Labradar Velocity puzzle

[BigTex]

I finally got a real chronograph (Labradar). I took it to the range today and it is much more consistent than my old beat up Prochrono. I have a problem and wondered if anyone here has ever seen anything like it. I took a great shooting rifle, and a known great shooting load and shot 32 rounds by the LR, of those 4 were extreme outliers (+40fps). The load was worked up last year (OCW) and is as follows:
6.5x284
JLK 140gr VLD
H1000 57.1gr
Lapua Brass (4x fired, annealed each time)
CCI LR magnum
2thou neck tension
40thou jump

The velocities in order were as follows:
3028
3038
3077 wtf?
3039
3041
3079 wtf?
3033
3037
3030
3030
3039
3063 wtf?
3024
3040
3036
3039
3039
3035
3052
3080 wtf?
3036
3028
3035
3032
3025
3036
3032
3037
3031
3051
3026
3024

The SD is 15.1, but if you disregard the 4 outliers, the SD is 6.9.

I know you cant throw out numbers, but what would cause a load to be so consistent and then throw a wild velocity now and then? I have been reloading for years and take extreme care in brass prep, weighing powder, seating bullets, etc. I'm just a little puzzled. Any Ideas?

 

[spife7980]

That can be due to anything. That’s why I scoff when people say their SDs are always single digits or an SD of 3 or so. Add in 10 more shots and you’ll get an outlier that will double the SD. Maybe it’s due to brass properties, maybe it’s the bullet, maybe it’s the powder, maybe it’s the primer. Maybe you let the case sit in the die longer, maybe it was lubed differently, maybe you drug the expander ball through differently, maybe it’s just a bad piece resulting in different sizing. Maybe that bullet is .0002 wider or .001 longer in bearing surface. Maybe the powder rods were all longer vs shorter and different surface area burned faster, maybe your neighbor started their dishwasher and the scales power condition changed, maybe you just breathed on the scale. Maybe it was a primer with more or less pow. If you have those pieces of brass pull them and see if they shoot differently from the rest on the next firing cycle. Weigh bullets and bob green comparator. Better powder scale. Better primer seating. Better brass sizing.

Personally I think they are due to the brass processing.

See if that outlier makes a lick of difference on your down range paper target.

 

[leftyk82]

If the Labradar is much more consistent than your old chrono, then I'd think these findings are an improvement over previous velocity tests.

 

[BigTex]

That can be due to anything. That’s why I scoff when people say their SDs are always single digits or an SD of 3 or so. Add in 10 more shots and you’ll get an outlier that will double the SD. Maybe it’s due to brass properties, maybe it’s the bullet, maybe it’s the powder, maybe it’s the primer. Maybe you let the case sit in the die longer, maybe it was lubed differently, maybe you drug the expander ball through differently, maybe it’s just a bad piece resulting in different sizing. Maybe that bullet is .0002 wider or .001 longer in bearing surface. Maybe the powder rods were all longer vs shorter and different surface area burned faster, maybe your neighbor started their dishwasher and the scales power condition changed, maybe you just breathed on the scale. Maybe it was a primer with more or less pow. If you have those pieces of brass pull them and see if they shoot differently from the rest on the next firing cycle. Weigh bullets and bob green comparator. Better powder scale. Better primer seating. Better brass sizing.

Personally I think they are due to the brass processing.

See if that outlier makes a lick of difference on your down range paper target.

I get where you are coming from, there is a myriad of things that it could be. While I do take the utmost care in processing brass and double weighing powder, I am not perfect. It just looks weird how they are laid out. It would make more sense to me if they were all evenly dispersed between 3030 and 3080 instead of 85% in the 3030's and 15% way high with nothing in between. The exercise in frustration continues in the AM.

 

[BigTex]

If the Labradar is much more consistent than your old chrono, then I'd think these findings are an improvement over previous velocity tests.

I agree, I never trusted the numbers on the Prochrono, just used as a baseline then got velocity from drops at distance. I trust the Labradar, the velocity spread is just very oddly dispersed.

 

[Milo 2.5]

I'm with spife for the most part. What happened downrange?
I'm the classic, load shoots downrange, chrono a few a for dope, I'll shoot more to tighten numbers rather the other way around. There is so much being said of sample size, need bigger. All I can say if you need a 40 shot sample size and you are going to make assumptions or decisions based off it, every single rd needs to be the same. From brass prep, to powder weighing, to bullet seating force. You really cannot have a "scientific" experiment w/o scientific input.
If you feel certain rds need to be culled, do it upfront.

