.243Win chamber length

[the_buckshot_kid]

I made a chamber length gauge for my .243Win from a sized and trimmed case. The chamber measurement I got (checked 3 times) was 2.6475". Now, for just an accurate hunting rifle is it feasible to set the bullet .0020" off the lands and make the OAL 2.6455" or should it be a little closer?

 

[gamestalker]

OAL is not linear across the board, it changes with the bullet. Some bullets have a longer profile, thus the olgive or where the bullet contacts the lands is going to in a different location from one bullet to the next.

Then there is bullet design, a soft point is going to have a rather inconsistent nose, banged around during shipping, what ever.

To accurate determine distance off the lands, one needs to measure from the olgive.

First make sure you have a piece of brass that drops freely in and out , thatof the chamber by gravity alone. Then I seat a bullet until it just makes contact with the lands. Contact can be determined when chambering the round by hand, not with the bolt. When first contact is found, the cartridge will just barely stick to the lands, but will fall out when you take your finger off the case head and very lightly tap the barrel, or there will be a couple seconds of delay before it falls out when you remove you finger from the case head without tapping on the barrel.

Once you have found .000" to the lands, measure your seating die from the top of the stem to the base of the die. This measurement will only apply to that bullet, so document the die measurement for that bullet part #, that way you won't have to go back through the same process each time you load with that bullet. Now that you know what the die measurement is for that bullet, just adjust the seating stem up or down the number of thousandths jammed, or off the lands you are wanting to shoot.

GS

 

[jwrowland77]

I start all my new loads at .02" off the lands and go from there

 

[witchhunter]

You can start there, but that doesn't mean you will end up there. I too start at .020 short, for what that is worth. You may end up .060 short or .005 long, it will depend on your rifle and load.

 

[Bart B.]

I don't think it makes much difference in most rifles how far the bullet jumps to the lands. Many people shoot .308 Win ammo the same length over 3000 rounds in competition and the last bullet jumps .070" or more further to the rifling than the first one. Accuracy stays the same through 600 yards.

Especially when a .243 Win round erodes away the rifling at its origin about .001" for every dozen or two shots fired; twice that of the .308 Win. Are you going to seat bullets a thousandth shallower every dozen or two loads you assemble?

Because the .243 case headspaces on its shoulder, the distance from case head to any point on the bullet is meaningless. Its the distance from the case shoulder to the diameter on the bullet that first touches the rifling that controls how far the bullet jumps. The case head will be off the bolt face by a few thousandths. On the .243 Win, that diameter is somewhere between that of the bullet down to about .236" which is the bore diameter.

 

[243winxb]

243 Winchester- Factory Chambers

I don't think it makes much difference in most rifles how far the bullet jumps to the lands.

I agree. I shoot bullets from 68 gr to 90 gr. For the most part, the base of the bullet is very near the neck/shoulder junction. Seat the bullet here, then try different powders. Pick the best powder, then fine tune OAL.

[/URL][/IMG] Click for larger photo.

 

[gamestalker]

Aside from the fact that nearly every rifle I've ever loaded for using a typical weight bullet has produced very good accuracy when seated up to or jammed into the lands.

But as I said, that aside, I find that when starting the load development with the bullet already at the lands, I'm free to adjust back off the lands without having to deal with pressure increases / spikes, thus I don't have to adjust the powder charge. Where as if I've already completed the powder charge development with bullet backed off the lands, that when I start seating the bullet closer to the lands, I'm very likely to encounter higher pressures, thus I'm forced to do my charge work up all over again.

GS