I get nice four pointed patterns from an old rifle with four lands/grooves.

Looks like a diamond, about 1 1/2 to 2 inches across, and there are small half inch groups at each of these axis points.

Some loads tighter, some looser.

Wondering if this is just runout problems on my bench, or maybe a sign of worn throat area?

Hornaday 170 RN and Sierra Match kings 200 grain, and Speer Semi Spitzer 170 grains do the same things. other bullets run wilder.

Thanks for helping.

Oh, its a .318 8X57 JR, and swaged bullets, firing at about 2300-2500 fps.

nice little diamonds, right around my site point.

Jamiester---

"Swaged bullets"?? Up or down? If they're squeezed down and have a jacket, what you're seeing is jacket seperation.......a "bubble" between the jacket and the core.

To maintain accuracy with bi-metal bullets any changes of diameter should be UP, not down.

I've never noted ANY pattersn on a target that lead me to consider them any indication of throat erosion. You can gauge throat erosion by visual inspection with a bore scope, or by careful measurement of contact with the throat with the use of a comparator of some form. You would have to use the same bullet used for any original measurement in order to gauge the erosion reasonably accurately.

You might try varying your seating depths of your loads either way. By seating the bullets out further you are "chasing" the lands and minimizing the effect of throat wear.

btt