.243-> 6mm Rem

[oldmanr]

Because I mentioned that I read on line forums,I now have unlimited amount of info........One of the maintainance men from work wanted to know about converting a .243 ar to 6mm Rem. My thought was "Why mess with it?".He says that he is getting Jamming problem from his automatic Rem and wants to upgrade to an AR platform. Does anyone make this rifle or do this conversion?

[dk17hmr]

I think the 6mm Rem is going to be to long for an AR10 platform. If it were a bolt gun yes it could be rechambered but the 6mm wont work in the magazine of the R25.

Is he using reloads or is he using factory ammo in his 243?

[Kraschenbirn]

When you say 'converting a .243 ar', I assume you're talking about an AR-10/AR-10 clone (such as the Remington R-25)? If so, FWIW, I see two main issues:

1) The nominal shoulder dia. of the .243 Win. is .454" opposed to .4294" nominal shoulder dia. for the 6mm Rem while the base diameters are, essentially, the same. In other words, the 6mm Rem. chamber has considerably more taper than the .243 which means that it's not going to be practical to rechamber the existing barrel so he's going to be looking at a one-off custom barrel...i.e $$$.

2) The nominal case length for the 6mm is a just a touch under a quarter-inch (.190) longer than the .243 Win with the same nominal neck length for both cartridges which raises the issue of whether or not the 6mms will function in the AR mags without deep-seating the bullets (thus reducing powder capacity and raising chamber pressures).

If it were me, I believe I'd concentrate on determining the cause of the "jamming problem" rather than attempting a conversion to what appears to be a less-than-suitable caliber.

Bill

[oldmanr]

I think That he just has "magazine envy" The people that he hunts coyotes with are all into the Ar type platform. Most use the .223 and one has the .243 Ar-10. I would just find the jamming issue and stick wirh what he has( The rifle was his fathers), I guess I hold more to sentimental value than mag capacity or cool factors.
But what the heck... I told him that I would throw it out and see how it bounced..

[dk17hmr]

Is it a bolt rifle? or an AR-10/R25?

If its a bolt gun a 6mm AI will clean up a 243 win chamber but to do a straight 6mm the barrel needs to be set back.

[oldmanr]

His rifle is a semi-auto Rem. 742.He is well set up for reloading in this and wants to keep using the cartridge.I do not know why he thinks he needs to dance around like this as changing over the cartridge of a rifle is more expensive than buying new reloading dies.
This is his adventure and I am trying not to kick him around to any one veiw point.

[Johnny_Cyclone]

The 742 was available in 6mm Remington. That part is not the problem.

THE PROBLEM is: It can not be rechambered from .243 Winchester to 6mm Remington due to the shoulder taper of the 6mm Remington.

THE FIX is: It can be rechambered to 6mm Remington Ackley Improved. This will eliminate the tapered case walls of the 6mm Remington cartridge and eliminate the bulk of the original .243 Winchester chamber.
(basicly, even though the 6mm Rem starts big it gets smaller towards the shoulder where the .243 Win does not)

THE NEXT Could be problem: If made into a 6mm Ackley he may need to modify his magazine feed lips... maybe not.

The good news is that the 243 Winchester and 6mm Remington were both considered "short action" rounds in the 742 and used the same magazine as seen in a replacement mag list: 7mm-08REM, 257Roberts, 308WIN, 6mm REM, 243WIN and 260REM.

Where as the 30-06Sprg, .270WIN, .280REM, .25-06REM, and .35Whelen are listed as 742 "long action" cartridges.

Anyway, thats what I think he will run into

[Mk42gunner]

Since it is a 742, I will bet the chamber is dirty, maybe even with a slight bit of rust in it.

The easy cure, if the chamber isn't rusted too badly is to find the take down instructiuons on the internet and use a M-14 chamber brush and patches to get all the grubiness (is that a word?) out. Lube the bolt locking lugs well when reassembling and it should work.

I think I used an 8" cresent wrench to take the barrel off of mine. I know the .30-06 742's have a bad reputation, but I can't remember if the .243's beat the action rails up or not.

Robert

[Johnny_Cyclone]

oh wait.... dog gone it.. I mis read and thought he was wanting to rechamber his 742 not buy an AR10 in .243 Winchester and rechamber it to 6mm remington... sheesh. where was I..:killingpc

The AR10 I know nothing about, except that the .260 Remington seems to be the hot topic around work and the cafe.