reaming a 243 handi

[Deerhunter#1]

has anyone reamed a 243 to either 243 ai or 6mm and if so how were your results. Thinking of trying my first project and this might be it.

[quickdtoo]

I have a Thumbhole Ultra Varmint 6mm Ackley that started life as a 243, shoots 87gr Vmax pretty good, it's only been to the range once, needs forend work tho....or a better shooter behind the trigger!! 

Tim

[jeneks84k10]

I am interested in this as well. Just picked up my new .243 heavy barrel on the way home from work today and would be interested in the AI

[jlj1948]

I think you will have to go with the 6mm remington ai.I don't think the 243ai will clean up without seting the barrel back

[necchi]

I don't think the 243ai will clean up without setting the barrel back

 Right, that's what I had too learn here too. The AI shoulder angle needs to be punched out further because of the angle, that's where the extra powder goes.
To compensate the chamber,, the barrel needs to be cut and set back.
 An easy thing to do with a barrel that's threaded into the receiver, but not so easy with a break action single.
Moving to a longer case can be done, the AI can't.
Check out Steves pages with case dimensions and compare; http://stevespages.com/page8d.htm

[quickdtoo]

A 243 Win can be rechambered to 243 Improved without setting the barrel, you just won't be able shoot factory ammo in it, it would be handload only after steps are taken to fire form the brass to deal with the increased headspace, either loading with a long COL so the bullet is hard into the lands, or forming a false shoulder to headspace on, see handloading for an improved chamber in the FAQs. You can effectively set the barrel back tho by refacing the chamber face by filing it back and cutting the AI chamber, then fitting it to a frame(see barrel fitting in the FAQs), I've done it on a 270 Win. I have a couple improved rimless H&Rs besides the 6mm Ackley, a 280 and a 35 Whelen, both have slightly larger case capacity than the standard ackley version due to the deeper chamber, neither will fire factory ammo, the 270 AI will.

Tim

 http://www.gboreloaded.com/forums/index.php/topic,203614.msg1099060066.html#msg1099060066

[keith44]

Since the Ackley Improved version of any cartridge is simply minimum or no body taper and a 40 (ish) degree shoulder cutting the chamber is a snap without barrel setback.  For rimless cartridges that head space on the factory shoulder factory ammo should still fire in a AI chamber, unless you are also making a shorter necked cartridge.  The shoulder ends at the same place on the neck of both factory and AI cartridges.  Now some of Lyle Kilborne's work also included shortening the neck by increasing body length, and these will not fire factory ammo that headspaces on the shoulder.

[necchi]

So you guy's are saying that you CAN go to an AI chamber in NEF just by blowing out the shoulders?
What about 223, 7-08,,,?
 
 If that's the case (ouch) what would be a good size expander to use for the 223?

[jeepmann1948]

A 257 sizer will create enough of a false shoulder to fire form your rounds. Just neck the the 243 case up , them neck just enough of the neck down to 243 until the case will chamber in your rifle .
A good rule of thumb is to expand the neck one caliber larger than the parent case .
 These so chambered rifles should be clearly marked "Wildcat Only Cartridges" so no one fires a standard round in them

[audrey1216]

I have thought about reaming my 243 handi barrel to 6 mm AI, in part to have something different but also (because it has a long throat) to get the bullet closer to the lands.  It is an ejector barrel and I am concerned that with less taper, extraction could be an issue.  Those of you that have done something similar, is this concern valid? Also, for those of you that have reamed a 243 to 6mmAI, did you ream it by hand or have a gunsmith do the work? 
 

[quickdtoo]

I had a gunsmtih do my 6mm Ackley, I already had the reamer and a Hornady hydraulic forming die, so I traded the reamer for his rechambering of two rifles, the Ultra and a CVA Optima Elite. I wouldn't worry about the ejector, it can always be converted to a factory extractor if necessary, I've done a couple dozen of em, see the FAQs on that, I personally prefer a modifed extractor over an ejector myself, so do many members here, they always work! 

Tim

[Spanky]

How much of a gain can you get with the improved chambering?
 
 
 
Spanky

[thejanitor]

I personally prefer a modifed extractor over an ejector myself, so do many members here, they always work! 

Tim

+1  I thought I loved my ejectors until I got the ejector modified to this extractor Tim is talking about. VERY nice and it sticks out farther than the regular extractors by a noticable amount which lets you wear thin gloves and still grab or flick a spent round.  thejanitor

[quickdtoo]

How much of a gain can you get with the improved chambering?
 
Spanky

Depends on the parent chambering, those with the most case taper provide the biggest gains, less for the straighter cases, 4D used to have a chart with the % increase, but I haven't found it since Fred updated his site, seems to me the 6.5x55 and 30-40 Krag had the biggest improvement. Fred touches on it in his reading room.

http://4-dproducts.com/submenu/Wildcatting%20on%20a%20budget.pdf

Nosler and Hodgdon both have data for the 280 and 280 Improved that you can get and idea of the increase in performance, Nosler is in a 26" barrel, Hodgdon is 24".

Tim

http://www.nosler.com/Reloading-Data/280-Remington-140-Grains.aspx

http://www.nosler.com/Reloading-Data/280-Remington-Ackley-Improved-140-Grains.aspx

http://data.hodgdon.com/main_menu.asp

[audrey1216]

Doing a quick google search, it looks like going from a standard 243 to a 6mm AI the case capacity increases from 52.8 grains to 59.5 grains, which is about an 11-12% increase.  I understand there is some general rule that velocity goes up (with pressure kept the same) at a rate 1/4 of the increase in volume.  If that is true then the velocity increase for the conversion looks like it would generally be less than 100 fps.    I wasn't looking to increase velocity but was just looking to tinker and get the bullet a little closer to the lands (for some reason the bullet jump bothers me  )  I wonder if there is much benefit to less bolt thrust with the AI version.   

[quickdtoo]

Here's a 6mm Ackley and 243 Win comparison pic, both loaded with 87gr Vmaxes, and a couple 6mmBr articles on the 6mm Ackley.

Tim

http://www.6mmbr.com/gunweek042.html

http://www.6mmbr.com/gunweek021.html