Weighing Pellets - Insane question

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Saltlake58

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Apr 9, 2015
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Utah, United States
OK, so I have a regulated Marauder in .22 pushing the 14.3 grain Crosman Premier Domes at 800 to 825 fps for 30 shots. These are unsorted from the tin pellets.

I know that if I shoot JSB 18.3 grain pellets in the same setup the FPS drops to 740 or 750 fps. The JSB is about 29% heavier than the Dome's so I can see the relationship between weight and speed.

Question - Using 14.3 as a starting point, how much extra weight is required before seeing a noticeable speed change? Pellets in the tin tend to weigh between 14.2 to 14.5 grains for a 3 / 10 grain difference between. Does that 3 tenths grain difference between low to high make any noticeable difference in shooting? That's about a 2% change in weight low to high.

Many thanks for putting up with the insanity.
 
Insane answer (only because, I gave up the 'insanity' of precise weighing). 

If you truly want to see the impact on speed (or on a fixed target) of 3/10ths of a gram.... 1. Eliminate all other variables beside the weight diff. Done. 

Yeah, I know that is way to stupid sounding to be useful but think about it. Head size and mold seams are probably contributing just as much or more to accuracy, although 3/10g is on the high side. Skirt size can be too but as long as the skirt is a snug fit to your barrel (and you won't know this if using a magazine) I think you sized it by loading it, or close enough that the air blast will cover the rest.

Weight is probably the only one that really matters over the chrony and that impact is probably best tested with your gun. Accuracy at any reasonable distance brings all the other stuff into play.

In my spreadsheet, and I guessed at a speed, a 14.2 and 14.5gr pellet are about a 1/3 of an FPE apart using 710fps as the speed. I should have solved for FPS, sorry but I already closed the file and I'm wiped out.

Would a squirrel at 25y notice the diff. Probably not. Would a 3/8th" field target at 12y notice, prob not but maybe. Would a Benchrest target at 25m notice... probably...
 
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Saltlake,

Using your numbers above, a 14.2 grain pellet at 800 fps should hit at 55 (if you use a 30 yard zero) about 3 inches lower than your zero.

A pellet that weighs 14.5 grains, everything above the same, will come out of the barrel about 9 fps slower. This translates as about a 3.3 inch drop at 55 as compared to your zero. That's about a difference of 1/3 of an inch.

The heavier the pellet, the less difference that minute weight difference makes. If you had the 18.3 grain pellets with the same weight variation, it would be less. That's why I get upset and a little anal about my sorting of 8.4 grain pellets. When you weigh an entire tin, and you get weights from 8.08 grains up to 8.74 grains, and anything and everything else in between, that's a HUGE percentage of pellet weight variation, because the pellet is so light.

Welcome to my world!!!!

Shoot Straight, 

Tom Holland 
 
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Only reason I ask is pellet drop over 50 yards. If I'm shooting a group, when should I expect to see pellet drop.

I ran a spreadsheet after posting, and using a 14.0 grain, keeping the energy at about 20 fpe, you can go up to 15.2 grains and only drop 30 fps to maintain about 20 foot pounds energy. That's 1.2 grains, almost 10% before the speed drop becomes really noticeable. That 30 FPS seems to be within the margin of error for my regulator, so seems immaterial.

Just wondering if I was completely up in the night, or somewhat on track. Tells me that weighing is just to get rid of the really wild outliers, and putting pellets in piles in wider weights is just fine. Going to the 100th of a grain is truly insane.

Last batch I weighed, I lumped into 3 weight categories. It was JSB .25 caliber 25.4 grain, for now, and for what I shoot, I doubt any more accurate groupings wouldn't mean anything.
 
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Tom - when I start shooting 100 yard bench I'll be a bit more accurate on the weights. I'll probably never do field target as my legs are shot due to Muscular Dystrophy.

At 8.4 grains, a tenth of a grain would make a HUGE difference. Even the 14.3 grain has a larger margin of error. Point well taken.

