Who thinks my scale is jacked?

[sierracharlie338]

So here is my dilemma. I have been loading on a Rangemaster 750 scale for the past couple months while my house has been for sale and my FX120i has been in storage. I have been working up a load for a rifle I plan to hunt with next weekend. The two outings I have had are showing me, what I consider to be, inconsistent results. I will post the two trips in consecutive order to show the charge/speed charts. Everything was done exactly the same from start to finish for these loads despite being loaded at two different times. The only other variable is the Magneto speed which I have more faith in than the scale, quite honestly. Anyway look at the data and let me know what you think.

Any thoughts are appreciated

SC

 

[Stammster]

I'm not seeing anything all that odd - especially if you are plotting only 1 shot at each charge weight. The variance could easily be within margin of error on powder weight, case capacity, seating depth, etc.

Are your concerns over the sawtooth at the lower charge weights only?

Here's another possible explanation if you can't believe it's one of the above....Was your central HVAC running during the first loading session? We're you listening to music with a radio on your shooting bench during the first loading session?

If yes to either of these, that can throw your scale off a little when it give you the final reading. At least that's been my experience when comparing my Chargmaster to my secondary higher resolution digital scale. AC is now off so it's not blowing on the scale, and the radio is on a shelf separate from the bench. Otherwise I was seeing up to 0.10-0.15 gr different, rather than 0.04-0.08gr.

 

[sierracharlie338]

I'm not seeing anything all that odd - especially if you are plotting only 1 shot at each charge weight. The variance could easily be within margin of error on powder weight, case capacity, seating depth, etc.

Are your concerns over the sawtooth at the lower charge weights only?

Here's another possible explanation if you can't believe it's one of the above....Was your central HVAC running during the first loading session? We're you listening to music with a radio on your shooting bench during the first loading session?

If yes to either of these, that can throw your scale off a little when it give you the final reading. At least that's been my experience when comparing my Chargmaster to my secondary higher resolution digital scale. AC is now off so it's not blowing on the scale, and the radio is on a shelf separate from the bench. Otherwise I was seeing up to 0.10-0.15 gr different, rather than 0.04-0.08gr.

I'm mainly looking at the huge jump from 49.9 at 2882 FPS to 50.1 at 2943. Seems like a large jump for the .2 grain difference.

Here's a side note: I shot a three shot group of the 49.9 charge weight and all three shots (according to the magnetospeed) were 30 FPS faster than the 2882 originally posted on trip one. This group was half inch though.

The only exterior variable is trip one was shot around 70 degrees and trip two was around 80 degrees.

No AC running, loaded in the garage, door closed. Yes music but phone was about 5 feet from scale.

So in short,

 

[Stammster]

I see. If your shot on the first day of shooting at 49.9 was 2905-2915 fps, would you be concerned? Seems that shot was low fps compared to the upward trend from 48.9-49.9gr. Also the 50.1gr was just a bit high fps compared to the trend 50.5-51.7gr. It could easily be 2915-2925 fps. Otherwise I'm not seeing any issue. Temp may have had a little factor, but that should have shifted all the day 2 data.

My bet is just random error in those 2 loads, especially the 1 shot at 49.9, since your other 3 shots you mentioned on day 2 seemed to be in line with the trend set on day 1. Again, seating depth, charge, case capacity, bullet weight, neck tension, etc. could have compounded and you are just seeing the outliers in a 25-40 fps ES. Velocity isn't just about charge weight.

Also scale calibration from one day to the next is possible. Hopefully not with the proper setup calibration. I always weigh with a 60.00 gr weight to verify, as that is pretty close to much of what I throw. Sometimes it's off a little, and I recalibrate. However, I'm not seeing that either in your case as the straight line velocity trends didn't seem to shift...just the 2 end points.

Why not plot data all on the same graph?

 

[JMW67]

was the rifle cleaned between the two trips if so I think thats what happened if not no idea

 

[sierracharlie338]

was the rifle cleaned between the two trips if so I think thats what happened if not no idea

Nope

 

[sierracharlie338]

I see. If your shot on the first day of shooting at 49.9 was 2905-2915 fps, would you be concerned? Seems that shot was low fps compared to the upward trend from 48.9-49.9gr. Also the 50.1gr was just a bit high fps compared to the trend 50.5-51.7gr. It could easily be 2915-2925 fps. Otherwise I'm not seeing any issue. Temp may have had a little factor, but that should have shifted all the day 2 data.

My bet is just random error in those 2 loads, especially the 1 shot at 49.9, since your other 3 shots you mentioned on day 2 seemed to be in line with the trend set on day 1. Again, seating depth, charge, case capacity, bullet weight, neck tension, etc. could have compounded and you are just seeing the outliers in a 25-40 fps ES. Velocity isn't just about charge weight.

Also calibration from one day to the next should be the same, but I always recalibrate and weigh with a 60.00 gr weight to verify, as that is pretty close to much of what I throw. Sometimes it's off a little, and I recalibrate. However, I'm not seeing that either.

Why not plot data all on the same graph?

Your explanation of the possible difference between 49.9 and 50.1 makes sense. As far as the prep and process of loading, everything was the same. Case capacity is a different story with this crap Winchester brass. Scale is calibrated every time I start loading. Who knows. The 49.9 charge weight shot a half inch group at 100 so I guess I won't read too much into it.

 

[Rick Richard]

Could be any number of reasons for that anomaly, but you mentioned Winchester brass. With that said it is possible you had a piece of brass that was significantly different in weight from the others and caused a drop in pressure resulting in the slower than anticipated velocity.

 

[L.Sherm]

Throw the chrono in the closet and if your load is repeatable and your happy with it thats what counts, what the targets telling you.

 

[The Oregonian]

You could buy a 50g calibration weight, or whatever your scale would use. That should help you determine if it is the scale. Or you could dig your FX out .

 

[milo-2]

How many shots per charge were fired to gather this data. If, like an above poster mentioned, it was 1 shot per, you really don't have data, you have rambling gathering of info.

 

[JMW67]

just curios do you shoot any groups from 50.7-51.1

 

[sierracharlie338]

You could buy a 50g calibration weight, or whatever your scale would use. That should help you determine if it is the scale. Or you could dig your FX out .

FX is coming out soon as I get back from this trip next week!!

How many shots per charge were fired to gather this data. If, like an above poster mentioned, it was 1 shot per, you really don't have data, you have rambling gathering of info.

Yep just one, looking for some potential flat spots before I waste a bunch of ammo. In a time crunch for a hunting trip next week.

just curios do you shoot any groups from 50.7-51.1

Not yet will be shooting some Saturday just for giggles.

 

[sierracharlie338]

@Stammster