243 Win rechambered to 243AI

[Methow Packer]

I'm looking to rechamber to 243AI to rid of the dreaded case stretch. I've always liked cases with 30 or 40 degree shoulders so that appeals to me. Definitely will appreciated the added velocity. Should be able to reach my velocity goals without too much pressure. I only shoot heavy for caliber bullets like 105 VLD or ELD-X. I don't need load this cartridge over 3200FPS. That should be plenty for good performance.

I've read somewhere that AI design reduces throat erosion. Barrels last longer than the standard 243Win. What's your opinion on that. Are there any reasons not to fire form for the AI? I've also heard that AI cases last longer mostly because of the shoulder dimensions.

What are some of you using for the heavier bullets. I'm using mostly RE23 for the 243 WIN.

 

[ballisticxlr]

RE23, 45.5 grains for a 115 DTAC seated to -.040 under AICS mag length makes around 3180fps in a 26" tube for me. SD's for me are tiny, so are groups. I could have probably gotten another whole grain in the case but pressures were mellow and speeds were right up at the limit for the rules of the game I play so, why bother. I got 1500 rounds out of my .243AI before the throat growth caused me to start planning my next barrel and 1800 rounds before ammo got longer than the mag and no longer keeping anywhere near my desired jump. One of the best rifles I've ever shot. Loud as **** with a JP tactical brake.

Barrel life you're talking about is actually throat life and it's a fact as far as I can see that sharper shoulders help with it. Look at the intersection angle of the flame, guided by the intersection of lines formed by following the shoulder through the neck. If the intersection point is in the neck then it's not in the barrel doing bad things to your throat.

As far as brass life, in as many as 7 loadings on Hornady brass I never once had to so much as bump a shoulder or trim a case neck. I ran zero headspace and my chamber was set up with only .002" of total diametric clearance to out of the bag Hornady brass which helped minimize working of the brass. I could easily get 10 loads out of those cases. Hadn't even started splitting necks yet.

 

[Methow Packer]

RE23, 45.5 grains for a 115 DTAC seated to -.040 under AICS mag length makes around 3180fps in a 26" tube for me. SD's for me are tiny, so are groups. I could have probably gotten another whole grain in the case but pressures were mellow and speeds were right up at the limit for the rules of the game I play so, why bother. I got 1500 rounds out of my .243AI before the throat growth caused me to start planning my next barrel and 1800 rounds before ammo got longer than the mag and no longer keeping anywhere near my desired jump. One of the best rifles I've ever shot. Loud as *Rule 4 Violation* with a JP tactical brake.

Barrel life you're talking about is actually throat life and it's a fact as far as I can see that sharper shoulders help with it. Look at the intersection angle of the flame, guided by the intersection of lines formed by following the shoulder through the neck. If the intersection point is in the neck then it's not in the barrel doing bad things to your throat.

As far as brass life, in as many as 7 loadings on Hornady brass I never once had to so much as bump a shoulder or trim a case neck. I ran zero headspace and my chamber was set up with only .002" of total diametric clearance to out of the bag Hornady brass which helped minimize working of the brass. I could easily get 10 loads out of those cases. Hadn't even started splitting necks yet.

Many thanks. Lots of good info. You have made my decision an easy one. I'll send my rifle to the smith soon.

 

[Methow Packer]

RE23, 45.5 grains for a 115 DTAC seated to -.040 under AICS mag length makes around 3180fps in a 26" tube for me. SD's for me are tiny, so are groups. I could have probably gotten another whole grain in the case but pressures were mellow and speeds were right up at the limit for the rules of the game I play so, why bother. I got 1500 rounds out of my .243AI before the throat growth caused me to start planning my next barrel and 1800 rounds before ammo got longer than the mag and no longer keeping anywhere near my desired jump. One of the best rifles I've ever shot. Loud as *Rule 4 Violation* with a JP tactical brake.

Barrel life you're talking about is actually throat life and it's a fact as far as I can see that sharper shoulders help with it. Look at the intersection angle of the flame, guided by the intersection of lines formed by following the shoulder through the neck. If the intersection point is in the neck then it's not in the barrel doing bad things to your throat.

As far as brass life, in as many as 7 loadings on Hornady brass I never once had to so much as bump a shoulder or trim a case neck. I ran zero headspace and my chamber was set up with only .002" of total diametric clearance to out of the bag Hornady brass which helped minimize working of the brass. I could easily get 10 loads out of those cases. Hadn't even started splitting necks yet.

Forgot to ask. What is your fire forming procedure. What powder and powder charge.

 

[ballisticxlr]

I used 39.5 grains of RE23 for fire forming with 108gr ELD's. Could do a hotter load but there was no need to to get good forming and the cooler load would not be as aggressive on the brand new throat. Both the fire forming load and the final load seemed to like Winchester primers. Since I was starting with factory new brass there weren't a lot of options for how so I relied on the zero headspace setting to keep things lined up. Zero issues with that method. I used the first 250 shots doing fire forming but it was accurate enough that I shot most of those loads in matches. Did pretty well. Once all the brass was formed I jumped right up to development of full power loads and found the 45.5 load very quickly.

 

[Methow Packer]

Goo

I used 39.5 grains of RE23 for fire forming with 108gr ELD's. Could do a hotter load but there was no need to to get good forming and the cooler load would not be as aggressive on the brand new throat. Both the fire forming load and the final load seemed to like Winchester primers. Since I was starting with factory new brass there weren't a lot of options for how so I relied on the zero headspace setting to keep things lined up. Zero issues with that method. I used the first 250 shots doing fire forming but it was accurate enough that I shot most of those loads in matches. Did pretty well. Once all the brass was formed I jumped right up to development of full power loads and found the 45.5 load very quickly.

good info. Know what to do. Thanks