Weighing the .177 pellets will become a big deal with my next gun as I intend it to be sub-12 foot pound. Why? No real reason other than I want something quiet, low powered, but accurate for the back yard.

It's all something to keep in mind when I sort pellets. .25 cal - bigger margin of error. .22 Cal, not so much, and the .177 pellets, really small margin of error.

One thing I learned is that if I intend to weigh .177 pellets, I need a better scale.

Do shoot straight, and thanks for the info. Validates what I was thinking.
 
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Saltlake,

Exactly...... All of my rigs are at 12 ft. Lbs , and the scale that I use I got from Hector Medina from Connecticut Custom Airguns, and was under $60. You can find a scale on e Bay or Amazon for around $25. Just make sure that it goes to a fine enough decimal. The scale I use has a resolution of 2/10 ths of a grain. Example.... 8.00,8.02,8.04 etc.

This resolution will be good enough for any caliber and weight pellet.

Hope this helps, 

Tom Holland 
 
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Tom - the scale I have has the same resolution,. but and it's a big but, it can't reliably repeat measurements. I think I paid a whole $10 for it on eBay. It's been OK, but I'll get a better scale before I get serious about the lighter .177 pellets. Definitely want to dip my toes into the sub-12FP world. I have a PCP Pistol that shoots about 6FP, but want a rifle I can tune down. Let's see, so far, Marauder and Impact, want something that can be tuned sub-12, and a also want a Dreamline. I did finally take your advice and get a compressor though. Got it about 2 weeks ago. Sure is nice to have air.

This can be an insanely expensive hobby, but I LIKE IT!

Thanks for your help
 
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Hadn't even given a Challenger a thought. If I heard correctly, Crosman just filled a large order for ROTC or something like that with Challengers. On the 12Fp gun, I'd intended to go fairly inexpensive with something like a Gen 2 Fortitude when they become available and tune it down to about 12. Read an article that new adjustments in Gen 2 will allow zero hammer spring preload = about 12 fpe. Only reservation with something like that is the trigger, as the old trigger had an 8 pound pull. Gen 2 is supposed to be substantially lighter.

Let's just say, keeping an open mind here.
 
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Saltlake,

You might want to poke around some of the Crosman forums, I'm sure some guys have tweaked and modified their triggers on Crosmans "budget" guns. You might even be able to put a Marauder rifle trigger group on it, or even a Marauder pistol trigger group. Maybe a Challenger trigger group. Crosman likes to "recycle" and or "duplicate" interchangeable parts for maximum cost reduction. I do know between the rifle and pistols, there are many interchangeable parts. Something to ponder and consider .

Hans and Ray Apelles have used 1720T pistols hopped up to 12 ft. Lbs, and have them in a Challenger stock with a longer barrel. As I said, with a Crosman product, there is room for easy modifications.



Tom Holland 
 
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All true. I have a 1701P, and the carbine stock so maybe that's where I start. It's incredibly adjustable and has a nice trigger as well.

Also, now I feel a bit stupid. I've been having problems with the scale getting accurate measurements. weighing a pellet, lifting off the scale, and then replacing on the scale, would give different weights. thought the scale had gone bad.

I put in new batteries and recalibrated the scale and suddenly, much more likely to get a duplicate weight. I'll do a bit more testing, but a new scale might not be needed.
 
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Tom - A question on scale accuracy. I swapped the batteries for new. Now it's much more consistent and I've learned you need to leave the pellet on the scale for about 5 seconds to allow the scale to give a final reading. Even with new batteries, it may be 2 - 100ths off when I weigh the pellet a couple times. Example, I may get a 14.33 on the first attempt and a 14.35 on the second attempt. That difference could be caused by anything from dust to friction on the scale parts. Do you look for the same weight each time, or is a couple 100ths close enough?

These seem insane questions, but in the sub-12 foot pound world, they also seem to make a difference. On an 8.4 grain pellet the .02 grain difference is pretty small. Is that close enough in your world?
 
