Simple test loading GMX and TSX bullets with same components using factory COL and recommended loads from each bullet mfg. External bullet dimensions are very similar but bearing surfaces differ (grooves) as does bearing material (composition).

TESTED 308 Winchester 150 monolithic Hornady GMX and Barnes TSX using Varget powder, Fed 210 primers, COL 2.740 (GMX) and 2.785 (TSX). Rifle Merkel KR-1 with 22 inch bbl.

Gr..GMX...TSX (fps @ 10 yards)
40..2444...----
41..2471...----
42..2547...----
43..2600...2588
44..2664...2652
45..2696*..2684
46..----...2771
47..----...2812

*Max load... All cautions about working up loads for individual rifles. No pressure signs My interest was related to comparative velocity. Max vel was not reached in either group, and my velocities were under expectation. Max powder was exceeded in Hornady by 0.1 grain. COL appears important to normalize the groups. Re precision, all fell roughly in a 3 inch circle at 130 yards. Thought you might be interested and I would appreciate any thoughts.

Interesting information. Thanks for sharing it. Have you tested the GMX on game?

Not much difference.

I am guessing the grooves on the TSX reduce pressure, hence velocity slightly lower?

I attributed reduced TSX velocity mostly to the increased COL which increases case capacity at ignition and for this rifle, there is still some freebore. I wonder why Hornady uses the same COL for monolithic GMX, bonded Interbond, and lead cup and core SST.

This rifle has much better precision with 150 monolithic and 165 SST because of its 1:12 twist (I think) compared with my single shot Merkel K3 (1:10 twist) which shoots 165 monolithic and 180 gr cup and core (NBT, AB, SST) with better precision. The lengths of the 150 mono & 165 lead are very close as are the lengths of the 165 mono and 180 lead.

Re GMX use on game, no immediate difference, but I don't have as much experience with it. I have had some amazing occurrences with the TSX wonder bullet. I know not everyone likes it, but I do. I've had no negatives. I think the GMX will be similar.

This seems reasonable.

In four different 30 cals (308, 30-06, 300 WM, 300 H&H) have never been able to get GMXs to shoot as well as TTSX or TSX bullets. Not a big deal for hunting accuracy but no reason to change as no bad experiences with Barnes.

Unless my math is bad we're talking 12 fps in each set.....that does not seem like a lot. You can get that much variation in a string of shots with either bullet I bet.

The GMX has Grooves also though. Unless their geometry are different.

The GMX has 2 smaller relief grooves and the TSX has 3 larger ones. Hard to say for sure which bullet has more bearing surface, but I'm guessing it's the GMX. It's also a bit harder gilding metal, rather than Barnes pure copper, so that could be part of it too.

Seems to be the case in a select few. I know in my .223AI I could only get 3200fps out of a 50 grain TTSX.
I stepped up to a 55 grainer ( with one more driving band and hence more bearing surface...) and voila! 3500FPS

Correct, this effect is especially noted in the newer .257 80 gr TTSX which Barnes notes as edging 3800 in a 257 Bee with a way too short 24" bbl.

Put it in a No. 1 with a 30" barrel and you're gonna blow by 4000 fps with a proven big game bullet. Finally living up to Roy's claims !

Antelope beware.

+1. The accuracy difference isn't that big (1/2 MOA vs 1 MOA) but because of the difference in accuracy and they are pretty much the same price, I hunt and have great results with Barnes. If GMX's were significantly lower priced, I probably hunt with them.

Don't forget outer diameter of the bullets!

I don't have firsthand experience with the bullets that you tested, but I have seen differences between different makes/models within the same caliber. This might not apply to your comparison, but just because we "think" they are .308 cal, they might actually measure differently. For example, I found that the 140gr BTSP measured slightly larger than the 140gr NAB for the .277 cal.

That said, I wouldn't dismiss the differences in bearing surface that Jordan mentioned.

That's the problem. I have had 3 pass-throughs and no GMX expansion on California Blacktails!

I was hunting the lead-free zone and the bullets failed to expand with lung shots and the deer all ran 122, 145 and 137 yards respectively and no blood for first 75 yards or so. If it was not out in the open and if I was not confident in my shot, most hunters would have lost those deer.

For this season, I will be trying the LRX or TTSX. In lead-free areas I do not have much choice.

Try the TTSX...always a winner for me.


From what little Ive seen the GMX don't expand as much but they expand....and yours probably did.


Be prepared to not see any TTSXs after you've shot them. Chances are they will completely penetrate as well...

Oops! Fotis you are right!

I was thinking the Etips when I posted.. I typed before my brain engaged. My bad.

The ETips seem to expand. This one was pretty well tortured.

http://forum.nosler.com/viewtopic.php?f=50&t=33333

The problem with monos is expansion when they are NOT well tortured