Pellet Diameter Thread

I'm curious to try some different pellets, and I'm wondering if anyone out there can help... by measuring their pellet head diameters.

What I have noticed with JSB pellets has me worried. Diameter of the head varies between tins, and some won't shoot in my guns.

If anyone can take the time to measure their pellets with a caliper, I would think the results might be interesting. Some of the pellets are out of round, but all pellets I measured were quite consistent in size and shape, when taken out of the same tin, at least.

So far I have found

22 caliber:

1. Crosman Premier 14.3 grain 22 cal domes, 3 tins measured:
Very slightly oval heads
Maximum head diameter 216.5 mil, average. Essentially no variation
Minimum head diameter 216 mil, average. Essentially no variation
Consistency: high enough to be basically 100%

2. JSB Heavy Exact 18.1 grain 22 cal, 2 tins measured
A. Tin #1
Maximum head diameter = 215 mil, nearly perfectly round with only
a spot here or there measuring 214.5 mil
Consistency: high enough to be basically 100%
B. Tin #2
Maximum head diameter = 214 mil, also essentially round with a
a spot here or there measuring 213.5 mil.
very high consistency

3. Daisy 22 wadcutters, weight 13.6 grains. 10 tins sampled.
Consistently out of round.
Max diameter = 216 - 216.5 mils
Min diameter = 214- 214.5 mils
quite good consistency.

177 caliber:
1. Crosman Premier Ultra Heavy 10.5 dome, 1 tin sampled
Consistantly out of round
Max diameter 176.5 - 177 mil
Min diameter 175 - 175.5 mil
very high consistency

2. Crosman Premier Super Match wadcutters. 1 tin sampled
Quite round at average of 175.5 mil, with a high spot of 176 mil. Quite consistent.

3. Daisy 177 wadcutters. 2 tins sampled.
Head diameter = 174, pretty much on the spot and quite round and quite consistent.

I am using cheap calipers with half a mil resolution. For reference, the 22 JSB's in the smaller tin fit loose in my rifle and fall into the bore (chamber or muzzle end); the larger tin barely touches, sometimes. The Daisys fit good, and the Premiers are a little tight.

In 177, the Daisies have wiggle room, the Crosman Super Match are just barely touching the bore and fall into the crown, and the 10.5 gr Ultra Mags fit real well. Not too tight, not loose at all.

So far, all pellets that fit good also shoot good (at least at short ranges). The biggest accuracy problems for me have been with the undersized pellets.

Well, there's a really good reason Daisy 177 flatheads are crap in many guns. Head diameter of 174 mils!??? They're just too small for the average bore, and they are terrible in my own.

The Daisy 22 wadcutters aren't exactly concentric, but they are at least sized right. And up to 20 meters or so, they are plenty accurate in both of my Crosman 22 air guns. For punching paper or close range pests, they work great. Esp when you can buy them for cheap. They are exiting straight, but don't fly that great.

I read somewhere that in Europe, some of the pellet manufacturers (JSB, specifically) put the actual pellet head diameter of the lot right on the bottom of each tin. Down to the nearest hundredth of a millimeter. And there can be quite a bit of variation, lot to lot. So for 22 cal pellets, there would be a sticker on the bottom such as "5.51mm", or "5.49mm." (so far, I have noted a 1 mil variation between my first two tins of JSB, and I have yet to measure any difference in pellet head diameter between tins of American (Chinese made) pellets!)

So this thread was hopefully going to help us Americans figure out what sizes, or range of sizes, we might expect when we buy tins of these pellets that aren't marked. (But no one seems to give a rat's tail.) If concentricity of the head matters, my JSB pellets would be in first place... but they are pretty mediocre is accuracy when the head is too small for the bore.

My first experience with JSB suggests that maybe JSB dumps some of their undersized pellets on us, because hardly anyone in Europe wants to buy 5.44mm pellets, lol. But of course, I probably just had bad luck. Ted of Ted's Holdover/Edgun has measured his JSB pellets with a micrometer. Same exact JSB pellet I am using.

