AR308/243 Questions

[MarkB]

Hi All,

I appreciate all of the help throughout my AR308 build, which is now an awesome shooter.  My 2nd build is very similar, but .243 caliber/20" SS LW heavy barrel.

Using same gas block (JP low profile, adj) and rifle length gas tube, gun won't eject spent case.  I've adjusted the gas up and down without any luck.

Beginning to wonder if the gas port hole in barrel might be too small.  Hoping someone knows what diameter should be, and any other ideas for me to check out.

Thanks,

Mark

[tlcoy1911]

I have a new 20"DPMS 243 barrel and the gas port is .082" or drill # 45.

I have not fired this yet to know if works but thats the factory size.

When you pull the gas block off, check the "smoke" ring aroung the port to be sure the hole in the gas block lines up with the port in the barrel

[MarkB]

Thanks.  I will check for that, and get a #45 :)

[98Z5V]

MarkB, who is the barrel maker?  If it won't even eject, and the gas port is the culprit, then that gas port has to be grossly undersized. 

Another thing I'm thinking - take the adjustable gas block out of the equation for this part, for a minute.  The gas port could be WAY oversized - the bolt carrier is trying to start it's cycle too fast, due to increased gas pressure of a large port, and the case hasn't contracted yet.  The case is still expanded out into the chamber walls, and that will stop the bolt carrier in it's tracks.  However, the adjustable gas block, dialed down, should have caught something like that. 

Check for a rough chamber, too.

Does the bolt carrier even move, when you fire?  Have someone beside the rifle, watching for that.

[MarkB]

barrel is a Lothar Walther.

after I get a #45, I can check size to see if under/over-sized.

I'll also check the chamber.  chamber didn't like remington as they stuck, whereas winchester manually ejected fine.

don't have local place to shoot, but can check for bolt movement next weekend.

Thanks for the feedback.

[MarkB]

took gas block off last night.  it appears that the hole in gas block did not match up exactly with barrel hole--have discoloration on both gas block and barrel next to gas port holes.  am trying to post some pics.  will try to center better and try again this weekend.

also tried to find a #45 (.082") drill bit, but best could come up with was a 5/64 (.078125") and wouldn't you know it, the barrel gas port hole is smaller than that.  seems like i will have to re-drill as well.

[98Z5V]

Drill slow (drill on a slow speed, pressure very slow/light).  Last thing you need to do is get through it fast enough to tag the opposite inside of the barrel when the bit goes through. 

Barrel steel might be tough, but the bits will get right through that gas port hole.  <thumbsup>

[unforgiven]

What brother Tom said,don't want to kiss the other side :o You could put tape on the bit to act as a stop.

[MarkB]

thanks for the suggestions.  i ended up hand-turning the bit and was easy to tell when i broke thru.  this weekend should tell whether these two things resolve my problems.

[bowhunter020]

I'm so glad I read this thread.  I've been looking at doing a AR-15 in 5.56 and getting a bigger caliber for hunting.  Now that I know I could use a AR308 lower for a .243 caliber that's what I'm getting!!  Thank you 308ar.com members!!!  Unless that's a bad idea.  Hunting purpose 90% of usage.

[MarkB]

glad to be of help, bowhunter :)  I can tell you that right now, .243 ammo is MUCH easier to come by than .223/5.56 or .308.  by searching around, i can still find good deals on various bullets for reloading (except .223).

good luck on getting parts!

[SPBCTS]

Still have a soft spot for the .243....it was my first rifle. Good flat shooter, too.

[BLKSHEEP]

I've often wondered why the military hasn't used the 6mm/.243? , it seems to me to be a great compromise between the low energy of the 5.56 & weight of 7.62 ammo.  <dontknow>

[Robocop1051]

I've often wondered why the military hasn't used the 6mm/.243? , it seems to me to be a great compromise between the low energy of the 5.56 & weight of 7.62 ammo.  <dontknow>

Too long of a chamber for automatic weapons... That's why they made the 6.8 SPC

[BLKSHEEP]

I'm a novice so please educate me...most of us have 308Ar's which are longer casings then the .243, I can imagine that a shorter casing could allow for a faster rate of fire in full auto & possibly less failures <dontknow> <dontknow>

[98Z5V]

6mm isn't a standardized NATO cartridge.  Simply based on that, the .mil will never use it, unless it's NATO approved.  Specialized units are another story altogether.

[Tripledeuce]

    Actually, Blacksheep, the 243 win is slightly LONGER  than the 308 Win.

    2.045 vs 2,015.

  Not really enough to make a big difference, but the 6mm bullet must be seated deeper to feed through the mag.  Thats considering the 105g 6mm vs the 150 g 308.

  Respectfully

  Terry

[BLKSHEEP]

Good info. thanks <thumbsup>

[MarkB]

just an upadte:  was able to shoot the .243 last weekend.  resetting the gas block and enlarging the barrel gas port did the trick.  a couple of adjustments on gas block and it ejected shells and locked open on empty.

next step will be getting new scope.  any recommendations for coyote hunting out to 300-400 yds?

[98Z5V]

next step will be getting new scope.  any recommendations for coyote hunting out to 300-400 yds?

Nikon Coyote Special.  Damn good scope, and right inline with what you'll use it for.  <thumbsup>