180GMX loaded with Varget very bad accuracy.

[Sam82]

Hello to all. Im new to forum and new to reloading.

Quick question. Im loading 180GMX in .308 with Varget. I. Loading with Hornady load data. My ladder 31 33 35 37. Was going to start to narrow down after this but the accuracy was extremely bad and velocities were low. The gun is a Rem 700 26in 1&12 twist. The groups would not even hit the paper at 100M. Velocities were average 1800 on the low working up to about 2100 on the top of the ladder.

I was also laddering out some other loads with the 168 SK HPBT and varget. These groups shot very well. Definitely narrowing down the OCW with these.

I also shot some 178ELD-Ms and they did ok. Not as well as the 168s.

Mabey the barrel just can't do the heavy bullets? I have searched and found that others are able to shoot heavier with a 1&12.

Forgive me for Im new to loading and only looking to learn.

Thank you.

 

[Sam82]

Here's a picture

 

[Dusty Stevens]

Bad wrong twist rate. I like 11.75&12 for 168. Your twist could be slower than marked as well, plus that bullet is longer than a lead core which amplifies the twist rate issue

 

[divingin]

Too heavy and long a bullet. I suspect if you shoot at a closer target, you'll get hits on paper that show the bullet going through sideways. a 1-12 is marginal for a standard 180 grain bullet; with a monolithic copper bullet (which requires a faster twist as it's less dense and hence longer), I think you'd be well into the wildly unstable range.

Start by loading either a 175 or lighter lead core bullet (which will probably be close to unstable), or a 150 or lighter monolithic.

 

[troupe]

As mentioned, your twist will not work with that bullet. GMX's are iffy on accuracy in some guns.

 

[Fast14riot]

The holes are already starting to oval, they will be tumbling in another 25-50 yards. Too long of a bullet for your twist rate.

 

[Ned Ludd]

As a general trend, longer [heavier] bullets tend to require a faster twist rate to [gyroscopically] stabilize. As Dusty noted, copper monolithic solid bullets tend to be much longer for a given weight than traditional lead-core bullets. Thus, they usually need a much faster twist rate than you'd expect for the same weight lead core bullet. You still might be able to stabilize lead-core bullets in the ~180 gr weight class with your 1:12 twist barrel, but when you add the extra length of the copper monolithic, it is not sufficiently stabilized. In such a scenario where the bullet is just barely stabilized (i.e. a gyroscopic stability coefficient (Sg) of perhaps 1.0 to 1.1 or so), groups can open up significantly, and the holes in the paper often become oblong because the bullets weren't going straight through the target. In other words, they are right on the edge of tumbling due to insufficient spin stabilization. Once the Sg gets down to around 1.0 or below, let's say if you had a barrel twist rate of something like 1:13, the bullet would likely be going through the paper sideways, or keyholing. FWIW - although bullet velocity from a given twist rate barrel is part of the Sg equation, only rarely is it possible to overcome the effect of an insufficient twist rate barrel by speeding up the load. To do so will typically require a greater increase in velocity than can be achieved at safe operating pressure.

The Berger Bullets website has a twist rate calculator, if you're interested in playing around with the numbers:

Twist Rate Stability Calculator

Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.

bergerbullets.com

In order to use this with bullets from other manufacturers, you will need to make (or find) some dimensional measurements on your own as the GMX will not be listed in the pull-down menu. Nonetheless, it can be a useful tool to check for potential stability issues. Also, if you're interested in learning more about this and other topics related to external ballistics, I would suggest obtaining a copy of Bryan Litz' book, Applied Ballistics for Long Range Shooting as another very useful reference:

Applied Ballistics For Long Range Shooting 3rd Edition

store.appliedballisticsllc.com

 

[Coyotefurharvester]

Were the charge weights in your post correct? You may want to check, you seem very light.

 

[Gary in MD]

Were the charge weights in your post correct? You may want to check, you seem very light.

That’s the same thing that I thought right away

 

[Bocephus]

All great answers. Bet you’re glad you joined!

 

[jr600yd]

Yeah, your charge weights sound a little light. You’ll get much better results using 150-175gr bullets.

 

[Gary in MD]

It’s not apples to apples but Hodgdon lists, for a 180 grain Speer, a starting charge of 41.0 grains of Varget up to a maximum of 45.0 grains. You’re well below their minimum charge, Hornady’s maximum is 43.2 grains. You need to step on the gas.
Gary

 

[1bamashooter]

Yeah up those charge weights 44.4gr of varget was my load for a 175gr SMK or Berger. Where did you find those charge weights?

 

[Sam82]

Thank you everyone for your replies. Learning is my favorite thing to do.

