139gr CX loads for 7mm-08?

[yakimanoob]

Hey folks,

Is anyone loading the 139gr 7mm Hornday CX in 7mm-08?

The Ace Hardware near my house started carrying them for ~$0.80/ea, so I just picked up a box of 50. I have H4350, RL-16, and IMR4064 on hand, and Hornady and Hodgdon post data for those so I'll give them a shot. I'm curious what kind of results other folks have been getting. My rifle really liked the factory GMX superformance, so I'm hoping I can find a powder combo that these bullets like since they're available locally.

Cheers!

 

[dcreiss]

I haven't reloaded for the 139 CX but have run half a box of the loaded superformance round through my 7-08, I was unimpressed with accuracy through my weatherby vanguard s2 just as I have been unimpressed in loaded or reloaded prior version Hornady GMX mono's. Minute of dinner plate type of accuracy.

 

[jbseamus83]

I haven't loaded the CX. I have loaded the SST and the GMX in 139 gr for my 7mm-08. I've had fantastic results using IMR4350. Below is a pick from testing different loads with the SSTs and the IMR4350 outperformed all of them. This was the best group, but every group I have shot has been under 1" at 100 yds. And I'm not shooting a super expensive rifle. It's a Savage Axis II. Sectional density is the same on the CX as the GMX. I would try the H4350 you have first and go from there.

 

[yakimanoob]

Thanks! I have a test run of the CXs loaded over H4350 and ready for my next range trip. The next two weeks are crazy but thankfully I've got plenty of time before hunting season.

 

[Alpine01]

I suspect you will get a pretty good load developed with a little bit of work. I have a 7mm RM load developed for the CX-150 with H4831SC. Getting 3160 fps (avg) and 0.51 MOA (max) over a 40-round load confirmation cycle. Std deviation is just under 8.5 fps. That was good enough for my needs.

 

[yakimanoob]

I'd be thrilled with that result.

 

[yakimanoob]

Following up on this:

So far the most promising load combo is the 139 CX with IMR4064 (test load was 38.0gr) at ~0.8 MOA 5-shot group. That's obviously not going to win any bench rest competitions, but it's about as good as I'm able to do with this rifle on an average day (and about as good as the best-performing factory loads in this rifle). I had an issue with my chrono setup when I shot those and didn't record any velocity data, but Hornady reloading data suggests it should be in the vicinity of 2600fps. Hodgdon data indicates I could go up several grains so I should be able to get significantly better speed next round with 40gr, and if the accuracy is still promising I'll push the velocity a little harder.

Hornady advises 2k fps as a minimum velocity for proper expansion on game, so I'd like to get to 2700fps at bare minimum so I'm still at 2k fps ~350yds.

I did pick up a lb of Varget recently too and will give that a shot; hoping I can land above 2800fps eventually, or I likely won't stick with the CX bullets. 2k fps is a pretty high minimum, especially compared to the ~1800 fps of Nosler E-Tips and the ~1600 fps of the Barnes 139gr 7mm LRX and Hammer HHTs.

 

[Sheltowee]

You're right, 2000fps minimum impact velocity is pretty steep. Keep in mind that expansion is a continuum and not binary-- even if 2000fps is the minimum, you aren't going to get a ton of performance at that threshold.

 

[D4570]

Here is the elephant in the room.
ALWAYS strip your barrel down to clean steel when you go from gilded bullets to mono copper. I don't know why but, every copper bullet I have shot will always shoot better in a barrel that is fouled with only all copper bullets. Yes, it's a real thing. AND most copper bullets need a little jump to the rifling's. Don't try to get it right up against them.

 

[yakimanoob]

For sure; I've had much better results with monos after thorough barrel cleaning with both regular solvent and then copper solvent. Can't say I've noticed a difference when going between lead and monos (I use lead bullets for practice and monos for hunting) but definitely the monos are more picky about barrel cleaning.

Not exactly the subject at hand though

 

[std7mag]

@yakimanoob,

If you're using an optical type chrono, try moving it 5' further out.

I had reading issues with my Beta Master. Come to find out the muzzle blast was affecting the chrono. Moving it just 5' further away solved the issue.

Varget will probably show you some better accuracy, but isn't going to give you any more velocity.
The IMR4064 is very accurate in my friends rifle, but he kept the accuracy and increased his velocity with H4350.

