Is my 6mm rifle capable of shooting 243?
- Thread starter shmitty
- Start date
Jim Watson
New member
This would be news to RCBS, Lee, and Hornady who show the same shellholder for both.
Yes, the rim thickness is a bit different so the 6 mm has a few thou slop in the usual shellholder but it is still .125" from bottom to deck so it will load properly.
Has nobody here tried to actually chamber a .243 in a 6mm to see if it is even possible in the zombie onslaught? Don't fire it except in emergency, of course.
Well, not me, I don't have a 6mm. I did the best I could and read the saami blueprints, and let me tell you, somebody owes me.
The shoulder to base length of the .243 is over 0.2 inches shorter. shoulder diameter is .455 vs .429. Best I can gather is that it's going to depend on the dimensions of the chamber and the individual rounds as to whether that shoulder will be small enough on the ammo to slip past the center of the chamber, and allow it to headspace on the shoulder. If it did headspace on the shoulder, that thing has 0.2 inches of slop at the base. That could turn out to be dangerous. If it does manage to lock in on the chamber and hold tight to the base, you could actually fireform .243 brass into 6mm, but the case length will still be about 0.2 inches shorter.
So as best as I can tell, t's going to depend on the individual ammo and chamber as to whether it can fit into the rifle, but as far as I can tell, if it does fit, it may not cause any problems to fire new factory rounds once in the wrong rifle. I think that it would be an incredibly stupid idea to fire .243 in a 6 mm and reload for it with .243 dies. That seems destined for failure.
Yes, no answers there in all of that time I spent reading diagrams and putting this together.
The shoulder to base length of the .243 is over 0.2 inches shorter. shoulder diameter is .455 vs .429. Best I can gather is that it's going to depend on the dimensions of the chamber and the individual rounds as to whether that shoulder will be small enough on the ammo to slip past the center of the chamber, and allow it to headspace on the shoulder. If it did headspace on the shoulder, that thing has 0.2 inches of slop at the base. That could turn out to be dangerous. If it does manage to lock in on the chamber and hold tight to the base, you could actually fireform .243 brass into 6mm, but the case length will still be about 0.2 inches shorter.
So as best as I can tell, t's going to depend on the individual ammo and chamber as to whether it can fit into the rifle, but as far as I can tell, if it does fit, it may not cause any problems to fire new factory rounds once in the wrong rifle. I think that it would be an incredibly stupid idea to fire .243 in a 6 mm and reload for it with .243 dies. That seems destined for failure.
Yes, no answers there in all of that time I spent reading diagrams and putting this together.
Jim Watson
New member
I can imagine Bubba cramming .243s into Dad's 6mm, or especially in Grandpa's .244. But like you say, reloading with .243 dies to do it again would be dumb.
SAAMI does not even bother to list .243 in 6mm as a dangerous combination, so as you see on the drawings, it might not be feasible without out of spec gun or ammo. Or a very heavy hand on the bolt handle like the moderator here once said was what the Japanese designed the 7.7 for, to grudgingly accept captured .30-06.
SAAMI does not even bother to list .243 in 6mm as a dangerous combination, so as you see on the drawings, it might not be feasible without out of spec gun or ammo. Or a very heavy hand on the bolt handle like the moderator here once said was what the Japanese designed the 7.7 for, to grudgingly accept captured .30-06.
I heard that information about the 7.7 as well, but thought that it was probably not exactly correct. It seems to me that it was kind of weird that a weapons designer would create a cartridge for his military with dimensions based on being able to capture ammo from the enemy. That way of thinking kind of seems to be as negative, fatalistic, assuming that they will need, or even bother with taking ammo from the bad guys. At the time, the war, iirc, wasn't really expected to happen. They believed that Pearl Harbor would intimidate us so badly that it wouldn't even happen. The japanese felt that they were pretty invincible, didn't they? Would they really have thought that they would want to use captured ammo in their rifles?
Sure, the case was very similar to the 30-06, and the rimmed version is almost identical to the .303 british, I have read, but it seems to me that this was probably a case of mimicking available designs. They could have copied german or other designs.
Sure, the case was very similar to the 30-06, and the rimmed version is almost identical to the .303 british, I have read, but it seems to me that this was probably a case of mimicking available designs. They could have copied german or other designs.
Jim Watson
New member
Oh, I think the .30-06 in 7.7 thing is totally bogus but the board moderator with long experience in ammo and reloading put it out as gospel.
I doubt the Japanese fighting in China were planning ahead to war with the USA. And if they had wanted to copy the .30-06 they could have done a better job of it, as the Imperial Navy had done with the .303.
I doubt the Japanese fighting in China were planning ahead to war with the USA. And if they had wanted to copy the .30-06 they could have done a better job of it, as the Imperial Navy had done with the .303.
Mike Irwin
Staff
Yes, you CAN fire a .243 in a 6mm Remington chamber.
The shorter .243 case will chamber just fine. Headspace will be incredibly off, though.
