GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: Mole2017 on May 16, 2018, 10:41:25 PM
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So I weighed most of a tin of pellets, but there's story here. (I managed to shoot some comparisons. See reply #7 below)
I was looking for something to do with a 15 year old mentee that was coming to visit yesterday and decided something involving manual lab skills, measurements, precision, and statistics would be nice...ah, weighing pellets! I've been wanting to do a tin anyway.
The original plan was to use a mechanical balance, but that would have been slow going. (Still a good exercise though!) However, I happened to be in another shop and they had a nice electronic analytical balance that could resolve to the nearest milligram. I asked to borrow it and took it to the shop. At the last minute the kid had to cancel, but I decided I should at least preview the assignment to make sure I wasn't asking him to do stupid work. (I hate assignments like that...)
Long story short, these digital scales are nice, but you do have to work in a draft free space if you want it to settle on a number to the nearest milligram. In retrospect, I could have set the scale to grains, but then again, 0.01 grain is smaller than a milligram and a little more work to wait for...
Anyway, I pick a pellet that is close enough to 8.4 grains and make that my "standard"--always and frequently zeroing the scale with that pellet, keeping it separate from the others. That way every pellet is +/- some small number of milligrams from that and I only have to write bin labels like 0, +1, +2, -1, etc. By the way, another thing about these scales is you should plan to verify the warm up time needed. I found that for the first few minutes the zero kept creeping away on me by a milligram or so. Once warmed up, it wasn't a problem. (Now, if I had a 20 gram range scale in the first place, there might be less warm up, but this unit was 210 gram capacity...)
After some time, I managed to weigh the whole tin (and reweigh some of that, as the case was...). I'm pretty handy with tweezers and developed a routine: after putting one on the scale, I'd pick up the next one; by the time I had it ready to put on the scale, I'd read the weight of the one on the scale, set the next one beside it and snatch the weighed one, binning it and picking up the next pellet while the scale settles on a number.
Looking at the little petri dishes with the pellets in them, it didn't look like a nice Gaussian distribution (bell curve), but I used the scale to count them--an awesomely handy feature!--and plotted the data...
Viola! a bell curve! (Below) I was half expecting there to be multiple concentrations, e.g. output from several distinct dies, but instead it does appear to be a normal, er, rather a typical (shouldn't use "normal" here--that is another type of statistical distribution...) bell curve type group. [Edit/Correction: my bad here, normal is the same as Gaussian. I had the "uniform" distribution on my mind...]
Good to know, for what it's worth. I'm curious next to see if the 550 mg pellets are much different than, say, the 545 mg pellets. The whole range of the chart amounts to +/-1.6 percent variation about an average of 546 mg (8.38 grains), so that seems pretty tight already. In grains, the data runs from 8.29 to 8.56 grains.
Enjoy! Please chime in if you've seen trends for other pellets. The only thing I'll add here is a musing about the inexpensive digital gem scales you can get on eBay and elsewhere these days...A 20 gram range is going to help you (as opposed to 200 gram), but are they good? Once this unit I had access to was warmed up, everything was repeatable to the milligram. I saw a guy test a cheap gem scale on Youtube and he got three different numbers for the same pellet...Anybody have any experience to share regarding those?
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The .177 9.8g Winchester domes had got head size consistent... and weight was centered around 9.5-9.6-9.8 in each tin pretty decently with about a .3g-.5g range... sorted did improve vertical stringing. oh they did vary weight a lot between tins... lightest down about 9.3g in a 9.6g centered tin... and 10.2 in a 9.8 centered tin was the heaviest...
but
they are defunct...Now ther are a 7.9g pellet... still have not tried any of the new ones
https://www.pyramydair.com/product/winchester-177-cal-pellets-9-8-grains-round-nose-500ct?p=1036 (https://www.pyramydair.com/product/winchester-177-cal-pellets-9-8-grains-round-nose-500ct?p=1036)
in the customer comment is a descripion of the weight break down...
" I individually weighed 131 pellets. They averaged 7.64 grains. 19% weighed 7.5 grains, 44% weighed 7.6 grains and 26% weighed 7.7 grains, with the remaining 11% falling at 7.4 and 7.8 grains. I also weighed an additional 100 by bulk and they averaged 7.64 grains "
he was upset a touch though because pyramid need to change the advertised weight from the old 9.8g...
