243ai to 260 ai

[nuclabuyer]

Is there any reason that you couldnt neck up a 243AI to a 260AI. Basically I found a bunch of Lapua 243 AI brass that has 1-2 shots on them. I know that you can neck up 243 to 260, is there any reason that you wouldnt be able to neck up an AI version??

[BillPa]

Is there any reason that you couldnt neck up a 243AI to a 260AI. Basically I found a bunch of Lapua 243 AI brass that has 1-2 shots on them. I know that you can neck up 243 to 260, is there any reason that you wouldnt be able to neck up an AI version??

No, it shouldn't be a problem provided the headspace-head clearance is the same. Keep in mind, wildcats and Improved cartridges do not have an "official" specification, so depending who made what there many be differences in both the chambers and brass. Some have discovered this using Nosler 280 Imp brass in their existing chambers. After forming, Improved cartridges headspace the same as any other cartridge, in this instance from the breach face to shoulder. A few simple measurements would tell the tale.

Bill

[nuclabuyer]

I was thinking that since he has like 400 of them, I would just headspace off his case and then I would be set for a while. I would run it through the FL sizer and then headspace it as tight to the case as I can get it..

[BillPa]

I was thinking that since he has like 400 of them, I would just headspace off his case and then I would be set for a while. I would run it through the FL sizer and then headspace it as tight to the case as I can get it..

Sounds good except for the "tight as I can get it part". What I would do, run the brass through you FL die barely bumping the shoulder then just bottom the barrel on a piece of brass, not tight plus two turns. ;D When the barrel bottoms on the case (or gage) its out of room, anything more your just crushing the snot out of something and accomplishing nothing. If you just bottom the barrel, when you snug the nut the headspace will increase about .002", exactly where you want it.

One other thing. Since that brass was fired in another chamber make sure your chamber isn't smaller in diameter than the body of the brass, as-is or resized. Sometimes the body diameter of brass fired in another chamber is larger and your die doesn't reduce it enough giving the impression all is well shoulder wise when in fact you've reduced the body diameter sizing and bumped the shoulder more than intended. Remember, headspace and head clearance are "Length" only dimensions, don't let diameters fool ya.

Just a few tips form one that has done this more times than I care to remember at times! ;D

Bill

[dfrosch]

Something to think about:

The distance to the neck/shoulder junction on a .243AI is about .030 longer than on a .260AI. If you just bump the shoulder a couple thousandths, then your datum dimension will be about .025 longer than what a normal .260AI usually runs. Headspacing a normal .260AI barrel with that case will result in an abnormally large gap between the bolt head and the barrel.

Do you really want to shoot a rifle with that much unsupported case?

<edit> Before you screw the barrel into the action, drop one of these cases in it and measure how much is sticking out. It should only be about .125.

[BillPa]

Something to think about:

The distance to the neck/shoulder junction on a .243AI is about .030 longer than on a .260AI.

Your confusing two different issues.

There is a difference between the PARENT cartridge junctions in an improved chamber, but the same as the parents, once formed the headspace - Head clearence is the same within the same family.

Here are the current crop of improved cartridge I have.



Notice the first three, the 22-250,6-250 and 250 improved version of their parents. They all share the identical headspace - head clearance lengths. In fact I made and use the same gages for all three setting/re-setting the barrels.

The gages (Kiff) for setting the chamber length are different however. They&#39;re based setting headspace on the junction for correct head clearance using the parent cartridges, typically .004" longer at that point. Possibly where your confused on the .030" issue is using and forming the parent in an improved chamber, not improved to improved.



Once formed the cartridge head clearance for an improved is measured the same as the parent, on the breach face to datum, not on the junction. The only difference in the neck-shoulder junction position is the amount it protrudes into it due to the diameter of the neck. Beyond that the only difference would be due to the reamer specs one specified.

Bill

[dfrosch]

Bill,

Perhaps I am confused.

