Fire forming 243 Ackley

J

JEC

Guest
A friend plans to get a 243 AI and reckons he just needs to fire regular 243 rounds to create the new headspace... is this safe?
 
I agree with Butch. Pretty straight forward. If he has a stiff ejector spring he need's to take it out if possible. I have learned over the years that when I chamber a 280 Ack barrel for someone I need to hold the chamber depth -.004" or they will get missfires with factory ammo, then I'll get a phone call. It doesn't hurt anything as the brass will shorten up when fired. Jam the bullets hard into the lands.

Dave
 
Actually chamber a sized empty brass first... if the bolt does not close hard on that case you need to make it do that.

Jamming a bullet into the rifling will not guarantee the best fire formed case. The bullet will simply be driven into the case by the firing pin driving the case forward until the shoulder hits the chamber. At that point the case is off the bolt face and when the pressure hits... the case simply stretches just ahead of the web until the rear of the case moves back and is stopped against the bolt face.

To fire form so you have the strongest case is quite easy... make the case neck larger in diameter so it will not chamber at all... then size the case just enough so the bolt closes hard ... That case will not be driven forward and will not stretch.. it will result in a much stronger piece of brass.

All Ackley Improved chambers should be made so all factory ammo is a crush fit on the brass, not the bullet. If not, the brass should be altered before firing or the chamber correctly head spaced.
 
Dennis

I read almost all your posts / replies on this forum and this time I think you have proved that you operate on a higher level than most!
:cool:
 
remmy700 said:
Dennis

I read almost all your posts / replies on this forum and this time I think you have proved that you operate on a higher level than most!
:cool:
Click to expand...

Amen to that ...........my favorite rifle is a 257 Rob Imp. My first rebarrel project and headspace with gages checks perfect but I've always been plagued with cases splitting just ahead of the web or misfires when fireforming new brass.
 
Thank You Dennis--

You, Al in Wa., and I [now others] know how to properly fire-form cases. The difference is when I tell them they usually tell me I'm full of "stuff" and how long they have been just jambing the bullet in the lands and worked perfect for them!

Steve Moore
 
pduryee said:
Amen to that ...........my favorite rifle is a 257 Rob Imp. My first rebarrel project and headspace with gages checks perfect but I've always been plagued with cases splitting just ahead of the web or misfires when fireforming new brass.
Click to expand...

Did you use an Ackley Improved go gage or the standard .257 Roberts go gage? The improved go gage is .004" shorter than the standard go gage. Using the wrong go gage will make a difference in getting case head separations.
 
I'm a little confused. Are Ackley cases typically shorter than the factory cases they are derived from?
 
Ackley improved cartridges are chambered with a crush fit on the factory original case. That's why P. O. Ackley recommended that they be chambered .004" shorter than the standard cartridges go gage. .004" is the thickness of a sheet of printer paper. So, yes they are shorter than the parent cartridge, but only .004" shorter. That's why when rechambering a factory barrel to Ackley Improved the barrel shoulder needs to be set back at least .004" or a full turn of the barrel if you have to realign iron sights.
 
Thanks Mike for the clarity.

I've chambered a few barrels, but never tried my hand at an Ackley. I bet
.004 is a pretty tight crush fit when you are going to fire-form the brass. I guess thats the whole purpose though. If you have a tight chamber that is
.004 shorter than the parent case, I don't see how the firing pin can push the case any farther forward, like what Dennis was saying. If it is tight on the bolt face and the shoulder, how can there be enough slop to push it forward and then back to the bolt??

I'm not saying anyone is wrong or right, I'm merely trying to gain some insight on the subject.. Afterall, you guys know more about this than I do..
 
pearidge said:
Thanks Mike for the clarity.

I've chambered a few barrels, but never tried my hand at an Ackley. I bet
.004 is a pretty tight crush fit when you are going to fire-form the brass. I guess thats the whole purpose though. If you have a tight chamber that is
.004 shorter than the parent case, I don't see how the firing pin can push the case any farther forward, like what Dennis was saying. If it is tight on the bolt face and the shoulder, how can there be enough slop to push it forward and then back to the bolt??

I'm not saying anyone is wrong or right, I'm merely trying to gain some insight on the subject.. Afterall, you guys know more about this than I do..
Click to expand...

What I was saying is you can not reply on a bullet jammed into the rifling to hold a case against the bolt face for the best method of fire forming (because the case will be driven forward until the shoulder contacts the chamber) ... if the case is not a crush fit to start with, the bullet will simply be driven into the case as the case moves forward when the firing pin hits the primer with 22 pound of force... it requires a crush fit on the brass for the strongest fire formed case.

A loose case is held ahead by the firing pin... and under pressure grips the chamber walls.. until the pressure builds up enough the the brass stretches just ahead of the heavy web area of the brass... and that heavy part of the brass then moves back until it is stopped by the bolt face. This area that is stretched is the very same area that will fail when you have a head separation.
 
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Because of the difference in shoulder angles, the only place that an un-fire-formed case has to headspace in the chamber is right where the neck meets the shoulder. This part of the chamber has a radius that gives the effect of a really shallow shoulder angle. With some feel at bolt close the driving forward is held to a minimum, but if you let the case "take a run at it" the amount that it can drive forward in the chamber is increased. Normally I am a big fan of headspace gauges, but if I were building an Ackley, I would buy all of my brass as one one lot of whatever brand I planned on using, and headspace to the feel that I wanted. We did one for a friend for Lapua .243 brass that way, ordered a reamer based on the output of a FL Die and the length of the cases (to minimize the post fire forming gap at the end of the chamber). It worked out really well. There were no problems, and it is very accurate.
 
Ahh, I'm with you now. I've been wanting to experiment with an Ackley lately, so now I know how to go about it. Thanks Guys..
 
One more thing, how many of you guys use a different barrel as a designated fire-former? Basically, to save wear and tear on your good one. It seems like a good idea to me as long as both chambers are cut with the same reamer.
 
set it back .004

I just completed this task and followed the suggestion from another thread in this forum to chamber it .004 short. This worked great. Fireforming was very accurate too...no separate bbl needed for me. I just used the fireform operation to practice and get accustomed to the new rifle (prone 1K gun). 48g of H1000 behind the 115VLD's are killer accurate.
-lige
 
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