6mm rem vs. .243


December 20, 2007, 07:53 PM
I've got a Ruger M77 bolt action chambered in 6mm rem, and a set of reloading dies for 6mm rem.

Not so many 6mm rems around anymore, and mostly gone from mainstream reloading component suppliers as near as I can tell (brass and bullets).

What's the deal with .243? I seem to recall some dust up between the two when they were first developed with .243 becoming the mainstay and 6mm fading to black.

Can I shoot .243 in this rifle?

Can I reload .243 brass and bullets with my 6mm dies?

Is 6mm rem the same as .243 or not so much?????

If not, are there any cost effective options to re-chamber the rifle to a more mainstream caliber?


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December 20, 2007, 08:17 PM
The 6mm remington is a better cartridge in my opinion than the 243. It has more powder capacity and can achieve higher velocities.

No, you cannot shoot .243 cartridges in your ruger. You also cannot form 6mm rounds using 243 brass as the 6mm is a longer case. I do believe you can form 257 roberts brass into 6mm but I don't see much point in that.

It's a great cartridge for reloading since it uses .243 diameter bullets so there is a wide variety out there to choose from. 6mm brass can easily be found on the web. I just checked midwayusa and it's about $28 for 100.

I own a browning 78 in 6mm and love it. It's an excellent deer caliber, is easy on the shoulder, and is versatile as I can load 55gr bullets for varmints or 105gr for deer.

December 20, 2007, 08:18 PM
Two different cartridges/action lengths that share the same bullet. 6mm is based on the 7 X 57mm, and .243 is based on the .308 case. And it goes further because the .308 is a shortened version of the .30-06 which traces its roots back to the same cartridge that spawned 7 X 57.

You can't shoot .243 in a 6mm.

You can't reload .243 with 6mm dies.

The 6mm is a superior round, IMO. The .243 is more popular because a good number of shooters favor the shorter action, or as a starter rifle for the young, or recoil sensitive. Both are excellent combination Varmint/Deer rounds, but if your focus is more on deer, your better gunned with the 6mm.;)

December 20, 2007, 08:25 PM
The 6 mm and the .243 are NOT the same. The 6 mm and .244 are. Whole problem started when the .244 was first brought out. It had a twist rate suitable for (IIRC) lighter bullets. People wanted to use heavier bullets which were not stabilized properly and it ended up with a reputation of being inaccurate. So the rifle was renamed the 6 mm and had a twist rate to stabilize the heavier bullets. Or maybe it was the other way around:confused:. But by then the .243 had established itself and never looked back. This is all based on my dim memory from back then so time may have scrambled things somewhat. But it was something like that.:D That said, the 6 mm is a good cartridge and performance is, for all practical purposes, identical to the .243.
Someone who knows the story well will correct me I am sure.

December 20, 2007, 08:29 PM
Relax, ONV, your memory still works!;)

Rem's rate of twist for .244, and the lighter bullet weights was 1 in 12.

December 20, 2007, 08:30 PM

December 20, 2007, 08:34 PM
I believe the modern twist rate for the 6mm is 1:9.

highlander 5
December 20, 2007, 08:37 PM
The 6mm rem and 243 Win are two different cartridges though very similar in performance. They both use .243/6mm dia bullets but the 243 is based on a necked down .308 case Where as the 6mm Rem is based on .257 Roberts or 7mm Mauser case. As I recall the 6mm Rem was called the 244 Rem and was designed as more of a varmint round than a deer round and the 243 Win was a dual purpose deer and varmint. The rate of twist in the 244 would not stabilize bullets over 90 gr where as the 243 would'
Remington realizing this blunder change the rate of twist and renamed the cartridge the 6mm Rem. 243 Win can't be loaded with
6mm Rem dies. There should be an ample supply of both 6mm brass available and just about every bullet manufacturer has several 6mm/243 dia bullets.
I've never owned one but IMHO there is nothing wrong with the 6mm Rem for varmint/deer hunting.

December 20, 2007, 10:42 PM
The .243 win is prone to throat erosion where the 6mm rem is not, I would choose the 6mm with a 1:10 twist myself.

December 21, 2007, 05:25 PM
I first started loading 243 and 6mm in the mid 60s.

History from my 1960 Load Notes
The 6mm Rem (244) is based on the 1895 6mm Lee Navy. http://www.spanamwar.com/lee.htm The Navy brought out this high-velocity repeater, the 6mm Lee Navy--a rather innovative arm for the period that was unfortunately a tad ahead of its time and was withdrawn from service after only a few years. The round did have the distinction, though, of being the first rimless load used by the American military. It is the parent cartridge for the 30-03/30-06, having the same base diameter, rim diameter, and rim thickness. Although the 7X57 was undoubtedly the inspiration for the 6mm Lee Navy, the 7x57 has different base diameter, rim diameter, and rim thickness, and in addition was Berdan primed. When Remington developed the .244, their primary objective was a high performance varmint cartridge with a maximum bullet weight of 90 grains. Because 257 Roberts cases were available, they were used to form the .244. The 1-12 twist and was ideal for 75-90 gr bullets.

