.
Ammo: I used to have free access to a full ballistic lab. One test i ran was using 20 round batches of ammo:
1 Normal ammo, weighed charges.
2 same ammo with de-burrred flash holes.
3 #2 with a uniformed primer pocket.
Conclusion: De-burring the flash hole made a noticable improvement in SD.
Chrony: If you don't aim at the same spot on the far side of the Chrony (like at a target) the path through the screens will vary and velocity will vary. So far as I can see, this aiming variation is about 15 fps.
Suggestion: de-burr you flash holes. I jig my electric drill in a vice, and touch the inside of each case with a drill bit. It skims off the flash quickly. Also, run a test using increased neck tension. Neck size the cases withthe decaping rod and expander button removed. See if this helps.
1 Normal ammo, weighed charges.
2 same ammo with de-burrred flash holes.
3 #2 with a uniformed primer pocket.
Conclusion: De-burring the flash hole made a noticable improvement in SD.
Chrony: If you don't aim at the same spot on the far side of the Chrony (like at a target) the path through the screens will vary and velocity will vary. So far as I can see, this aiming variation is about 15 fps.
Suggestion: de-burr you flash holes. I jig my electric drill in a vice, and touch the inside of each case with a drill bit. It skims off the flash quickly. Also, run a test using increased neck tension. Neck size the cases withthe decaping rod and expander button removed. See if this helps.
