308 Win. heavier the bullet th larger the group

[oldhoward]

Hi comments please.
Rifle: Remington SPS Varmint 26 inch barrel 1:12 twist
Results with heavier bullets show larger groups as bullet weight increases. This surprised me as I expected the 168 to 175 grain range to perform much better than the 155 grains. Question I have is how do I improve results with 168 grain to 175 grain bullets? Would like to shoot 500-600 yards in windy conditions.
Results at 100 yards:
200 Sierra smk only one out of three shots on paper shooting upper right hand corner of a target, probably all would have been on the paper if shooting center target bulls eye. Group would have been near 3 inches best guess. Bullet to long??
175 gr Sierra smk 1.75 inches ( 5 shots) averaged length x width/2 outside of group measurements
168 grain Sierra smk 1 inch vertical string 10 shots all touching. More powder??
168 Berger vld’s .486 inch 5 shots, averaged length x width/2 outside of group measurements
155 smk .490 inch 5 shots, averaged length x width/2 outside of group measurements
All loads with remington brass, cci benchrest primers, and Varget powder.
200 gr. 38 grains Varget, 175 smk 41.7 grains Varget, 168 gr smk 42.5 grains Varget,
168 berger vld 44.5 grains Varget, 155 grain smk 44.8 grains Varget

Thanks Howard

 

[spclark]

How many rounds on the barrel? Anything done to "accurize" your rifle over what the factory sold you? What kind of sighting arrangements?

1:12's a good choice for 155 - some 185's, anything heavier benefits from 1:11 or even 1:10.

Your Varget loads seem a little light compared to what I've used. Do you have access to a reliable chronograph / see any indications of pressure signs with the loads your using?

 

[oldhoward]

Hi SPCLARK,
This is a new factory rifle on the first loadings. Scope Leupold 6x24. Loads were mostly from Sierra Manual's accuracy loads. No pressure signs at all. Just worked on the trigger a little, the rest is still factory, for now. I usually work with the 22 thru 6mm's. I have not seen twist rate have that big of impact before?

Thanks SP for your help

 

[XTR]

For Targets:

With the 175s you should probably be loading over 43.5 or so of Varget. (I load a lot more for 1000 yard shooting) The 155s you can load up to 45 or more, I know guys using a whole lot more, like 2 whole grains more, for F-TR, but they are on the ragged edge and running 3000FPS or more, you don't need to go there. You can blow stuff up.

The 168 is a good bullet out to 600, but if you ever try to push it further it will go wonky. It is not stable when it goes transonic, and it has too low of a BC to get out to long range super sonic.

The 1:12 won't stabilize the 200 grain bullets, esp at the low velocities you are shooting, leave that one for the magnums and the guys with 1:10s in F-TR.

For hunting:

The 308 that I hunted with shot 165SGKs really well over about 43.* Varget in LC brass. Thicker brass, higher pressure for lower charge, but for hunting it got the job done (sub MOA at 200)

 

[Bob3700]

I agree with the fellows that your loads are a bit light. That said, everyone else is probably running a custom action with pretty tight tolerances in an aftermarket bbl.

One thing that you might want to consider is recoil. With 155 gr bullets the recoil is reasonable, start heading up toward 175 and 185 gr bullets and it becomes more noticable. That means the gun is jumping around a bunch more either in your shoulder or on the bags. You may need to hold on to the rifle differently (more firmly) when bullet wt. goes up.

Just a thought as often we tend to overlook the gun handling part and focus on the loads and rifle.

Bob

 

[DennisH]

With the 175s you should probably be loading over 43.5 or so of Varget. (I load a lot more for 1000 yard shooting)

I agree with the above.

I shoot 175's, 185's, and 190's . . . with a stout load of Varget! Very hard on brass, but no pressure signs

Start low and work up to see what your gun can handle. I have 10, 11 & 12 twist barrels.

My 12 twist barrel shoots 190's fine with 43.5 grns of Varget. Different bullets did better with a slightly larger load.

 

[Turbulent Turtle]

With the 175s you should probably be loading over 43.5 or so of Varget. (I load a lot more for 1000 yard shooting)

I agree with the above.

I shoot 175's, 185's, and 190's . . . with a stout load of Varget! Very hard on brass, but no pressure signs

I would call that a pressure sign. What other sign are you waiting for? A light in the sky?

 

[DennisH]

Quote from: DennisH on Today at 07:40 PM
Quote
With the 175s you should probably be loading over 43.5 or so of Varget. (I load a lot more for 1000 yard shooting)
I agree with the above.

I shoot 175's, 185's, and 190's . . . with a stout load of Varget! Very hard on brass, but no pressure signs

I would call that a pressure sign. What other sign are you waiting for? A light in the sky?

To be exact, I usually get 15 rounds out of my Lapua Brass. On my heavier loads I only get about 8 to maybe 10 rounds. This is the only sign I am getting. No pocket issues or cracks, Loads are very accurate and I will buy the brass to keep winning. I know what signs to watch for, and after shooting roughly 1k rounds, I have a consistant wear pattern without any "excess" signs!

When I do have "high" pressure signs, I immediately stop and those loads are unloaded! I have seen a person blow up a bolt head, it only takes one time to see this and you DON'T forget!

For all, most of the time you will notice signs with your primer. Second, you will notice pressure signs on the head of your brass, mainly excess scratching or scars in the name stamped in the brass. If you see a round mark around the ejector pin on the brass, STOP immediately! At this point, your almost ready to see the "light"!
Dennis

 

[oldhoward]

Thank you all, I appreciate your efforts. I will step up the loads as you advised.