Originally Posted by Rangefinder
Assemble a dummy round and seat the bullet very long with just enough neck tension that the bullet doesn't move freely inside the neck. Chamber it. It wil hit the lands and push back into the neck. Eject it, measure it, and then adjust your seating die to it. Then make micro adjustments deeper to keep the bullet just off the lands. THAT is your maximum OAL according to chamber. Now, max OAL according to magazine may be somewhat shorter.
I see that several people use this method with apparent success. I tried it in all my guns and was never able to get reliable results.
I use Lee collet neck dies so I can adjust neck tension easily and repeatable.
I was never able to get good results in any gun.
I always found that if the tension was light enough so the bullet wouldn't stick in the rifling it was so light I couldn't reliably measure or even handle the cartridge. If it was tight enough to handle and measure reliably it was tight enough that the force required to slide it into the case caused it to stick in the rifling and pull back out on extraction.
I had considered using a drop of glue on the bullet and leaving it chambered until the glue dried but I never tried it.
The Hornady OAL gauge is an inexpensive, easy, reliable solution for me.