Home Forums Hunting & Shooting Ask The Gunwriters 243, 243AI, 6mm Rem & 6 AI capacities

Please list the case capacities of: 243 Win, 243 AI, 6 mm Rem and 6mm AI. It would be best if the same method of measuring is used. Please state the method used. Thanks

Rick,

These are approximate water capacities with a typical lead-core 100-grain bullet seated:

.243--50 grains
6mm--52 grains
6mm AI--56 grains

The 6mm AI is from .257 Roberts AI info. Have never measured a .243 AI but would expect it to be grain or so more than the 6mm.

243AI has 57gr capacity according to QL, but have never measured, it. It lists the 6mm as 54.40, 243 as 50gr. I did not see the 6mmAI listed, but 257AI was listed as 63gr.

240 WBY is listed as 64 and the 6x284 is listed as 67grs.

Thanks guys. I am ordering a NULA in some sort of a 6mm on Monday and can't decide on the ctg. Normally detest wildcat's but could live with a 6mmAI, maybe. Just can't get too excited about a 243 and the 6-06 seems a bit too much. Sorry Dober. So it is either a 6mm Rem or the AI version in a M24, yes M24 action.

What about a 6-284? Wouldn't require any fire forming...

The only capacities I'd be looking at here would be was did I have a short action or a long.

If short, then 243 Ai is the way I'd go. If long, then 6/06 is the way I'd go.

Dober

Three Winchester .243 cases with water to the neck and shoulder junction held 53, 52.3 and 52.7 grains of water.

Three Winchester .243 AI cases (same lot) held 54.7, 54.6 and 55 grains of water.

Note the regular .243 cases had been once fired and neck sized so their internal capacity was a tad more than if they had been FL sized down to factory ammo specs.

+1

I think the M20 has a 3 inch magazine which would be a very good fit for the 6mm AI--can't see any advantage in the M24 if you're going to use either the 6mm AI or the 243 AI--just carrying around more weight...

Melvin Forbes at one time had a short necked version of the 6AI that still had a longer neck than the 243. I assume you could form them from .257 brass in one pass then fire form so not much more effort than the 6AI. It would come closer to splitting the difference between the 6mm and 6/284.

Sort of a 240 short Gibbs.

I have never wanted short actions around cause I develop a habit of short stroking the longer actions. In addition I like a lot of magazine. If I dont like a ctg then I can rebarrel. Also, I like to seat the bullet out. Have found it adds about as much as "improving" a chamber. Mule Deer suggested a 240 but the brass, although great, is about a buck sixty each! Have had two 6-284's but that was before there was brass for the 6.5-284 and I had issues sizing the 284 cases to 6mm despite using multiple steps. So am back to 6-06 as the easiest choice. It has lots of horsepower, so I don't need to run it at the max and yet will outrun most everything. Kind of like my automobile come to think of it. OK Hello Dober (was the pic of your 6-06?)

I may have coloured glasses on... But there seems to be something wrong with this picture....

A guy who's spending 3K for a rifle is COMPLAINING about the price of brass? Now that just makes no sense at all!

Depends on how much you shoot and how many times you reuse brass. I never shoot more than three shots from any piece of brass. Just me but I try to have 500 cases for each rifle which is why I have a fewer rifles now than in my past. I have 4-5 at any one time. More than that and one goes. BUT they all get used.

Then why not just get a .25-06? Or is that not loony enough?

You could go with the 6mm Stuver (6mm-6.5x55 Ackley Improved). It's what all the cool kids are running these days.

And a really cool cartridge it is!

If I built a 6mm other than a BR or 243, I would seriously look at a 6/6.5x47 Lapua. Great brass - similar speed - stellar accuracy, reasonable bbl life, forget trimming like a 243, and it feeds as is w/o mods like a BR might need.

It's what my 'smith' shoots, and sub 2" at 600 yds gets my attention!

All you do is bump the 6.5 brass down to 6mm, load and go. Simple.

That said, brass and die cost will be more expensive, but nor forming.

A 6mm XC would also be of interest to me.

Having owned several custom 6mmBRs, and seeing how accurate they are, pleasant to shoot, and deadly thru deer to 400 yds, I am sold on the value of a ctg. that has a proven track record of accuracy as it's SOOO easy to load VERY accurate ammo for and get anywhere from .1-.5 moa....all day long w/many bullet combos, esp. assuming you use an 8" twist.

Do a little research on the above rounds if inclined.

In the end, for a sporter rifle - esp. ULA a 243 likely will shoot as good as you can, but I would defintely use an 8" twist in whatever you build. Properly built and loaded, I like all 6mm's thru 6AI, but would stop there before getting a bbl burner like a 6/284.

That's just my thoughts. Good luck.

I want a 6mm because of the bullet selection. I grew up shooting a 25-06. I shot a lot of deer antelope and many many jackrabbits. With the heavier bullets it gets pretty close to 270 Win recoil. It is really good but I live in coyote country and I want something less like my 270's.

I would go 6XC or 6mm Remington.....fast twist in either one....but that's just me.....

Each to his own, but I wonder why one would want to use cases only three times, even if pretty heavily loaded? It would seem that if they only last for three uses before the pockets get loose, one might be well above 60,000 psi. I shoot a .223 using Lapua cases pushing 40 grainers 3780. I have four hundred cases and haven't lost or discarded even one after eleven loadings. (Your experience may vary.)