260 Ackley Improved Advice

[SmartDonkey]

I recently purchased a 260 AI barrel and am having a few issues with it- The first being that it was throated very short and with some bullets I can't even load to 2.8 coal without being in the lands. I purchased some Berger ammo to use for fire forming- but it wont chamber due to it being about 2.86. So I need to have the throat cut to accept longer bullets. Just wondering what seems to be the sweet spot for the 260 AI with bullet choice- does it do better with standard 140's at a higher velocity or does it have enough extra speed that I should throat it for the heavy 150's? The barrel is a 1 in 7 so twist shouldn't be a problem.

And the other question-- I head spaced it so that the bolt half way closes on a 243 go gauge, and if I really wanted to I could probably make it close. Even then the bolt close on my hand loads is pretty tight. I realize the "crush" reason on a ackley- but I ran all the brass through a FL sizer before I loaded it- and it is still that tight. Would there be any issue in backing the barrel out a tiny bit more? How much force should it require to close bolt on a standard round in a AI chamber?

Target shooting at 1000 to 1400 yards. Thanks.

 

[ZEROGUY]

Sorry to be late to the party but figured I could offer some help sharing my experience.

My .260 ackley bbl would close on virgin lapua .260 brass with minor resistance, just noticeable.

Sounds like you have a bbl nut?

If so, I would headspace it with a piece of factory .260 brass (pull the bullet) so that it also closes with minor resistance.

Then, with your handloads, just seat your bullets .010-.020 off the lands and work up.

I never bothered running factory in mine, just started fireforming with handloads.

My current load is seated less than .020 off the lands and is 2.775 OAL with 140 eldms.

I hope you didn’t cut the throat.

My guess is your throat, like mine, is designed for plenty of room to chase the lands while staying within mag length.

And FWIW Mine is pushing the 140 eld-m’s at 2950 with 44.4 gr of h4350. I think the 150’s would be worth exploring in a 1:7 with this chambering.

 

[XLR308]

The 150smk is going to hog up a hell of alot of space in the case if your barrel is throated that short.
I think the real benefits of the 260AI are squandered cramped in a short action.
The pic below is the 150smk at the lands in my 65cm with the SAAMI. 199" freebore just for reference of the bullets length.

 

[SmartDonkey]

Thanks for the replies- after a week of no responses I kind of forgot about this thread- that's why I'm so slow on this. Yes, this has barrel nut- It is a X-caliber barrel on a ARC Nucleus LA. If this barrel was on a short action I would probably leave the throat alone- but on the LA it doesn't make any sense to waste that much powder space.

I did back the barrel out a small ways- but am still getting a little resistance closing the bolt on hand loads, enough that the case is still held in place on fire forming without the bullet having to be jammed into the lands. All I have done so far is fire form 20 rounds- but even then I had to load at 2.780 OAL.

I don't know how many different specs are out there for 260 ackley- but I'm still working to figure this chamber out. I sent the barrel back and x-caliber looked at it and said that it was in spec with their reamer- but that their reamer kept the same OAL and throat as the standard 260 rem. If that is the case I don't understand why I cant chamber some factory 260 rem ammo? They were good to deal with and paid shipping both ways- but they have removed 260 ackley as a option from the order form.

My plan now is to wait until my 150 bullets show up and then take the formed brass and bullets to the Gunsmith and get the chamber matched up.

 

[tho98027]

The 150smk is going to hog up a hell of alot of space in the case if your barrel is throated that short.
I think the real benefits of the 260AI are squandered cramped in a short action.
The pic below is the 150smk at the lands in my 65cm with the SAAMI. 199" freebore just for reference of the bullets length.
View attachment 7169226

What is your Coal at the lands with the 150’s? What velocity have you settled on?

 

[Scotts556]

I recently purchased a 260 AI barrel and am having a few issues with it- The first being that it was throated very short and with some bullets I can't even load to 2.8 coal without being in the lands. I purchased some Berger ammo to use for fire forming- but it wont chamber due to it being about 2.86. So I need to have the throat cut to accept longer bullets. Just wondering what seems to be the sweet spot for the 260 AI with bullet choice- does it do better with standard 140's at a higher velocity or does it have enough extra speed that I should throat it for the heavy 150's? The barrel is a 1 in 7 so twist shouldn't be a problem.

