Plug gauges and chamber throats

shil · #1 10-13-2011, 09:59 AM

To measure chamber throats for cast bullet use; with a plug gauge, is it better to use a plus-tolerance gauge or one with minus-tolerance? The manufacturer-stated tolerances are to plus or to minus .0002".

Frank237 · #2 10-13-2011, 11:15 AM

I bought a set of Chinese gauges from ENCO 2 or 3 years back. I went with the MINUS gauges as thats what Venturino bought and he wrote the article on using the plug gauges to measure cyl throats.

In my opinion the gauges are worth it if your a serious shooter and bullet caster. I found a few revolvers that were oversize, one that was way under.

FN in MT

jepp2 · #3 10-13-2011, 08:16 PM

I bought the 250 pin set .251" to .500" minus set on the online auction site. Total was less than $75 shipped. Couldn't be happier and makes measuring so easy and accurate.

Walter Rego · #4 10-13-2011, 09:21 PM

I also just bought the .251-.500 pin gauge set from a dealer on ebay. The set weighs A LOT and comes in a cheap pine box so shipping is $35 but you can it delivered for about $50 which is not bad considering how many gauges are in the set (250 gauges !). They are individually wrapped in cosmoline soaked tissue paper so must be cleaned before use and I wipe them off with an oily patch after handling as I'll bet they will rust easily.
Get the minus set. That means all gauges are actually .0002" less than the marked size, In other words if you are measuring a .44 caliber cylinder and you try a .430" marked gauge, the gauge really measures .4298" which will slip in a .430" chamber without binding. It's close enough for determining which diameter bullets you want to use.
I have had some surprising results, a Model 25-2 .45 ACP that shoots very well with FMJ hardball measures .455". I would have thought S&W would hold the tolerances of their target revolver closer to .452 but like I say it shoots well with ball. I haven't yet tried cast bullets in that gun.
And I have found with several guns, one chamber measures just a little tighter or looser than the others. That could be the one that causes flyers. Or maybe not...

fredj338 · #5 10-13-2011, 11:43 PM

I don't think it matters as long as you know which you are using. I also bought cheap set of gages, well worth the money IMO for serious cast bullet shooters. Then you just need to find a guy to open the throats up if they are too tight.

shil · #6 10-14-2011, 05:13 PM

Thanks, Everyone, for your input!