6 mm Rem reamer in .243 Win barrel

[wmitty]

Will a 6 mm Remington chamber reamer clean up a .243 chamber without setting the barrel back a thread? I've got a 24" m 700 barrel I'd like to rechamber to 6 mm if the reamer will clean up the existing chamber at the shoulder location.

[LAGS]

NO
A 6mm Remington is not as wide as a .243 Win
Look at all the case dimensions and you will see that the shoulder of the 243 is .454 1.56" from the back of the case.
The 6mm Rem is only.429 at 1.72 ahead of the case back.
You would probably end up with a chamber with a buldge or ring in it from the wider shoulder of the .243 chamber.
Your guess is as good as mine how wide the 6mm case is at the same spot where the .243 shoulder ends up.

[Ballistics in Scotland]

There is no substitute for the SAAMI specification and a piece of old-fashioned graph paper. Only if it is an old rifle or one of unknown origin, it would be useful to make a chamber cast and find out whether it actually is to SAAMI specification.

http://saami.org/specifications_and_information/index.cfm

[GabbyM]

All the 243's I've worn out with light high velocity loads. Wore the bore from chamber to muzzle. Not much chance for a set back.

If the bore isn't over .245" you can use it for a cast boolit shooter. 84 grain cast over 11.0 grains of Unique and you've a 1,900 fps shooter.

[nekshot]

you could do the 240 wby if the action is up to it. I always wanted one of those, why I don't rightly know!

[wmitty]

Well, another idea knocked in the head... guess it'll be just a plain ol' .243!

[Artful]

https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcR-HkXWpFkVD9fi_sLwH3PJOo2xWVkwi5CvEoeBgEnDam1xkLw_SQ
the 244 Ackley Improved/6mm Ackley Improved might work but you need to check with
who is making the chambering reamer for you as it's not SAAMI standardized.
http://www.angelfire.com/sd/6mmackley/images/6mm_6mmAI.jpg

But of course the 6mm is a longer cartridge than 243 so requires a long action instead of the short action to be magazine fed and not a single shot - something to keep in mind.

[Blackwater]

I think Lags and Artful have it nailed. The 6mm. is based on the old 7x57 case, as is the .257 Roberts. They had the more tapered cases that were once preferred for good feeding and extraction. More "modern" calibers like .308 & .243 have less body taper, so the more tapered 6mm. reamer won't take out the current chamber fully unless you shorten the barrel from the breech end and rethread and rechamber. That's a classic solution for a worn chamber throat that enables one to get extra service out of a "shot out" barrel. I can't recall exactly, but I believe at least some of the early Warren Page wildcats, like the .240 Page, the .240 Pooper and .243 Super Pooper were designed to clean up .243 chambers complately, and of course, the 6mm. Ackley should do so as well. That's a hot rock caliber that's not given to extremely long barrel life, but while it lasts, it's a ring-tailed tooter for speed and trajectory. The std. 6mm. is my favorite of the 6mm. clan of ctgs. Not too hard on barrels, gives better case life than the .243, and gives a bit of extra vel. over the .243, which is always nice. It generally, though, tends to shoot best at pressures that are more moderate than the .243's, though, which somewhat negates the vel. advantage, but gives significantly longer case life. My son's old 6mm. Ruger 77 took well over 30 deer and all with a single shot. Not a bad record for a deer rifle, and he did almost all of it with the 85 gr. Speer PSPBT bullet. Always gave excellent penetration on our 150 lb. avg. (for a mature buck) southern whitetails, with internal damage that was always enviable. Of course, he knew deer anatomy and was good at placing his shots in the right place, or he'd never have been able to accrue a record like that, but ALL calibers require good hits in the right places to work well. Just some FWIW if you're considering a 6mm.?