0.01mm difference

[tsokasn]

Hello everyone!I have a question.
I've been given 10 pellets' tins.Four of them claim to have 4.5mm diameter.The rest of them claim to have 4.49mm.Is there any difference between the two?
Thank you.

[peepsight]

There sure is. One will give a tighter group than the other, but it will be so small that you may not see the difference.

Just test fire the 2 different sizes from a machine rest or bench rest to determine which group size is tighter, then stick with that.

Peepsight

[tsokasn]

peepsight
My greetings and thank you.

[Shooting Kiwi]

You might find the result of actually measuring the pellets interesting. I would bet that the variation in diameter of the pellets within each group is much greater than 0,01mm. If the error is less, please let us know the make and type of pellet, because they are more consistent than I can buy!

[JeroenH]

Shooting Kiwi,
How would you measuer the pellet diameter if you need to measure @ 0.01 mm accuracy?

[JohnD]

0.01 mm is 3.9 ten thousandths of an inch. Micrometer calipers are available that read in ten thousandths of an inch, but trying to measure something as soft as a pellet to any real accuracy is difficult indeed. The pellet manufacturers use optical metheds to scan and sort the pellets.

[Shooting Kiwi]

Thanks JohnD, I wondered how the pellets were sorted by the manufacturers. A single diameter measured, of course, tells you nothing about the roundness - I wonder what the manufacturing tolerance for roundness typically is. I'll measure some pellets when I can liberate some time.

JeroenH - To mechanically measure a soft pellet, as JohnD alludes to, really requires a standard force to be applied to the pellets for each measurement. This force should be as little as practicable. Callipers and micrometers can easily apply enough force to deform the pellet. A dial gauge, mounted on a comparator stand is an easy and safe way to measure, to 0.005mm or less. It's rather a fiddle, however. The dial gauge probe should be fitted with a large, flat foot, rather than the standard ball end. However, in spite of this counsel of perfection, a good digital micrometer, used gently, will show 0.01mm differences fairly reliably. Alternatively, you could set a micrometer or calliper to a given dimension and sort pellets into bigger and smaller categories (small ones drop through the aperture!). Repeat, changing the micrometer dimension, and so on, until patience exhausted!

Does anyone have objective evidence that any of this is worth doing?

[Fred Mannis]

Does anyone have objective evidence that any of this is worth doing?

It is a lot more fun to shoot the pellets than it is to measure them. :-)

In addition, it is the group size that is of importance, not pellet diameter or variance in pellet diameter. So, if you really do want to spend the time, spend it on measuring group size for different brands, sizes, lots.

[Shooting Kiwi]

Agreed, measuring these things is ridiculously boring. Agreed, the performance of the ammunition is its only important parameter (oh, perhaps price also). But there is absolutely no point measuring group size for different lots of ammunition unless you can be sure the lots really are different, are separable and that there is a neglegible spread of diameters within each lot. You could have a situation where the variation in size within lots exceeds the variation in nominal size between lots.

Perhaps really good pellets are individually graded to better than 0.01mm dia., with a neglegible spread, but do we know? Do we know the shape of the distribution curve for each lot? From my, albeit limited, experience, the spread of diameters is more than you might expect. So, if you are serious about this, I can see no alternative to measurement. Oh, and you should probably weigh them into sub-lots also. I think there are more important things in life...

[jrmcdaniel]

At 55 yards (Field Target max range], weight is far more important than any other variable. A constant weight translates to a constant velocity (or, at least more "constant").

At 11 yards, about the only thing that matters is whether the groups are small. (For really small groups, use domed pellets if allowed.)

If one were to be really anal, weighing would again be the first step in selecting pellets. (Weighing requires a scale accurate to .01 grains -- otherwise, forget doing it.) Group pellets into .05 grain bins. Shoot all of a bin at a time -- the actual weight is not as important as that all pellets in the group weigh the same (approximately). The other advantage of weighing is that it requires manual inspection. The combination of a look and a weigh will get rid of any "flyer" pellets.

Best,

Joe

[Fred Mannis]

Joe,
I agree, and not hard to do if you have access to a modern electronic lab balance. Do you have any data you can share with us? Particularly interested in Beeman Trophy, which I use for Pistol Silhouette.

Fred