Home Forums Hunting & Shooting Ask The Gunwriters 280 AI and 270 AI

Since the 280 AI has become so popular I couldn't help but wonder why a 270 AI wouldn't also become popular if promoted by the gun press and manufacturers ? I understand that we don't really need a 270AI but then again one could argue that we didn't really need the 280 AI either and yet it has become wldely used and available.

Common people who don't twist turrets, own laser ranger finders, or feel the need to shoot VLD bullets buy 270s and are blissfully content until told differently. Sometimes good enough really is good enough.

The 280AI is a vehicle for those in search of elusive perfection, higher speed without the recoil. The 7mm SAUM is a short action 280AI, but it is about as under appreciated as it could be.

One factor is the .270's SAAMI maximum average pressure is 65,000 PSI--as high as they allow for ANY cartridge.

Half or more of the reason the .280 AI gets more velocity is SAAMI's MAP for the standard .280 is 60,000 PSI, because it was originally introduced in Remington's semiauto rifle. When SAAMI accepted the .280 AI they standardized the MAP at 65,000.

Just "Ackley Improving" most rounds doesn't gain much extra powder room, and in fact in some basically none--as in the .35 Whelen AI, because there's no enough shoulder there to gain significantly more room.

The reason reason most Ackley Improved rounds gain significantly more velocity over the standard version are handloaders "work up" loads until they see "pressure signs," then back off a little. This generally means pressures a lot higher than data or factory ammo for the standard rounds.

About the only real advantage in AI'ing any cartridge is reduced case-stretch, due to the sharper shoulder maintaining headspace more firmly in the chamber.

Mule Deer please don’t tell Dogzapper that. It will break his heart.😁
GreggH

Having limited experience with AI's, I don't see this as a minor thing. It has been right up there with sliced bread for me shooting and loading for an AI. The cases don't seem to budge even a little in several firings.

It's not a little deal--especially if you shoot a lot of "colony varmints" with a .223 AI.

On the other hand, many newer commercial cartridges have shoulders steep enough to do the same thing. 40 degrees isn't actually required; 30-35 will do as well if you're careful when setting the sizing die.

Are AI cartridges more accurate due to better brass fit in chamber?

I shoot a 270 improved it is called the 270 WSM. It doesn't eclipse the 270 Win. by all that much, most loads only gaining 100-150 fps. I can't get 130s to 3,400 fps like some claim to and much over 3,300 is pushing it in my rifle. The WSM is only moderately popular and it is hard to compete with the original 270.

I would not be surprised if the 6.5 PRC out sells the 270 WSM. As Mule Deer wrote with out the pressure advantage the 280 has the 270 AI doesn't gain that much and uses a grain or two more powder just to get up to the 270 Win. speeds. Real world it will gain 50-100 fps over the standard.

The AI can show an accuracy gain but most of it is due to custom reamed chambers. Ackley claimed improved powder burn but this hasn't been proven. It does produce more uniform pressures with a 30 degree shoulder being optimal, the 40 has some of the same effects.

The shoulder angle has no effect on accuracy, but some claim a shorter fatter case does improve accuracy.

Ahhh the brutality of truth!

I have had a 270 Improved in a 15” pistol barrel. I loved it & it was very accurate. The 130’s would run 2950 fps.

I have two 280 AI’s. They are both customs and very well capable of making me a one gun hunter.....if, I wanted to be.

my dog knows more about guns and chambering than you do

PO Akley said .270 W was one of the cartridges that did not improve, likely because of the MAP being what it is.

I thought most of the powder volume gain was from lessening the body taper, not just the little shoulder angle increase? If that's the case then the volume increase would be close to the same on the .35 Whelen as it is on the .280 AI.

Not saying any of it worth it, just trying to understand.

AI's do look cool.

That was enough for me to try it (once) with a 338-06 IMP.

Made no sense but I do love the round!

std 280 with a 9", 24"
160g-162g
IMR 7828
Fed 210
Win brass
2930 fps
Load right out of the Nosler #4 manual, not for pumps and semi auto's, and Nosler reduced the load in later manuals

Also, the 280 AI shoots the 175g-180g at the same speed.

No flies on a 180g ELDM at 2800 out of a std 280 with Lapua formed brass from '06....about as idiot proof as they get....in the AI with Lapua '06 brass, you are looking at 2900+ depending on your barrel bore dia, throat dia, and bbl length.

I copied this load from another member here, everyone that shoots the std 280 with the 180 eldm wants one. A .796 BC at 2800 with match accuracy is impressive, to say the least. Not much powder, recoil with a brake and limbsaver is pure Honey!

There's not much taper in the .270, .280 .35 Whelen case to remove. Even with the sharper shoulder and less taper, the .280 AI only gains about 4 grains of powder capacity over the standard .280--which translates to about 50 fps of velocity gain in loads around 3000 fps, with both cartridges loaded to the same pressure in the same barrel length.

But the .280 AI also gains about another 100 fps over the standard .280 due to a higher SAAMI pressure for the .280 AI, 65,000 PSI versus 60,000 in the standard .280.

Which is why I would choose the 280 over the 270 only if I was a handloader. And at that one willing to develop my own loads.

Thanks John. 👍

I can follow all that. What confuses me is no one ever promoted a 270-08 or 25-08 for that matter. I know both are recognized wildcats. Only ever read 1 article on the 25 super (not sure of the spelling) by Van Zwoll I believe. Seemed intriguing. So...... why no 270-08?

While probably not the issue today with Re 15, the 375 Wby/AI can pick up 200 f/s over the standard H&H and especially with long spitzers. 4064 burn rate is a bit fast for the H&H and the 4350 burn rate a bit show but easy to get full pressure loads in 375 Wby/AI with 4350.

Actually in the late 1960s in Australia the 270 Imp and 218 Bee Imp (On Martinis) and that was because of powder. We mainly had the old 4831 which was a bot slow for 100 grain Hornadys in the 270 so the 270 Imp did better than increase incase capactity would suggest. For the 218 we had 4740 which was used in Canadian military 303 and like 3031 burn rate and too slow for the 218 and so the 218 Imp.

My feeling, that is I am not 100% sure, is a sharp shoulder and parallel body seem to speed up the burn rate of powder.