I measured my two tins at 5.44mm and 5.46mm, and poor accuracy due to being undersize. Ted measured 3 tins of the same pellets at 5.50mm, 5.51mm, and 5.52-3mm. And the largest pellets had accuracy issues due to being too large for his bore. His "magic" tin at 5.50 from 10 years ago has been the best performer in his gun.

I don't know how that pellet sizer is supposed to work. But if you're pushing it all the way through one end, out the other, it's just sizing the skirt.

In fact, I have noticed the skirts on Crosman Premier 22 domes has a good bit of variation. This might make a difference in accuracy for an Olympic shooter, but I have found no issue after sorting some out and seeing the difference. As long as the skirt is bigger than the bore, it doesn't seem to matter, although I have seen reference to someone using a skirt flaring tool to GREATLY increase the diameter of the skirt, in order to obtain a bit higher velocity. I guess that works the same as increasing the crimp on a revolver round to make the pressure have to build higher before dislodging the projectile into the bore.

As for which is more important, well. Skirt is thin and conforms to the bore. If it's larger than bore size by a safe margin, it's the right size. The head doesn't have as much give. If it's too small for the bore, it is going to exit the crown tilted to one side, and it'll start out with a bit of error from the direction of the bore before it stabilizes. The direction it takes will be random, depending on which way it was tilted when it exited.

OTOH, if the head is too big, it can take too much force to push down the bore, and this would seem like it can cause the pellet to deform from the huge pressure spike from behind and the head that "doesn't want to get out of the way," and/or cause a greater variation in velocity. If the skirt is "too big," it'll just get squeezed down to the right size. So skirts are always made to be at least a little "too big," if not more than a little.

You really want the head to be just big enough to not have any wiggle room and maybe just enough to get a very slight engraving of the rifling, in my best guess. Any less is a problem, and any more isn't doing any obvious favors. In theory, the pellet head just has to ride the lands of the bore without any wiggle room, while the skirt gets pushed down to the size of the lands, and the pressure fills it back out, again, to engrave into the grooves.

BTW, if you want to size the skirts of your 22 pellets, you can go to the hardware store and buy a piece of 1/4" brass tubing from KSN engineering and slightly chamfer the end. The ID is the exact size of a JSB pellet skirt. If you have a skirt that is undersized or dented, all you have to do is flare it out and then force it through the tube. But in my experience so far, this is not very important if the skirt is slightly bigger or smaller, as long as it's bigger than the bore. And I have never found a pellet with a skirt that isn't at least bigger the average bore by more than a few mils.

Skirts are generally big enough that even when they're obviously oval, they will often still fill out when they get pushed into the chamber. The big dents are the main problem.

Other random thought: If I could find a 177 bore that was 174 mils at the lands, I bet the Daisy 177 wadcutters would shoot pretty well.

Well then, this seems borderline pointless, to me, as an average shooter. When you close the bolt on your Olympic 10m pistol, the pellet is pushed into the chamber, and the skirt is sized as you load it. There might be a big enough difference for some people to notice, but certainly not for me.

I haven't slugged the entire bore, yet. But all you gotta do is stick the pellet head into the crown to find out if it's tight or loose! Undersized pellets will fall in under gravity, and if they're loose enough you can even rattle them around.

My Crosman springer is approximately .2155 to .2160, land-to-land.

My Crosman 1322 is approximately .2170, land-to-land, but I think it is loose at the muzzle end, because undersized pellets get good engraving on the head, when recovered, and even slightly loose pellets shoot with acceptable accuracy. I am guessing that once the pellet skirt is engraved with the head aligned in the tighter part of the bore, the pellet is staying pretty straight as it exits the loose muzzle.

My Crosman 1377 is approximately .176" across the lands.

Again, these measurements are just what I get with my own cheap calipers.

About "borderline pointless" maybe so......weren't you the fellow, though, who started this thread by measuring the diameters of pellet heads?

