Hornady GMX problems - help needed

[CharlieTN]

Bit of background. I'm not new to reloading but am new to precision rifle, shooting and reloading.

Rifle is a Remington 700 SPS varmint in B&C stock with Weaver 3-15x50 EMDR. So far I've been working up a load using the Hornady 168 BTHP, H4895, Win brass and CCI 200 primers seated to 2.8" C.O.L. and have been getting 5 shot groups between .505 and .837 at 100 yards. I'm quite tickled with these considering my lack of shooting experience.

Here's the problem. Loaded up some of the Hornady 165 GMX with the same brass/primers and powder using data I could find. Did 3 loads between 41.5 grains and 42.5 to see how they shot. Seated to 2.811 (longest I could with the BDL setup). Best group was 2.5" and the worst was 3.5". I stopped middle of the first group and walked away from the rifle for a moment to make sure I was doing my part, concentrated on my setup and again, all over the place. This was after turning in consistent .7 - .8 groups with my target load.

Any tips, tricks, hints, or suggestions for what I might be doing wrong? I'm using a Rock Chucker, basic RCBS .308 dies and hand weighing each charge.

I was hoping these would work for a hunting load since they have a similar bc as the 168 BTHP.

Thanks,

Charlie

 

[former naval person]

Re: Hornady GMX problems - help needed

Charlie...I remember when Barnes first came out with their line of monolithic bullets (In fact, I still have most of the box!)they were inconsistent in their accuracy. Some "writers" insisted that they got superb accuracy...the overall consensus was not good. In my rifles they gave the 3.5 to 4 inch groups you report for the GMT. Much tinkering later, I understand that the Barnes monolithic bullets work well. It may be the same for the GMX...more R&D needed. Hornady has been exploring many new technologies/applications to increase their market share. This one may have found its way to market before it was ready for the multitude of rifle/barrel combinations out here.

 

[FLIGHT762]

Re: Hornady GMX problems - help needed

I was excited to get some of the .270 GMX's for may Tikka T-3 lite in 270 Win. The rifle shoots under MOA with almost all loads. I did the same as you. Used a tried,accurate powder and found I wouldn't get groups better than 2.5 MOA. Tried about 5 different powders, no luck. I even called Hornady CS and sent 15 bullets back for them to test. The test results: they shot fine in their test rifle. They even sent me test targets with data.

Bottom line was my Tikka was not going to shoot the 130 grain bullet accurately.
I moved on to using Barnes TTSX, which shot MOA.

I'd try a couple of different powders and see if you get any better results. You may as well.

I was disappointed in the GMX line and I'm very hesitant about trying any of the other GMX's.

If you try the Barnes line of lead free bullets, try their Tipped TSX.

 

[trailrider121]

Re: Hornady GMX problems - help needed

Well with my finding using GMX's, is that they have a secant design and are very sensitive to seating depth. I have shot these GMX's out of 3 rifles and had great results, but they do require some time. I use the Berger seating method of 3 shot groups with the bullet .010", .050", .090" and .130" off the lands if mag will accept the oal. One off those groups should print a good group.Of coarse using a good node with these.

Most of my good loads with gmx's have been .100" off the lands have produce the best.Seems like to be seated far off lands.

 

[CharlieTN]

Re: Hornady GMX problems - help needed

Thanks for the response. I've still got a few so I'll have another go. My max oal (measured by a Hornady OAL gauge) is 2.951. I might be able to seat them to 2.851 and still fit in the BDL configuration. I'll see how that goes.

Charlie

 

[FLIGHT762]

Re: Hornady GMX problems - help needed

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: trailrider121</div><div class="ubbcode-body">
Most of my good loads with gmx's have been .100" off the lands have produce the best. Seems like to be seated far off lands. </div></div>

I must say, I didn't test with a lot of different COL. My COL was about .25" off of the lands. I don't have any .270 bullets left, but I do have a few in .30 cal. 165 grain that I tried in a friend's .300 Win. Mag. that shot about 2 MOA.

I'll try a few in my .308 Win. @ about .100" off of the lands and see what happens.

 

[rusty815]

Re: Hornady GMX problems - help needed

From my experience, GMX rounds like to be seated close to the lands, I get great accuracy this way out of my 270 and 7mm-08, if your mag restricts you and you can't reach the lands, I suggest looking at the TTSX, which uses a tangent ogive that is easier to find an accurate load.

 

[trailrider121]

Re: Hornady GMX problems - help needed

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FLIGHT762</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: trailrider121</div><div class="ubbcode-body">
Most of my good loads with gmx's have been .100" off the lands have produce the best. Seems like to be seated far off lands. </div></div>

I must say, I didn't test with a lot of different COL. My COL was about .25" off of the lands. I don't have any .270 bullets left, but I do have a few in .30 cal. 165 grain that I tried in a friend's .300 Win. Mag. that shot about 2 MOA.

I'll try a few in my .308 Win. @ about .100" off of the lands and see what happens. </div></div>

Flight,

Here a load I work up in my 300 WM using 165 GMX/ RL22. The GMX end up performing best .120" off the lands.