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6SLR vs 6CM

Made perfect sense. I actually got my last barrel swap so close that one piece of Scotch Magic Tape would not let the bolt close without forcing it. But somewhere I read that Scotch Transparent Tape is slightly thicker and a better choice to use.

On your 243 McGowan... I bought a set of flat feeler gauges for seating bullets. I've got the seater adjusted for the longest (I think) bullets and slip a feeler gauge between the case and shell holder if I want to seat the bullet slightly deeper. The gauges were a little too wide to fit in the shell holder but a good pair of scissors took care of that. Anyway, a feeler gauge might hold the case up far enough to let your f/l die size the cases.
 
Virgin brass can vary quite a bit, especially the cheaper stuff. I would measure several pieces with the Hornady headspace gauge and use the longest one (I think).

Gotta run. Be back tonight.
 
I just sent you a PM Nomad47 but, I'll put it on here also! For headspacing the .243 A.I. it would be a good idea to get the proper go gauge and then you can still use the std. .243 Win. go gauge as a no go gauge! Just trying to be right about it folks!

Mike
 
I'm not a 24 hr campfire member but I found this with a google search.

"ok, any ai chamber MUST be cut so the parent cartridge headspaces properly in the new ai chamber. if this is not done, it can cause a dangerous excessive headspace condition. thats the entire pricipal of ai. therefore, you won't find ai guages. you must set the barrel back and then rechamber using the ai reamer till the action will snugly close on the go guage. you need the standard go guages for each cartridge."

And this.
"Unless I'm misreading the above statement by "hornsurgeon" IT IS WRONG! You most certainly can find Ackley Improved headspace gauges.

The Ackley Improved "GO" gauges are shorter than the standard/parent chamber "GO" gauges. The standard/parent "GO" gauge is the same length as the Ackley Improved "NO-GO" gauge. So if you already have the standard/parent gauges for each of these, all you need is the Ackley Improved "GO" gauges."

It still seems to me that headspacing for a 'crush' fit of new brass would make fireforming easier - no false shoulder or jamming bullets.
 
On the idea you must have a "crush fit" on an AI type chamber to properly fire form brass (and so you do not have excess head space), I do not agree that is always correct, at least in practice. With the 243 Imp 30Ëš, I settled on the standard 308 "go" as the "go" for that because it worked best in that application. When I tried a .002" under go as the "go" gauge (.002" under go as the "go" is what is typical with Ackley chambers) I had problems with factory brass that I could not even get to chamber (both Lapua and Winchester brass) and many cases were so far more than a "crush fit" at that shortened head space that it was impossible to chamber them in a civil manner. I needed more head space in the chamber for it to work easily, well and properly and going back to the standard 308 "go gage" was what was needed. A little front/back play with a cartridge in the chamber is not a problem with this type of wildcat and based on my testing, even a + .006" slop fit (which is quite a bit) will not create an ignition issue or a brass forming or safety issue. If you are bumping the shoulder .006" on every reload of the brass on a consistent basis, then your brass will break down prematurely, but if you are just firing out the head space .006" on the first forming, that's no big deal at all.

My posting here is based on actual testing and results and most of it was pure "trial and error" type testing to find out what worked for the application at issue.

In addition, with the 6mmAR Turbo 40 cartridges that we fire form in AR-15's, there is no possibility of doing a "crush fit" (i.e. the rounds would not chamber properly in a semi auto and would jam), so we set them up to fit easily in the chamber and do a lot of the fire forming magazine fed in a match, some in the rapid fire sequences, and we have no issues with that at all.

Robert
 
So you are basically headspacing off the neck/shoulder junction as that would be the common point. But you aren't stretching the brass as much since your cartridge is a 30 degree shoulder. Since the AI has a 40 degree shoulder, the brass is stretched more (with case head separation as a possible result) unless the headspace is adjusted to produce that 'crush' fit.
I need to compare reamer prints to see what the difference is in growth.
If I do the 243 AI, I plan to buy 200 cases and measure every one to the datum point. Since Savages have the barrel nut, I can adjust headspace to the longest case. Or I could bump a few of the longest cases if need be. My chamber might be a couple thousandths longer or shorter than the standard AI but as long as my dies are adjusted accordingly, I don't see an issue.
I haven't made up my mind yet, but the 243 AI has two advantages over your 243 IMP 30. 1. Dies are readily available from several sources - and cheaper. 2. Criterion chambers the 243 AI as a Savage pre-fit.
 
