My 7mm with the Nosler Accubond LR projectiles I had seated at the suggest COAL, made up a dummy round so I can see how far out I can seat them...........................Hopefully ready to test this weekend.
I didn't have any success with dummy rounds for finding my OAL. The Loose fit method didn't give repeatable results and I didn't want to buy more equipment, so I used the method below.
I use my cleaning rod to determine the OAL of my reloads.
With the bolt in and cocked, I run the solid one piece cleaning rod down the barrel till it touches the face of the bolt. I mark this location on the cleaning rod (tape and felt tip work well)
Take the bolt out and feed the projectile I want to measure into the barrel, use a chopstick or similar to hold it in place. Feed the cleaning rod back down the barrel until it touches the tip of the projectile. By playing with the chopstick and the rod you can feel when it touches the lands. Once you're happy that you've got the position, mark your rod again.
Take the rod out and measure the distance between the marks (with vernier calipers, not a ruler). This is the total length that will allow the bullet to touch the lands.
This is too long. If you set them at this distance, you are likely to get over pressures in your reloads and not be accurate.
I repeated this approx 10 times, cleaning the marks off between each go, and got results that were consistent. (8 times with identical length, 2 that were 0.03 - 0.04mm out)
With these results, I subtracted 0.05mm off the consistent result (hunting rounds, so not target) and made a dummy round at that length. I then made sure that it chambered correctly without any tightness or marking of the projectile (felt tip marker all over the projectile, this shows scratches really well) Also make sure that the projectiles aren't too long for your magazine etc. There are maximum overall lengths that your rifle will accept. Mine being a 243, its still shorter than a 308, so this wasn't really a problem.
Once you've sorted this, play with your powder loads according to the powder manufacturer handbook (mostly available online) and go and test them.
Ensure that all rounds chamber smoothly and you have no signs of over pressure etc.
I didn't go back and play with the length after this as I was happy with the results for a hunting bullet once I found the powder load and type I liked. I've only had to do this measurement once for each different type of projectile that I've tried.
