“If you doubt it, think of this. A team of ten shooters is representing their country in an international shooting match. Do you think each rifle in the team will have ammunition suited to only it? Of course not. Further more, the match ammunition they use will be loaded heavier than off the shelf ammo of the same calibre.”
Well, as a shooter, and coach and a team officer on a number of national and international rifle teams, I can assure you that each rifle is different and has its own loads.
If we go to a match where the ammo is supplied and all teams use the same issued ammo, we take several rifles per shooter and each shooter tests the ammo in his guns to find the rifle that likes the ammo. The differences can be startling. I remember going to Bisley one year and discovering that one of my rifles was a tack driver with ammo that most of the other 1000+ shooters found to be mediocre. My rifle grouped around 1 minute with ammo that was 2 to 3 minutes in most other rifles. At 900 and 1000 yards, I missed the bull only twice that week. I won the competition with a record high score.
If the competition is a “bring your own ammo” event, the team executive will specify which bullet the shooters should use (currently the Berger 155.5) and each shooter will develop the load that works best in his rifle. Favourite powders in 308 are VHTN140, N150 and Varget, with a few RL15.
Velocities (pressures) are hot. We are getting around 3,000 fps (30” barrels) but it is interesting to note that the variations in rifles is such that this velocity is obtained with powder charges varying by 2 grains.
My ammo in Pat’s rifle would be very mild and his ammo in my rifle would blow the primer clear out and ruin the brass. Different rifles. Same make of barrels, similar reamers. Seen it so many times I have stopped questioning it and just accept it.
A team will typically field 40 to 50 top notch rifles. If you have been involved with many teams one develops a lot of experience in comparing what would look like identical rifles. The only thing identical about them is that they all accept the same factory round. The results are all over the place, unless each is fed the ammo developed for it.
To answer the OP question, I use 50 round plastic boxes with masking tape/Sharpie labels. I have quite a few rifles in some calibers, so each rifle has its own ammo.
In the case of hunting rifles, I have fewer duplicate caliber rifles, so it may be that the two or three rifles use different bullets, so in addition to the box labels, each round can be calssified as to what rifle it belongs to.
I only have two 270's and as it happens, when I bought brass on two occassions, the first 100 were brass and the second 100 were nickle, so that makes it easy not to confuse the ammo.
On a huntign trip, mixed ammo could be a disaster. Especially so if any of the ammo is neck-sized only.
Another thing to watch out for is headstamped calibers not matching the round. My 8mm ammo is all made with 7x57mm brass.
I have used 308 brass to make 243, 7-08, 6.5-08, 358 and even 356.