260AI versus 260?

Howdy Al,
I for sure want to you to know that I do really appreciate your input and opinions. I think I know what you mean by not being able to feel this "stuff". I get myself in trouble on the internet sometimes because someone thinks I am being arrogant, etc. When it is just that it is hard to get somethings across by typing a few sentences. I am pretty darn sure that if the folks here were sitting face-to-face things would be way different. Not being able to see the look in someones eyes and face and not being able to get immediate feedback or clarifcation leads to many misunderstandings, in my opinion.
Take care
Jim
 
Ackley improving.......

I think one reason good enough for delving into the world of Ackley Improved rounds is 'cause you wanna'.
A few thoughts after 'AI-ing' several barrels:

-an unknown number[?] of gunsmiths still will 'improve chamber' an existing factory rifle without setting the barrel back on a rimless type cartridge. OK on rimmed rounds when 'improving' but NOT OK with rimless rounds.

-even if you ream to a 'tight' chamber, I agree that even the standard of 0.004" tighter headspace is usually not tight enough! I set mine [I beleive Alinwa does too] to crush fit factory rounds with DEFINATE FEEL. This is really more like a 0.010" under standard headspace. I take a few different brands of ammo on hand [or borrowed] and run them ALL through the new chamber to check for 'fit/headspace'. Factory ammo has been found to be far undersized on occasion. Those rounds are not considered as test fit rounds. I've opened even an OLD box of Winchester brand .257 Robt. and found 2 out of the 20 rounds to have VISIBLY short slope shoulders. For those two rounds to have a crush fit would have required the AI chamber to have been about 0.100" short!!! So I have the habit of looking down along the row of rounds when set on a flat surface to be sure no flawed cases are in the batch. Probaby a rare thing now days, but it happens.
Anyway, correct chambers on AI guns are for some reason, a hard thing to come by. I think arguments on headspace on AI chambers are common! I think I must have read and REread P.O.'s books a dozen times to be sure I fully understood his theorys.

-full length sizing of fired AI rounds is rarely needed. I'm guessing the case is very comfortable in it's new chamber with slight body taper.

-building an Ackley Improved rifle is fun. Might not give as miraculous results as some say, but still it is fun to play with one.

-you got to overlook some of P.O. Ackley's opinions on AI rounds. Why? Because he did NOT have the much improved slow burning powders we have today! If the .280AI is soooooooo good, then the .270 AI must be, too. P.O. said the .270 was way overbore as is much less in AI form. He WAS right,,,but he is not 'right' today because NOW we have cooler burning, less erroding slow burning powders he did not have. [Can you tell I have a .270AI reamer I'm wanting to use???:D].

I would not advise anyone to just build an AI round if you're wanting magum performance from a standard round. I would recommend you build one if you've read a LOT about the process and just want to have fun.

-true performance from 'standard' rounds can usually be had by just reloading. Not all factory rounds are loaded to max. I believe even the old 30/06 gets a boost from factory ammo because it is still loaded to what I call only 'warm' because of all the arms made for it being in various states of 'condition',,,,such as older military arms. I noticed this shooting factory .270 Win ammo side by side with factory .30/06 ammo. Did not have a chrono at the time but it sure sounded like the .270 stuff was loaded hotter [ok,,a poor poor way to compare, but I've read similar accounts as well!].

-factory UNimproved ammo is great stuff. Don't think that just by reaming to IMPROVED that your going to reap leaps and bounds of extra power. To read some accounts of us Ackley Improved fans you would think factory unimproved rounds were all "CB caps".:eek:

Just a few thoughts by one who has enjoyed watching a factory case come out of a rifle looking 'different' after being fired in an improved chamber.

.17 Ackley Hornet [truly a favorite but really a wildcat]
.22 K hornet
.223 AI
.250 Savage AI [a favorite]
.257 Robt. AI
.30/30 AI
.30/06 AI.
.
......maybe others,,,that's all I remember building and owning for now.
 
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jimfinn said:
I have just ordered an 6.5 barrel and am leaning towards having it chambered in 260 or 260AI. This will be a hunting rifle, probably on a Model Seven or 700 action. Max barrel length will be 26".
I'd appreciate any thought or experience on the gain going to a 260AI comapred to the standard 260.
Thanks
Jim
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I'd suggest that you answer some questions about yourself and things you want to do:

What creatures are you planning on hunting?
What terrain do you hunt in?
What range do you consider morally and practically suitable for hunting?
Do you handload all of your ammo?
Do you enjoy brass forming and reloading?
Are you concerned about barrel life?
What bullets do you intend to shoot?
Do you want to use a magazine fed short action?
Do you want (not necessarily need) more velocity and energy than the 260 will deliver.

If you limit yourself to the 260 and 260AI then you should have answered your own question, mostly related to your desire to rework the brass when you load (or reload) it. If you don't think the capability of the 260 Rem cartridge is optimum for your needs there are lots of other good 6.5mm cartridge choices including 6.5 Grendel, 6.5x47 Lapua, 6.5 Creedmoor, 6.5x55, 6.5 Rem Mag, 6.5-06 6.5 Saum, 6.5 WSM, and last (but not least) the 264 Win Mag.

