I have an 243 AI with a slow 1-13 twist. Problem I have is, that any bullet I use (up to 70 grain) is nearly 70 thou of an inch off of the lands before I have enough bullet in the case. Is this okay. I am not getting great accuracy from it at the moment (I can when fireforming, but not with it running AI loads).
If this is the case, can I realistically get the chamber re-reamed if I lose 1/4" of barrel...

.070" off the lands is on the long side. What bullet weight are you fire forming with? Are you fire forming with factory ammo or handloads?

I went back and read your post on the Small Caliber forum. I understand you are fire forming with handloaded Lapua brass and a 70 grain bullet.

Do you neck size only after fire forming or full length size?

Try the 55 grain bullet with the 1:13" twist at AI velocities.

If it's an older barrel I can believe it. They came with very long throats. They made the Weatherby free bore look scant.

I use my 243AI mainly for deer hunting and I use 100 gr bullets so I don't have to worry about hitting the lands. But even after setting the barrel back for the improved chamber I can't even start to hit the lands with 55 or 75 Ballistic tips. But I don't care anyway because those bullets belong in 22's.

Like I said they have throats that would make Linda Lovelace envious.

Your smith could re-chamber but remember your use of longer bullets will cause them to be seated deeper in the case eating up case capacity.

This is one of them deals where there is no free lunch.

Best wishes, Bill

Find the best Harmonic you can using the never improved upon Creighton Audette Method. Then begin Seating "deeper" and you might hit a great Null spot.

One of my rifles shoots one particular bullet extremely well Seated 0.268" Off-the-Lands, yes more than 1/4".

And for some reason your particular barrel might not like that "specific" Bullet. Just because you want to use a particular Bullet, doesn't mean the rifle will like it at all. You could always try a different Brand.

Best of luck to you.

Johnny F. From your other post regarding this cartridge I suspect that possibly you are not getting enough bullet pull/neck tension. That would improve ignition consisteny. Good luck with your endeavors.

quote:

Originally posted by Johnny foreigner:
I have an 243 AI with a slow 1-13 twist. Problem I have is, that any bullet I use (up to 70 grain) is nearly 70 thou of an inch off of the lands before I have enough bullet in the case. Is this okay. I am not getting great accuracy from it at the moment (I can when fireforming, but not with it running AI loads).
If this is the case, can I realistically get the chamber re-reamed if I lose 1/4" of barrel...

I would try a .265" bushing with FLRS. Only size part of the neck, the unsided part will center the round in the chamber after 2 or 3 firings. If the bullet starts out in the center of the chamber, the jump to the rifling will not matter as much.Try seating the bullets deep so the base of the bullet is at the neck\shoulder junction, this will increase pressure to burn the powder better. If all else fails, cut the barrel and rechamber. Supply the gun smith with a dummy round FLRS with the lightest\shortest bullet you will use, seated with the base of the bullet to the bottom of the neck\shoulder junction. Then he can give you a tight headspace with the bullet sitting in the rifling. NOTE: The dummy round must be FLRS with a standard die, NOT a bushing die.

good information here Read what alinwa has to say about AI