Robert,

We're not talking crush fit on the brass to a point where you have to beat the bolt down with a hammer to close it! We're talkin crush fit on the brass to the point there is some resistance to the bolt handle going into the closed position. Not sure if you read this entire thread or not but, you would have seen where Bill and I are going to cycle some virgin brass to get the feel where the optimal headspace is along with utilizing the proper gauges! Also, the suggestion of having +.006 slop in the headspace on a custom chamber and barrel I don't agree with! If I wanted sloppy headspace I would have purchased a factory rifle?? The need to have the virgin brass meet at the neck shoulder junction somewhat snug is so we don't have to jam bullets to fireform brass!

Mike
 
One issue when headspacing is discussed is forgetting there is a difference between traditional headspacing and Savage barrel nut headspacing.
Obviously, with the traditional method headspacing can only be changed on a lathe. But on a Savage there is some 'wiggle' room.
 
Bill, If you go with the .243AI I have a go-gage for it. PM me when your ready and I can mail it out to you, then just return it when your done. I have two .243AI's, a 14tw on a 700 action and a Criterion 8tw for a Savage. Both shoot very well, killed three WT's with the Criterion and 105 gr. A-Max this year. I don't expect either to live a long life but knew this going in to it. On a side, just barreled a 788 action with a 3 groove, 8tw PacNor chambered in 6-6.5X47 Lapua and am really impressed. Haven't chrono'ed yet, too freakin' cold, but trajectory says I got good velocity with the A-Max. 41 grains of 4350 versus 47 grains of H4831, you decide. I have a 6.5X47 Lapua go-gage also and Criterion chambers the 6X47L. ::)
 
Thanks for the offer, MrM. I haven't decided 100% on the 243 AI yet, but I'm leaning that way. And if I do go with the AI, I'm going to buy my own 308 go gauge (since I will likely swap barrels twice a year). And I will turn the barrel 1/8" more after it contacts the go gauge. That will set the heaadspace at .002" less than the .308 go gauge.
 
Just throwing this out as another alternative - if you have your base brass already for whatever you intend to use (i.e. .243 Imp 30Ëš, 243 AI, etc.) - you can set up your barrel head space and chamber off the existing base brass (as opposed to a head space gage), then you can put it right where it needs to be based on the actual brass you will be using and fire forming. With a Savage barrel, this could be done very easily.

I have also done this before and it worked very well.

Robert
 
Robert, thanks, that is a good point. And something I would strongly consider. However, due to my living in a motorhome, I have cut my rifle inventory down to two rifles with multiple barrels, so I swap barrels frequently. And I think I should use a go gauge so the barrel gets headspaced the same every time it gets re-installed.
By the way, I don't have the brass yet. But I will probably buy 250 pieces of Winchester brass and cull out the worst 50.
 
This thread has been down for a while but I just wanted to ask you guys with experience with these cartridges, I am going to rechamber a 6br barrel for hunting and steel safari competitions. Its a pacnor barrel finished at 22" .Action is a savage and I am looking for a cartridge capable of reliably feeding out of the magazine.
Leaning towards a 243 or a variant mentioned above. Thoughts on the slr or cm in a shorter barrel.
 
I'm still waiting on my Criterion 243AI barrel I ordered back in mid Feb, so I can't comment on the AI. But I am quite pleased with my 6SLR - 28" 8 twist Bartlein 5R shoots 105 AMax and 105 Hybrids at 3200 MV.
 
skyav8r said:
...and steel safari competitions.
Click to expand...

The CM is the most popular caliber in the top 5 these past few years at the Safari. Most of the top 5 is a 6mm caliber of some sort even though everyone says you need a 260 to do well at this game.
 
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