sorting pellets

[jusanothajoe]

just wondering, what do most people use to measure head size when sorting pellets ? I looked at some digital calipers all the way up to the $200+ range, the measurement accuracy was +/- .02 mm
when head sizes are measured by .01 mm, seems like alot of room for error. Or am I thinking all wrong ?

[dryanw]

I got a digital caliper from Amazon for 12 bucks and it works fine. I think it is accurate to .01mm.

[jusanothajoe]

I was looking through a tool catalog and noticed the calipers

[JMJ in NC]

Harbor Freight Centech 6" Digital Caliper is about $12 on sale. Accuracy of .001", resolution of .0005". This translates to accuracy of .025mm, but the MM readout resolution only goes to 2 decimal places, so that translates to .03mm "accuracy".

Accuracy is what the manufacturer warrants (conservative), but resolution is what the actually readout displays.

This will be fine for sorting pellets. We have $12 Centech calipers and $200 Mitutoyo calipers at work. Roughly the same accuracy & resolution. I use a Centech caliper at home. If you want better accuracy, move up to a micrometer, which has higher accuracy and limits the force you can apply when measuring.

For calipers, we keep a gauge pin handy and check/zero the caliper before taking a series of measurements.

Measuring technique is important as well - apply the same force to the measured object as when you zero the caliper. Lead is soft, so measure with a light touch. I'm sure there are videos online demonstrating proper technique. With micrometers, technique is doubly important, as the heat from your hand can affect the measurement (.0001" accuracy).

Another way to sort pellets is to roll them down a slight incline from a known starting point/orientation. The skirt diameter is larger than the head diameter, so the pellets will arc as they roll. The larger the head diameter, the shallower the arc. This gives you a qualitative indication versus a quantitative one.

JMJ

[gandalfretlaw]

I think the device is pretty accurate to itself. +/- .03mm doesn't mean it's going to measure one pellet 4.50 and the next 4.53 and they'll be the same size.

In my experiments I found that a particular gun favored certain ranges of head sizes. It wasn't terribly picky, +/- .01mm seemed fine. The pellets that worked best were the loosest that shot accurately. Looser and they became wildly inaccurate. Tighter and they started slowly getting less accurate. I don't think the skirt size is much of a factor as it's designed to crush to size.

For my gun that meant 4.48 was perfect. 4.46 was too loose. 4.52 was too tight. I don't sort pellets. I just found out what size it liked and then choose pellets that match that. RWS Superdomes and RWS Basic match work very well. The Basics are a little looser. RWS Hobby Match are too tight, probably around 4.52. Another gun may love them. I want to try them in my Gamo Big Cat.

[jusanothajoe]

I'm thinking if accuracy is .03mm then you COULD measure two pellets that are the same size and get .03mm difference. may be all wrong. We have precision mics at work that are accurate to within .0002 of an inch. and the manufacturer told us that any reading you take COULD be off by .0002 of actual. and I am not being argumentative, just wondering out loud.

[gandalfretlaw]

There is accuracy and precision. Accuracy is getting right on the fist time. Precision is hitting the same mark every time regardless of where that mark is. I'd think the accuracy might be +/- 0.03mm but the precision would be much tighter.

[jusanothajoe]

This is why I was a Mechanical tech and not a machinist. lol