Checking my tantals diameter

[Blarelli]

I have a tantal which I have posted about before which is wildly inaccurate. It has been suggested that I have a barrel that is the wrong diameter for this rifle, and I am now going to check that. I have a caliper that will measure to the hundredths of a millimeter, but I can't even take the freaking muzzle break off. Any help there?
Anyways, once I do succeed in getting the muzzle break off, do I measure the diameter from the lands or the grooves of the rifling? Also, I'm not even sure what the barrel diameter should be. Anybody know what the barrel diameter of a 5.45x39 rifle should be?

 

[HorseSoldier]

Does the muzzle brake have a spring-loaded detent button at the rear -- if it does, you just push down on the button and unscrew it (but remember AK muzzle devices are reverse threaded).

On the barrel size, I'm not sure. The 5.45 bullet itself is just barely shy of 5.56mm (0.2236" versus 0.224" if Wikipedia is to be trusted).

 

[Blarelli]

It does have a little button on the butt end of the muzzle break. I've tried pushing that down, and cranking on it but it hasn't budged.

 

[HorseSoldier]

If the detent is spring loaded but the brake won't unscrew (remember, it's threaded backwards), I suppose it's possible who ever built the rifle soldered or welded it in place. Any indication of that?

 

[Blarelli]

Nothing I can see. I'm really sick of this rifle. It has given me nothing but heartache. I think I might go pawn it tomorrow.

 

[Deus Machina]

Calipers not designed to measure a bore are an inaccurate tool for the job. That can work to your advantage, anyway, because the better way to measure the inner diameter is to slug the bore.

This is simple. Get a brass rod that will slide down the barrel, and a ball or loose bullet made of the softest lead you can find. Force that down the barrel with the rod, so it takes the rifling. Then measure that. Accurate, no need to take the muzzle brake off, and your calipers are exactly the tool for the job.

A gunsmith should be able to do that cheap and quick, if you can't find a bullet on its lonesome for it or aren't sure about giving it a shot the first time.