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I don't believe measuring pellet heads are pointless, else I wouldn't be doing it. It's obvious that an undersized pellet head can't exit the muzzle straight. With a bullet, the driving band can hold the bullet straight, so any bore riding part of the bullet is generally made slightly smaller than the land-land diameter. With a pellet the driving band is just the edge of a skirt. The bore riding part of the pellet has to fit the bore, or the pellet will be tilted the entire trip down the bore, including when it exits. Whichever direction it happens to be tilted, it will veer off in that direction before it stabilizes into a head-concentric flight/spiral.

Most diabolo pellet heads have a thin edge around the head that rides the bore, so that if it's slightly oversize, it can be a slight crush fit to the lands without adding too much friction/drag. But too big, you can still have a problem. Too small is always a problem.

Gloob: As I mentioned, the idea of sizing and the effectiveness of such was the subject of much discussion...pro and con. I think that the cons won out. I no longer take the trouble to use a sizer.

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That may be the case for skirt diameter. It is commonly accepted that head diameter is significant and important information. And it seems like it's common sense, to me.

I would think that would be useful for sorting pellets. Say you bought two tins of JSB's and put them together, like I did. Then found out that they were two different sizes.

I have never come across pellets that significantly varied within the same tin, though. So once a sample of pellets is measured, the rest of the tin is going to be pretty much the same, and you can stop. I think I'd rather spend the money on a micrometer, which can measure to a higher resolution and also the concentricity of the head.

I will not be buying anymore JSB's for my rifle until Crosman Premiers let me down. I love the Crosman Premiers domes in both 22 and 177.

JSB could easily be better, if I had any way of buying them in the right size. As far as I can tell, you can get a tin of JSB with heads anywhere from 5.44mm up to 5.53mm, and there's basically no way to know what you will get. For the price, you can count me out. They may have better concentricity of the head and more consistent skirts, but that doesn't matter when you can't buy the pellet size you need. I think there's an opportunity for one of the high end retailers to sell these pellets by head diameter at a premium.

Every tin of Crosman Premier domes I have measured has been a consistent head size. In 22, that has been 5.49-5.50mm in maximum head diameter, which suits my rifle. The 10.5 gr 177 domes I have bought have measured right on 4.48-4.49mm (per my calipers), which is slightly larger than all the other pellets I have tried, and it produces the tightest groups in my 177 airgun.

Just keep in mind that the bore at the muzzle may be smaller than the rest of the bore. Some airgun manufacturers "choke" their barrels by constricting the bore slightly at the muzzle.

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I'm aware of this. AFAIC, the result would be similar. You still want a pellet that will be a tight fit in the crown/choke, but not offer too much resistance. I just want the pellet head to barely be able to hold itself in the rifling of the crown against gravity. I'm not exactly sure that a choke would make fit more or less important. But I suspect it would shoot overly tight pellets a little better.

Well, I have another data point. I scoped my newest rifle, a cheap 500 fps Ruger Explorer to get a better idea of what was going on. It appears the bore is tighter than my other 177 gun.

All my pellets are absolutely terrible in this gun, except for the Daisy 177 wadcutters, which are pretty good. This include two other kinds of wadcutters with essentially the same shape and weight as the Daisys.

All pellets are a super tight fit in the crown, except for the Daisys which are just slightly loose. It appears like a pellet too big for the bore can be even worse than one that is too small. Even the Daisy's don't drop into the muzzle by themselves, but with a little push to get past the crown, they fall the rest of the way in until the skirt hits the crown.

Interesting to note that the 10.5 gr heavies print way to the right, about an inch and a half at only 9 yards, but with an enormous spread, so it's hard to say, exactly. (I can't get a "group" out of any of the other pellets, and these are probably the worst). I dunno if it's because they're heavier or because they're bigger. But they're also the biggest diameter pellets I have, and they happen to shoot the best out of my other airgun.

Go figure. The cheapest Daisy 177's out-shooting 3 other pellets by a mile, including two kinds of Crosman Premiers. This appears to support the importance of head diameter. If it wasn't for the Daisys grouping ok, I would think there was something seriously wrong with the gun.