If the extractor holds the case onto the bolt face with enough force, the firing pin will fire the cartridge, and the bullet will head down range, but with reduced velocity (and chamber pressure) due to the excess chamber space.
The case itself will be fire formed to something resembling a 6mm Remington with almost no neck.
The shorter .243 case will chamber just fine. Headspace will be incredibly off, though.
If the extractor holds the case onto the bolt face with enough force, the firing pin will fire the cartridge, and the bullet will head down range, but with reduced velocity (and chamber pressure) due to the excess chamber space.
The case itself will be fire formed to something resembling a 6mm Remington with almost no neck.
Mike Irwin
Staff
"Or a very heavy hand on the bolt handle like the moderator here once said was what the Japanese designed the 7.7 for, to grudgingly accept captured .30-06."
Ah jeesh, not that crap again.
"I doubt the Japanese fighting in China were planning ahead to war with the USA."
Japan had been planning on fighting a war with the United States since the 1920s. Actively planning it, because they wanted a lot of our possessions in the Pacific.
The 7.7x58 mm Arisaka round is based heavily on the .303 British round's ballistics with a similar, but modernized, case that would work better with modern powders.
Thinking that ANYONE could force a .30-06 round into the chamber of a Type 99 by hand with enough force to shorten the .30-06 case by nearly 1/4" is... well... not too bright.
Ah jeesh, not that crap again.
"I doubt the Japanese fighting in China were planning ahead to war with the USA."
Japan had been planning on fighting a war with the United States since the 1920s. Actively planning it, because they wanted a lot of our possessions in the Pacific.
The 7.7x58 mm Arisaka round is based heavily on the .303 British round's ballistics with a similar, but modernized, case that would work better with modern powders.
Thinking that ANYONE could force a .30-06 round into the chamber of a Type 99 by hand with enough force to shorten the .30-06 case by nearly 1/4" is... well... not too bright.
Jim Watson
New member
Well the expert did say it would take a boot heel on the Arisaka bolt.
Mike Irwin
Staff
Of course the Japanese NEVER thought of making their rifle rounds 64mm long so that they could use .3006 and we couldn't use their ammo...
God that is a stupid theory.
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God that is a stupid theory.
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Blindstitch
New member
Rumors that I just started say for every 100 Arisakas issued one 30-06 chamber reamer was issued just in case.
Now can we get back to the 243 vs 6mm.
Now can we get back to the 243 vs 6mm.
Hmmm I wonder. I don't have any spent cases but here is a half shot box of old 243. I don't have another rifle
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Here are pictures of model and caliber stamp. Clearly a 6mm RemAny chance you wrote down (and still have) the ser# of the one you used as a kid?
I've never seen a Mohawk in anything but .243. I have one. Also have Model 600s (not Mohawk 600) in .222, 6mm, .308, & .350Rem Mag.
Any chance that old ammo (.243) has some fired cases??
The 6mm case is 0.078" longer from the base to the base of the neck than the .243 is. .243 cases fired in a 6mm chamber will have the shoulder blown forward that amount, which would be obvious if compared to an unfired case, or one fired in the correct chamber.
The .243 case is also spec'd 0.024" greater diameter at the shoulder than the 6mm case, which might make it a crush fit in a 6mm chamber, depending on individual case and rifle tolerances.
As I see it, the possible options are (in no particular order)..
#1) you mis-remembered the caliber of the gun
#2) its a different gun, same make, & model, but in a different caliber...
(perhaps something happened to it, and your relative replaced it with the closest thing he could find?)
#3) its the same gun, but rebarreled from .243 to 6mm...
(same as #2, but relative shot out the barrel, and could only get a 6mm barrel to replace it with... if either one of these, you need to talk to that relative,)
I have no idea what actually happened, just naming possibilities....
#4) it is the same gun, a rare factory mismark and you never realized it as a kid...
#5) You are misidentifying a Model 600 as a Mohawk 600
One thing I do know is that you SHOULD NOT shoot .243 ammo in a 6mm chamber, (even if it does work). I don't know from personal experience if it will chamber or not.
If it were life and death, I'd say try it. It's not. 6mm Rem ammo and brass aren't common, but they are out there, still. If you handload, brass can be formed from several other cases, 7x57 Mauser was the parent case for the 6mm (.244 Rem).
I will tell you this from personal experience, if you have a case rupture in a Rem 600, some gas WILL hit you in the face.
If at all possible, some clear pictures of your rifle would be nice. The 600 series rifles went through several variations, with the Mohawk being the last ones catalogued.
Hope this helps. DON'T SHOOT .243 in a 6mm gun!
Take it to a gunsmith and have the chamber checked, that at least will settle if the barrel is properly marked, or not...
Good Luck, let us know more, when you can.
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Mike Irwin
Staff
"Rumors that I just started say for every 100 Arisakas issued one 30-06 chamber reamer was issued just in case."
Oh for the love of...
Oh for the love of...