Hornady 150gr GMX bullets in .308 Win - Load Help

[mtnman31]

I've been trying to develop a load for .308 Win using the Hornady 150gr GMX bullets. Everything I've tried has been over pressure. I've tried starting loads and even backed off some from that considering the bullets are lead free. I've tired suggested loads from a few of the powder manufacturers although I don't have Hornady's manual. I'm just not having much luck and getting frustrated.

My latest try was with RL15 and Win748. Both loaded to 2.800" COL. Using fed primers. Starting loads were showing flattened primers and a few starting to back out. Velocities were in the 2700 range and groups on target were decent. I've got a few other powders to choose from. These GMX bullets aren't cheap and I don't want to waste anymore of them without making any progress. Has anyone else used these and had any luck with them? Care to share any recipes? I do want to keep them loaded to magazine length.

My wife has coerced me to try the lead free bullets in my hunting load. These things are giving me fits and I don't want to just throw in the towel on these bullets. I've read some reviews stating that the GMXs work better when pushed to higher velocities. That said, my hunting is not anything over a few hundred yards.

Thanks

 

[gpoldblue]

I've been trying to develop a load for .308 Win using the Hornady 150gr GMX bullets. Everything I've tried has been over pressure. I've tried starting loads and even backed off some from that considering the bullets are lead free. I've tired suggested loads from a few of the powder manufacturers although I don't have Hornady's manual. I'm just not having much luck and getting frustrated.

My latest try was with RL15 and Win748. Both loaded to 2.800" COL. Using fed primers. Starting loads were showing flattened primers and a few starting to back out. Velocities were in the 2700 range and groups on target were decent. I've got a few other powders to choose from. These GMX bullets aren't cheap and I don't want to waste anymore of them without making any progress. Has anyone else used these and had any luck with them? Care to share any recipes? I do want to keep them loaded to magazine length.

My wife has coerced me to try the lead free bullets in my hunting load. These things are giving me fits and I don't want to just throw in the towel on these bullets. I've read some reviews stating that the GMXs work better when pushed to higher velocities. That said, my hunting is not anything over a few hundred yards.

Thanks

Since the bullet is a lead-free design...may have a greater bearing surface causing pressure....still should operate at starting loads. LOW pressure and/or excessive cartridge headspace can cause your symptoms. Can you slip a bullet easily into a fired case?? Is this in a bolt action or semiauto? 2700 to 2800fps is a good operating speed for a 150gn in a .308.
Be safe. Dan

 

[HTSmith]

Primers backing out sounds like a case sized too much or an oversized chamber (as spoken to above). Federal primers also have tendency to "flatten" more than others in my experience. When you seat new primers in these fired cases, are the pockets still tight? How far does the 2.800" OAL put your bullet from the lands? You may be truly over pressure, but I suspect something else is going on given only 2700 fps.

 

[mtnman31]

Since the bullet is a lead-free design...may have a greater bearing surface causing pressure....still should operate at starting loads. LOW pressure and/or excessive cartridge headspace can cause your symptoms. Can you slip a bullet easily into a fired case?? Is this in a bolt action or semiauto? 2700 to 2800fps is a good operating speed for a 150gn in a .308.
Be safe. Dan

Bullets slide in/out of fired case like one would expect. The rifle is a bolt action (Rem 700).

Primers backing out sounds like a case sized too much or an oversized chamber (as spoken to above). Federal primers also have tendency to "flatten" more than others in my experience. When you seat new primers in these fired cases, are the pockets still tight? How far does the 2.800" OAL put your bullet from the lands? You may be truly over pressure, but I suspect something else is going on given only 2700 fps.

None of the primer pockets felt loose when loading. I will check the fired cases to see if any now feel loose. A couple cases had the case head showing a little bit of flow into the bolt's ejector. The 2.800" COL has these bullets at a jump of .083" to the lands - sufficiently generous... Comparing the shoulders of sized and fired cases shows that the shoulder is moving forward .002-.003" upon firing.

As I mentioned, this has been frustrating me. If I can't get the GMX's to work in my .308, I may use them in one of my Encore wildcat cartridges - the 310 GNR. The 310 GNR should be able to push them to 2700-2800 without much fuss - out of a 15" barrel nonetheless.

 

[HTSmith]

Bullets slide in/out of fired case like one would expect. The rifle is a bolt action (Rem 700).



None of the primer pockets felt loose when loading. I will check the fired cases to see if any now feel loose. A couple cases had the case head showing a little bit of flow into the bolt's ejector. The 2.800" COL has these bullets at a jump of .083" to the lands - sufficiently generous... Comparing the shoulders of sized and fired cases shows that the shoulder is moving forward .002-.003" upon firing.

