243 into a 6mm?

[huntokanogan]

Would it be possible to take an old 243 that I own and have it reamed and made to handle 6mm rem. ammo?

Just curious. I have 2 243's and would like to have a 6mm instead of two of the same.
How would I do it?

 

[Gene]

Yes, the 6mm SAMMI specs are a bit longer than .243, so you could do it. But - how many rounds thru the old barrel? What is its condition? If the bore is not spotless, you are probably throwing yer money away and would be better to start fresh with a new barrel. There are many .243 bore wildcats around these days. But I would strongly consider the 6mmBR Norma because ammo is now available over the counter.

 

[EddieHarren]

Using a micrometer or calipers, measure a 243 Win case, at the body/shoulder junction. Then measure a 6mm Rem case at several points along the body taper. When you find the spot where the 6mm Rem is larger than the 243, it will show you how far back you need to set the barrel, in order to clean up the 243 chamber.

 

[backwoods83]

There is 1 possibly 2 setbacks to a 6mm rem #1 your limited on brass if you reload, #2 if your using a short action remington and load to fit chamber they will not fit in the mag.

 

[TMR]

I can be done, but finding 6mm brass at times is difficult. Why not ream it to 243AI? Then you will only have to buy 1 type of brass and can use your 243 ammo in a pinch in the 243AI, and have more performance than the 6mm Rem.

 

[shortgrass]

Most factory barrels don't have the 1" or more of shank that would be needed to cut a 'clean' 6mm chamber in your .243 barrel.

 

[Trickymissfit]

you cannot ream a standard .243 Winchester chamber into a standard 6mm remington. The .243's shoulder will not clean up. But what you can do is ream it with a 6mm AI reamer for a 100% cleanup.

I would recommend that you do at least a 1/4" shoulder setback to help clean out any throat errosion. With a 3/8th" shoulder setback you could also do a 6/250AI or with a 1/2" setback you could do a 6BG. You need to set the shoulder back as the standard .243 is well known to be hard on throats. Being as you probably have a bunch of .243 brass laying around, I'd do a 6/250AI. This round works very well with 22" and 24" barrels too.
gary

 

[rscott5028]

If you intend to use any of the heavier/longer/higher BC bullets for long range, you may want to check the twist.

That might be just one more good reason to rebarrel, or sell your 243 and buy a 6mm.

There appear to be a few good 6mm barrels available through Brunos, Grizzly, and maybe elsewhere depending on the contour you need. I just ordered one myself.

--richard

 

[TMR]

Setting the barrel back some is a given with any rechamber to clean up the throat.