260 AI vs 6.5 Super LR - 30 Degree Shoulder

[BearNaked]

I saw the 6.5 Super LR and thought it looked an awfully lot like the 260 AI. its a 243 win expanded to 6.5 bullet and then shoulder blown out to 30 degree. we isnt that the same thing as the 260 AI?

any way, i was looking at my next chambering and was just curious about these two calibers.

on the 30 degree shoulder, is it really that much better for your barrel? i was reading that it doesnt cause the fire cracking on the barrel.

http://www.6mmar.com/65_SuperLR.php

http://www.6mmar.com/260_Imp_30_.php

 

[NovaHunter]

I built a 260AI 40 degree shoulder and have been shooting it for about 18 months now. I have about 800 rounds down the barrel (don't have my exact roundcount if front of me this second).

Barrel is a 28in Pac Nor 3 groove. My current match load pushes a 142 SMK at 2980 fps using 44.2gr of RL17. I was able to push the 142 all the way to 3050 fps with good accuracy but started seeing some pressure signs so I settled on the 44.2 load. Shoots in the .3's at 100 yards.

It's a fun rifle to shoot. Fireforming is a slight pain, but the fireforming load is decently accurate so allows me to practice at medium ranges when fireforming. The PTG reamer Pac Nor had in stock matched the Redding Dies Midway carried (I sent the reamer specs to Redding before ordering) and the Lapua .260 brass was easy to get.

Overall I have been really happy with it.



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[BearNaked]

That is the same barrel i am looking at getting but going to get it in a 22 in so it can still fit into my case.

What is your fireforming recipe? I am at a toss between just doing the 260 or going 260 AI. i know the 260 AI is more expensive die wise and due to fireforming is going to be wasted materials.

 

[NovaHunter]

Reloading components were quite a bit more expensive. More so than I expected, but I went and bought the Redding competition dies so that was part of it. I purchased a set of .260 dies and .260 AI dies.

I'd have to go back and look up my fireform load. Formed 200 pieces in Oct. 2015 and just been using those since. I do remember starting low and working up my fireforming loads. What I found (and what others told me too) is that fireforming works better with a fairly stout load. The loads that were closer to minimum didn't form sharp shoulders, but loads closer to the book max formed very well in one shot.

The Pac Nor barrel has been great. Definitely would recommend it. It cleans very easily too. I picked the 3 groove since that was supposed to offer a little more speed and slightly longer barrel life. No idea if that is actually the case, but it does shoot well.

With a 22in barrel you are probably going to lose speed, and that might offset any gains you would see from doing an Ackley.

The only other major benefit is you don't have to trim with an Ackley. I have 5 loadings on my one batch of brass and haven't had to trim at all.

What are you planning on using this rifle for?

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[NovaHunter]

If you are interested, this thread chronicles my fireforming. Also shows some range reports and has most of my loads I tried too:

http://www.sniperforums.com/forum/showthread.php?t=50541

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[Rthur]

In this powder capacity range you should also check out the 6.5 addiction.
6.5x55 swede improved.
140's at 3050 no pressure.
Good barrel life.
Lapua brass.

R

 

[BearNaked]

The fireforming with a stout load makes since. that is nice to hear that 200 pieces have lasted you that long and there is no triming. do you full length size them or just neck size them?

i understand the 22" will get rid off some of the gains i should expect from the AI version but i am really stuck at that length as that is all my case will hold unless i get a new one which is another expense. damn pricey hobby.

This is going to be my competition/hunting rifle. kind of my all in one. I am rebarrel my savage model 10 with the prefit pacnor 3 groove. i am doing some long range challenges, i am not all that good but it is a lot of fun.

 

[Geno C.]

I'm at 46.5gr of H4381sc under 140amax. It's around 1/2moa and I'm using my old 260 barrel. I don't see it as wasted components since it shoots so well I can use it any time I want and get good results.

 

[NovaHunter]

Yep, definitely an expensive hobby.

