308 Win and 200 grain Smk's

[oldhoward]

Hi I am shooting a new Remington 308 sps varmint with 1 in 12 twist. I have loaded some 200 grain smk's with Sierra accuracy load of 38.5 grains of varget and cci br primer. Problem is only one bullet of 3 fired hit the target at 100 yards? The bullet hole looked sightly oblong not perfectly round. I also fired some 168 grain burgers with 3 shot groups in the .2's. I thought the 1 in 12 twist would stabilize the 200 grain smk's?
Do I need more powder? or is the 200 grain smk just to heavy for the twist?

Thanks,
Howard

 

[Keith Glasscock]

It should stabilize in a 12 twist *if* 1.393 is the length of the bullet.

The real test is whether it stabilizes in your barrel.

Several of questions:

How long are the bullets that you are using?
What OAL are you using?
Did you chronograph them?
What kind of brass?
How did the pressure look at 38.5? Did you work past 38.5 for pressure?
What was the temperature and altitude when you shot them?

I have some nodes for Varget and 200 grain Berger Hybrids, but they are more than a little hotter than 38.5

 

[oldhoward]

Bullet length was 1.397 - 1.395
OAL was2.867 about .047 off lands
no chrony data available, suspected velocity about 2275 fps estimated
brass was rem/peters
no signs of pressure
temperature was 50 degrees and foggy altitude was less than 100 feet.
also there was a typo in powder correct weight is 37.5 grains of Varget

 

[jbpmidas]

I have some nodes for Varget and 200 grain Berger Hybrids, but they are more than a little hotter than 38.5

Do you mind sharing those nodes? By PM or public?

 

[Keith Glasscock]

Not a problem posting my data under the following warning:

The data is safe in my rifle with the components shown. Changing components, especially cases, makes these shown loads unsafe in a hurry! Seating depth affects presures significantly! DO NOT shoot these loads without working up SLOWLY toward them. If you get ANY pressure signs, things will get severely too hot in a hurry. The difference between safe and unsafe can be as little as 0.2 grains!

This data is also shown on Dan Newberry's site with 200 SMK's. My testing correlates well with his data.

Low Node:
Berger 200gr Hybrid
OAL 3.012" (unpointed) (.010 jump to lands)
41.5 grains Varget (lot #4920) - Note: Lot #4844 was not as hot, so you have to work up your lot
CCI BR-2 primer
Winchester cases, trimmed, flashhole deburred, primer pocket cut to depth, and necks turned to .332 loaded

High Node:
Same as above except 42.9 to 43.1 grains of powder
Velocity: 2600 fps from a 3 groove benchmark barrel - 26" long.

Other notes:
Velocity increase for increased barrel length is negligible. My best data suggests that the increase from 26 to 30" was on the order of 20 fps. Powder is burning out in barrel. There is very little muzzle flower on a 30" barrel. The 26" had a good, solid flower.

Thoughts:
I suspect that the optimal length might be ~28" for Varget and heavy bullets (200+). Other powders provide better velocity, but lose temp stability. Everything is a trade-off.

I am currently testing a new Krieger barrel (30"). I have 200 rounds through it, and the accuracy at the 42.9 charge is in the 3's at 300 yards. 43.1 shows a slight increase in vertical, but it is still less than 1" at 300. I do, however, see horzontal divergence at 43.1 to 43.3, so I'm hanging it a little on the low side at 42.9 to avoid that.

I also know that Varget, while more stable than others, does make more velocity as it gets hot. Since I've been testing in 40 degree weather, a little headspace is appropriate.

Hope this helps.

 

[jbpmidas]

I only did a "ladder" test with the 200's and 208's. My test ran from 39.2 to 41.0. I'm in the process of putting together another .308 with a 10 twist, 24" barrel. I may ty these again, along with the 208's. The little testing I did with the 200 Hybrid past the ladder showed excellent 200 yard performance, but the velocity was lacking. It was under 2400 if I remember correctly. I had such good success out of the 185 Hybrid, I never tested any further on the 200 Hybrid and never tested past the Ladder on the 208's. Thanks for the info. I will complete the lader on the new barrel and see what I can get out of these "heavies!"

 

[M700]

"I also fired some 168 grain burgers with 3 shot groups in the .2's. "

Terrific accuracy! Then two out of three of the 200's don't even hit the target, and the one that hits isn't traveling straight. Hmmmm. I'd just load up a mess of that 168 gr ammo and happily bang away.

Then again, I don't like to fiddle around once I've got a good shooting load.

 

[oldhoward]

Here is some more info that makes me think it is related to mild loads. I fired a 10 shot group with 168 gr. smk's and it was vertical about 3/4 of an inch almost straight up and down. Next I fired 5 shots of 175 gr. smk's and groups oped up to about 1 and 1/2 inches in an oblong pattern. Next I shot 3 200 gr. smks and only one hit the target once, but I was shooting at the upper left bullseye on the target. Finally I had some 168 bergers loaded with 44.5 grains of varget and shot a 3 shot one hole group.
I thought the problem may be related to mild/low powder chargers.

 

[GermanS1]

The low MV isn't a huge factor in determining gyroscopic stability, although it is a factor. Shooting the 200 from a 1:12" twist is a marginal proposition and sometimes it just won't work.

Below is a picture of a 100 yard target fired with 200 Sierra in a 1:13" twist (it was a .30-06 but a very mild load). It can work, but the further you shoot, the worse it gets; by 500 yards the group had really opened up to unacceptable levels (see the second picture).

All shooting was prone, sling-supported, iron sights, so there won't be any Benchrest quality groups here, but it's how I normally test things.

Full article here: http://riflemansjournal.blogspot.com/2010/06/ballistics-heavy-bullets-in-113-twist.html

 

[oldhoward]

Thank You everyone. I appreciate your effort.
Salazar, great article well done.

Howard

 

[M14AMU]

TOO HEAVY??

No...it's TOO LONG!!

Stick with 150 to 155 gr. and you'll grin!! Shoot Varget!