New to 243 AI Question

[Legionnaire]

I've been reloading for a while now. The 243 Ackley Improved is my first wildcat, though, and I'm looking for tips on where to begin. I have searched the interwebs and read lots of articles and threads on the topic and have made records of lots of other folks' pet loads. That's given me a good idea of preferred powders.

Many seem to suggest that one start with max loads for the .243 Win and work up from there. Others have suggested that one can use 6mm Remington load data as a starting point, as the case capacity of the .243 AI and the 6mm Rem are pretty close. Does that sound right to you?

I am building a lightweight hunting rifle, so will be working up a varmint load (55-70 grain bullet), as well as a heavier medium/big game load (90-105 grain bullet). Rifle is a Remington Model Seven with a McGowen "Remage" barrel, 20-inch, 1:8 twist, light sporter profile. I have lots of .243 Win stuff to play with--IMR 4320 and 4350, H4350, Varget (off the top of my head) and a good selection of bullets from 58 to 100 grain. Mostly interested in your feedback on the idea of using 6mm Remington data as baseline. Thanks.

 

[newmexkid]

http://www.accurateshooter.com/cartridge-guides/243win/

 

[Will D]

I've been reloading for a while now. The 243 Ackley Improved is my first wildcat, though, and I'm looking for tips on where to begin. I have searched the interwebs and read lots of articles and threads on the topic and have made records of lots of other folks' pet loads. That's given me a good idea of preferred powders.

Many seem to suggest that one start with max loads for the .243 Win and work up from there. Others have suggested that one can use 6mm Remington load data as a starting point, as the case capacity of the .243 AI and the 6mm Rem are pretty close. Does that sound right to you?

I am building a lightweight hunting rifle, so will be working up a varmint load (55-70 grain bullet), as well as a heavier medium/big game load (90-105 grain bullet). Rifle is a Remington Model Seven with a McGowen "Remage" barrel, 20-inch, 1:8 twist, light sporter profile. I have lots of .243 Win stuff to play with--IMR 4320 and 4350, H4350, Varget (off the top of my head) and a good selection of bullets from 58 to 100 grain. Mostly interested in your feedback on the idea of using 6mm Remington data as baseline. Thanks.

 

[Farmerboy78]

I'm running 100gr sp, Lapua brass, and 44.3gr h4350 at Remington 788 mag length. 3078 fps

 

[Will D]

I had a 243 AI built twenty years ago on a Sako 579 action with a Shilen 24" 1 in 10 twist barrel. It sat in my safe until recently, when I mounted a Bushnell 4.5-30 x 50mm scope in Talley rings. Searching every source I could find for load data, I found what you did; i.e., begin with max 243 Winchester data and work up. Using Sierra HPBT bullets seated to 2,643" OAL, IMR4350 powder and Remington 9.5 primers in Lapua fire formed cases I'm getting average velocities for five shots of 3,243 fps, but with s/d of 24.73 fps. Accuracy is good, but I'm looking for better.

 

[Will D]

I'm using 45 gr IMR4350. The 2.643 OAL puts to 85 gr Sierra engaging the lands by about 1/8". No pressure signs yet. I'll be increasing the powder charge by 1/2 gr increments to see how s/d & accuracy is affected. Will post results.

 

[Will D]

I'm stuck with the Sierra 85 gr HPBT because I have a lifetime supply and my barrel has a 1:10 twist. I started with 45 gr IMR 4350 in fire formed Lapua cases and bullets 1/8" into the lands. Working up a half grain at a time extreme spreads and s/ds decreased until 47.0 grains produced 3,500 fps with 8.2 fps s/d. At that point the bolt of the Sako 579 was a bit sticky on opening, but primers and cases showed no signs of pressure. I have no plans to push the velocity further and may back off a half grain or so to extend barrel life.

 

[newmexkid]

Man, that is quite a jam. 0.125?

 

[Farmerboy78]

I shoot a 100 sp fb in a 1-10"

 

[ATH]

Jamming by 1/8"? I have to ask why if that isn't the only accurate configuration? Seems quite a risk. I've seen bullets pulled by rifling with less engagement than that.

I would not work from a different cartridge (6mm), volume is an important consideration but not the only one. With AIs it's a proven technique to start with higher end loads of the parent and carefully work up from there. I love the 243AI and that's the route I took.

 

[Gord0]

Jamming by 1/8"? I have to ask why if that isn't the only accurate configuration? Seems quite a risk. I've seen bullets pulled by rifling with less engagement than that.

I would not work from a different cartridge (6mm), volume is an important consideration but not the only one. With AIs it's a proven technique to start with higher end loads of the parent and carefully work up from there. I love the 243AI and that's the route I took.

At .125" you'd likely be pushing the bullet back into the case...