The old ones look quite different also...
Sister company... and the old picture...
https://www.airgundepot.com/winchester-round-nose-pellet-177-caliber.html (https://www.airgundepot.com/winchester-round-nose-pellet-177-caliber.html)
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So I weighed most of a tin of pellets, but there's story here.
I was looking for something to do with a 15 year old mentee that was coming to visit yesterday and decided something involving manual lab skills, measurements, precision, and statistics would be nice...ah, weighing pellets! I've been wanting to do a tin anyway.
The original plan was to use a mechanical balance, but that would have been slow going. (Still a good exercise though!) However, I happened to be in another shop and they had a nice electronic analytical balance that could resolve to the nearest milligram. I asked to borrow it and took it to the shop. At the last minute the kid had to cancel, but I decided I should at least preview the assignment to make sure I wasn't asking him to do stupid work. (I hate assignments like that...)
Long story short, these digital scales are nice, but you do have to work in a draft free space if you want it to settle on a number to the nearest milligram. In retrospect, I could have set the scale to grains, but then again, 0.01 grain is smaller than a milligram and a little more work to wait for...
Anyway, I pick a pellet that is close enough to 8.4 grains and make that my "standard"--always and frequently zeroing the scale with that pellet, keeping it separate from the others. That way every pellet is +/- some small number of milligrams from that and I only have to write bin labels like 0, +1, +2, -1, etc. By the way, another thing about these scales is you should plan to verify the warm up time needed. I found that for the first few minutes the zero kept creeping away on me by a milligram or so. Once warmed up, it wasn't a problem. (Now, if I had a 20 gram range scale in the first place, there might be less warm up, but this unit was 210 gram capacity...)
After some time, I managed to weigh the whole tin (and reweigh some of that, as the case was...). I'm pretty handy with tweezers and developed a routine: after putting one on the scale, I'd pick up the next one; by the time I had it ready to put on the scale, I'd read the weight of the one on the scale, set the next one beside it and snatch the weighed one, binning it and picking up the next pellet while the scale settles on a number.
Looking at the little petri dishes with the pellets in them, it didn't look like a nice Gaussian distribution (bell curve), but I used the scale to count them--an awesomely handy feature!--and plotted the data...
Viola! a bell curve! (Below) I was half expecting there to be multiple concentrations, e.g. output from several distinct dies, but instead it does appear to be a normal, er, rather a typical (shouldn't use "normal" here--that is another type of statistical distribution...) bell curve type group.
Good to know, for what it's worth. I'm curious next to see if the 550 mg pellets are much different than, say, the 545 mg pellets. The whole range of the chart amounts to +/-1.6 percent variation about an average of 546 mg (8.38 grains), so that seems pretty tight already. In grains, the data runs from 8.29 to 8.56 grains.
Enjoy! Please chime in if you've seen trends for other pellets. The only thing I'll add here is a musing about the inexpensive digital gem scales you can get on eBay and elsewhere these days...A 20 gram range is going to help you (as opposed to 200 gram), but are they good? Once this unit I had access to was warmed up, everything was repeatable to the milligram. I saw a guy test a cheap gem scale on Youtube and he got three different numbers for the same pellet...Anybody have any experience to share regarding those?
I found a lot of size & weight variation after weighing "8.44" grain JSB Exacts and "8.64" grain H&N FTTs........
(https://i.imgur.com/qYM2I1ih.jpg)(https://i.imgur.com/BQXUpgrh.jpg)
However the "Die B" cases of .177 CPLs from the cardboard boxes were extremely consistent in both weight and size.........
(https://i.imgur.com/bJk6B8Vh.jpg)
The 3 sorted boxes of die "B" weights only varied by about .10 grain. Even if I included the few lightest 7.98 grain and heaviest 8.16grain "plinkers" the weight variation for about 1750 weighed pellets was only about .36 grains.
