Thread: My 260AI Load Development Begins

With the rifle built and in hand I need to develop a load. Starting by fireforming but also a chance to try some different projectiles from Sirocco 130gn to LRABs at 142gn.

Using 0.5gn off max recommended for 260 with RE17.

I don't have a COL gauge so will do best with cleaning rod method.

Will update as I progress.





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Seems my COL is 2.800" with 142gn LRAB. From memory that is Saami spec with 260...

Be interesting to see how the LRAB go.

Cool rifle, will follow with interest, the scope looks like it's mounted back a bit, eye relief ok?

Yes it looks like it to me too but works perfect for me on max mag (16x).

Apologies - the first COL was with the 130gn Sirocco, the LRAB COL is 2.840". But already loaded the LRABs to 2.800" so might just leave the seating die and run them all through, worry about a proper COL for each type when shooting FF cases.

I'm just loving the barrel - Which you do when you have a 7 RM in T3 lite is it a wrapped barrel? and what contour etc is it wearing???

Also nice Stock and bottom metal - I bet if you had Euro glass on it instead of the Nightforce it would be halfway down the stock. But the guys are right seems a long way back for a nightforce may be take some video of yourself getting into position at different magnifications and see if you are doing something really different between the setups is my advice. You may spot something that really helps your distance accuracy by spotting when you are under strain in position.

1 good tip I had played around with for a while was going High and wide on the shoulder (one school of thought on positional technique) with the stock instead of the collar bone made big changes for me and I wasn't crowding the glass so much prone.
Just a thought. BTW took a bit to get used to...

Looking forward to seeing the results of this development. I've been sitting on parts to build my 30 degree 260 Improved for ages and seeing this will get my A into G. Keen to see what powder works best for you, other peeps say the N560 is the bizzo for the 260.

RE17 is meant to good so have a bit of that.

Here she is with a K624i. But changed mind as that is now on a model 7 7mmsaum. I like the scope where it is, but will know better after shooting...hate shooting off a bench and having to stretch to get a good sight picture.




All loaded up.



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So all those projectiles are hard into the lands ?

I don't think they are hard into the lands. I cycled through ok. Ideally touching I have read is good when FF.

If they aren't hard into the lands/bolt firmish to close, you will hurt the brass & have potential case head separation issues.....

Make sure you lube the bolt lugs with appropriate lube.

I prefer to FF without a projectile.

That reamer works pretty well with the couple of rifles I've built with it.

Originally Posted by Kiwi Greg

If they aren't hard into the lands/bolt firmish to close, you will hurt the brass & have potential case head separation issues.....

KG, can you explain the reasoning behind this?

How do you get it hard into the lands when you don't use a projectile? What difference does FF the case have with or without a projectile?

Originally Posted by outdoorlad

KG, can you explain the reasoning behind this?

How do you get it hard into the lands when you don't use a projectile? What difference does FF the case have with or without a projectile?

If the brass isn't hard onto the bolt face, when the firing pin hits the primer it pushes the case forward as far as the extractor or chamber will allow.

Then the powder ignites & the shoulder pushes forward & grips the chamber then the case head finds it has nothing behind it so slams back against the bolt, usually the primer has also backed out against bolt, then gets completely flattened looking a lot like an overpressure situation.

This sort of thing also happens when brass is too short for a chamber because of over sizing or sloppy Gunsmithing with long head spaced chambers.

This stretches the brass usually right where case wall meets the web.

With "proper" AI (Ackley Improved) chambers the neck shoulder junction is slightly shorter than the brass so it is reasonably firm against the bolt face.

Some brass is a bit short & some chambers are a bit long so this doesn't work sometimes.

There is a difference between AI & improved chambers.

A false shoulder is the way forward for an improved chamber.