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Saltlake,,

What I usually do, is make sure of several external factors are controlled by me. I'll explain.

Most likely, there's nothing wrong with the accuracy of the scale, even the cheaper ones like we have. More expensive and accurate scales probably fluctuate more do to their higher sensitivity, thus wonky readings.

The first thing you want to accomplish, is that you place the scale on a good, solid workbench or table. You don't want a table or bench that wobbles even a little when you rest your arms on it. If you do have said solid bench, don't put your arms on it anyway, to eliminate any movement.....yeah, the scales are that sensitive.

The second thing, is, as you said, leave the pellet on the scale for a few seconds more than you were. Most, not all, most, scales have an indicator dot or symbol that shows up on the screen when the reading is solid. This usually appears several seconds after the pellet is placed on the tray.

Make sure there are no wind sources in the same room that you are weighing your pellets in. Open windows, fans and ceiling fans, air conditioners, heat registers. Even a cooling fan from a computer across the room can contribute to inaccurate readings and fluctuations.

Make sure there is no traffic. Kids running around, or people walking past the weighing area will create a breeze as well.

Breathing. Make sure you don't breathe on your scale while weighing. I'll hold my breath briefly when the pellet is placed on the tray, until the reading is given. Just a few seconds, and you're good.

When you place the pellet on the scale, do so, but slowly. Your arm makes a breeze if you do it fast, and that could affect the scale for a few seconds.

If you want to do a test that will surprise you, try this......... take a piece of cardboard and fan the scale with nothing on it and zeroed, about a foot or more above it. The numbers will go nuts. Put the cardboard aside, and just use your hand, you'll be surprised how much it fluctuates.

Make sure of the above things, you'll be fine.

As for the fluctuations, don't worry about them. When I weigh a pellet for match use, that falls within my realm of acceptable pellets. For further clarification, I use roughly an 8.44 grain pellet.(this varies from gun to gun, but the principle is the same) With 8.44 as my standard, I'll separate a tin into my scale weights. I'll accept all 8.40,8.42,8.44,8.46,8.48 for further sorting. So even if the scale still fluctuates a little from 8.44, up or down a little, you're all good. The spread of those pellets velocity wise, only makes a 1-2 FPS variable, so it's negligible. This is my range of acceptable weights for my 12 ft. lb rigs.

Hope this helps, and I'm pretty sure that your scale will be fine.

Tom Holland 
 
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Excellent instructions. Watching your video right now (Episode 2). It's a great help. Already doing most of what you talked about, No wind, traffic, solid table, waiting for the scale to complete, etc.

For a strategy, since I shoot heavier pellets, I've decided group the pellets into +-.5% (one half of one percent). so, since the pellet is supposed to be 25.39 grains, I'll group with:

24.9 - 25.2, 25.3 - 25.5, and 25.6 to 25.9, anything outside of that is a complete outlier. The middle weight group is where I'll be doing most of my long range shooting.as I'm just trying to remove the bulk of variation, not all of it at this point. That might come later. a 1% spread will be quite a bit by your standards, but for where I am, it should be adequate.

Thanks for all the help, but now, back to the scales. I've also got about 2 tins of .22 caliber pellets to weigh for my Marauder. What we do for a hobby!!!!!!!
 
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Saltlake,

I would say that grouping would be adequate and sensible. The heavier a pellet is, with your above criteria, the more accurate the process would become, and vice versa. A 1 grain difference on a pellet of my weight, would be disastrous, but keep that 1 grain tolerance on a 50+ grain slug, and it'll be a nail driver. 

Also, being you are shooting a Marauder, I have found by removing the shroud, you can avoid minor temperature shifts, and the barrels natural harmonics without it will make it shoot a little more consistent as well. Accuracy is my main goal, it can sound like a cannon for all I care. I removed mine for Field Target competition, and I'll never put it back. If noise is a concern, you can easily fit it with a moderator. 