As I mentioned, this has been frustrating me. If I can't get the GMX's to work in my .308, I may use them in one of my Encore wildcat cartridges - the 310 GNR. The 310 GNR should be able to push them to 2700-2800 without much fuss - out of a 15" barrel nonetheless.

I'm stumped. Maybe too soon to go "leadless"?

 

[Bojo]

Rookie here compared to most .
Is this a new rifle with you trying new loads or a proven rifle that shot other lead core 150 grain well ? And just what is the od on those and how long is the bearing surface compared to a same weight lead core ?

 

[JFrank]

Starting load?
Barrel twist?
Choice of primers may be questionable, perhaps try CCI br -2

 

[mtnman31]

The rifle is relatively new with 1 in 10 twist barrel. I haven't worked up other loads for it although, I've worked up many .308 loads for other rifles over the years. The bullet OD is exactly .308". Bearing surface is longer than comparable weights. Starting loads were:
RL15 42.5gr
Win 748 43.5gr
Varget 42.5gr

I've got two other powders I'll try next week, IMR-3031 and good 'ole IMR-4895. I know I can just back off starting loads a bit more, but then velocity drops and the bullets aren't able to perform to their potential.
Thanks for the comments and help.

 

[JFrank]

This is RL-15 with a 1-10 twist 43.3 worked out with Sierras 168 bthp, notice the small x between shots 9-10

The rifle is relatively new with 1 in 10 twist barrel. I haven't worked up other loads for it although, I've worked up many .308 loads for other rifles over the years. The bullet OD is exactly .308". Bearing surface is longer than comparable weights. Starting loads were:
RL15 42.5gr
Win 748 43.5gr
Varget 42.5gr

I've got two other powders I'll try next week, IMR-3031 and good 'ole IMR-4895. I know I can just back off starting loads a bit more, but then velocity drops and the bullets aren't able to perform to their potential.
Thanks for the comments and help.

 

[mtnman31]

I ended up trying some IMR-3031, IMR-4895, and Varget. I got the pressure signs eliminated but velocities dropped well below where I wanted them. The Varget and IMR-4895 had good groups while the 3031 grouping was horrible. I've decided to stick with traditional lead core construction bullets for the .308.

I tried the GMX's in the 310 GNR cartridge I mentioned previously and had good results. I ended up using a load of RL-15 and got around 2900fps. Grouping is good but had a major zero shift from other loads I had previously shot through the gun. I'm very happy with the results because it is one of the few times I've actually worked up a load from scratch. I generally use the manuals and recommended loads (at least as a stepping off point) when developing loads. The load info I had from Reeder (the cartridge designer) had loads for H-4350 which didn't work out well for me. Velocities were only around 2200-2300 and the barrel wasn't long enough to burn all that powder (had a massive muzzle flash). Since it is a wildcat cartridge there just isn't much published info. I don't have the Quickload program to help and had little to work with. The RL-15 was fast enough that I wasn't wasting a ton of powder and got me to the velocities needed for the bullets to properly expand on target.

Over the next couple weeks I hope to see the true effectiveness of the GMX bullets when I take the pistol out deer hunting. The 310 GMR is an impressive cartridge and a load of fun to shoot. Photo shows the pistol and 310 cartridge next to a .308 for comparison.

 

[Bocephus]

I've been trying to develop a load for .308 Win using the Hornady 150gr GMX bullets. Everything I've tried has been over pressure. I've tried starting loads and even backed off some from that considering the bullets are lead free. I've tired suggested loads from a few of the powder manufacturers although I don't have Hornady's manual. I'm just not having much luck and getting frustrated.

My latest try was with RL15 and Win748. Both loaded to 2.800" COL. Using fed primers. Starting loads were showing flattened primers and a few starting to back out. Velocities were in the 2700 range and groups on target were decent. I've got a few other powders to choose from. These GMX bullets aren't cheap and I don't want to waste anymore of them without making any progress. Has anyone else used these and had any luck with them? Care to share any recipes? I do want to keep them loaded to magazine length.

My wife has coerced me to try the lead free bullets in my hunting load. These things are giving me fits and I don't want to just throw in the towel on these bullets. I've read some reviews stating that the GMXs work better when pushed to higher velocities. That said, my hunting is not anything over a few hundred yards.

Thanks

I can’t speak to your situatuon exclusively, but if your 700 has an S or RR prefix it may also have a firing pin hole that was lightly(?) chamfered at the factory. I had a new VTR in 223 that showed serious cratering on even the lightest loads. I finally realized the problem, called CS, was told it was an engineering change in all SA 700s.
Obviously an exec at Remington had a nephew that had aspirations of becoming an engineer.
Since then I have acquired a few more of these misbegotten “engineering changes.” Other than fired primers that are butt-ugly, if I keep the boltface cleaned regularly, it hasn’t been too much of a problem....except it really grinds on our common sense.