doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Skeets Bore Gauge - Accurate?

I have found that mine is very temperature sensitive. I keep it in a kit in the car in case I come across a gun for sale in my travels. When brought into a warm environment I have to rezero every couple of minutes as the tube expands. OTOH if I leave it in the house a few days I have no such problem.

Kensal makes an interesting and "accurate" point about determining 'choke" and not having to zero the instrument prior to use. Since choke is found by the difference between bore and muzzle diameters, assuming that the dial is firmly snugged and does not drift/alter setting it matters NOT that the gauge be pre-zeroed.
However, I like to know EXACTLY my bore diameter in various locations, so I zero the gauge prior to each session. (The passage of the three balls thru the bore also tells me the smoothness or roughness of the bore by FEEL as I push/pull the gauge shaft.)
And since the palest ink is better than the strongest memory, I make a dated entry of the measurements in the chapter for that particular firearm in my Firearms Log....along with any other work I did on that firearm on that particular date.
I have the 12" version of Skeet's Bore Gauge - and its only short-coming is that I can't measure the center 6" of a 30" barrel.

Recoil Rob, please explain to us how the gauge changes readings between the time you set it to zero with your ring gauges and the time you measure the bore, three seconds later. I suspect you don't use your gauge very much, or really don't understand how it works.

Eightbore, I think the rod from the brass bearing end to the dial is of a different material than the phenolic resin cover of that rod. They probably expand and contract differently with temperature changes. Thus the change in zero when whole tool warms up.

In extreme temperatures, I can see the brass contracting and expanding, but I don't believe it would be any more than a few thousands if that. The more likely hood would be the balls sticking.
I'm guessing that the holes for the ball bearings are a few ten thousandths smaller than the ball it-self, and I do believe that in extreme cold, the brass would contract faster than the ball bearings, causing them to act like they were stuck. On extreme high temperatures, like in the trunk of a car on a 100 deg day, the brass would expand more then the balls, and then trying to use it you might force the balls out.

Just my opinion.

I tried to make a smaller head for 20 ga., not so easy, everything is in relation-ship to the I.D. of the brass head, along wih the O.D. of the inside aluminum tube and O.D. of the balls.

I was teasing Recoil Rob, and I'm disappointed that you fellows took me seriously. A common bore micrometer does not change a fraction of a thousandth between zeroing it in the ring and measuring a bore two seconds later. Get serious. You are making more of this than it deserves. Do any of you actually own a bore micrometer?

Note the RR said he brought it from the car to a warmer environment. & he said it changed in "Minutes" not Seconds. Any precision measuing instrument can be temperature sensitive. Many micrometers now have insulating panels along the frame where you hold them. You can take a mic without these & take a measurement, then grip it in your hand for several seconds & take another reading & the heat from your hand will have expanded the frame a bit & give you a Smaller reading. The mic will have grown so the spindle will turn down to a smaller reading. I am NOT Kidding incidently, I used precision measuring equipment on a daily basis for more than 35 years.
Consider the length of the shaft in one of these gauges. The expansion will be based on both temp & length. Steel normally expands or contracts @ approximately .00000633 per inch per degree F. Brass @ .00001 per degree F per inch. Note there is one extra 0 in the steel so brass expands almost twice as much. The instrument should be so designed though that any teamp it was apt to be used in the ball bearings would never be larger than the holes. You aren't going to get a reading with press fit bearings. By the above formula an 18" steel rod would grow in length by .00114" for every 10�F increase in temperature.

I would surmise temperature has little or nothing to do with the sticky balls. I think it's related more to the ills of a toilet flush tank in a vacant house. Just simple stiction. Funny we all know all about this issue; must all be cheapos and own (or at one time borrowed and didn't return) the Skeets gauge. And don't be such a big Zero, Bill. Why set to a ring gauge when you can set the indy bezel to zip on the dial with the balls in the bore and read choke constriction the simple way: te-ehn, twen-ty, toity, foighty--yup 44 thou underbore.

jack

Jack, not sure whether you're being serious, but it's relatively important to set to a ring gauge, assuming you want an accurate reading of the bore diameter. Sure, you can read choke constriction without using the ring. Simple matter of the difference between bore diameter and choke. But if you're buying a Brit 12ga that's being represented as "in proof", and if you come up with a BD well into the .740's, then you know it's not--which may influence your buying decision, or enable you to negotiate a more favorable price.

Thanks, Larry. As you imply, there is a bit more to gun value than choke constriction.