Glad I can help.

Tom Holland 
 
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Tom - shot over the chronograph today. Started with 14.2 grain Crosman Premier Domes. Ran around 810 fps. Then switched to 14.5 grain Premier Domes. Speed dropped 10 to 15 fps or so on average. Didn't keep detailed shot strings, but seems to indicate physics do work. 1% increase in weigh translates to 1% or so decrease in speed.

I did discover that the variability of the gun is still way too high to do effective chrony work at the 1/100th grain level. I've got tuning to do. I've been playing with the regulator and currently have it set around 1900 PSI, and think it might be too low. I've been as low as 1350 and discovered that I only got 20 shots per fill, no matter how I set the gun. Still experimenting. Right now, it gets about 29 shots within 15fps, then drops like a rock. I'd like to get it higher, but just need more experimentation.

The last tin I weighed scored about 85 or 90% in the 14.2, 14.3, 14.4 grain range. Most in 14.3 and 14.4. That's about a 1.5% to 2% weight spread and will definitely impact FPS at the muzzle. Great discussion!

Many thanks for the info. It'll be invaluable as I go along.


 
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Saltlake,

The math does work.

I do think that with a .22 you should be able to get about 35- 40 good shots at around 20 ft. Lbs. I think a regulator setting any higher should not be to your advantage. I would say lower it a touch, like around 1600 psi. That should be more than enough. You probably need to change the transfer Bushing between the barrel and the valve. You also should back the transfer port on the valve out about 4-5 turns, but be careful as not to strip it, it does so very easily. Don't forget the setscrew to lock it. I would do one thing at a time, and check it. There are other things you can do as well, like lighten the valve spring, and install a lighter hammer. I think that 1900 is a little more than what you need. I'll see if I can get you a tuning guide to steer you the right direction.

Tom Holland 

Field Target Tech 
 
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Tom - I've got the tuning guides, but much of what I'm doing is experimentation so I can learn first hand. The complexities of a tube with 3000 PSI on one side of the regulator, 1600 or 1900 PSi on the other side, a plenum with a given amount of air, spring with a given amount of energy hitting a valve held in place by the air pressure, then pressurizing the transfer port, etc, etc. My son has an engineering degree and I think he'd find the fluid dynamics fascinating if I could get him interested. For me it's such a learning experience, and challenge I really enjoy it. 

I guess it's like in wood working. Some of us spend so much getting a perfect edge on the tools, we forget about working wood (that's me!)

I'll try about 1600 PSI. before installing the regulator, I observed that the gun tended to operate best between 280 and 1800 PSI, which is why I tried for 1800 PSI this time, but 1600 might be a good range to test. 1300 was too low, so if 1900 is too high, it might be a happy medium.

I don't intend to spend any more money on this gun, as I've purchased an Impact, but intend this gun to be my learning - test bed. I might spend a couple bucks on a lighter spring, which might make a big difference and if I remember correctly it is under $10. The Impact is too easy to adjust, so it's hard to really observe what's happening. The Marauder makes you work for it, and you learn more along the way. And in the end, I'll probably cave and buy the hammer as well. Just not this week.

One big take away from this conversation is how much pellet weight variation impacts muzzle velocity. At 800 fps, a + or - 1% variation alone can be a 16 fps on its own. Combine that with variations in the gun setup and it can translate into a large pellet drop at distance. Now that we've discussed I can sort of estimate how weight differences will effect the shot. That's the information I was originally after in this thread, and I now have a much better understanding - SUCCESS!

As always, many thanks!
 
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Saltlake,

I get what you are saying. For minimal cost, or cost effectiveness, the cheapest and best bang for the buck would be this:.....lighter valve spring, stronger, but shorter hammer spring (to prevent hammer bounce) that has a little play at rest, larger transfer port between barrel and valve. These things would only cost a few bucks, and you'll be amazed what the difference is. Keep us posted, I'm interested in where this ends up.

Tom Holland 
 
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