I go with the reloading manual and bullet weight and also powder that is for thr powder that I am using. You will note in the reloading manuals that there are different lengths for different bullets. I found this out when I had a MGM custom barrel and used the over all length listed which was way too much for the chamber. One member said to take an empty case and with a hacksaw cut a slit in the case close the slit up just a little take the bullet that you will be using place it in case just enough to hold the bullet in and slide it into the chamber as far as it will go and close action open and remove the case and bullet this will give you an over all length. you will need to back off a little so that bullet is not touching the lands. After I did this I found that I was almost 60 thousands too long and was having chambering problems, of course this was in a different cal round and a custom barrel but at least when I used his advise I found out what I need to do to get the correct length for that barrel. If you dont reload then someone else can jump in. I also found that at least in my case that the 223 would not handle a 70 grn bullet tried to keyhole because of the 1in 12 twist, I have another rifle with a 1 in 9 and it works perfect. 55 and 60 worked fine also had a problem in some of the 223 that has the lacker finish as they were hard to remove after firing. The 223 are fun to shoot and ammo is cheap if you dont reload. I think that most MFG take an overall length that they feel will work in all the different brands and go with that, just my opinion. Another sign you can look for is to load a round then remove it and see if you see any marks on the bullet from lands, also is the action easy to close and lock up or hard, when doing all this of course use all safty precautions.For the 55 grn bullet in hand gun loads list oal from 2.200 to 2.230 and in rifle for 55 grn bullet from 2.165 all the way up to2.260 all depending on bullet type and powder.
Deaconllb