Custom Project 280 AI and feeding

S

sikasambared

New member
Hi All Smithing Gurus,

I've finally got the cash together, and am ready to start the first steps of
the conversion of my excellent 270 win Sako 75 to 280 improved in a McMillan varmint stock -- with a #6 contour barrel with aggressive fluting to get the weight at least back to the weight of the original #5 contour.

I was originally intending to convert it to 280 RCBS improved -- since they have a shallower shoulder angle (30 degrees compared to 45 degree for the ackley), but the gun smith I have been talking to indicated that the 280 AI(45 degree shoulder) feed great through a predator action and really well through a rem 700. He suspects it will be alright with the sako 75, but can't say for sure. He is a quite a major gunsmith here in Australia (Qld).

I would like to test it.

Question 1.
If I load up a *dummy* 280 Ackley and put it in the mag and can get it to feed out of the mag -- is that the major concern out of the way?

Question 2.
Where do I find a piece of 280 AI brass????!

Kind regards,

Matt
 
Alright -- forget the second question -- I'm think I may have to machine a dummy 280 AI out of steel.

But the second question I really would appreciate some advice on:

Thanks,

Matt
 
Thanks for those endorsements of the idea -- it is encouraging to hear that others have succeeded.

If there is going to be a problem would it be feeding the cartridge out of the magazine, or more likely feeding up into the chamber?

Which do I have to look out for?

THanks,

Matt
 
As far as feeding improved cartridges goes, sharp shoulder angles feed better in controlled-round feed rifles because the cartridge feeds from the magazine under the extractor claw, and is held tight as it is fed straight into the chamber. Contrast that to a push-feed rifle where the cartridge has to slide across the breech and over the mouth of the chamber, having several chances to hang up along the way.
 
+1 Scorch

One other thing to consider. My first 280 was in 26" persuasion. I could post the same velocities in Nosler #5, using the preferred RL-19. The 280AI data in the same manual was almost identical, except posted in 24" and with more powder. The real telling difference will be if the AI is efficient with more than 80% case full. With my 280 and '06, best numbers at the chrony are at 80-85% case full.
 
If you happen to have PO's manual and plan to use his recommended doses of 4350 with a 140 grain bullet, DON"T.

I was hitting 3250 and having loose sockets 5% below his max.
 
If you happen to have PO's manual and plan to use his recommended doses of 4350 with a 140 grain bullet, DON"T.
Click to expand...
I'll second that piece of advice. I can't recall which magazine it was, but someone took PO Ackley's loads and pressure tested them, and found many of them were out and out unsafe, well over 70,000 CUP. They also found that his velocity estimates were very optimistic.

PO Ackley was extremely knowledgeable and talented, but he was a gunsmith and an experimenter, not a ballsitics expert. Piezo transducers and digital chronographs were not invented until the 1970s, about 40 years after he published most of his work, so the pressures and velocities he published were calculated estimations at best.
 
Thanks for the info guys. There is some decent load info around.

I will be using ADI loads: http://www.adi-limited.com/handloaders-guide/rifle.asp

Some of these powders are the same as commonly available US powders (varget being one I believe).

Performance is reasonably comparable to 7 mm rem mag -- without excessive pressures in this data -- so I wont be doing anything stupid!

Question 1 of 2:
My next problem is working out what contour my current factory sako 75 .270 win barrel is closest to. The numbers look quite different to anything I see in the Douglas ontours. As far as I figure, the thickest part is 1.12 inches
The end of the radius section is 0.82 and the muzzle at 22 7/8 inches is 0.653 inches.

Any idea if that is close to any common contour?

Question 2 of 2:
I was hoping to get a heavier contour and flute it back to equivalent weight of the current -- but am wondering is fluting detrimental to accuracy?

Kind regards,

Matt
 
Sounds like you have a #3 or #4 profile barrel on your rifle currently (factory profiles don't always translate well to Dougls' profile numbers). You could use a #4 contour and have it fluted with no negative effect on accuracy.
 
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