There are indicators and indicators. That sounds a bit ambiguous. Indicators are like optics, high end and low end.
You can buy a Chinese non certified (American Gage Design AGD) indicator for 10 bucks that works (has a dial and needle moves, but is it really 'indicating' accurately? You really have no easy way to tell....
Plus you need something to mount the indicator on to indicate, usually a magnetic stand. Those can be had cheaply too, again, about 10 bucks. The indicator stand can be cheap so long as it's rigid and 'locks
securely.
Going the other way, Starrett (what I use), Brown and Sharpe, Mititutoyo, Fred Fowler, all make many designs, all AGD certified for repeatable accuracy in the increments on the respective dial. You can even get digital readout indicators, AGD certified. None of these are 10 bucks. You can actually, depending on application, spend as much for a single AGD indicator as a mid priced scope (I have, numerous times), depending on application, but a quality AGD certified indicator will last a lifetime and hold it;s value if you ever decide to sell it. The Chinese non-certified 10 buck indicator is a throw away.
I use different Starrett indicator bases for different applications, all cost way over 10 bucks, but that's just me. The cheapo import base works, just make sure it locks rigidly. The base has to be rigid to hold the indicator from moving so the indicator can actually indicate what you want to measure (within the limits of the indicator itself, of course.
Then we come to dial calipers or sometimes referred to dial indicators. The difference between a dial indicator and a caliper is, a caliper uses a fixed and movable jaw attached to a mechanical drive mechanism or digital encoder to measure distance in thousands 0.001 or sometimes tenths 0.0001 and display the measurement on a round dial similar to a dial indicator or digital readout. In 99% of calipers sold, the measurement is indicated (on the dial or readout) in thousands 0.001. Most dial caliper measurements are only obtainable to 0.001. A micrometer (or other measuring device) is really needed to measure in tenths or better 0.0001 and that's not something a reloader needs to worry about because the gun or the brass/bullet isn't machined in tenths, thousands will do just fine.
My preference again is Starrett or Fred Fowler. I want a solid stainless caliper with inside/outside jaws and either an analog (dial) readout or a digital readout (encoder) with an easily switchable from SAE to Metric measurement equivalent (in a digital version). The analog readout will probably be SAE.
I also prefer an IP54 (International Precision) or better certified instrument. The IP rating tells you the instrument is water and dirt resistant and shockproof because you'll drop it sometime and it might get wet. The IP ratings only apply to digital encoded calipers. Mechanical calipers, at least good ones, are shock resistant but none are moisture resistant.
A nice and useful accessory for a dial caliper is a clamp on depth base (that clamps on to the rear of the caliper (only mechanical calipers, not encoders). The base gives you a flat surface through which the tail of the indicator extends as the jaws open and can be used as a depth indicator for recesses or holes. I use that all the time.
Some good sources for quality (and cheapo) indicators and calipers are...
MSC Industrial Supply
Enco
Production Tool and Supply
McMaster-Carr
WW Grainger
It's easy to differentiate between cheap and good and not just by price. If it's AGD/IP certified, it's not a cheap instrument and digital encoders are usually more than mechanical but each have their place. I have both.
A 6" jaw Caliper will be all the length you should require. I have them to 3 feet but thats not revel ant to what we do with guns.
I realize this post is a little long but there is a bit more to indicators than price, just like optics, it's complex.
I haven't touched on every aspect, just the revel ant to firearms aspects.
Hope this helps.....
