Spent a couple bucks at Brownells for chamber guage slugs. These are the ones that measure maximum brass length in your specific chamber. Measured both my 6.5 SAUM and my 264 win mag.
Bottom line, both chambers are cut with brass length potential of .030-.040 over book max case length. Based on my measurements, I won't have to trim brass for a very long time.
Looking forward to measuring chambers of my 270 WSM, 260, 308, 30.06, and 243. No telling how much time I have wasted trimming brass to book recommendations. I highly recommend these cheap gadgets!!!

http://www.brownells.com/reloading/...clair-chamber-length-gage-prod32925.aspx

Amazing! I presume the wide part is loaded forward?

Neat.

However, there are benefits of trimming, even when not needed, such as to square up necks, and absolute uniformity (especially when crimping or seating to a specific point on a bullet)

Yes. Over trim a sized case by about .150", start the guage in the case, bolt it in and close the bolt. Extract, measure.....bam! Now you have your chambers max case length. Do it a couple times to validate readings. All 3-4 measurements I did were within a couple thousandths of each other...

What a simple, but brilliant, idea!

Thanks.

I discovered this information well over 15 years ago on Varmint Al's webpage. I have been doing this method ever since. I rarely trim.

http://www.varmintal.com/arelo.htm#Case_Length


Based on his dimensions I made some chamber plugs on my lathe. Here is the link to the dimensions:

http://www.varmintal.com/alath.htm#Chamber_Length_Gauge

There are many interesting things on his site.

Thanks Al!

I figured that out and make my own on the lathe when I did an experiment to compare reloading dies for case growth and concentricity.

The thing to keep in mind is that chamber neck length does not work by itself.

It gets subtracted by how far back the shoulder case was pushed. Those who adjust their sizer die all the way down to touch the shell holder, need to trim shorter.

Clark,
Guages measure from the case base to the end of the case... I don't get what the shoulder dimensions would have to do with it? What am I not understanding?

Measured 3 more rifles...all had at least .025" extra length beyond max book case dimensions.

Absolutely true, but this new understanding alleviates the anxiety about case length concerns.

I highly doubt there is a rifle chamber out there that is right at book max case length for a cartridge. Probably most are .010-.030 beyond that.

Related- Even if you do choose to trim, you don't have to trim to book "trim length". You can set your length to trim length, max length, or anywhere in between. But, the problem comes in with factory brass being short, and even inconsistent. So, sometimes, if uniformity is the goal, book trim length must be used.

This. I made several tools like those years ago to check my real max length and they worked great but if you are going to crimp then uniform length is a must.

I've been using the $6 Sinclair inserts for many years and they've saved me a huge amount of time.... I don't think I've ever seen a factory rifle that's less than .015 over Sammi spec.

If you measure from the breech face to the end of the chamber neck, that is not how long the brass can be. When the firing pin pushes the case forward, the shoulder should stop it. If the shoulder has been pushed back, the case must be that much shorter to keep from pinching the bullet when the firing pin strikes.

I have been making chamber gauges, not cartridge gauges.