.260 Remington AI

[Jimmy]

Could anyone tell me if AI'ing a .260 Remington would be a good idea or not? Approximately what would the powder increase amount to and what would the velocity gains be? What barrel length would be best. Most importantly, would it be an accurate round if the rifle was put together properly? Does top end brass exist in the .260 caliber?
Thanks for any opinions.
Jimmy

 

[billmo]

Jimmy, The only question I can answer for you is the last one. Lapua makes a .308 case that can be necked down to the .260 I think. Bill

 

[2644ever]

Ackley Improving the .260 should lower the bolt thrust and the neck growth,not a real problem with the regular .260 anyway), it should also allow some worthwhile velocity gains. Using RL-22, it will be possibe to safely reach 3000 fps with a moly 140 grainer in a 28" tube. The improved version is every bit as accurate as the regular one if the components and the gunsmith that puts them together are top notch. The downside with the AI,particularly with a tight chambering job)is that you really must know what you're doing when you develop a load, as most of the usual early signs of high pressure have a tendency to disappear until you reach a point where you're waaay overboard.

 

[mysticplayer]

Been shooting my 6.5 mystic,my version of the 260AI) for several years now. Use it for F class comps. In a 30" barrel, I push the 139gr Lapuas to 2900fps. I can get to 3000fps but best accuracy is at 2900fps for this barrel.

My powder is H4831SC and works wonderfully. CCI BR2 in necked down and prepped Win 308 brass.

I really like this wildcat and it has been very easy to tune and load. Brass life is superb with my initial batch of brass approaching 20reloads. With the occasional annealing, no neck splits. I do bump the shoulders with a Redding 7-08AI body die.

Gun of the week #75 for more details.

For LR F class, I feel it is the best compromise of the 6mm's and 7mm's re: wind drift, recoil, barrel wear, barrel heat, accuracy.

Long barrel life too...

Jerry

 

[tillroot1]

I am also putting a .260Improved together, all here except the reamers, Jerry what is the difference in your case versus the standard improved case? what neck do you like to use? thanks, Ron Tilley

 

[mysticplayer]

The 6.5 mystic started life using a 6.5-08 AI reamer run deep. Measurements off my cases:

W/139 Lapua seated - outside neck diameter 0.292"
Fired - .295"
Neck thickness - 14thou. made from necking down Win 308 brass then neck turning. 100% cleaned up.
Estimated chamber neck diameter as 0.297-298"
Sized with a Lee collet 260R die for 4 to 5 thou of neck tension.

Neck is .24" long.
Shoulder diameter .459/460"
Case length is 1.990" which is shorter due to shrinkage of the 308 brass during fireforming. I never have to trim

OAL is 2.90" placing the start of the boattail right at the base of the neck. Load density is at 95 to 97% at 46.5gr. 47.5gr is at 100 to 103% - just slightly compressed.

The throating is done is a second step using a Dave Manson reamer with a 1.5deg leade. The Lapua is just off the lands.

So far after 1600/1700rds, I have not to adjust the seating length or load. Just keeps driving them into small groups. My second rifle has around 1000rds now and set up the same way with very similar performance. I use the same dies for both rifles but the chambers are a bit different in size. #2 is a schnick longer then #1.

Hope this helps.

Jerry

 

[BHarvey]

My Broughton is 24.75" and the velocities attained are quite quick before pressure signs with a variety of powders. It is accurate at pretty much any charge weight. The AI seems to respond and shoot well with pretty much whatever I load for it, something the standard 260 would not do.

Very flexible choice.