But have always heard the true Ackley Improved cartridges are simply the parent case with the distance from the case head to the neck/shoulder shortened by .004, the shoulder angle changed to 40º and the body blown out to a minimum taper. The neck/shoulder length being .004 shorter allows factory ammo to fired in an Ackley Improved chamber with a slight crush fit.

While I can&#39;t comment on your other AI&#39;s, I did a little research on the 22-250AI. Please look at the cartridge diagrams from Steve&#39;s pages...

http://stevespages.com/jpg/cd2503000ackleyimproved.jpg
http://stevespages.com/jpg/cd22250improved.jpg

These diagrams show that the shoulder starts at different places on the 250AI and the 22-250AI, 1.540 versus 1.524, or .016 difference. If these two cartridges have identical head - headspace lengths and shoulder angles, shouldn&#39;t they have the same head to start of shoulder lengths?


Thanks,
Dana

[dfrosch]

Bill,

Been looking at this a little more...

Midway lists both a 260AI and a 243 AI headspace gage from PTG.

http://www.midwayusa.com/viewproduct...tnumber=198003
http://www.midwayusa.com/viewproduct...tnumber=162079

Why would Dave Kiff make different ones for the AI&#39;s when he tells you to use the same one for the parent cartridges?

http://www.midwayusa.com/viewproduct...tnumber=643952

[BillPa]

Bill,

Been looking at this a little more...

Midway lists both a 260AI and a 243 AI headspace gage from PTG.

http://www.midwayusa.com/viewproduct...tnumber=198003
http://www.midwayusa.com/viewproduct...tnumber=162079

Why would Dave Kiff make different ones for the AI&#39;s when he tells you to use the same one for the parent cartridges?

http://www.midwayusa.com/viewproduct...tnumber=643952

The gages are different because they&#39;re based on the breach face to junction length, not on the breach face to shoulder datum as would be typical with the parents. The .004" difference is the amount crush fit on the junction of the parent, not on the shoulder. For the 308 family the datum diameter is .400" for a minimum chamber specification of 1.630", however the breach face to junction length varies cartridge to cartridge within the same family. Obviously, since the hallmark of Improved cartridges is the ability to chamber and fire the parent the head clearance is established on the breach face to junction length, much the same as forming a false shoulder. If your refer back to my drawing for the 308 family you can see why there are specific gages even within the same family for their improved versions.

The 250 Savage family is the same issue. Both the 22-250 and 250 Savage share the same SAAMI length of 1.579" on a .347" datum, but the junction is of a different length, again the reason for two improved gages.



In fact looking a gage for the Improved your first thought is someone goofed and mis-marked them. The shoulder angle appears to be the same as the parent,but it&#39;s length is based on the junction, not on the shoulder. Its also why using the parent GO gages as the NO GO for the improved works, they&#39;re .004" longer at that point. For consistency swapping barrels I made gages for my 250 based cartridges on the shoulder datum. IIRC I used a .420" datum for a length of 1.574 and 1.576", but I would need to recheck that to be sure, its been awhile since I made and measured them.

Bill

[dfrosch]

Hi Bill,

Thanks for being patient with me. I don&#39;t have any experience with Ackley Improved cartridges(just a couple Middlesteds). But I can&#39;t get past the trigonometry in this discussion.

Every member of the standard 308 family has a shoulder that starts at a .454 diameter and 1.560 length from the case head. Each one has a 20º shoulder that tapers to the neck/shoulder junction at a diameter about .031 larger than the bullet diameter. The smaller the bullet, the longer the shoulder. The Ackley cartridges start at the neck/shoulder junction(really .004 back in the Z axis) and the shoulder tapers out at 40º.

My crude drawing represents this:

[img width=600 height=375]http://i375.photobucket.com/albums/oo194/dlfrosch/Ackley-1.jpg[/img]

The location of the 40º shoulder varies depending on the length of the original 20º shoulder. I understand that my original number of .030 was liberal because I didn&#39;t take into account the smaller bullet diameter. But this suggests that the 243AI body is slightly longer than the 260AI. It also suggests that the bodies get progressively shorter on the Ackley versions of the 7mm-08, 308, 338 Fed and 358 Winchester.