 

[yakimanoob]

Interesting; my rifle doesn't seem to like H4350, even though it has such a strong reputation for performance. I'll let y'all know how the process turns out.

The chrono issue was my own tinkering; not the chrono's fault. I've been experimenting with a system that mounts my magnetospeed sporter to the OEM savage accustock to get it off the barrel, and the mount just wasn't holding it in the right position. It's a fun project though using my buddy's 3d printer and a carbon fiber rod I salvaged off a broken trekking pole

 

[std7mag]

Interesting; my rifle doesn't seem to like H4350, even though it has such a strong reputation for performance. I'll let y'all know how the process turns out.

The chrono issue was my own tinkering; not the chrono's fault. I've been experimenting with a system that mounts my magnetospeed sporter to the OEM savage accustock to get it off the barrel, and the mount just wasn't holding it in the right position. It's a fun project though using my buddy's 3d printer and a carbon fiber rod I salvaged off a broken trekking pole

That sounds interesting!

I never got a Magnetospeed because I was concerned about it possibly throwing off the point of impact with being attached to the barrel.

Mounting it to the front sling attachment would alleviate that.

I have a Caldwell picitinny mount that attached to the front sling on most of my rifles.

Could a quick detach mount for the Magnetospeed be done for that?

 

[yakimanoob]

I'm sure it could, but I don't know of any standard products you can buy to get the job done. The issue I had was that the bottom of the accustock forend is not parallel to the barrel, so the arca plate I attached meant that the magnetospeed wasn't parallel to the bullet's path and wouldn't read.

BTW, on my ultralight pencil barrel at least, mounting the magnetospeed to the barrel shifts POI by something like 8 MOA, so your concerns are well-founded .

 

[homebase541@]

In my opinion, the 7MMO8 is not a good round to be shooting monolithic bullets through. You can and it’ll work fine at close ranges, but that round just doesn’t have enough speed to be pushing monos. I like to make sure they’re above 3000 ft./s. I loaded up 140 Barnes TSX is in My Wife seven MM 08 a few years ago and she shot a cow elk at 300 yards four times in the boilermaker and none of those bullets opened.. it died?
You can go way down and bullet way and get some quicker speeds but not very much and the crappy BC just exacerbates your problem…
Monolithic bullets belong in a magnum cartridge in my opinion.

 

[homebase541@]

I have also found monos like to be seated about as far off lands as you can get… are you restricted to this gun and the use of monolithic bullets?

 

[yakimanoob]

In my opinion, the 7MMO8 is not a good round to be shooting monolithic bullets through. You can and it’ll work fine at close ranges, but that round just doesn’t have enough speed to be pushing monos. I like to make sure they’re above 3000 ft./s. I loaded up 140 Barnes TSX is in My Wife seven MM 08 a few years ago and she shot a cow elk at 300 yards four times in the boilermaker and none of those bullets opened.. it died?
You can go way down and bullet way and get some quicker speeds but not very much and the crappy BC just exacerbates your problem…
Monolithic bullets belong in a magnum cartridge in my opinion.

lol ok.

 

[yakimanoob]

Welcome to the forum btw @homebase541@.

 

[homebase541@]

Welcome to the forum btw @homebase541@.

Thanks….
I Love the 7mm-08 btw.
I steal it from my wife all the time…

 

[std7mag]

In my opinion, the 7MMO8 is not a good round to be shooting monolithic bullets through. You can and it’ll work fine at close ranges, but that round just doesn’t have enough speed to be pushing monos. I like to make sure they’re above 3000 ft./s. I loaded up 140 Barnes TSX is in My Wife seven MM 08 a few years ago and she shot a cow elk at 300 yards four times in the boilermaker and none of those bullets opened.. it died?
You can go way down and bullet way and get some quicker speeds but not very much and the crappy BC just exacerbates your problem…
Monolithic bullets belong in a magnum cartridge in my opinion.

According to Strelok Pro, the 139gr Hornady CX launched at 2,832fps (the typical velocity of a 140gr bullet from my 7mm-08AI at my 2,000ft elevation) still has 2,055fps at 400 yards with 1304 ftlb of energy.

No reason for needing a magnum for reasonable hunting distances with those numbers.