And the other question-- I head spaced it so that the bolt half way closes on a 243 go gauge, and if I really wanted to I could probably make it close. Even then the bolt close on my hand loads is pretty tight. I realize the "crush" reason on a ackley- but I ran all the brass through a FL sizer before I loaded it- and it is still that tight. Would there be any issue in backing the barrel out a tiny bit more? How much force should it require to close bolt on a standard round in a AI chamber?

Target shooting at 1000 to 1400 yards. Thanks.

I highly recommend that you get yourself and AI go gauge and headspace it properly. If it will not chamber a 260/243/308 win headspace gauge, your headspace is to tight and there is half your problem. Please headspace your barrel properly before you injure yourself or someone else.

And care to explain this crush factor? Ive owned 2 260AIs and they fired any factory ammo just fine without and stiff resistance from the bolt.

Scott

 

[SmartDonkey]

I highly recommend that you get yourself and AI go gauge and headspace it properly. If it will not chamber a 260/243/308 win headspace gauge, your headspace is to tight and there is half your problem. Please headspace your barrel properly before you injure yourself or someone else.

And care to explain this crush factor? Ive owned 2 260AIs and they fired any factory ammo just fine without and stiff resistance from the bolt.

Scott

Oh man.... the dreaded "you'll blow your self up" response. Thanks for the concern and I always strive to be safe.... but if it was that easy to cause injury there would be so few hand loaders that I could probably find Reloader 26 locally.

This is my first Ackley- so I wont claim to be an expert on them. But an Ackley chamber is not supposed to chamber a 243 go gauge. The standard round go-gauge becomes the no-go. This was done because the case is only supported at the base- because with the blown out shoulder they do not make contact at any point except the neck shoulder junction. By making the chamber shorter (.004-.006) it causes factory ammo to be "pinched" between the base and the neck shoulder junction. Obviously me saying "crush factor" was the wrong description. And I did back the barrel out a little more- but It still will not chamber the standard go-gauge.

If it did chamber a factory go-gauge I'm sure it would still be safe- but according to what I was told it is then not technically a ackley cartridge and just a "improved cartridge". And often with improved you have to jam the bullet into the lands so that you still have the multiple contact points to hold the case in place when forming.

 

[DAVETOOLEY]

Oh man.... the dreaded "you'll blow your self up" response. Thanks for the concern and I always strive to be safe.... but if it was that easy to cause injury there would be so few hand loaders that I could probably find Reloader 26 locally.

This is my first Ackley- so I wont claim to be an expert on them. But an Ackley chamber is not supposed to chamber a 243 go gauge. The standard round go-gauge becomes the no-go. This was done because the case is only supported at the base- because with the blown out shoulder they do not make contact at any point except the neck shoulder junction. By making the chamber shorter (.004-.006) it causes factory ammo to be "pinched" between the base and the neck shoulder junction. Obviously me saying "crush factor" was the wrong description. And I did back the barrel out a little more- but It still will not chamber the standard go-gauge.

If it did chamber a factory go-gauge I'm sure it would still be safe- but according to what I was told it is then not technically a ackley cartridge and just a "improved cartridge". And often with improved you have to jam the bullet into the lands so that you still have the multiple contact points to hold the case in place when forming.

Using a standard 243/260/308 gage for an improved chamber is a moving target. The HS will vary with neck diameter as the neck shoulder junction is the contact point. Not a big deal but you need to understand HS in that scenario varies with neck diameter.

 

[XLR308]

What is your Coal at the lands with the 150’s? What velocity have you settled on?

Just going off of memory the COAL was 2.945" @ .015" off the lands.
Haven't settled on a load since all I have shot with them was a seating depth test with a moderate load of H4350 to see how they would behave.
I chronographed the .015" off load only and it averaged 2680 fps.

 

[6brshooter]

I run 243 & 243ai, I've heard everything about use the 243 no go as 243ai, use the 243go gage as no go in 243ai..... I own a 243/260/308 go gage and a 243ai go gage. Theres enough issues in wildcatting that improper headspace shouldn't be one. Get a proper ai go gage.