Stupid question on an AI round.

[tammons]

If you have say an AI or other improved chamber that has the shoulder blown forward, and you want to shoot factory ammo in it,
IE blow the shoulder forward while shooting, what does the cartridge headspace on ??

I am assuming the rim ??

[Eric in NC]

No - on a rimless cartridge, it still headspaces on the shoulder. A proper AI chamber will actually be a little bit tight with factory ammo. That is why non-savage type barrels require you to turn them back a thread when converting a chamber to AI.

Now on rimmed and belted cartrdiges - it still headspaces on the rim or belt.

[tammons]

So on an AI cartridge the neck shoulder junction is in the same place.

But if the shoulder is blown forward on another improved cartridge, like a 6BRX
what does it headspace on ??

[Blue Avenger]

http://img.photobucket.com/albums/v675/gcidso123/savage/fireformed-zeroheadspace.jpg

http://img.photobucket.com/albums/v675/gcidso123/savage/201_5028.jpg

you can see on these cases that started life as .308 and were run through a .243AI die where the neck / shoulder meet. that is the contact point in factory ammo in an AI chamber.

[Blue Avenger]

Not sure who I copied the vid from, but thanks!


when you have it right the case touches the back of the bolt and the front of the chamber, keeping the case from sliding and only allows expansion which fills in the chamber space forming the new case.
http://img.photobucket.com/albums/v675/gcidso123/savage/fireformed-zeroheadspace.jpg

this video shows a case being fired with to much headspace.
http://img.photobucket.com/albums/v675/gcidso123/savage/headspacestretch-1.gif

If you have to much headspace, you can see where the primer moves back first and then the case follows. you can also see where the case get thin just above the web and the next reload will result in cracks and separation.

http://img.photobucket.com/albums/v675/gcidso123/savage/100_5172.jpg

http://img.photobucket.com/albums/v675/gcidso123/savage/img1274565224599.jpg

[tammons]

What about a case where the entire shoulder area is blown forward.

With a chamber like that the cartridge shoulder would not reach the shoulder area of the chamber.

[tammons]

IE forming a case like this ??

www.6mmbr.citymaker.com/i//6BRX_WEB2.jpg

[Blue Avenger]

What about a case where the entire shoulder area is blown forward.

With a chamber like that the cartridge shoulder would not reach the shoulder area of the chamber.

something has to hold it in place---
rim- .30-30AI
belt- 300wm in a 300wby ( not good)
rimless cases- Shoulder or Bullet jammed into the lands with the right powder charge. or false necks like I did with the .308 to .243

[tammons]

In the photo above none of the above would hold the cartridge in place except maybe the end of the neck where it meets the freebore, but now I got it, bullet jammed would do it. So in that case you could not shoot factory ammo to fire form the case.

Just curious more than anything.

[Blue Avenger]

you could also enlarge it to .30 caliber and then resize part of the neck.

[tammons]

Right, False shoulder, now I remember.
Its been a while.

[Eric in NC]

False shoulder or pistol powder and cream of wheat to blow the shoulder forward.

You asked about an AI round - what you are looking at is not an AI round. One of Ackley's "rules" was that factory ammo had to work.

[tammons]

I was actually interested in both types. The AI and then another type with a shoulder blown forward.

[Uncle Jack]

".....I was actually interested in both types."

Well, which do you want an answer to....apples or oranges?

uj

[tammons]

Apples and Oranges.

[dcloco]

".....I was actually interested in both types."

Well, which do you want an answer to....apples or oranges?

uj


Oraplorangles!! :)

[Uncle Jack]

My point is that Parker Ackley specifically designed his series of "Improved" cartridges to accommodate factory ammunition of the same caliber. Most other "Improved" or wildcat designs do not and require "Jamming" the bullet into the lands for headspace to fireform without undue excitement.

uj

[pdog06]

We went thru this in a classified ad a while ago and unfortunately it was deleted.

For an AI headspacing, the GO gauge for a standard round(i.e. 243) now becomes your NO-GO for your AI round(i.e. 243ai). There is .004" difference in the headspacing between a standard and an AI round, so a factory standard round would still chamber with a slight "crush" feel.

I headspaced mine the way Fred said to do it and it came out perfect. Setup your AI FL die and run a pc of unfired standard brass thru it. This will bump the shoulder .004". That pc of brass is now your GO gauge. Then for the NO-GO you can use either the standard 243 GO or scotch tape on the rear of the pc of brass. I checked it both ways as a NOGO and it was the same.

I also ran a factory loaded round in it and it chambers with the slight "crush" feel that it is supposed to since it is .004" longer. So you CAN form your brass by shooting factory standard loads thru it. As a matter of fact I hope to run some thru mine today ;).

Heres a great read on page 13. It explains it in detail, with overlay pic of a standard case, AI case, and gauge.

http://www.clymertool.com/catalogue/ClymerCatalogueVol11.pdf


The BRX isnt an AI chamber so it'll be different. Id say check over on 6mmbr site. Or maybe in the link I gave you as I didnt check to see if it mentions the BRX.

[tammons]

Thanks Guys,

Very informative.

[pdog06]

Heres a link to an article on 6mmbr that shows all the 6br variances(including the BRX) and their differences. At the bottom of the page it tells how you can headspace/fireform those type of improved chambers. Looks like a BRX has a shoulder pushed out .010", so forming a false shoulder seems to be the way to go, according tho this link.

hope this helps.

http://www.6mmbr.com/6BRImproved01.html