Things learned:

Twist rate on rifle to slow for heavy bullets. The rifle started as a Rem 700 VTR. Upgrades to rifle are Magpul Hunter 700 stock with magazine well, Triggertech Special trigger adjusted down to 1lbs. Burris XTR II 5x25x50 milrad scope with SCR reticle, Burris Extreme rings and Burris 20 MOA rail. The chamber on this thing is huge. My form fired brass neck diameter is .344. I’m necking down to .334 to get a couple thou neck tension. The lands are way out there, measured at 2.360 with the Hornady comparator. I used a combination of the RCBS precision mic and the good old slide a bullet into empty fire formed case and chamber it 10 times averaging the numbers. This rifle may only be so capable with the factory chamber.

GMX are for hunting and made of mostly copper and there for larger than a lead projectile of same grain. I will be honest, I grabbed these of the shelf because they a very long and I thought I could get closer to the lands. The 168GR Sierra HPBT (which shoot the best groups so far) would be clear out of the case if seated .020 off. I guess I’m stuck with a large free bore until a rebarrel.

As for load data. There is a website xxl-reloading.com that lists data for all the major bullet manufacturers. You have to subscribe $20 to access the data for a year. Now I ether read this data wrong somehow or the website has it listed wrong. The rifle seemed to thud rather than bang the rounds out. I thought this data to be low compared to the 168 SK and 178ELD-m data.

MIN Max Fill rate Pressure Vel 23.6in barrel Vel 18.9 barrel

30.9 gr | 2 g

37 gr | 2.4 g

98.6%

49646 psi | 3423 bar

82%

2362 fps | 720 m/s

97%

2277 fps | 694 m/s

95%

Ned Ludd. Thank you, sir, for you reply. I will definitely familiarize with the twist rate calculator. As soon as I am finished with this post, I will follow link to purchase Applied Ballistics 3rd Addition. I will read the crap out of it. The only education I have so far is the Speer Manual that came with RCBS stuff and the internet and now you!

I have enjoyed shooting through out the years and now I am very much enjoying reloading. When I let go of my very first hand loaded round (168 SK HPBT, F C case, Federal 210 primer, 41gr. Varget) it hit 3 o’clock off center 2.5in. That moment was epic to me. Now all I need to do is dive deep in to barrel harmonics, SD/ES node, seating depth and all the rest. I want this factory pig to shoot out to 1000 consistent. When I do, I will have earned a rebarrel and trued action. And then start all over.

Sorry for the novel.

Thank you.

 

[Fast14riot]

Twist rate correlates to projectile length rather than weight. Typically length goes up with weight, but lighter materials (Cu vs Pb) must be longer to keep same weight.

 

[Dave M.]

Hello to all. Im new to forum and new to reloading.

Quick question. Im loading 180GMX in .308 with Varget. I. Loading with Hornady load data. My ladder 31 33 35 37. Was going to start to narrow down after this but the accuracy was extremely bad and velocities were low. The gun is a Rem 700 26in 1&12 twist. The groups would not even hit the paper at 100M. Velocities were average 1800 on the low working up to about 2100 on the top of the ladder.

I was also laddering out some other loads with the 168 SK HPBT and varget. These groups shot very well. Definitely narrowing down the OCW with these.

I also shot some 178ELD-Ms and they did ok. Not as well as the 168s.

Mabey the barrel just can't do the heavy bullets? I have searched and found that others are able to shoot heavier with a 1&12.

Forgive me for Im new to loading and only looking to learn.

Thank you.

Use the Berger stability calculator



A stable bullet is anything over 1.4 (even though Berger uses 1.5) and likely lower than about 2.0 (starting to really overspin the bullet).
Your bullet is approx 0.78. That’s terribly unstable. I’m actually surprised that you didn’t see keyholing on the target.
Dave

 

[Capt. Oblivious]

Besides the fact that they are most probably to long for our twist a180gr Mono bullet is not the right weight mono for a 308, you need and want speed for a mono to work like they were designed for. Drop down to a 155gr ish Mono and you will be in much better shape.

 

[Sam82]

Hey fellas
Here's my groups from this morning
Open for interpretation...

 

[Dusty Stevens]

Are you using wind flags? Whats your setup on the bench? What was the distance

 

[WVRJ]

168 grain Match Kings are one of the more length tolerant bullets out there.I have a VTR in 308 and I shoot the Hornady A-Max 168's but if I want them to shoot their best I have to go longer than magazine length and single load them.The new production 700's are even worse.Their throat is so long that a 168 grain MK will fit between the neck of a case and the lands.I've looked at 2 of them so far.How can the idiots who bought Remington ever expect something like that to shoot?They took the same worn out tooling and thought they could sell off some junk because of the name.The name's already been ruined,and if they ever hope to make it,they'll have to rebuild the trust in the name and that's not gonna happen.