weighing pellets (yet again)

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Saltlake58

Member
Apr 9, 2015
2,907
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Utah, United States
So, I'm trying to tune my gun and the numbers are everywhere (well, not as close as they should be). Speed is varying about 3.4%, 812 to 840 fps. Average is right where I want it at 828, but want more consistency. Average weight is 34.01 (in this tin)

Then it hit me, I'm shooting straight out of the tin. The pellets are JSB 33.95 in .25 cal.

After weighing 120 pellets, I see a weight range of about 1.4 grains over 120 pellets. That's about 4% 

So, the speed variance is 3.4% and the weight variance is about 4%. Seems like a pretty close relationship.

If I get some time to shoot in the next couple days, I'll run an experiment where speeds of lightest and heaviest are compared, try to validate how tight the relationship is.

Has anyone else already don the physical experiment and can validate the relationship? Saving me the time of doing so?
 
For the reason you stated I weigh mine. I sort into batches of close weights (a few hundredths of grain) and keep shots for groups from same batch. I don't care if they are heavy or light, just that each mag gets taken from same batch. If the group is a bit high or a bit low doesn't bother me. Just that group is tight and Extreme Spread is lowest possible.
 
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Those responses make me feel better, I'm not nuts thinking half a grain affects point of impact. I'll be shooting weighed pellets, maybe within 2 tenths to see if the chrony numbers tighten up later this week. I guess it's all part of learning these things. The complexities of airguns!

Click to expand...

I'd recommend keeping each tenth separate. Try that and see if you get tighter groups. I sort to like 5-6 hundredth.
 
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I weighed more pellets today. So far, the low is 33.1 with a high of 34.8. That's 1.7 grains difference in a 34 grain pellet. Yeah, that can make a significant difference in muzzle velocity and POI at a 100 yard target. 10 or 20 yards, maybe not, but at 100 where every minute thing is magnified, yeah, it'll make a difference.

I'll weigh up a couple batches, by 1/10 grain and do some testing this week. Could be interesting. Maybe there is a 1 to 1 relationship with weight and velocity. Maybe not quite 1 to 1, but close. but I'll bet there is a significant relationship.
 
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Hammer is maxed. Absolutely no play in the hammer spring. The gun is a gen 1 Impact with some upgrades.

I weighed more pellets, and am amazed at the spread.

Lightest was 32.6 with heaviest at 34.9. that's nearly 7% of the advertised 33.95 weight. Only one each of the 32.6 and 34.9, but plenty in between.

Now that I have a bunch sorted, I'll chrony a test batch later this week (I hope, all depends on time).
 
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Hammer is maxed. Absolutely no play in the hammer spring. The gun is a gen 1 Impact with some upgrades.

I weighed more pellets, and am amazed at the spread.

Lightest was 32.6 with heaviest at 34.9. that's nearly 7% of the advertised 33.95 weight. Only one each of the 32.6 and 34.9, but plenty in between.

Now that I have a bunch sorted, I'll chrony a test batch later this week (I hope, all depends on time).
Click to expand...

Smart-test it for yourself. Then you will actually know.
 
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If you can’t raise the hammer….then lower the reg pressure.


Mike
Click to expand...

I went through the normal Impact tuning procedure where I start at about 90 bar, and the hammer spring not maxed out. then increase the reg pressure till the speed drops, then bring hammer spring up to overcome the reg pressure on the valve. I settled on about 110 bar and maxed out hammer spring. That allows me to shoot the 3395 heavies about 830 or 840. That seemed like a broad spread, so I thought what else could effect muzzle velocity, which is where pellet weight came from. I plan on testing the lightest to heaviest sometime this week to see if shooting a single weight (to the tenth of a grain) tightens up the FPS spread.

Gun is a gen 1 Impact with a Power Plenum and X Barrel installed. Once I shoot the various weights, I should have a better idea of the impact pellet weight has.


 
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Well, I shot a couple strings tonight. The string that really stood out was finding a batch of pellets that are within 1/10 of a grain.

String 1:

25 caliber Impact Gen 1

Pellets all weigh 33.90 to 33.99 grains. No other changes were made from last string a few days ago. Spread dropped from 28 fps to 11 fps just by weighing and selecting same weight pellets.


Shot count: 10
Low: 826
Hi: 837
Avg: 831
STD Dev: 3.4
Spread: 11.0

7/26/21 7:05:10 PM,828
7/26/21 7:05:24 PM,833
7/26/21 7:05:28 PM,830
7/26/21 7:05:32 PM,835
7/26/21 7:05:36 PM,828
7/26/21 7:05:39 PM,833
7/26/21 7:05:42 PM,828
7/26/21 7:05:45 PM,830
7/26/21 7:05:47 PM,837
7/26/21 7:05:52 PM,826

I guess that means for high accuracy shooting, I'll be weighing. It seems to work. 


 
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Haven't gone to the range yet to test latest modifications. Those are just chrony numbers, but my experience is that more consistent speeds = removing one random element that effects my shooting.

Just finished another set of tests to see how much 1 grain difference in weight makes, and it's about 20 fps. with luck, I'll be able to get to the range next week. Oh, how I'm looking forward to retirement
 
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Centercut - typically I shoot at 75 yards (lane limit at the range I shoot at.) they have a 100 yard range, but I prefer the 75 for ease of target setting. However, my goal is to shoot consistently at 100. That's why I'm putting in the effort to work consistency into the gun so if I miss, I know it's me and there are no excuses. Besides, I'm a control freak and having absolutely consistent shots is kind of the holy grail of shooting.

I probably won't be at RMAC this year (work is a pain, as you probably know), but someday!

Every one enjoy!
 
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Nation,

As many of you know, I shoot Field Target competitively. I've sorted pellets by weighing, checking head size, resizing, rolling, and inspecting the domes.

My general go to projectile has been either a JSB, or Air Arms 8.44.

I've chronograph an entire tin of JSB'S in the past, and found a 53 FPS difference between the highest and lowest within the tin.

I've also weighed an entire tin. What I found, was absolutely atrocious. I found pellets that weighed anywhere between 8.08 grains, on up to 8.74 grains. I also found that only about 40 pellets in the tin actually weighed 8.44 grains.

I've done the same with Air Arms as well. The FPS spread was considerably less at around 35 FPS or so. The tolerance of the Air Arms pellets was closer as well, with the lightest pellet weighing 8.22 grains, and the heaviest weighing 8.66 grains.

I did not do tests on either for accuracy, or lack thereof. 

What a can attest to, is, before sorting, I would get 5-6 "mystery " shots in a 60-72 shot match. Once I sorted by weighing them, I'd get maybe 3-4. After going through all of the culling methods I mentioned above, I'll get 1 or 2 in the course of 2 matches combined. I'll always sort using all of my above methods for a Grand Prix match, or Nationals. I don't usually do that for local matches, and some of my scores definitely reflect that. 

Tom Holland 

Field Target Tech 

Fieldtargettech.com 
 
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