I have rifles in 6.5 Grendel, 260 Rem, and 264 Win Mag. they have completely different characteristics. I woudn't say which is "best" without being honest about the above questions. The only AI cartridge I use is the 280AI, where the difference from the parent cartridge is more dramatic than between the 260 and 260AI. Personaly I woudn't go to the bother to do a 260AI. There is an extra step of forming the cartridge the the first time it's used. I consider the 260 Rem to be quite good the way it is.
 
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I shot a 260 for several years before switching to the AI. Now, when I switched, I cut the tenon off a 25.75" Broughton and re-threaded and rechambered that barrel for AI. With a 45 grain charge of H4831SC, the 260 would give me 2770 fps, and the AI with the same load gave 2850 fps.

The load was a 139 Scenar with 45 grains of H4831SC, a BR2 and Lapua 243 case.

Another load was 45 grains of AA3100 and in the 260 it gave 2780 fps. The AI with the same charge gave 2900 fps.

I chronographed several other loads that I had shot before and the AI gave anywhere from 50-120 fps gain. Remember, this is also with a 1" SHORTER barrel.

The sharper shoulder does seem to burn powder more efficiently.

Chrono was a PVM-21.

But for a hunting rifle, I would go with a standard 260. Reason is the AI does not feed as well and might screw up a 2nd shot should you need it.
 
B. Harvey said:
I shot a 260 for several years before switching to the AI. Now, when I switched, I cut the tenon off a 25.75" Broughton and re-threaded and rechambered that barrel for AI. With a 45 grain charge of H4831SC, the 260 would give me 2770 fps, and the AI with the same load gave 2850 fps.

The load was a 139 Scenar with 45 grains of H4831SC, a BR2 and Lapua 243 case.

Another load was 45 grains of AA3100 and in the 260 it gave 2780 fps. The AI with the same charge gave 2900 fps.

I chronographed several other loads that I had shot before and the AI gave anywhere from 50-120 fps gain. Remember, this is also with a 1" SHORTER barrel.

The sharper shoulder does seem to burn powder more efficiently.

Chrono was a PVM-21.

But for a hunting rifle, I would go with a standard 260. Reason is the AI does not feed as well and might screw up a 2nd shot should you need it.
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Mr Harvey, now you've defied the laws of physics! :)

I've been privy to a LOT of blown out, necked up/down/ AI'd or otherwise "improved" cartridge cases and chambers and this is the first time in my experience that anyone has ever stated that making a combustion chamber larger makes velocity go up with the same charge.

I would ask others who've experienced this to please chime in with B. Harvey...... I need to find out for myself if and WHY this could possibly be true.

I might need to start a fresh thread for this :cool: You've piqued my interest!

al
 
123 scenars and the 260 Rem. Goodtimes, mild and a joy to shoot.
 
My 260 with 123 scenars

These were on a windy day, I had under an hour to site in at 100-yards, had three rifles to get on paper that hour and this in one of them. Rushed shots, but knocking down subMOA. Pretty sure the flyer was my trigger work - I was not doing my part. Super fun to shoot. Can't wait to try her out at 600+
 

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I have a 260 and it is a great rifle. Accurate, flat shooting and does very well in the wind compared to the 308, but if it was for just hunting I would stay with the 260 or jump up to a 6.5-284 or a 264 mag. Barrel life is not a factor for most hunting rifles. The AI is not worth the effort when the 6.5-284 and 264 win. mag will both out velocity the 260AI. As far as the accuracy I believe the quality of barrel, gunsmith and your reloading abilities will be the deciding factor on that not the caliber.
 
alinwa said:
Mr Harvey, now you've defied the laws of physics! :)

I've been privy to a LOT of blown out, necked up/down/ AI'd or otherwise "improved" cartridge cases and chambers and this is the first time in my experience that anyone has ever stated that making a combustion chamber larger makes velocity go up with the same charge.

I would ask others who've experienced this to please chime in with B. Harvey...... I need to find out for myself if and WHY this could possibly be true.

I might need to start a fresh thread for this :cool: You've piqued my interest!

al
Click to expand...

I did not expect the velocity to up at all with the same loads. But I can tell you that fire formed vs unformed brass also had different velocities with the same load, and the formed brass was faster. It would seem that a formed case reached it's pressure peak sooner since it did not take time and pressure to form the case.

The barrel was the same one I had put 1700 rounds on in standard 260 and had been set back once at around 1000 rounds. All loads were at .020" off the lands and erosion was not a factor. I wanted to do the testing with the same barrel to start getting some load data on the AI before putting a new barrel on the rifle.

We know that when using a faster than optimum powder, that you have left over case capacity. We also know a faster powder reaches peak pressure sooner. But, is this due to the left over capacity, or due to the faster powder?

Now, my standard load for a 260 was 42.5 grains of IMR4831 that gave 2740 fps on a 85 degree day. In the AI this load was around 2830 fps. I had to back it down 1.5 grains to net 2740 fps in the AI.

So, it appears that the AI makes a given powder reach it's peak faster, or burns it's charge more efficiently.


