Downside of fast twist 243 over 6cm?

[Adam Gibbs]

Is there a downside of going with a 1:8 243 win over a 6cm? I'm liking the idea of going with a light recoil 6mm for target shooting and hunting. I don't shoot or hunt at ranges that would push either cartridges limits. I do hand load.

 

[Alex Genereux]

The only potential downside I could see is if you are buying a factory rifle then the chamber would be saami and that may limit how far out of the case you can keep the heavier for caliber bullet you are trying to shoot out of a faster twist being you are hand loading. If you are limited by saami chamber you may have to push the bullet further down in the case potentially eating into your powder capacity. Now if you are building a rifle you could have the chamber cut so that the heavier bullets stick out further and you should get more velocity because the .243 has more case capacity then the 6cm.

 

[MT-nuffgun]

One of the downfalls of the .243 is case trimming . You could take it to a smith and have it reamed to AI and viola, you now have a cartridge that has more volume than the creed and no case case trimming needed. I have heard the tikkas are great when reloading short action cartridges as far as free bore is concerned. My goal is to get the t3x lite stainless in the new fast twist .243 and have it Ackley improved. My bullet of choice would be the 108 eldm.

 

[ddowning]

I find 30 degree shoulder cases still need to be trimmed a bit. 40 degree cases can go a lot of firings without trimming in my experience. Technically, when you have to trim the brass is flowing out of somewhere in the case. That means you would likely get more case life out of a chamber with a sharper shoulder angle. Unless you shoot A LOT you will not notice in reality.

Looking at the saami chamber dimensions, the 243 Winchester has about a 0.0160" freebore. That is plenty to get the base of the bullet out of the case, typically. If it is not you could run into donut issues depending on how you size brass. The truth is, the freebore on saami 6 creed is slightly less from quick math, so you would have the same situation with the same bullets. Both have a 1.5 degree leade angle, which is typically what is accepted as the best for accuracy.

The last thing is mag length. If you want to load close to the lands in an aics mag you will be pushing it. A non-binder plate mag will solve this issue.

If you plan to Ackley improve as many have suggested, it is not a simple matter of running a reamer in. To make the fireforming work as designed, the barrel must be set back to create a slight crush fit on virgin 243 brass. If all that is done is chase the chamber with the Ackley reamer, you will need a hard jamb or a false shoulder for fireforming. That really isn't a huge deal as long as you are aware and comfortable with that process. Fireforming brass in a long chamber with no way to keep the case head against the bolt face COULD result in much shorter brass life or even failure.

Those are the idiosyncratic differences. In practical application, the only real difference is factory ammo availability.

 

[sveltri]

One of the downfalls of the .243 is case trimming . You could take it to a smith and have it reamed to AI and viola, you now have a cartridge that has more volume than the creed and no case case trimming needed. I have heard the tikkas are great when reloading short action cartridges as far as free bore is concerned. My goal is to get the t3x lite stainless in the new fast twist .243 and have it Ackley improved. My bullet of choice would be the 108 eldm.

I just did this with a Cabelas version Tikka. Still fire forming, but couldn’t be happier at this point. Pic is with bare muzzle. Rokstok should make it slightly lighter significantly more badass. I don’t remember who on here recommended the M+ magazine, but I am loading with the boat tail at the neck/shoulder junction with room in the mag.

 

[Adam Gibbs]

One of the downfalls of the .243 is case trimming . You could take it to a smith and have it reamed to AI and viola, you now have a cartridge that has more volume than the creed and no case case trimming needed. I have heard the tikkas are great when reloading short action cartridges as far as free bore is concerned. My goal is to get the t3x lite stainless in the new fast twist .243 and have it Ackley improved. My bullet of choice would be the 108 eldm.

This is kind of the route I was trying to go. Ideally I'd get a t3x in 6cm but that's not a thing. But a 1:8. 243 is. Buy it and have it chopped to 18" and add a can. I don't know much about AI, I do like to keep common and factory chambers when possible.

 

[chicoredneck]

If you want to shoot factory ammo you will not find modern high bc bullets designed to shoot in a 1/8 twist loaded for the 243 outside of some boutique loaders.

Barrel life in the 243 is said to be shorter than the 6mm creedmoor due to the shoulder angle. I’m not sure of the validity of this, but the 243 has a reputation for burning out barrels around 1K.

The sammi chamber dimensions of the 6mm creedmoor lends itself to finer accuracy potential over the 243, all else being equal.

 

[hereinaz]

They are very similar if you hand load. The differences are marginal and some differences only matter in specific situations. If you AI the chamber, there are even fewer differences.

 

[ddowning]

If you want to shoot factory ammo you will not find modern high bc bullets designed to shoot in a 1/8 twist loaded for the 243 outside of some boutique loaders.

Barrel life in the 243 is said to be shorter than the 6mm creedmoor due to the shoulder angle. I’m not sure of the validity of this, but the 243 has a reputation for burning out barrels around 1K.

The sammi chamber dimensions of the 6mm creedmoor lends itself to finer accuracy potential over the 243, all else being equal.

I looked at the reamer prints again. I misread the throat and freebore stuff bouncing down the road. 6 creed has way better saami specs. You want a tight freebore diameter and more length than the 243 saami. 1.5 degree leade angle is still considered favorable. Best way to get an accurate 243 is to spec a reamer and take it to a good smith or throat out an existing chamber with a throating reamer.