Home Forums Reloading Big Game Rifles GMX vs. TTSX Pressure

Anyone loaded these two in otherwise identical loads (powder, bullet wt.) and noticed a difference in pressure? With TTSXs becoming unobtanium, I want to try some GMX. I’ll be loading .338 185gn. I have many loads for the 185 TTSX and researching just how much work up is warranted. I’ve found e-tips are very different for example, curious where GMX fit in there.

In monolithics a lot depends on how many grooves are cut in the bullet's shank--which is why E-Tips usually result in more pressure/velocity than GMXs or TSXs of the same weight and diameter--E-Tips only have one groove, around the area where the ogive meets the bore.

The .338 185 TTSX has three grooves, and the 185 GMX has two. Thus the GMX has a little more bore-bearing surface.

Also, the metal for the monos has some effect. Barnes uses pure copper, which is softer and "grabbier" than the gilding metal (a mild brass, copper alloyed with a little zinc, used in most lead-core bullet jackets) used in the E-Tip and GMX. This tends to reduce the pressure generated by the GMX.

My guess, based on some experience with both the TSX and GMX, is pressure will be very similar.

Perfect, thanks JB!

I did experience more pressure with the GMX in several rifles. Not a huge deal. Accuracy unfortunately was abysmal in all. No luck with that bullet or the interbonds for some reason.

FYI, I recently did some tinkering with the 7mm 139gr GMX, 140gr TTSX, and 145gr LRX in the 7RM. These are each 5-shot averages.

139 GMX, 67.5gr 7828ssc, RP brass, CCI250: mean - 3250 fps
145 LRX, '', '', '': mean - 3134 fps
140 TTSX, 68gr 7828ssc, RP brass, CCI250: mean - 3219 fps

So in this case the load with the GMX appears to have generated more pressure than the TTSX load, even with 0.5 gr less powder. The 140gr TTSX has 3 relief grooves, the GMX has 2, and the LRX has 2 also.

Not sure if this means to load up the two groove bullets more or stop at listed maximum? I like the TSX, TTSX,and LRX and am just now loading the ETip and GMX. What I am doing now is dropping back a grain of powder for the two groove bullets.

That was the 185-grain GMX? Did you try the 185 TTSX?

I'm toying with the idea of loading the 160 grain TTSX or either of the 185s... and loading down a bit, at that... given my only likely targets in the foreseeable future are paper, eastern whitetail, or maybe a hog or two...

-Chris

Honestly I never had any trouble getting accuracy out of ant TSX/TTSX/LRX. Especially in my Bees which have freebore. The GMX just did not want to cooperate. Tried it in 30 cal and 375 cal. No joy!

I was loading the GMX and TTSX 250 gr. 375's in my 375 Renner. Same powder and weight of powder for all testing. I saw two things. The GMX was about 10-25 fps faster than the TTSX in a given load. The TTSX was much more consistent and accurate. My go to bullet. Terry

Interesting. I’ve found the TTSX to the easiest bullet to find very good loads with and was hoping the GMX could fill-in while the TTSXs are unavailable. Fingers crossed, but sounds like others are having experience with GMX similar to what I’ve had with e-tips. Simply not as easy to find accuracy. We’ll see.

Thanks, guys; interesting.

-Chris

Interesting comments.

I have gotten excellent accuracy with all three brands of monos. In fact perhaps best is from 100-grain Nosler E-Tips in my NULA .257 Weatherby. Also had the 70-grain GMX out-shoot the 62-grain TTSX in two 1-8 twist .22-250s.

But I do tend to play with more powders than many handloaders, and also perhaps play with seating depth more.