If the shoulder starts in the same place on all of them, then it seems like the crush fit needed to chamber factory ammo would be lost on the larger bore cartridges or the smaller ones would have too much of a crush fit.

Is there something wrong with my logic?


Thanks,
Dana

[BillPa]

Hi Bill,

Thanks for being patient with me. I don&#39;t have any experience with Ackley Improved cartridges(just a couple Middlesteds). But I can&#39;t get past the trigonometry in this discussion.

Every member of the standard 308 family has a shoulder that starts at a .454 diameter and 1.560 length from the case head. Each one has a 20º shoulder that tapers to the neck/shoulder junction at a diameter about .031 larger than the bullet diameter. The smaller the bullet, the longer the shoulder. The Ackley cartridges start at the neck/shoulder junction(really .004 back in the Z axis) and the shoulder tapers out at 40º.

If the shoulder starts in the same place on all of them, then it seems like the crush fit needed to chamber factory ammo would be lost on the larger bore cartridges or the smaller ones would have too much of a crush fit.

Is there something wrong with my logic?


Thanks,
Dana

Refer back to this drawing and quit with the geometry-trigonometry stuff, it easier than that.


Headspace and head clearence are the SAME for the entire 308 UNALTERED family based on a .400" diameter datum point which is approximately mid point on the shoulder.

Chamber Headspace - 1.630" min chamber , 1.640" max chamber.
Cartridge Head clearance - 1.627" min - 1.634" max.
Gages - 1.630" (GO) , 1.634" (NO-GO) based on the min chamber and max cartridge.

The COAL, neck length or junction play no part what so ever in those dimensions! None, nadda.... The reason the gages are interchangeable across the entire UNALTERED 308 family.

Here I&#39;m measuring both the 308 and 30-06 GO gage and cartridge. I&#39;m not sure if it was a 308, 7-08, 260 or what. The same as the one below, it may have been a 25-06, dunno. Notice I&#39;m not measuring anything but the case head to shoulder datum.


Back to this......


Assuming the cartridge, head clearance is established on the shoulder of all those cartridges EXCEPT in an improved chamber. Head clearance is then established on a different point, the junction of THE PARENT. Since that point varies within the same family due to the neck diameter protruding into the shoulder, a alternate method must be used to chamber and fire it safely.



The first two cartridges are the 22-250 and 250 Savage and their improved counterparts. The third set are true wildcats, the 270-308 and the 270-08 Improved. I call your attention to the first two. Notice the ring on the junctions and shoulder length on both the parents, the point head clearance is established in the improved chambers. Notice the difference in the shoulder lengths. Although the 270-308 is a true wildcat it too headspaces the same as any other 308 based cartridge. Its based on the 308 Winchester, same COAL length and simply necked to 27 caliber as does the "New" 338 Federal, actually the old wildcat 33-08. To form the improved version I simply chamber the 270-308 and fire it in the improved chamber and instantly a 270-08 Improved piece of brass.

How head clearance is on the parent in an Improved chamber is established is much the same as this....


On the left is a 222 Rem Mag cartridge partially necked to 20 caliber to form 204 Ruger brass. On the right is a fire formed piece simply chambered and fired in a 204 chamber. The false shoulder provided the necessary head clearance to move the shoulder forward .050" and change it to 30*. In the case of a TRUE improved the junction serves the same purpose, establish head clearance ( or the lack of it) to chamber and fire the parent, not a cartridge within the same family, but the PARENT or one made by adjusting the junction or forming a false shoulder.

Its also the reason for NOT resizing the parent to form improved cartridges so they chamber easily. You may push the junction back destroying the required .004" crush for correct fire forming.

If some clown simply runs a improved reamer in a standard chamber without setback its not an improved chamber, but something else, a wildcat. It may be where you heard about a .030" difference, from one that THINKS they know. Its also why some have problems up the gazoo with Improved cartridges, they try using their own ideas rather than following P.O.&#39;s simple instructions.

Bill