I've only neck sized so far. I do have a body die if I need to full length re-size the case but haven't used it yet.

My barrel was a Savage pre-fit as well. My action is a Shilen DGR, which is basically a Stiller Predator threaded to accept Savage barrels. The build project was fairly straight forward, but their are some details and extra steps which are important with doing a AI vs. a factory round.

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[Supersubes]

I saw the 6.5 Super LR and thought it looked an awfully lot like the 260 AI. its a 243 win expanded to 6.5 bullet and then shoulder blown out to 30 degree. we isnt that the same thing as the 260 AI?

any way, i was looking at my next chambering and was just curious about these two calibers.

on the 30 degree shoulder, is it really that much better for your barrel? i was reading that it doesnt cause the fire cracking on the barrel.

http://www.6mmar.com/65_SuperLR.php

http://www.6mmar.com/260_Imp_30_.php

The principle difference between the two is where the shoulder pivots to make the new shoulder angle, and how it gets there. In the AI, the fireforming step moves the shoulder forward to the new angle, increasing capacity. The SLR is created in a sizing die by pushing the shoulder down at its junction with with the neck. Youre actually reducing capacity slightly in the SLR, but gaining neck length(with no need for fireforming step). Some brass is more friendly to the SLR treatment. If the shoulder is thick, the SLR alteration will create a donut. I believe thats the reason Win .243 brass is most popular for the parent case.

 

[BearNaked]

The principle difference between the two is where the shoulder pivots to make the new shoulder angle, and how it gets there. In the AI, the fireforming step moves the shoulder forward to the new angle, increasing capacity. The SLR is created in a sizing die by pushing the shoulder down at its junction with with the neck. Youre actually reducing capacity slightly in the SLR, but gaining neck length(with no need for fireforming step). Some brass is more friendly to the SLR treatment. If the shoulder is thick, the SLR alteration will create a donut. I believe thats the reason Win .243 brass is most popular for the parent case.

Thanks for that explanation. It finally makes sense to me. 260 is the way I'm going to go.


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[Supersubes]

Ive never messed with the slr, but i like the idea of it. Not an AI fan at all, been there done that. Having messed with the 47L, creedmoor, and .260 for many thousands of rounds each, I just cant see much difference in any of them on target. With the introduction of lapua CM brass, seems like a perfect compromise. The stout case head of the 47L, and a bump in capacity.

 

[308Gunner]

I am shooting a SLR, as far as brass I have used 7-08 260, 308 and 243 to make the 6.5 Super LR. I was getting 2930 out of a 22" Broughton with 140's but I backed off to increase brass and barrel life.

 

[Sig Marine]

I saw the 6.5 Super LR and thought it looked an awfully lot like the 260 AI. its a 243 win expanded to 6.5 bullet and then shoulder blown out to 30 degree. we isnt that the same thing as the 260 AI?

any way, i was looking at my next chambering and was just curious about these two calibers.

on the 30 degree shoulder, is it really that much better for your barrel? i was reading that it doesnt cause the fire cracking on the barrel.

http://www.6mmar.com/65_SuperLR.php

http://www.6mmar.com/260_Imp_30_.php

In your thread title, you're asking about a .260 AI, which stands for Ackley Improved and has a 40 degree shoulder, whereas the link you are providing is to Robert Whitley's site and his ".260 Improved with 30 degree shoulder" version. They are not the same.

 

[BearNaked]

In your thread title, you're asking about a .260 AI, which stands for Ackley Improved and has a 40 degree shoulder, whereas the link you are providing is to Robert Whitley's site and his ".260 Improved with 30 degree shoulder" version. They are not the same.

well now you are really getting me going. Is 30 degree better than 40?

 

[Sig Marine]

well now you are really getting me going. Is 30 degree better than 40?

That is the question! Those who have replied to your thread and have the Ackley would be the ones who might know but my research has shown that some have feeding problems with the AIs. I think the AI as a little more case capacity than the 30 degree but I'll take feeding reliability over capacity. I'm still doing my research but I've been thinking about Robert's improved version and am leaning that direction for a long action, switch-barrel build.

