RFI Hornady GMX 70gr loads, Black Hills and the like.

I am looking for any extra information I can get in regards to the Hornady GMX 70gr load for 5.56mm, I know Black Hills makes a load and Hornady of course. I know it has a great B.C. and sectional density. It is marketed as barrier blind, 95% copper/5% zinc composition. Does anyone have experience with this particular load or know if this meets DocGKR's criteria? It looks like the 55gr GMX load made his list, I have had excellent luck with the 300 B.O. loaded GMX and am wondering if the accuracy and expansion lives up to the hype on paper. The purpose for the GMX for me would be a general defense load for two legged, pest control (pigs about 250lbs max). The pro's as I see it is being able to produce a practice load that runs really close to factory loading,(HDY 68gr AMP), good factory load performance across my range of needs, lastly rounds I can use in both an SBR or my 14.5". Right now I can't really see any negative aspects thus far and am wondering if I am just ignorant of something/blind.

Over on 24HourCampfire.com, they actually shoot a lot of flesh with bullets and write about how it did and how the bullets handled the journey.

My general understanding of monometal bullets is that they need more velocity to expand reliably, so you typically go light for caliber to get the best results. On heavier for caliber bullets, you start to see more reports of unimpressive expansion.

Especially since you're looking at 14.5" and shorter barrels, I'd stick with the 55gr because you're giving up velocity out of the gate. I might even look at bonded options instead. No firsthand experience with the combination you're proposing, but I've at least put my money where my mouth is with my own purchases.

Also, technically the 5% zinc makes the GMX metal a brass, so if you load such a round into a legal pistol, it actually is (as I understand it - IANAL and this is not legal advice; do your own due diligence) by the letter of the law "armor piercing ammunition," and someone might be able to have a problem with it. Notice there are no GMX bullets engineered for "handgun" cartridges, only rifle cartridges. Barnes bullets avoid this pitfall by being 100 percent copper.

I avoid shooting bullets with yellow-looking jackets through barrels I care about, because when you look up the hardness of any zinc-copper brass alloy with enough zinc to look yellow, it's roughly double that of pure copper, as I remember. It's been a couple years since I actually looked it up. Not saying it will destroy your barrel quickly, but it directionally isn't the way I want to go.

Sidenote, it's interesting to me that the GMX bullets are considerably more yellow in color in photographs than typical jacketed bullets, even those sold by Hornady. "Cartridge brass" that cases are made from is ~10% zinc, and has its characteristic yellow color. A typical "gilding metal" jacket alloy is about 5% zinc and much redder in color. PR statements from Hornady ~ten years ago when the GMX line was launched indicate they are the same composition as Hornady's jacketed bullets, but that is inconsistent with the appearance difference. I suspect they often contain more zinc than most jacket alloys, and that the composition may vary between particular bullets as a means of tailoring terminal performance characteristics.

A possible advantage of GMX versus Barnes is that you may be able to go back and forth between GMX and jacketed without issues, whereas with Barnes pure copper, at least in rifles, it's recommended to clean all the jacket fouling out of barrels before starting with Barnes, or you risk less than optimal accuracy and accelerated copper fouling.

I recall hearing Defoor talk about how very effective the “brown tip” (Barnes 70gr TSX) ammo was overseas. But that was against people in the open. If my memory serves Doc GKR said they tend to shear their petals in windshields. Many agencies I’ve been around use a TBBC in 5.56 to get to bad guys behind stuff, but the exposed lead tip can cause them to be less accurate at longer distance. As we so often say here, the mission drives the gear, but I’m not sure I understand why you need barrier blind ammo for doing ammo testing. From the OP it appears shooting things with 2 legs or 4 isn’t your goal, much less critters inside vehicles. Maybe I missed something in your post though.

@OlongJohnson

Thanks for all the info. I have been looking at the Barnes stuff as well, I've used their 110gr Tac-TX load in 300 B.O. as well and it does very well. I will look at it more, (so damn expensive). As for loading into a pistol all my stuff is SBR'd so I don't think I'll have trouble. I also don't really travel out of state with any of them. There is a lot of other info in your post I'll definitely have to look into with regards to barrel life that isn't something I had taken into the equation with the Zinc being in there and its effects on barrel wear, (really I am just completely ignorant here). I honestly won't be shooting tons of the stuff, mostly it will be the 68's for practice and fun. 70's when I need to shoot something that is destroying stuff. I wanted to stay away from 55gr as my barrels don't seem to like them at all. I am unsure as to how GMX 55gr loads will fair though as they will be longer.

@El Cid, the reason I talked about Doc's list is because I consider it to be the standard to which I compare everything else to since I am no ammunition expert. My post including information about composition and marketing is just to provide the information that I had so I could avoid receiving that same information. It was not because I necessarily need a bunch of barrier blind stuff. I wouldn't mind having that ability but it isn't really the focus. I primarily want something that will expand in animals and people if need be just the same inside the home and on my property. This round looks/looked like a round that would pair nicely with the plinking round that I can load and shoot for practice on the regular, (reasonably cheap) and essentially allow me to stock only two rounds, (both are available in a factory loading and in components) which is really a requirement for me. Having just one/two loads that are ballistically comparable will really cut down things logistically with loading and simplicity in use. Also, I believe your memory does serve you correctly I think Doc stated TBBC, SOST, then GMX for intermediate stuff none of which I am really sweating and why I didn't just buy more TBBC/SOST type ammo. Truth is I can get the GMX a fair bit cheaper than a lot of other stuff locally through an L.E. distributor I can also source the 68's in bulk for about 18-19 cents a round.

This is second time Barnes has been brought up here and my hunting buddy mentioned it as well. I've thought about them but the expense of them turned me off. I will have to look at them more and compare them to something else I can roll for practice. Maybe I can make it work I was just hoping to keep things reasonable. I was really hanging my hopes on GMX working. Maybe I'll just use the 68's for everything else and just keep a few boxes of TBBC around instead if this isn't going to work. Not like I'm going to shoot anything more than 100 yards away anyways so switching mags for 62gr stuff really won't matter. Fucking OCD. I should go post to that thread now.

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Originally Posted by Mike C

There is a lot of other info in your post I'll definitely have to look into with regards to barrel life that isn't something I had taken into the equation with the Zinc being in there and its effects on barrel wear, (really I am just completely ignorant here). I honestly won't be shooting tons of the stuff, mostly it will be the 68's for practice and fun. 70's when I need to shoot something that is destroying stuff.

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I'd be surprised if you find any discussion of barrel life being affected with GMX. I can't recall reading about it. My comments are just me applying a little engineering and reaching my own conclusions based on data. As I said, I don't know how big the effect might be, it's just directionally expected that a harder metal will cause greater wear. And I can't speak to the size of an effect relative to other causes of throat erosion, such as powder selection, rate of fire, etc.