I had a .243 rechambered to 6mm-06 AI. I was hoping to simply neck down 25-06 brass and then fireform using regular 6mm-06 data. however necked down 25-06 brass is nowhere near to chambering in my gun. i was under the impression that an AI improved chamber should still be able to chamber and safely fire the parent cartridge.the 25-06 and 6mm-06 should use the same headspace gauges. i haven't done a chamber cast yet to determine exact dimensions but am thinking of sending the gun back to the smith to cut the chamber longer so i can stick to my original plan. has anyone else loaded for the 6-06AI of regular 6-06? what are your experiences with the cartridge and your opinion of what i should do with my gun. any thoughts appreciated.
6mm-06 Ackley Improved question
- Thread starter jbmauser
- Start date
I may be wrong here Jb but here's my take on it. A 30.06 shows the length from the back of the case to the bottom of the neck as 2.109, 270 shows it as 2.156 and the 25.06 shows the length as 2.186, the longest of the three. Have you got a 270 case that you can neck down to 243? I think that will work. I would try using 270 before 30.06 first as you will have less brass in the neck to contend with later. It's fine if you are set up to either inside or outside neck turn but I think I'd try 270 brass. Let us know if it works.
Qc_BearHunter
CGN Regular
- Location
- Pont-Rouge, Qc
Don't forget to trim the .270 case because they are longer than 30-06 cases.
You have made many assumptions. The "parent case" is the 6mm-06, not the 25-06, and why do you think they should use the same headspace gauges? Even if they do, substituting a necked down 25-06 for the headspace gauge is not apples and apples. What are the specs for the Wildcat 6mm-06 AI (or the 6mm-06 for that matter), or should I say which one of the many in use did you choose?
If you own the reamer or have access to it, measure it. Otherwise, a simple chamber cast will answer your questions. The other alternative has been mentionned - find a 30/06 based cartridge that you can neck down and that will then chamber (e.g. 270, 280 or 30/06). After fire-forming, you'll know what you're working with.
You must have very little taper in that round, as reaming out a 243 chamber will require that to clean it up for 6mm-06, unless the barrel has been set back - but yours is an AI. Very cool - I am looking forward to hearing more, as I have played with the idea of rechambering my 243 to 6mm-284, which is similar, but would be a bit smaller than your 6mm-06 AI.
Last edited:
You may have a chamber cut with taper and shoulder angle the same as an Ackley Improved chamber but you don't have an Ackley Improved cartridge in the sense that there is no true factory 6mm/06 cartridge to use as a start.
An Ackley chamber is cut to require a slight crush fit when closing the bolt on a factory case and is intended to allow firing of a factory load in the rifle either for fire forming or shooting.
The gunsmith who cut the chamber may have left it a bit shorter than required for you to simply use an available factory case. The question what did he have in mind as the datum base for the shoulder and did he allow for the increasing length of the case at the neck as the caliber diminished? You may have to take a chamber cast and get it measured up to see what changes are required to the chamber or have custom dies eventually made. It may be possible to use a shorter bodied die such as 6mm Rem to set the shoulder back a bit but you will have to be careful doing this not to set it back too far. You should feel firm resistance on the final downward rotation of the bolt when chambering a case to ensure proper head spacing.
An Ackley chamber is cut to require a slight crush fit when closing the bolt on a factory case and is intended to allow firing of a factory load in the rifle either for fire forming or shooting.
The gunsmith who cut the chamber may have left it a bit shorter than required for you to simply use an available factory case. The question what did he have in mind as the datum base for the shoulder and did he allow for the increasing length of the case at the neck as the caliber diminished? You may have to take a chamber cast and get it measured up to see what changes are required to the chamber or have custom dies eventually made. It may be possible to use a shorter bodied die such as 6mm Rem to set the shoulder back a bit but you will have to be careful doing this not to set it back too far. You should feel firm resistance on the final downward rotation of the bolt when chambering a case to ensure proper head spacing.
I shoot a 240 Gibbs (another improved 6mm-06, a little more case capacity then your 6mm-06 AI). There are different datum lengths for all the 06 offspring. As pointed out, the 6mm-06 is a wildcat, not a factory cartridge. You should really do a chamber cast and then figure out which brass you can use. I also found with my Gibbs, when using 30-06 brass, that I had to turn down the outside of the neck after I necked down the cases to 240/6mm. - dan
thanks for the info and thoughts everyone. i do realize that since the 6mm-06 is not a saami cartridge itself that there is no real parent cartridge for my AI version. a look at the forster part numbers for headspace gauges shows that the .30-06, .270, 25-06, 6.5-06, 338-06 and 35 whelen all use the same headspace gauges. research i did before having the rifle rechambered showed that simply necking down 25-06 brass to 6mm was a common practice with no other work involved too fire regular 6mm-06. this led me to believe that it was common practice when chambering to 6mm-06 that regular 30-06 headspace gauges were used and if that was the case that i should be able to neck down, trim to length, and if needed turn neck diameter down of any of these 06 family cartridges to chamber in my AI improved version. these are however all assumptions as there are no saami specs for the 6mm06 or AI version and that every chamber is going to be slightly different. a chamber cast and custom dies are definitly in the plans but i was hoping to get shooting faster and cheaper in the mean time. although a chamber cast really should be done before i do any shooting. i will try necking down some 270 and 30-06 brass later today and try that for chambering. i have tried to bump the shoulder back on necked down 25-06 brass with a 243 die and have been able to chamber after that but the case buckles when doing this and i would not fire it like that. while i have been reloading for over 10 yrs now this is a new challenge and i would like to hear more from those of you more familiar with wildcats and improved cartridges. my only other improved cartrige experience was with a .303 Epps which headspaces on the rim like its parent cartridge the .303 british. fireforming was a simple operation for that cartridge. just load regular .303 british loads and fire then resize being careful not to push the shoulder back to much with readily avail .303 epps dies.
No need for custom dies. Once you know the cartridge dimensions, you could neck-size with a Lee 6mm-284 or 243 WSSM F/L sizer, and F/L size (when needed) with a F/L die set from the 30/06 family, with the sizing "button" removed.
Please find your Shift key. That, and the long rambling sentences makes your otherwise thoughtful posts difficult to read. Just a friendly tip.
Please find your Shift key. That, and the long rambling sentences makes your otherwise thoughtful posts difficult to read. Just a friendly tip.
So I did some experimenting today and found that I could chamber necked down 30-06 brass without bumping the shoulder back at all. What I found was that the brass had to be trimmed to 2.470". After trimming to this length I could chamber the brass with no resistance. My next step was to size the neck on a 30-06 case in small increments until it would just chamber. This leaves a bright ring on the base of the neck after chambering and should provide a secure headspace point. Obviously a chamber cast would have shown this and should be the first step for anyone doing loading for this type of cartridge. I will stil do a chamber cast before firing to determine the proper trim to length, neck diameter for clearance, etc. Thanks for the grammer and proper English tips. Sorry if my posts are hard to read. I'm just a gun nut who loves to shoot and hunt not an English major.