(https://i.imgur.com/fiTuQ8Rh.jpg)(https://i.imgur.com/4YEPYx7h.jpg)(https://i.imgur.com/IIEjjumh.jpg)
LOL....I did find however that instead of the bulk of boxed CPLs weighing 7.9ish grains my last cases of die "B"s weighed 8.00-8.06 grains.........
(https://i.imgur.com/5h5eoc8h.jpg)
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Assuming the head diameter is consistent (and therefore the bore drag consistent).... That 1.6% weight range will cause an ES of 0.8% total, from slowest to fastest.... because the FPE should remain constant, and the velocity varies with the square root of the weight.... If you discard the pellets lighter than 543 mg, or heavier than 552 mg., the range drops to just under 1%, and the ES to less than 0.5%.... at the cost of only about 40 pellets....
Bob
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Thanks David
Now have your Mentee, do the Yarrh roll test, on each group of pellets,
then have him shoot the different groups, to see if he can figure out what is going on, etc. ;)
Tia,
Don
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been weighing and rolling for a while now. yes you will see that curve. and another in each wieght grouping after they get rolled.
ME? I take the group at or closest to the "advertised" wieght, and the one on either sdie and roll those into the subgroups. Use those for shots of record. you may wnat to test your zero when you swithc to a new group
I also discard (into a container for unimportant shots) the lightests and the heaviest. What your after is a consistent wieght and head/skirt diameter.....
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Oh the scale I used was the little Lee powder scale... accurate to 1/20th of a grain... and yep you need still air...
https://leeprecision.com/powder-handling/lee-safety-powder-scale/
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Well everybody, I got around to testing two groups of pellets. Wanting to shoot ten shot groups, I selected the two extremes that could supply that many, those being -2 mg and +9 mg from "zero" (which actually wasn't the average). On the chart that started this thread, they were the 552 and 541 mg pellets. That covers about 94% of the population, there being only a few mg to beyond each.
Conclusion? Inconclusive, probably. Looking at the 30 yards 10 shot groups in the first picture below, it does look like a draw. The outside diameter of the outer rings on those bulls is 0.6"; a dime is 0.7". If there is a difference, the statistics and shooting ability seem to be covering it up.
But there is a catch here: this is only my second outing with a bipod. A week or two ago I was out and did things differently at the table. For that matter, I may not have even had the table set up the same as I had to shim the feet for the location I was on. Anyway, the second picture is some 30 yard 5 shot groups. You see right away that the point of impact shifted from the technique changes. Would they have opened a little more if I doubled the shots? Maybe. Suffice it to say I won't have a definite answer until I get more time on the bipod. And weigh out some more pellets...it might be a while :P
All these were shot with the R10 using the Air Arms diabolo field pellets.
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David
Great info and groups,
FWIW,
I have found that when shooting from a bipod, that has a hard surface under the feet, that the bipod will bounce with each shot,
I use a piece of carpet or the closed cell foam under the feet, greatly reducing, the bouncing off the hard surface of the table/bench, for a bipod.
If you don't have the info, check here, with photo's etc,
https://www.airrifle.co.za/threads/39444-Pellet-Sorting-Inspection-Batching-and-measuring (https://www.airrifle.co.za/threads/39444-Pellet-Sorting-Inspection-Batching-and-measuring)
HTH,
Tia,
Don
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run that test again at 40, 45, 55 yards and see what ya get.......
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run that test again at 40, 45, 55 yards and see what ya get.......
Certainly will try. Until I get another tin of pellets, I'll have to set some aside from the adjacent groups for when I'm over to a friend's house that has more space.
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Yep at short range does not matter as much... as for sending the heaviest against the lightest well that will show potential vertical stringing...
I do wonder if it sort of evens out because the heavy while coming out slightly slower will also have a very slightly better B.C.
Thing is every rifle is just a touch different also... so any test really only applies to that barrel at that speed with that pellet... It may point to a general trend tho...
I do know out of my crosman .177 pumpers and the Winnie domed it made a difference but the spread of weights was pretty wide... .6g is about were it showed IIRC... would have to find my notes to say what speeds were...
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"Thing is every rifle is just a touch different also... so any test really only applies to that barrel at that speed with that pellet... " And Id add: at your place.
what works for you at sea level likely wont have the same results for me at 4800 ft......