In a 223/AI I have seen the same thing but the difference in charge weight for a given velocity is half of the 260/AI.
 
I'm happy with my 260 AI, it goes nicely with my others ..257 Rob AI , 35 Whelan AI, and 6-06. It doesn't shoot too bad either. This is five shots with Hornady 95 Vmax and 50 grains of W760.
260-2.jpg
 
Hi Louis,
Here are the answers to the questions:
What creatures are you planning on hunting? I have heavy rifles that I use for moose or where I feel the need to have something that will handle a big bear. For this rifle, I'd be using it for carbou, sheep, goats, and Wisconsin white tails. It would be perfect for the small Sitka black tails we hunt on Kodiak, but that is where the concern for big bears comes it.

What terrain do you hunt in? From tundra to mountain side. It will be a pretty light (8 lbs range with a small scope).

What range do you consider morally and practically suitable for hunting? I am pretty much a 250 yard or less hunter. I'll strech it out another 50 yards or so if I know the distance, have a steady rest, and the time to pull it off.

Do you handload all of your ammo? Yep, all of it. I feel dirty when I buy factory ammo.

Do you enjoy brass forming and reloading? Reloading and forming cases, within reason, are part of the fun. I currently form cases for a 30 WSSM wildcat, I form my 7-08 brass from 308 Lapua, I have a high velocity 6.5 wildcat based on the 300 UM case that I do radical case forming for. The 6.5 wildcat is a good round, but the chamber tolerances are so tight that and it is so straight wall and sharp shouldered, that it is more for the range than hauling through the rain, dust, etc.

Are you concerned about barrel life? Yes I am. I'd like to be able to get 2,000 plus rounds out of it. It would not be used for varmints or lots of rounds fired through it at one sitting.

What bullets do you intend to shoot? I like the Barnes Triple Soks 130 for hunting. I'd like to try the Hornady 140 A-Max's or some Berger VDL's just to see what sort of accuracy I can get out of it.

Do you want to use a magazine fed short action? Yes. This will go on either a Model Seven or a Stiller short action repeater Predator.

Do you want (not necessarily need) more velocity and energy than the 260 will deliver. I have other rifles to go to if I want much more velocity or energy than a 260. I am thinking of cutting the barrel to 26" to start. If I can get to the 2750'/sec range with 140 grain bullets I'd be happy. The AI is interesting as it is something different and if I can gain another 50-100'/sec without having barrel life suffer much, it may be worth it to me.
But I am not married to the AI concept for this rifle.

Thanks all, for all the great info to chew on. I was thinking I wouldn't get much response to my initial post!
Jim
 
Jim: I admit to being a 6.5 junkie since my teen years. Of all the messing around and the fun you will have, I don't know of a more rewarding bore than the 6.5?

With all that said, I would give a long look at messing around with the 6.5X55 and all the tweaking done to that case. Without a doubt the makers of the best brass in the world routinely make brass for this chambering.

I went through the different iterations of the 6.5-08/.260, 6.5-06, .264 Winny, 6.5 Grendel ad nauseum and found at the end, the 6.5X55 will run with the big dogs and many times run, better. The sweetness of the bore being the underling appeal for me the way the bullets handle the wind.

I know that whatever you decide to chamber to, you will have a lot of fun with this bore diameter, I know I have.:D

By the way, at my request Woodleigh is making hunting bullets for the 6.5 and if you would like to try some, give me a call.
 
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260

I think for the things you have listed a regular 260 would do a fine job with the 120-130 gr class when working my drift and drop charts the AI version doesn't really start to take over till 500yds but that said I do hunt with my AI in a 700 rem thats been converted to a single shot and bagged 4 whitetails with 4 shots, two of them about three seconds apart 6.5 has awesome penetration hear tell thats why the Swedes like that caliber so much.
 
Redrock said:
I think for the things you have listed a regular 260 would do a fine job with the 120-130 gr class when working my drift and drop charts the AI version doesn't really start to take over till 500yds but that said I do hunt with my AI in a 700 rem thats been converted to a single shot and bagged 4 whitetails with 4 shots, two of them about three seconds apart 6.5 has awesome penetration hear tell thats why the Swedes like that caliber so much.
Click to expand...

How does the AI "take over" at 500yds?

al
 
Stated earlier in this thread, come on Al, keep up. Look it up on your balistic tables I'm sure you have them your a 600yd guy
 
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Thanks Guys,
As I wrote earlier, the barrel is still months, maybe as many as 6, away and I can't say any decision is final until I hand it to a gunsmith for chambering. But I am leaning towards the 260AI. Why? I don't see a downside that bothers me. They are only, extra work to form cases, lack of off the shelf ammo, and more expensive dies. None of which are a big deal in my mind.
The up side? I like things that are a bit different and I like to tinker. And maybe I'll get a bit more velocity while still staying within reason.
I did think about the 6.5X55 and the idea of having a rifle chambered for such a historical round is attractive. But I already have lots of good (such as Lapua) 308 brass that I can form for the 260. I also use the brass in my 7-08. So when I order brass it can be used either way depending on my needs at the time. Not a huge thing but a plus for the 260 nonetheless.
Thanks again to all
Jim
 
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