 

[BigTex]

I'm with spife for the most part. What happened downrange?
I'm the classic, load shoots downrange, chrono a few a for dope, I'll shoot more to tighten numbers rather the other way around. There is so much being said of sample size, need bigger. All I can say if you need a 40 shot sample size and you are going to make assumptions or decisions based off it, every single rd needs to be the same. From brass prep, to powder weighing, to bullet seating force. You really cannot have a "scientific" experiment w/o scientific input.
If you feel certain rds need to be culled, do it upfront.

Every single round in this test was loaded the exact same.

 

[Milo 2.5]

Every single round in this test was loaded the exact same.

Ok, did everyone feel the same when you seated a bullet, because neck tension could be a part of this?

 

[BigTex]

Ok, did everyone feel the same when you seated a bullet, because neck tension could be a part of this?

Absolutely. Cases were annealed and sized with a Redding Type-S FL bushing die. All seated with identical pressure per my arm, I do not have a torque gauge on my press. Redding Type-S micrometer seat die.

 

[BigTex]

Maybe I'm putting to much stock in all of the low SDs flying around on here. Probably most calculated for 5 shots. From what I've read in the last few hours a TRUE SD of 15 over a large sample size is ok.

 

[Farmerbrown32]

That can be due to anything. That’s why I scoff when people say their SDs are always single digits or an SD of 3 or so. Add in 10 more shots and you’ll get an outlier that will double the SD. Maybe it’s due to brass properties, maybe it’s the bullet, maybe it’s the powder, maybe it’s the primer. Maybe you let the case sit in the die longer, maybe it was lubed differently, maybe you drug the expander ball through differently, maybe it’s just a bad piece resulting in different sizing. Maybe that bullet is .0002 wider or .001 longer in bearing surface. Maybe the powder rods were all longer vs shorter and different surface area burned faster, maybe your neighbor started their dishwasher and the scales power condition changed, maybe you just breathed on the scale. Maybe it was a primer with more or less pow. If you have those pieces of brass pull them and see if they shoot differently from the rest on the next firing cycle. Weigh bullets and bob green comparator. Better powder scale. Better primer seating. Better brass sizing.

Personally I think they are due to the brass processing.

See if that outlier makes a lick of difference on your down range paper target.

Very well said. I agree.

 

[Farmerbrown32]

If the said load shoots well at long distance just leave it and enjoy it.

 

[Subwrx300]

I finally got a real chronograph (Labradar). I took it to the range today and it is much more consistent than my old beat up Prochrono. I have a problem and wondered if anyone here has ever seen anything like it. I took a great shooting rifle, and a known great shooting load and shot 32 rounds by the LR, of those 4 were extreme outliers (+40fps). The load was worked up last year (OCW) and is as follows:
6.5x284
JLK 140gr VLD
H1000 57.1gr
Lapua Brass (4x fired, annealed each time)
CCI LR magnum
2thou neck tension
40thou jump

The velocities in order were as follows:
3028
3038
3077 wtf?
3039
3041
3079 wtf?
3033
3037
3030
3030
3039
3063 wtf?
3024
3040
3036
3039
3039
3035
3052
3080 wtf?
3036
3028
3035
3032
3025
3036
3032
3037
3031
3051
3026
3024

The SD is 15.1, but if you disregard the 4 outliers, the SD is 6.9.

I know you cant throw out numbers, but what would cause a load to be so consistent and then throw a wild velocity now and then? I have been reloading for years and take extreme care in brass prep, weighing powder, seating bullets, etc. I'm just a little puzzled. Any Ideas?

I work with radar in another industry and it's impressively consistent compared to optical devices. If you really want to get a "true verification" of velocity you need a second measuring device to figure out whether it's likely to be the bullets actual speed or the Chrono. For instance, the Oehler 35 uses three screens so it can double check the reading from A to B and B to C. If erroneous or too big a gap, it can toss the data.

Radar typically gives BIG errors when there is an issue (like 2-3 times the actual velocity. But the Labradar uses the microphone to pickup the shot and does some basic math with distance from mic (offset distance), speed of sound and distance bullet entered radar field to give muzzle velocity. That can have some effect on readings but it's been pretty Johnny on the spot in my testing.

However, like @spife7980 said, outliers are part of the game. I know that when I get SDs of 5-10fps for 5-10 shots, they are still just a sample of all the possible shots you are going to take with that load. I still strive for single digit SDs in development but mainly because if it's low during multiple 5 shot groups, it's just more likely to be low when I need it to count at a match. I just hope my outlier doesn't happen on the KYL stages or 900+yd targets when I need the points.

 

[supercorndogs]

Mark those pieces of brass and try again.