Tuck is right. I have these gauges in most calibers I shoot. Most chambers have an extra .010" to .020" and several guns all the way to .030". These things SAVE ALOT OF TRIMMING!! Also a way of measuring throat errosion on the big boys like my 300 wby and 30-378.

Bob gives good advice here.

I know several guys ( self included ) who have trimmed .020 or more under length so they would not have to trim as often.
This method is not the ultimate in BR style accuracy enhancement, but even letting the brass grow at it's own rate back to trim length does not seem to cause any serious accuracy robbing variance if they are all reasonably close to each other in length. ( By reasonably close I mean the brass was trimmed at the same time and fired with similar loads, the same number of times . )

Just .02 from a guy who does not own a scope over 20 X, or a rifle over 14 LBS.

Travis F.

Each rifle chamber will vary somewhat. You can determine the true length by useing a Sinclair Chamber Length Gauge . The Gauge cost $5.25 for a Cal. I have have found that most chamber necks are longer than Specs.but there was a exception . You could be cutting a case shorter than you need too if the chamber is longer than Specs. www.sinclairintl.com is the web site to look up if you won,t more data.