243 col

[Splinter]

I have just started reloading and am pretty confused on COL. Is COL important in pressure increases when you go under the maximum length, or is it more important that you dont go over/touch the rifling? I loaded some 243 speer fmj and used a factory federal 80 psp to set bullet seating depth/col. Will I be safe with these settings? I will put up the measurement of it if needed, cant remember it right now.
thanks

[Fjold]

Minor variations in seated length are not dangerous until you start touching the lands and even then if you have worked up to the that load with the bullets in the lands and aren't seeing any pressure signs you are still probably OK.

If you have worked up a load near maximum and then change the seating depth to touch the lands you can get in trouble with pressure.

[scrat]

ok lets talk about this. lets say 30-30 150 grn bullet, versus 170 grn bullet.

The 150 grn bullet depending on manufacture is usually smaller in length than the 170 grn bullet. The overall length is 2.55. Now when loading with different bullets you have to make sure you follow proper load data. WHY. Because if you load both the 150 and the 170 grain bullet at 2.55 over all length the 170 grain bullet will be seated farther inside the shell casing. If the powder was the same powder charge it could be dangerous as the case pressure will be very very high. The reason being is there needs to be a certain amount of air gap between the bullet and the powder. Also seating a bullet farther in than what is recomended will aslo increase case pressure. how much will the increase be all depends on certain criteria. Such as powder, powder grains, primer, then bullet seating depth. Now it is common to have some variations on your COL. Just as long as they are not a huge amount of variations then it should be ok to shoot.



#2
Your greatest accuracy will come from finding out how close you can seat a bullet with it getting close as possible without touching the lands of your rifle. Each rifle is and will be different. COL you go by in a manual is based on SAMMI specs. Here is how to find your guns COL.
1. Go shooting
2. take one the shells do not size it.
3. load a bullet only with no powder or primer. Load the bullet approximately .030 longer than SAMMI COL.
4. Chamber the round in your rifle. then carefully remove the round.
5. Chambering the round will force the bullet into the case to the exact COL.
6. now subtract .005-.007 from that measurement.
7. That is your optimum COL for your rifle. Start loading rounds to that length and you will see an increas in accuracy.

NOW what you have to remember is that different bullets will touch the lands differently depending on the bullets ogive. So when changing bullets you will have to remesure your rifles oal.

[Fjold]

ok lets talk about this. lets say 30-30 150 grn bullet, versus 170 grn bullet.

The 150 grn bullet depending on manufacture is usually smaller in length than the 170 grn bullet. The overall length is 2.55. Now when loading with different bullets you have to make sure you follow proper load data. WHY. Because if you load both the 150 and the 170 grain bullet at 2.55 over all length the 170 grain bullet will be seated farther inside the shell casing. If the powder was the same powder charge it could be dangerous as the case pressure will be very very high. The reason being is there needs to be a certain amount of air gap between the bullet and the powder. Also seating a bullet farther in than what is recomended will aslo increase case pressure. how much will the increase be all depends on certain criteria. Such as powder, powder grains, primer, then bullet seating depth. Now it is common to have some variations on your COL. Just as long as they are not a huge amount of variations then it should be ok to shoot.

The first consideration for maximum powder charge is bullet weight. You would not have identical maximum powder charges for the 150 and 170 grain bullets. You would have smaller maximum charges of the same powder for the 170 grain bullets which would give you more room in the case.

There is no requirement to have any air gap at all between the base of the bullet and the powder charge. I routinely shoot my 375 H&H with a compressed charge of powder using the bullet seated directly on top of the powder. Look in any reloading manual and you will see data for compressed charges for a huge variety of cartridges.