Fire forming 260AI

[alphapygmy]

I'm getting a 260AI project going and had a question about fire forming the brass using the cream of wheat method and a false shoulder. Since I need to expand the necks for the false shoulder anyway would there be any advantage to using Lapua 308 Palma brass. The neck is already expanded, the small primer makes a stronger case head, and if the necks come out thicker I could turn them down to fit the chamber and not be so sloppy. Or should I just use 260 Lapua brass and go that route? Thoughts?

[bootsmcguire]

Why do you need a false shoulder for an Ackley improved chamber?

If properly headspaced, you should have the .004" crush fit against the regular 260 shoulder. No need for false shoulder.

FWIW, I have done some of my early load development while fire forming. You can't get a final load that way, but it does let me test some different bullets and powders to try and find the ones that the barrel likes. JMHO.

[foxx]

I have had good results with 260 Lapua. Of course, the chamber will determine whether you will want heavier/thicker brass on the neck. I know my McGowen 260AI really likes the 260 Lapua brass. Very tight chamber.

I also have a Shaw 260 AI that Apache Gun Works just made for me. I am using Nosler brass for that one (I wanted a different brand for each of the two AI's) and I notice the neck on the Noslers open up a little more than the McGowen. I did not think to measure the outside diameter of the fired brass and compare them before reloading them, so I cannot say for sure if the difference is the brass or the chamber dimensions. Good articles from Accurateshooter.com indicate that when Lapua started making 260 brass, it made it pointless to try to form them from anything else.

Boots: I agree. I find fire forming the brass with actual bullets is not all that wasteful. Its surprising how well they shoot while doing so.

[alphapygmy]

I wanted to use the false shoulder method to help with consistency of length of the fire formed cases. In this article http://www.6mmbr.com/260AIforming.html Chris Long says he had no more than .001" length variation after fire forming. Years back when I had a 338-06AI I had maybe 4-5% that moved with the primer strike and formed a little short. No big deal for cheap 30-06 brass but these days with Lapua being a buck a pop and the scarcity of components in my neck of the woods I thought about giving his way a try.

[Luke45]

I wanted to use the false shoulder method to help with consistency of length of the fire formed cases. In this article http://www.6mmbr.com/260AIforming.html Chris Long says he had no more than .001" length variation after fire forming. Years back when I had a 338-06AI I had maybe 4-5% that moved with the primer strike and formed a little short. No big deal for cheap 30-06 brass but these days with Lapua being a buck a pop and the scarcity of components in my neck of the woods I thought about giving his way a try.

Im by no means an expert on ackleys, but i do have 2 ackleys now that ive put together. as boots said, as long as its headspaced correctly, the crush fit will not let the cartridge move foreward when the primer strikes and you should have uniform brass. ive used the crush fit headspace method on my 280AI and 22-250AI and havent damaged a fireformed shell yet and they all come out as consistently as the brass i was using.

[chukarmandoo]

It all depends on the cases used for the 260. Such as 7mm-08 needs a false shoulder, as Billpa pointed this out to me a while back.

[scope eye]

The best way I have found to fireform brass, is to jam the bullet into the lands, the brass comes out 100% formed that and at the same time you can some load development, so when the brass is formed you have a pretty good idea already, of where you stand and don't have to waste even more barrel life, and reloading supplies to come to the same conclusion, plus at least you get more trigger time, and I don't care who you are that is something you can never have enough of.

Dean


PS: Don't kid yourself fireforming with COW erodes the throat just as much, or even more than firing a bullet, due to all those hot gasses going straight to the throat unimpeded, I picture it sort of like a acetylene torch effect, instead of having a bullet to damper the hot gases, I have seen and used both methods, that is how I am in a position to come to this conclusion.

[emtrescue6]

Like Dean,when fireforming my 257 AI I accomplish the same thing by loading my bullets long and into the lands...it's keep from creep and I have not had any proud primers and always get nice fully formed brass....

[alphapygmy]

Fire-forming method aside, the question I was curious about was small primer Lapua brass. Is it only to increase strength in the case head or is there an accuracy benefit? Both 6BR and 6.5x47 use it and both were designed for accuracy. I don't plan on running nuclear hot loads I was just wondering about any accuracy benefit for a target rifle.

[emtrescue6]

I would pass on the small primers...you won't need the added strength and the smaller primers will provide less ignition.

[scope eye]

Fire-forming method aside, the question I was curious about was small primer Lapua brass. Is it only to increase strength in the case head or is there an accuracy benefit? Both 6BR and 6.5x47 use it and both were designed for accuracy. I don't plan on running nuclear hot loads I was just wondering about any accuracy benefit for a target rifle.

Both cartridges that you mentioned hold 30 some odd grans of powder, and usually faster burning powders at that, with the 260 AI we are talking 50gr of much slower powder, so as far as I am concerned that is a nogo on the small primers.

Dean

[BillPa]

Fire-forming method aside, the question I was curious about was small primer Lapua brass. Is it only to increase strength in the case head or is there an accuracy benefit?

Years ago in the mid-late '70s Remington produced 308 UBR barass. Dimensionally it was 308 Win brass with SR primer pockets, withIIRC .080" flash holes and was intended to reform into BR brass. Those who used it AS-IS in rifles chambered for the 308 Win reported having had hang fire problems. If it was the powders used and or the quantity of them I don't know, but evidently German Salazar has the same concern with the Palma brass today.

My first impression, therefore, is that this was one heck of a lot of work for no noticeable improvement under typical Palma conditions. Elevation dispersion was the same and the scores were about the same. Increased risk of reduced ignition under adverse conditions for no performance gain under ideal conditions is a poor trade-off. I'll shoot this brass brass again at least once, but I don't see any magic - not that I expected any.

http://riflemansjournal.blogspot.com...rimer-308.html

Bill

[alphapygmy]

Thanks, exactly the info I was looking for! Saves me a bunch of work as well.