Range Report cold temperature and high b.c. bullets

[psinclair]

has anyone had problems stabilizing high b.c. bullets in cold temperatures? ive been working with a 6xc and 115 vlds loaded to 2950 to 3000 fps. testing at 5 to 20 degrees f.
a friend told i should check into this.
i cant get it to group better than 1" at 100 meters.
thanks for any input!
bartlein bbl 27" 1 in 7.5 twist.

 

[BryanLitz]

Re: cold temperature and high b.c. bullets

It's a matter of twist and stability, not necessarily BC.
For the 115 VLD's we recommend a 1:7" twist to insure stability in all conditions. I've shot them out of a 1:8" twist 6mmBR and had them work just fine, in the warm summer air. I suspect if I tried it this time of year, I'd have the same stability/accuracy problems you're seeing.

Stability depends on a lot of things, air density being one of them. Colder air is more dense, so it's harder for the bullet to stabilize in it, even if it's the same muzzle velocity and twist rate that works well in warmer (less dense air) conditions.

It may <span style="font-style: italic">seem</span> to be related to high BC bullets because they usually have the most strict twist requirements. Shorter lighter bullets are comfortably stable in all conditions, but the long heavy bullets need a little more care and attention to conditions.

Hope this helps,
-Bryan

 

[psinclair]

Re: cold temperature and high b.c. bullets

thanks bryan,
ill be using the rifle for coyote hunting so i need it all year regardless of temperature. what about the 105 vld?

would an unstable bullet enter the target off axis(key hole)?

the 115s seem like they are entering the paper square.

ive shot long range coyotes this winter with my .308 (155 scenar @ 2980 fps) in temps as low as -35 f. without any problems other than adjusting for more bullet drop. that bbl is 1-11 twist.
can this be achieved with a 6xc?
thanks, pat

 

[BryanLitz]

Re: cold temperature and high b.c. bullets

Pat,
Seeing as how you're right on the borderline of stability with your 1:7.5" twist, they're probably straightened out by 100 yards. If you place a paper real close (10 to 20 yards) to the muzzle, you might see some minor keyholing. It's at the close range where the damage to accuracy is done for marginally stable bullets.

I'm sure the 105's will work well for you in all conditions with your 1:7.5" twist. At least they'll be stable.

The 155 Scenars only need a 1:13" to be stable in all conditions, so your 1:11" is giving them plenty of stability.

Good luck with those Coyotes,
-Bryan

 

[psinclair]

Re: cold temperature and high b.c. bullets

thanks for the help bryan,

i will load some 105s a give them a try tomorrow. i was begining to pull my hair out!

ill get back in here and post my results...

thanks again, pat.

 

[landcbeitner]

Re: cold temperature and high b.c. bullets

You might try the 108gr Berger BT it shoots well in any condition from my 26" 1:8 243 win. They are not jump sensitive either.

 

[psinclair]

Re: cold temperature and high b.c. bullets

another option..that may make more sense as a hunting bullet. im always nervous seating into the lands when hunting. i jump my 155 scenars .002 in my .308.
how far are you jumping the 108 in your .243?

thanks, pat

 

[BryanLitz]

Re: cold temperature and high b.c. bullets

Please note the 108 BT is a Target bullet and is made with a thicker jacket. It's not made to expand like the VLD Hunting bullets. Maybe you would rather it doesn't expand if you're just hunting coyotes and are worried about pelt damage, just wanted to mention it.

The VLD's are certainly more sensitive to seating depth than the non-VLD bullets. However, more and more people are finding that they don't necessarily need to be jammed or even be very close to the riflings. Many people are reporting best accuracy with as much as 0.100" jump. Hunters find this especially appealing because it allows you to load mag length rounds and avoid bullets sticking in the throat.

It's worth a try.

-Bryan

 

[Frank Green]

Re: cold temperature and high b.c. bullets

PGS, If I understand your initial post you are getting 2950-3000 at 5-20 degrees? Did you clock them over a chronograph at this temperature or at a different temp.? If so you should be o.k. If you clocked your rounds at a warmer temperature than as the temp. drops your powder will not have the same burn rate. You could be losing 100-150fps vs. shooting the gun at 60 degrees. This could be part of the problem also.

I use a 7.5 twist on my 6x47 Lapua and shot the 115 Berger VLD's just fine. One one or two of the days of the F-Class Champ. the day started out around 28-30 degrees F. My gun shot just fine at a 1000 yards. No accuracy problems. I haven't shot the gun in any colder temperatures than that.

I want to thank Bryan for making the post and comments. I agree with him 100% and it's what I've told shooters for years. According to my twist rate calcs. The 115 Bergers need a min. of 7.77 twist at 3000fps. That's why I'm running a 7.5 twist. I don't like running my stuff on the ragged edge. I'm not comfortable at all with the 8 twist. I've tried it with 115 DTACs in my 6mm Rem. and it shot fine but wouldn't shoot the Bergers. Temp was around 45 degrees.

Running on the ragged edge of the twist and being stable like Bryan said. Different temperatures, elevations (sea level vs. a guy shooting at 5000 feet), air density, etc....all can play a part.

The 105's will should be just fine in your 7.5. Steve shot our shops F-Class gun at the champs. and it is in 6x47 Lapua also. It's a 1-8 twist barrel and I loaded 107 Sierra's for it and it shot excellent with no problems.

Later, Frank
Bartlein Barrels

 

[psinclair]

Re: cold temperature and high b.c. bullets

hey folks,

just got home from hunting and tried some 105 vlds in the 6xc.
at 100 meters for 5 shots all in one ragged hole! the load is 39.0 grs. RL17, fed 210M, just touching the lands. its 23 degrees
f. mv was 3046 ave. and extreme spread was 16 fps. easy bolt lift and nice round primers.

thanks guys!!
now i can sleep at night!!
bryan& frank, you guys are the bomb!!!

 

[Frank Green]

Re: cold temperature and high b.c. bullets

Cool glad it's working for you. I still think it should shoot the 115's. Might have to play with some loads.

It just also might be that the 7.5 twist at those temps. is still just on the ragged edge.

Later, Frank

 

[psinclair]

Re: cold temperature and high b.c. bullets

frank, thanks for all the input!

ill keep you up to speed on my load testing.

i definatly live in an extreme proving ground, 110f in july to minus 50f in january!

keep up the good work!

p.s. i love those 5r bbls you guys make. they shoot lights out!

pat