 

[NovaHunter]

Most Ackely chamberings are 40 degree.

The sharper 40 degree shoulder increases case capacity slightly vs. a 30 degree. The sharper shoulder also limits case growth better.

Sharper shoulders can present feeding problems however. Think of a sledge hammer vs. an axe. If you are trying to wedge open a small split in a piece of wood, does a flat end of a sledge hammer work better, or a tapered axe? The axe obviously works better. Tapered 20 degree rounds like the 260 and .308 slide into the chamber and feed better, vs. improved non-tapered rounds with sharp almost flat shoulders. The 30 degree shoulder kind of splits the difference between the Ackley and the straight .260 in my opinion.

Can't stress this enough though. Whatever you choose you need to make sure your chamber reamer, headspace gauges, and reloading dies all match the exact same chamber. You don't want to buy a chamber reamed for a 30 degree shoulder, and use headspace gauges and reloading dies for a 40 degree case.

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[MarinePMI]

Pretty sure some of Ackley's cases also included some with 30* shoulders (like the .17AH for example). It wasn't about shoulder angle per se, it was about increasing case capacity...

 

[Sig Marine]

I believe all Ackely chamberings are 40 degree.

The sharper 40 degree shoulder increases case capacity slightly vs. a 30 degree. The sharper shoulder also limits case growth better.

Sharper shoulders can present feeding problems however. Think of a sledge hammer vs. an axe. If you are trying to wedge open a small split in a piece of wood, does a flat end of a sledge hammer work better, or a tapered axe? The axe obviously works better. Tapered 20 degree rounds like the 260 and .308 slide into the chamber and feed better, vs. improved non-tapered rounds with sharp almost flat shoulders. The 30 degree shoulder kind of splits the difference between the Ackley and the straight .260 in my opinion.

Can't stress this enough though. Whatever you choose you need to make sure your chamber reamer, headspace gauges, and reloading dies all match the exact same chamber. You don't want to buy a chamber reamed for a 30 degree shoulder, and use headspace gauges and reloading dies for a 40 degree case.

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BearNova...Thanks for the thread and Nova...Thanks for your input. Your information matches what I've gleaned in my search about the Ackleys. Not that all have feeding problems, just that they can occur because of the shoulder angle. I think Robert Whitley's Improved 30 is a viable alternative for me since I want to use a long action for seating the 140s out beyond SA magazine length and have it feed reliably. If there's the option to increase case capacity a little as well, I might as well use it.

 

[NovaHunter]

Pretty sure some of Ackley's cases also included some with 30* shoulders (like the .17AH for example). It wasn't about shoulder angle per se, it was about increasing case capacity...

Thanks, edited my post

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[BearNaked]

i am stuck to the short action so i think i will just do the regular 260 rem as i wont get much benefits out of it in the short action and only running a 22-24" barrel. this would be more of a PRS style gun so i need reliability as well.

 

[BearNaked]

Can't stress this enough though. Whatever you choose you need to make sure your chamber reamer, headspace gauges, and reloading dies all match the exact same chamber. You don't want to buy a chamber reamed for a 30 degree shoulder, and use headspace gauges and reloading dies for a 40 degree case.

this is no joke. i will make 100% sure that i get everything that matches. while my face isnt the prettiest, i would still like to keep it the way it is.

 

[Rmk9494]

I am shooting a SLR, as far as brass I have used 7-08 260, 308 and 243 to make the 6.5 Super LR. I was getting 2930 out of a 22" Broughton with 140's but I backed off to increase brass and barrel life.

What powder are you using and are u still running that 6.5 slr?

 

[308Gunner]

I am now running Varget in Peterson small primer brass and a Mosler RDF 130 and I am getting 2920 without pushing it. I was using H4350 for the 140’s but after shooting the 130’s I switched to Varget. You can see the results in the 6.5SLR thread stupid accurate and low sd and es