Home Forums Hunting & Shooting Custom Rifles & Wildcats Chambering 280AI

to all you 280AI rifle loonies..any suggestions/tips for Chambering a 280AI..."saami specs"...."crush fit"..maybe a super gunsmith that does 280AI's..thanks in advance for any replies

oldguns, I'm having mine put together by Redneck, I know he has worked them in the past and I'm sure mine will turn out as well, drop him a note.

Now that they are SAAMI specs you may want to buy your favorite smithy a new reamer

A good AI chambering should cause a wee bit of impedence to the bolt drop when chambering std. brass.. The AI neck is usually .003 back re: headspace from the std..

I do them fairly tight relative to the brass supplied... It's best to have 20+ empty cases sent with the rifle.. I'll gauge to the longest of the bunch so the owner should (operative word there) have little real difficulty chambering virgin brass.. At times, depending on the lot (as in 'lot run of brass) the owner may actually have to bump back the neck just a tad before fire-form in order to close the bolt.. It's a bit of a delicate balancing act between too close, too far and JUST RIGHT...

I've got a new .280AI reamer in the drawer - just waiting for use..

Talk to Redneck. He built mine and it's a shooter! Not to mention you'll have it back in your hands in the time it takes most smiths to return a call.

Mine was done by Kirby Allen--Allen Precision shooting [APS] in Texas.

Well done

FWIW
Wes in AZ

Headspace gauges for the improved are made .004" short. This is occasionally insufficient "crush" with some brass. Of course, with Nosler now selling formed brass, the chamber should certainly accept that brass. I have usually gone with -.006" on a standard (not AI) gauge. GD

Thanks for all the replies. This may be a stupid question but...if the 280AI is "SAAMI specified" and I do plan on using Nosler brass and ammo..wouldn't one just chamber the rifle to 280 SAAMI specs??

It's what I would do unless the owner is specifying a non-SAAMI throating.. That gets quite specific and will demand a specially ground reamer thereby increasing the cost overall by the price of the reamer and the additional machining for the throater..

That is my point. As I said before, the old standard was to chamber .004" short and many (myself included) went with .006".
Now that the 280 AI is a SAAMI standard, the headspace is established by Nosler's drawings and, I would assume, the headspace figure is taken to a datum line rather than the junture of neck and shoulder. Gunsmiths should now, properly speaking,cut chambers according to the prints. All of this is too complex for a simple hillbilly like myself. GD

Kirby is an amazing smith but he is in Fort Shaw, Montana, not Texas.

OOOPS !!! I guess that I forgot that there are other places than Texas!!!

This brought up several maybe dumb questions.

What is the datum point? Isn't it typically half way between neck and shoulder, or does it vary by cartridge?

Can a body reamer be made with no neck and then separate neck and throat reamers be used for different calibers? Would there be any savings or would the separate neck/throat reamers end up costing more than standard reamers? Would there be a greater chance of eccentric chambers ( a miss match of case body & neck)?

For correct chambering of the 280 Remington Ackley Improved the barrel has to be put on a lathe and be setback one full turn in combination with proper cutting depth of the reamer to achieve the "crush fit." Usually .0625" or one barrel thread on a sixteen threads per inch barrel. Then the goal is to cut the Ackley Improved chamber .004" inch short with a 280 AI reamer. For example with the 280 AI, the bolt should not close on a 280 Remington "GO" headspace gauge and with the breech locked behind it, a standard 280 Remington cartridge should make contact in the Improved chamber at the junction of the neck and the shoulder in order to fire form perfectly without case stretching.

I had mine chambered (in a Ruger No. 1A 7x57) by a very good local gunsmith. He didn't have a .280 AI headspace gauge, but I had new Nosler brass and provided a few cases. It works perfectly, and fireforms .280 brass nicely as well.

While not going into the travesty of rechambering a perfectly good 7x57 (!), I would be curious as to the actual headspace dimension yielded by using the Nosler brass as a gauge. In the end, as with all AI cartridges, a workable technique is a good technique. Even with proper "crush", it is possible to fireform brass which ends up short.
I have to confess to not being a real fan of "improved" cartridges. This is illustrated by the fact that I've never had one although I have drawers full of reamers for them. The only cartridge of this variety I have used was the 22 PPC which is essentially a 220 Russian Improved. GD

I had mind built by a local smith and he did a very good job. My rifle forms brass really well and i have never lost a case during forming. I have formed brass with cream of wheat and the regular way with hand-loaded 280 and factory ammo. If i build another i will do the work myself.

greydog,

Believe me, I have enough 7x57's to spare one!

This rifle also shoots .280 AI Nosler ammunition quite well. The only brass that caused any problems was handloaded .280 ammo with brass that had already been fired. Once in a while one would fail to go off, at least the first time. But this is common with any already-fired brass in AI chambers, because fired brass lacks the tiny radius at the juncture of neck and shoulder than causes the "crush" fit.

I'm not all that big a fan of AI cartridges myself. I have owned several in the past, ranging from the .22 K-Hornet to the .35 Whelen AI, and generally found the results not worth the trouble. Their biggest virtue is reducing case stretch, which is a nice thing when loading 500 prairie dog rounds. But neck-sizing pretty much does the same thing.

I only did this on to see if the .280 was the magical round so many people claim it is--and because I can get new brass from Nosler. Actually, I kind of like it--but I don't have any illusions that the .280 AI is some sort of vast improvement over the standard .280, or for that matter the .270 or .30-06.

Another round i have been thinking of trying is the 6.5 x 280 Ack Imp. I would use the Nosler 280 Imp brass to form the case from.

Greydog, why is it still possible to come up with a short case even with a crush fit? Short enough to fail to fire?

The 7x57AI is magic MD...:)