Sorting 30cal -- weight does it really matter?

[Percula]

Using an online ballistics calculator, looking at the trajectory of a 51gr pellet... If I increase the weight by 0.2gr the amount of drop at 50y, 75y and 100y doesn't change. Increase by 0.6gr, no change. Increase by 1.2gr, no change. Increase by 5gr, no change! Tried this on a couple of calculators, with the same result, no change in drop with a 5gr change in weight.

So it begs the question, does the typical weight variances in a tin matter?

 

[Guest]

"Percula"Using an online ballistics calculator, looking at the trajectory of a 51gr pellet... If I increase the weight by 0.2gr the amount of drop at 50y, 75y and 100y doesn't change. Increase by 0.6gr, no change. Increase by 1.2gr, no change. Increase by 5gr, no change! Tried this on a couple of calculators, with the same result, no change in drop with a 5gr change in weight.

So it begs the question, does the typical weight variances in a tin matter?

The idea that a few tenths of a grain matters stems from the relative error introduced by those few grains and how much slower/faster the pellet is launched because of that change in weight. In a 50 grain projectile a half grain variance is a 1 percent variance. In a 10 grain projectile a half grain variance is a 5 percent variance. So the larger the projectile the larger the absolute variance can be before it affects trajectory. The percentages probably are a better indicator.  If BC does not change and muzzle velocity does not change drop will not change either. Typically a heavier pellet is also launched at a slower velocity... so..

 

[Percula]

"oldspook"

"Percula"Using an online ballistics calculator, looking at the trajectory of a 51gr pellet... If I increase the weight by 0.2gr the amount of drop at 50y, 75y and 100y doesn't change. Increase by 0.6gr, no change. Increase by 1.2gr, no change. Increase by 5gr, no change! Tried this on a couple of calculators, with the same result, no change in drop with a 5gr change in weight.

So it begs the question, does the typical weight variances in a tin matter?

The idea that a few tenths of a grain matters stems from the relative error introduced by those few grains and how much slower/faster the pellet is launched because of that change in weight. In a 50 grain projectile a half grain variance is a 1 percent variance. In a 10 grain projectile a half grain variance is a 5 percent variance. So the larger the projectile the larger the absolute variance can be before it affects trajectory. The percentages probably are a better indicator.  If BC does not change and muzzle velocity does not change drop will not change either. Typically a heavier pellet is also launched at a slower velocity... so..

Excellent! Sounds like I need to get a chronograph set up and make some runs. I suspect as you point out that at this heavy of a weight (low percentage of variance) it'll make very little difference. It'll be a while before I get one setup, but will report back to this thread when I do.

Thanks much!

 

[Percula]

Last weekend I bought (10) tins of JSB 30cal 50.15gr pellets from AoA. That's a total of (1500) pellets. There is a sticker on each tin indicating what I assume is a lot number and size of 7.62mm. I used a pelletgage (www.pelletgage.com) to sort by head size.

The pelletgage is a "go - no go" gauge. It has hole sizes from 7.58mm to 7.67mm in 0.01 increments. The way the gauge is used is fairly simple, you drop a pellet head down into a hole, if it passes through catching on the skirt you move to the next smaller hole and repeat until the pellet will no longer fall through the hole. You do NOT push the pellet through the hole, but because of the tight tolerances of the gauge the pellet must be perfectly vertical to insure if its blocked or not blocked. I found if I lightly touched the skirt of the pellet it would align vertically nicely. So if the pellet say passes through the 7.64mm hole but will not pass through the 7.63mm hole you know the pellet is between 7.63mm and 7.64mm. 

Here are my results listing the "no go" size of the pellet.

7.62mm -- (52) -- 4% of the total pellets
7.63mm -- (870) -- 58% of the total pellets
7.64mm -- (478) -- 32% of the total pellets
7.65mm -- (73) -- 5% of the total pellets
7.66mm -- (22) -- 1% of the total pellets
7.67mm -- (8) -- <1% of the total pellets

I had (3) pellets larger than the gauge would measure.

Those with a mathematical mind might notice something in those numbers... Typically you would expect something like a "bell curve" to form, in this case the smaller side of the bell curve didn't form. The smallest pellet was the 7.62mm. I suspect that JSB has something in place that is excluding anything smaller than 7.62mm. One might logically draw the conclusion that the stated size on the tin and the lot/size sticker is the minimum size of the pellet and not the exact size of every pellet. Rather that conclusion is correct or not who knows...

These will be going through my RAW BM500x. I will have some bench time this weekend, all I can say is I really hope my gun likes 7.63mm pellets haha!

I plan to get a chronograph next month and will further sort by weight and size. I will post with velocity stats.

My end goals...

1) Find the head size that works best in my gun.
2) Find the weight of the ideal pellet size in my gun
3) Consistently put the projectile where the reticle is!

 

[sharroff]

I'd weigh those 7.63's. I got 2+g variation per tin.

 

[Percula]

"sharroff"I'd weigh those 7.63's. I got 2+g variation per tin.

I did a weight sort on a tin (150) of the 7.63mm... I'm not seeing the variation you did in this tin. 48% of the pellets are within 0.3gr of each other and 83% are within 0.8gr of each other. The median weight was 50.3gr so for 48% of the pellets its a 0.60% variance in overall weight, and a 83% have a variance of 1.59% of the median weight.

I'm going to need to chronograph these to see the variance in velocity. 

 

[Percula]

I got some trigger time today. Working with 7.63mm sorted by weight ranging from 50.0gr to 50.4gr. I shot about (100) at 25m and another (75) at 100m. I shot at 25m first, then at 100m.

At 25m I had several "unexplained" shots that at the moment I put to wind changes, as the wind was brisk this morning.

At 100m I also had several unexplained shots, but this time it was a lot harder to blame the wind as it had calmed significantly by this time. What do I start seeing in my scope... spirals! I didn't get a count, but my gut tells me somewhere around 35% were spiraling.

I need to do some more at 100m to get more accurate numbers on spirals, but its looking like the bulk of my recent purchase are going into the "not to be trusted" bin. This might explain why others have reported that the 44gr works better in their gun.

This was with my RAW BM500x