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

The theory was (and, I suppose, is), if a line drawn along the angle of the shoulder, hits within the neck, throat erosion will be reduced. I've never seen any concrete data to back this up but it makes some intuitive sense. Geez, I hate trying to type anything on this damn site. I'm outa here! GD

LJB Thanks, that’s the first I’ve heard of this “ reverse donut “ when necking down with the bushing dies, but it does make sense. Thank you for sharing your experience.

This throat protection is why I’m more interested in the 6.5-280 AI in a long action.
The 6.5 PRC has lots of features to recommend it though.

An overlooked benefit of going 'Improved' for some is going to a shorter barrel and getting the same velocity as you had for a longer barrel.

Example, my high country backpack rifle was a Remington 700 Ti in 260, 22" barrel.
I installed a 20" factory take off 260 Rem that was Improved with a 40 degree shoulder.

This made it for me, a much more comfortable rifle to pack and more handy just having two less inches barrel, and 4 ounces less.

Anyone who has packed in and hunts high know this. Ounces and inches count overall and it makes a positive difference, and I was still able to maintain the original velocity when it was a 22" barrel.

Shots were long, even to 700 yards, and that little extra speed made the difference for that 20" barrel, and I could maintain my scope settings.

I would think that if going 270 Improved, if you could find that sweet spot powder (maybe a little slower powder) for the particular bullet weight you want to shoot, it would be worth it. Fun for sure trying anyways!

The 30-06 Improved is in my sights now, another one worth investigating. I have an 8lb keg of IMR 4831 that says yes!

I found a 40-page Australian military study from 2005 that looked intensively at barrel erosion, "Understanding and Predicting Gun Barrel Erosion," put together by Ian A. Johnston. It is by far the most comprehensive collection of information I've seen on the subject, and where I obtained most of the demonstrated info on barrel erosio-including info on neck length and shoulder angle I summarized the findings in a magazine article quite a while ago, which was eventually expanded into a chapter in GUN GACK II.

The only cartridge that looks like it would truly benefit from an "AI," would be the 6.5x55mm.

... but have yet to find the need.


Other cartridges, like the .270 WCF, cover that nicely.




GR

I like that idea of going improved with some cartridges and shortening the bbl. Makes sense.

Somewhere in PO Ackley's writings he said the only cartridge he couldn't really improve was the 270W. I figure it's just really hard to improve on perfection.....

I built a 30-06 AI in the early 90's, and it ended up liking IMR4831 the best for accuracy and velocity. I used both 180g X-Bullets and 200g NPT's. Killed two moose, two caribou, two elk, a deer and a pronghorn with it. IMR4831 can be temp sensitive though. If I had to do it all over again not sure I would that again though.

Interesting read. I went through the AI thing more than a few years ago, with my first, a7x57 AI. Course this was before LRF and dialing scopes..the added velocity gave me a little insurance, case I mis-judged distance to a target. MD is exactly correct..I pushed the case, cause it was "Improved". The cases didn`t last long, primer pockets went first. I then had to FF new cases. That got to be a PITA. I think I got a little smarter. I now have a standard 7x57, LRF, and dialing scope for 'Long" shots. Can`t say I miss the "extra" velocity, case problems, etc. If I need more snort, I use a different tool. Sounds like we all have them...tho I still have two AI`s.

Has anyone lost velocity when going AI? That is what I experienced when I converted a 243 to 243 AI. I had to increase my load by 2 grains to get back to were I started. It does look cool though and gives you something to talk about at the Range.

TEXMAG

Increased case volume. Same amount of powder as before in a larger case equals less pressure, and that equals less velocity.
The idea of an improved cartridge is to primarily increase powder capacity.

My point exactly, you use most of what you gain to get back to were you where. The brass does look cool though and doesn't need much if any trimming.

TEXMAG

It's been done, was a guy down in Arizona or somewhere down that way loved his BLR 1 st generation you know the one that the mag stuck out 2" at the carry balance point anyway he liked his blr more than his bolt 270 but liked.277" bullets. So he designed a reamer on the 308 case to 270-308 , bought a 24" Douglas barrel had his smith thread it a cut the chamber.he claimed by chrono that he could get 3000 fps with 130's and ball powder. Of course like everyone else it all but shot one hole groups. That article was in either Rifle or Handloader way back when in 2 digit issue numbers. That guy is prolly 80+ years old now if he survived and didn't get aids from using that gun and cartridge. Probably damn near get the same ballistics in a 308 with 130 ttsx loaded hot without risking your health or bank balance. Mb

Magnum Bob
Long ago there was the 25 Durham which was an “improved” 308 necked to .257. Pretty fair outfit.

Before that there was a 270 on a 300 Savage called the 270 Titus. Was created by Utah barrel maker Bliss Titus. He converted 99 Savages.
There were 1950-1960’s vintage.
Rick

Back to the 6.5-06 versus 6.5-270 or 280 AI. All of them can still use the 06 brass it will just be short and may never need trimming. I am not sure how many rounds you would need to shoot to see scorching at the front of the chamber but if shooting 38 special in a 357 mag chamber is any indication you would scorch the throat before the chamber became a problem.

There were 25&27 IHMSA's on both the Savage and 308 cases for silhouette shouting.

Having owned a couple of supposedly, "barrel scorchers" for over 50 years, I have yet to see any issues. Of course they are only fired 20-30 times a year, because I use other rifles for casual shooting and to maintain proficiency. I will be gone long before they are worn out.
I cannot believe that a 280 bullet fired from a .270 case is going to be much different than the same bullet fired from an 06 case. I use Nosler or Hornady brass for my AI, no need to mess with fire forming. Early on when I did not have cases specifically for the AI, I necked down and fire formed 06 cases, which is a waste of time and energy if commercial brass is available.

Kinda fond of the .270/.270 myself. Usually load it like a hot 7x57.

Tag Reverse Donut Type S Bushing

I still like my 250-3000ai. 100 grain bullet at 3200 fps has killed a bunch of deer. By the same token I’ve played with a bunch of other ones and found the difference to be minimal. Still enjoyed working with them. There are so many great rounds out today the need for AI stuff is not what it once was imo!

According to P.O. ACKLEY FIREFORM IMPROVED WILDCATS FROM CURRENT FACTORY CARTRIDGES

"... But the 270 Winchester Ackley Improved was a different story altogether, another customer request that resulted in a wildcat inferior to the standard cartridge.

P.O. wrote that the standard 270 was already "overbore," so a 40-degree shoulder with minimum taper couldn't offer much improvement, if any."


P.O. ACKLEY FIREFORM IMPROVED WILDCATS FROM CURRENT FACTORY CARTRIDGES
Cartridge:
270 Win. Ack. Imp.

Performance Gain over Factory:
Little or none with more powder

Ackley Comment:
Not recommended, factory 270 is better




GR

Lot's of common folk never heard of a 280 either.