I will add that after shooting them side by side with Barnes, the Barnes typically shoot better.
There are two exceptions:
1. My 222 prefers the 55gr GMX over any Barnes from 50-62gr.
2. I have standard loads of 60gr H4831sc under 130gr GMX, T/TSX always ready for any 270 that might find it's way home. Out of the nine 270's that we own, only one shoots the GMX's better.
I .did use that rifle about 10 years ago on a mule deer, it died. Recovered one bullet out of two that were shot. Nothing earth shattering, it worked.
For the rest of the rifles, it is about an even split on TSX vs TTSX preference.
That is with 222, 22-250, 6.5 Creed, 270's, 300 H&H, 338-06, 375 H&H.
So did you also use the same seating depth (as in off-the-lands) with the GMX as you did the Barnes? Noted that you used the same powder charge.
Monolithic bullets are not all the same. Have found accuracy can vary somewhat with the type of bullet, including ogive, the exact metal/alloy they're made of, etc. Barnes TSXs are made of pure copper. GMXs (along with Nosler E-Tips) are made of gilding metal, the slightly hard copper alloy used for most (but not all) lead-core bullet jackets.
Consequently they all differ slightly in what powder charge and seating depth results in the finest accuracy.
