what are the basics for 300?
 

I have a couple of 300 fireball guns and I am having some trouble getting them to run.

so rather than bring up all my issues (for now) can you post some basics that pertain to 300 specifically?

I have lots of 5.56 guns that I have no problem getting to run, but there is something about the wisper that is getting me puzzled.

my guns are accurate, but all of them seem to be single shots or will only half cycle with not enough power to even eject the spent round.

all have adjustable gas blocks (wide open) and standard buffers. oneeven has the gas port opened up on the barrel.

what am I missing?

The position of the gas block on the barrel has alot to do with it. The powder you use also has something to do with it.

ok, pistol position gas block 125 gr corbon 300 wisper ammunition 10.5 inch barrel.

I think I might have one gun figured out though I think the gas block is not aligned and no gas is getting through.

Sort of had this issue. My block was lining up, but was just a little off. The result led to me getting enough gas on some powders to cycle, but on other loads(that work in similar guns) no dice. I finally got her lined up perfect and now my rifle runs great. I am able to run the "lighter" quieter powders and the 300 WTF cycles and BHO.

lighten you buffer to around 1100 gr and try it.
I run a 16" barrel with a pistol position gas port drilled to .116" It runs great with subs and full speed loads!:grin:

The easiest way I've found to align a gas block on a barrel is by sound. With the barrel removed from the upper receiver and with the bolt and carrier removed, cover the muzzle with a finger and blow air though the barrel from the chamber. The position is like blowing a trumpet but not trying to produce a tone. The sound of the hiss of the air coming out of the gas tube is very sensitive to how well the barrel and gas block holes are aligned. Clamp the block when you find the small "flat spot" in the sound of the hiss in both the axis of rotation the block around the barrel and moving it fore to aft.

Do others use this method? When I first assembled AR's I tried other methods using careful measurements or small pins in the ports which work but they took special tools, were much slower, and were less reliable for getting good alignment.

My method is to look at the pin holes or set-screw dimples through the respective holes in the gas block.

I think I have a total blockage, the bolt doesn't even move when fired.

on the other gun (16" bbl, carbine gas block location)I will try the lighter buffer, but I may still need to do some tweekage on the gas block.

Sounds like a good place to start. The method above where you blow air into the barrel to find the "sweet" spot of the gas block is how I do it as well. I just put a dummy round in the chamber and blow air down the barrel while I set the gas block.

well, I feel like a complete idiot......
as this is my first time with useing a adjustable gas block I found out my problem.

I didn't have the adjusting screw backed out NEARLY enough.

I was under the assumption that a few turns was all I needed.

turns out the screw needs to be backed out almost 1/4 inch of visible threads.

now I am worried of losing the screw, are there any tips on keeping the screw in place so it doesn't fall out?