260 Ackley Impv

[RemingtonSPS]

I have a DTA SRS coming. I have two questions about the 260AI (1) With 140gr JLK's using Lapua brass, what barrel length would it take to reach 2900fps? (2) I have heard guys use 243 lapua brass necked up but it forms a donut on the inside of the case at the neck/shoulder junction. Does it do this if you neck down .308 lapua brass?

If I can't get 2900fps+ with a 24-26" barrel using the Ackley I will probably switch to the 6.5 SAUM.

I did a search and found one guy running the 140's with a 26" barrel around 2900 but he said he was getting pressure signs. Anyone running a 24" barrel getting 2900fps safely?

 

[mattmcg]

Re: 260 Ackley Impv

Personally I have had better luck simply fire-forming 260 REM brass by Remington for good 260 AI cases. I've fire-formed hundreds and have loaded these 4-6 times (typical useful life at high velocity +2950fps) without any donut issues. With shorter case life given the high pressures, you'll replace your brass quicker than dealing with donut issues.....

 

[mattmcg]

Re: 260 Ackley Impv

And I see these velocities from my 26" barrel running 139gr Scenars and H4831 SC powder. FYI....

 

[RemingtonSPS]

Re: 260 Ackley Impv

Just what I was looking for thanks. What was the accuracy like at 2950fps?

 

[260shtr]

Re: 260 Ackley Impv

My Dad's 260 AI has a 28" barrel and runs 139's 2940 fps with no pressure. H4350. don't remember the load weight, but REM brass and BR II primers. Shoots in the .3-.4 range.

I wouldn't be afraid to cut it to 24".

 

[RemingtonSPS]

Re: 260 Ackley Impv

Anybody have experience using lapua 308 brass to make 260 ackley? I'm thinking the stronger cases might help me get to 2950fps with a 24" barrel. Anyone tried moly? I know some guys use win 7-08 brass.

 

[mattmcg]

Re: 260 Ackley Impv

Its easier to neck up Lapua 243 Win brass than to neck down the 308 brass. I've tried both and the 308 neck shoulder junction after sizing down wasn't as clean as necking the 243 up.

I used the Sinclair neck turning expander die with proper mandrel to neck up and then press it using a Redding 260 AI full length sizer die to make sure they were all close to identical. From there fire form.

If you do a Google search, you'll find that DemiGod has an article on sizing up the Lapua 243 Win cases to 260 which will allow you to fireform to 260 AI. Does this seem like a lot of steps, well it is. That is exactly why I went back to Remington 260 REM brass and will stay there until I win the lotto and buy Norma 260 REM brass or Lapua begins making 260 Rem cases.

 

[Red_SC]

Re: 260 Ackley Impv

I'm running 2935 with 130 Bergers out of a 24" barreled .260 using H4350 and hBn. I haven't tried, but could probably run the 140's at close to 2900 before seeing overpressure signs in my rifle and South Carolina heat. You'd be fine with a .260 AI, I'm sure.

I'm currently using Lake City Match .308 brass necked down to .260. You WILL have to neck turn, it gets thick necking it down that much. I do have a bunch of 7-08 brass I'll use soon, but need to get hold of a chrono so I can match my current velocity. To change from 7-08 to .260 is just a resizing operation, and you can leave a small false shoulder on the neck if you need to to get firm chamber contact for fire forming.

 

[buffybuster]

Re: 260 Ackley Impv

Most of the guys I know running 260Rem are using Winchester 7mm-08 brass necked down. Seems to be working well with no neck turning required and avoids the donut.

 

[RemingtonSPS]

Re: 260 Ackley Impv

I was unaware Norma made 260 brass. I will probably start there. Thanks for the info guys. Can't wait to get this build going. Gonna multicam the DTA. Should turn out really nice, and light.