.280AI New Rifle Build - Barrel Twist & Free Bore Question

[JMRhino]

Unless you're going to be using 195 gr 7mm bullets a 1:9 is good. Heck it will do ok with even 180 gr ELDM's.

I can't imagine using anything greater than 175s and I know those are probably on the upper limit of the ideal range for this cartridge. I have a 300 WSM if I ever feel the need for true a true magnum with a bigger bore size but it looks like the 280AI is a winner in sheer efficiency.

 

[FOTIS]

That makes perfect sense to me sir. With 175's the standard 1:9.5 twist will do great.

 

[Rem Jim]

I want to build a "big brother" to my current Tikka Lite in 7-08. I believe that I have decided on a Tikka action with a TBD brand barrel chambered in .280AI. I would like to have a 1/8 twist rate and longer free-bore to have the capability to use heavier bullets with higher BCs; however, I still want to be able to hunt with more traditional weights and projectiles in 7mm for whitetails. Is there a penalty for having too much free-bore for traditional projectile weights in 7mm (think 120gn -165gn) with traditional seating depths and COALs? I will mostly be hunting with Barnes TTSX 120s, 140s or NOS 140 ABs but want the capability to go heavier if ever needed.

Ultimately, I know it's not super critical either way because I know 165s out of a 280AI will handle everything I want to do at reasonable hunting ranges, but I thought since I am building from the ground up, might as well give myself options for future tinkering...

Final question (for now) - I have seen .280AI brass advertised as "280 Ackley Improved" and "280 Ackley Improved w/ 40-degree shoulder." Don't all 280AIs have a 40-degree shoulder? Why the distinction?

View attachment 29626

I want to build a "big brother" to my current Tikka Lite in 7-08. I believe that I have decided on a Tikka action with a TBD brand barrel chambered in .280AI. I would like to have a 1/8 twist rate and longer free-bore to have the capability to use heavier bullets with higher BCs; however, I still want to be able to hunt with more traditional weights and projectiles in 7mm for whitetails. Is there a penalty for having too much free-bore for traditional projectile weights in 7mm (think 120gn -165gn) with traditional seating depths and COALs? I will mostly be hunting with Barnes TTSX 120s, 140s or NOS 140 ABs but want the capability to go heavier if ever needed.

Ultimately, I know it's not super critical either way because I know 165s out of a 280AI will handle everything I want to do at reasonable hunting ranges, but I thought since I am building from the ground up, might as well give myself options for future tinkering...

Final question (for now) - I have seen .280AI brass advertised as "280 Ackley Improved" and "280 Ackley Improved w/ 40-degree shoulder." Don't all 280AIs have a 40-degree shoulder? Why the distinction?

View attachment 29626

Great Cartridge I Have several 280 AIs Here is the problem of using a 280 AI in a Tikka T3 action .
The mag lenght is TOO short to allow a long coal with heavy weight bullets . Even 150 160 s are handicapped by the coal limitations of the t3 mags .
So T3 is a Great action to build on if your happy with 140 -150 grers and some 160s too
But if you want to shot monos your gonna use up a lot of powder space or even cup & core like the 175-180 seat Deep . A Barnes 160 LRX needs a 3.795 coal to perform Well from a 280 AI you only have 3.340 MAX
Build a 284 Win on your tikka and seat the bullets out long with lots of free bore and it out performs the 280AI with the heavies .
CHEERS
Hey JMHO

 

[JD338]

I can't imagine using anything greater than 175s and I know those are probably on the upper limit of the ideal range for this cartridge. I have a 300 WSM if I ever feel the need for true a true magnum with a bigger bore size but it looks like the 280AI is a winner in sheer efficiency.

The 280AI is well balanced and pretty efficient. Yes you can go with a larger case but it’s with diminishing returns.

JD338

 

[JMRhino]

Great Cartridge I Have several 280 AIs Here is the problem of using a 280 AI in a Tikka T3 action .
The mag lenght is TOO short to allow a long coal with heavy weight bullets . Even 150 160 s are handicapped by the coal limitations of the t3 mags .
So T3 is a Great action to build on if your happy with 140 -150 grers and some 160s too
But if you want to shot monos your gonna use up a lot of powder space or even cup & core like the 175-180 seat Deep . A Barnes 160 LRX needs a 3.795 coal to perform Well from a 280 AI you only have 3.340 MAX
Build a 284 Win on your tikka and seat the bullets out long with lots of free bore and it out performs the 280AI with the heavies .
CHEERS
Hey JMHO

I considered 284 Win a year or two ago and it does interest me but it may be too similar to my 270 WSM and 257 WSM. I’m sure you are correct with respect to the stock mag length being too short. Since I’m building from the ground up I assume there may be an aftermarket solution for the stock and mag for the tikka action. I really appreciate your input.