From http://www.reloadbench.com/cartridges/6mmr.html For reasons that no one can explain (or prove), deer hunters decided that the .243 Winchester with its 10 more grains a bullet was a better choice. Or at least this is the traditional explanation. Possibly a factor even of greater influence was the rifles the two cartridges were available in. The .244 was offered in the Model 722, a rifle about as handsome as a fence post. The .243 was available in the sexy little Model 70 Featherweight. When it came to looks, there was no contest.

Around 1958, Remington started rifling all .244" caliber barrels with the 1-9" twist, but nobody seemed to notice. In 1962 when the new Model 700 rifle was introduced, the only 6mm cartridge it was available in was the .243 Winchester, but during the next year the .244's name changed to 6mm Remington and reintroduced in the Remington bolt action.

Winchester modified the 6mm Lee Navy case a bit and in 1935 introduced a cartridge of its own design called the .220 Swift.

Practically Speaking:
Load data on 100 gr bullets lists the 6mmRem as having a 200 300 fps advantage over the .243. My experience loading for several weapons in each chambering shows that accuracy loads for 6mm Rem were at/or nearly at max, while accuracy loads for .243 were well under max, thus the spread in handload velocities is even greater when accuracy was included in the mix.

I have seen the argument that this 200 300 fps difference was insignificant. I disagree because:
1. I have taken 5 bull elk with 6mm Rem w/100 gr Nosler Partitions, one shot kills. I have taken many more with 300WinMag, and a few with 270 and 30-06. I do not suggest hunting elk with 6mm, but to point out that I have a knowledge/experience base to qualify my statements in 2. below.
2. Based on one above the 300WM puts down elk with a lot more authority than with a 30-06. The 300WM is only 200 - 300 fps faster than the 06 with 180-200 gr bullets. This velocity difference is significant. The 200-300 fps advantage of the 6mm over the .243 is significant in the same manner.

In addition, the longer neck of the 6mm yields better accuracy, less throat erosion, and longer case life.

December 21, 2007, 08:32 PM
Thanks for the replies, very informative.

December 22, 2007, 01:15 AM
I have not seen the 2-300 fps diff in the loadings between my 243 and 6mm. Then again, I do not have long barrels on my 2 guns either. I own 788's in the both of them and do not try to max them out. I certainly have not seen the speed diff in the 55 grain offerings that I use on pd with either of them. I am sure that there will be differences in speed between the 2 depending on the powders that were used. I have mainly used Varget in mine. RG

December 22, 2007, 01:35 PM
The .243 win is prone to throat erosion where the 6mm rem is notWho says that?

If anything the 6mm would cause throat erosion sooner then the .243.

It burns slightly more powder, (2 - 5 grains) at the same pressure, (52,000 CUP) and gets slightly more velocity (100 - 200 FPS).

All that adds up to potentially greater throat erosion in the 6mm then the .243 Win, although neither one of them is especially known for problems.


December 22, 2007, 01:59 PM
RCmodel is correct...the 6mm is the same bullet with more powder and about 100-150fps velocity increase...would prob eat throats a little quicker

December 22, 2007, 02:38 PM
rcmodel and BsChoy:
It is generally agreed that the abrasive effect of unburned powder is the cause of throat erosion. My experiences and those of the general shooting public show that the .243 is notorious for throat erosion, due in part to it's short neck.

The longer neck of the 6mm (almost twice the length of the .243) allows more powder to burn before reaching the throat. The result is less throat erosion in the 6mm. That is not to say that the 6mm does not have throat erosion, just a lot less than the .243.

December 22, 2007, 03:46 PM
The .243 became more popular because it was not a MM and the 6 was. That does not mean much today, but it did back when. ;)

I too agree that, at least on paper, it is a better round. That means didly squat, as I have no experience with either.

December 22, 2007, 03:49 PM
Boo-hoo-hoo, creepy metric system: Hoo-ray beer!;)

December 22, 2007, 03:57 PM
The entire world, except for the US is on the metric system.

Did you ever wonder how much this contributes to our reduced sales of products on a global scale (Balance of Trade), and could it be a factor of why our economy is in the toilet?

Things they don't talk about on the evening news.

December 22, 2007, 04:34 PM
Shoney, the only problem with the metric system is that we didn't follow up on maybe the one good idea Jimmy Carter ever had! Funny, when you consider how many people complain about doing fractions.

WA was correct though; several fine cartridges have been handicapped in the US by nothing more than a metric designation. Nonetheless, I had to take a jab at him!;)

December 22, 2007, 05:26 PM
Shoney, not to jump the subject but, I don't think that the small diff in neck length allows THAT much more powder to be burned. But since I have no imperical data than I cannot prove this. In addition, bullet speed has a large hand in eating the throat of a rifle as well not just the powder. I would be willing to say that the 100-200 or so fps increase in the 6mm would make up for the "longer neck" theory and eat as much if not more throat than a comparably loaded 243...but again I have no imperical data just a deduction

December 22, 2007, 07:59 PM

December 22, 2007, 08:21 PM
When compared to the 6mm Rem. I think the neck length coupled with the case shoulder angle contributes to the shorter barrel life of the .243 Win.

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