Gunsmithing chamering an AI. Headspace???

[skog]

When cutting an AI chamber what headspace gauge do you use? Do you use parent cartridge but loose neck when fire forming? Do you use a live parent round as a go and and a go gauge as no go? Or do you use actual AI go and no go gauges? I have done 1 AI, it was a 257 roberts AI. I used actual AI gauges and I couldnt close the bolt on a factory loaded round. I ended up going back and using a live 257 roberts round (with firing pin removed from bolt) as a go gauge and a factory 7 mauser go gauge as a no go.

Thanks

 

[dsink]

Re: chamering an AI. Headspace???

I use the ackley improved go and no go guages. You wont the bolt to be hard to close on the parent case to ensure your case will fireform properly and you wont have any case seperation..

 

[jaclthr]

Re: chamering an AI. Headspace???

If you don't have Ackley proper guages available then set your chamber to .005/.006 short of the parent GO guage. This will allow crush when chambering parent case as dsink said for proper and safe fireforming cases.

 

[DAVETOOLEY]

Re: chamering an AI. Headspace???

One issue when using the std cartridge go gage is the neck diameter. On the std chamber you're using the shoulder for the reference point, full contact. On AI chamber you're using the junction of the neck and shoulder in the chamber as the datum line. The larger the neck diameter the shorter the chamber is going to be as it lets the gage go further into the chamber in relationship to the shoulder. I fought this for years with a 243 AI. I have reamers with 4 different neck diamters. Best just to get a 40 degree go gage and know it's right. With that being said once you fireform the brass your headspace becomes zero. Adjust the reloading dies to match your chamber.

 

[Swedeshooter]

Re: chamering an AI. Headspace???

I only made one AI and one ppc chamber but used the same method. I use a full length sized case for headspace gauge and that has worked fine for me.

 

[Clark]

Re: chamering an AI. Headspace???

10 years ago I chambered a 257 Roberts Ackley Improved with a piece of new Winchester 257 Roberts brass as the go gauge.

I now believe that was .004" too long.

The result was that trying to full form brass in one step makes a case separation 0.1" behind the shoulder in either Win or Rem brass.

The rifle is glass bedded and very accurate, I did not want to take it apart and re set the head space.

After ~ 100 documented experiments to find a process, I have settled on a two step process:
1) Lube up the case with a high pressure lube like moly grease, Lyman moly bore cream, or Moly-Dee cutting fluid.
2) Load the case with 10 gr pistol powder.
3) Fill the case the rest of the way with cream of wheat cereal.
4) Fire the case pointed straight up with no bullet at home, or put Ivory Soap in the case mouth to hold in the cream of wheat, and fire horizontal at the range.
5) A half shoulder is now formed. Load a full power 257RAI load and expect full accuracy.
6) The shoulder is now fully formed.

 

[Innovative]

Re: chamering an AI. Headspace???


For chambering you'll need a set of Go/No-go gauges.

<span style="font-weight: bold">......</span> AFTER THAT <span style="font-weight: bold">......</span>

Fire one round in your chamber, and that case is as accurate as a casting of your chamber. Insert it in the <span style="font-weight: bold">Digital Headspace Gauge</span>, and zero the gauge. (That calibrates the gauge to your particular chamber.) Then measure your first handload to see how far you're pushing back the shoulder. It should be -.001" or -.002" at the most. This removes all guess work about where your shoulder really is.

Then it's easy to adjust your die height accurately for reliable chambering and no chance of headspace separation.

- Innovative

 

[Clark]

Re: chamering an AI. Headspace???

Larry,
I get the feeling you have never fire formed new brass in an Ackley chamber that was head spaced with a standard go gauge.

Here is what happens:
The fit seems perfect as the bolt just closes with a tiny extra force.
The firing pin pushes the case forward.
Pushing back on the case at the base of the case neck is the sharp edge that is the base of the neck in the chamber.
The sharp edge cuts into the brass.
The brass keeps going forward.
When the cut is wide enough to resist the force, the primer starts taking the damage.
The round goes off.
The brass expands and grips the walls.
The pressure pushes back on the case web.
The brass stretches.
The new brass case is extracted and reveals a separation.
Throw the once fired case in the trash.

What needs to be done at headspacing is to make the chamber so tight, that chambering the new brass makes a cut so deep in the base of the case neck, the the firing pin cannot push the case any further. This means the bolt handle is not easy to close with new brass and the bolt will not close on a standard go gauge.

 

[Innovative]

Re: chamering an AI. Headspace???

Clark ........

You're right, I haven't worked with Ackley chambers. However, I'm sure you can get Ackley go/No-go gauges for installing a barrel.

I've only seen one way to get a headspace separation, and that's to stretch hardened brass too far - too many times.

I have several customers using our <span style="font-weight: bold">Digital Headspace Gauge </span>with Ackley calibers, and when used as I discribed above the cases last as well as any other caliber.

- Innovative