Loading for accuracy and I am stumped! Actually in disbelief!

chrismc

chrismc

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Hey
I am loading for a Tikka varm 7-08. I have gone thru the regular 'load for accuracy' routine, and got great groups followed by shotgun groups... I tried diff bullets/powders/primer combos and it was all the same - 1/2 moa followed by 2-4 moa, followed by 1 moa...

So i got myself a Sinclair OAL measuring tool, to see if I could get precise "0 to 20 thou off lands" to see if that would change things.
Here is where I am baffled. First, the sinclair tool works great! Anyhow, I measured a berger VLD 140... 2.96" COL to rifling - did it three times, all 2.96" to rifling. I also measured to ogive and came up with the same silly numbers.
Then I did a NAB 140 - 2.97" COL to rifling x 3....
Then I did the dremel to neck trick, and seated a bullet, and chambered/closed bolt, removed and checked length x 3 on both bullets.... same numbers as the sinclair tool.

The specs are 2.80, mag length is 2.815.

If I load to max mag length, that means I have a jump of almost 150 thou to the rifling!!! I checked my math again, and yes, 150-160 thou...

Then i measured a Berger vld 140 as it would sit in the case if I were to change the bolt stop and mag to a long action setup and load to 20 thou off rifling... there would be less than 1/8" of the VLD being held in the neck.

I am thinking this is contributing to the huge variances I am seeing in group sizes. is there any fix for this set-up? I am thinking of setting the barrel back a few threads and re-reaming...

Any thoughts on this long throat? Is this normal for some rifles???? Suggestions?
 
im no expert, but if your rifle is shooting good and then as the barrel warms-up it starts to open up significantly I would check if the barrel is touching the stock somewhere in the barrel channel,

sometimes if you use a bipod the stock can bend and put pressure on the barrel
 
My 700 .308 shoots 185 vld's 100 thou off the lands at a coal of 2.900 just did the sweet spot test and that's where she likes em plenty of bullet in the neck and increased case capacity shoots 45 gr of RL 17 no pressure always sub MOA in a factory gun and usually closer to 1/2 MOA
 
Yes the action screws are set proper and the stock is set up correct. The issue is that if get the long action bolt stop/mag and then I seat bullets to 10-20 thou off, there is very little bullet being held by the case neck. I should prob take a pic and post it - looking at a ttsx 120gn, i dont think there would be any bullet in the neck if 10 thou off... its not easy to load a 7-08 to 2.95"!!!!
I just dont know WT heck Tikka was thinking when they made such long throats on Varm guns, and coupled this with the shortest mags on the market. Maybe I am missing something, but it just doesnt make sense!

So the answer is to set it back 0.125 me thinks
 
If you switch to the Sierra bullets you will notice an immediate reduction in overall group size.

I went through MANY brands in my 7-08 before I settled on SMK's for target and SC II's for big game.
 
I load 140 bergers to 2.985, single feed, no problems. My rifle gets away with loads quite a bit over max, probably the extra case capacity.
 
Chasing the lands didn't work, maybe try seating the bottom of bullet shank to the shoulder / neck junction of cartridge. Don't let a magazine limit the accuracy potential of you rifle, what you're shooting at isn't shooting back.
 
when you resize your once fired brass trying resizing only 2/3's of the neck .

what you will be left with is a slight bulge that will fit your chamber perfectly while the remaining sized part of the neck will hold the rear of the bullet in alignment .

i try to seat my bullets 15 to 20 thou off the lands .

has the rifle ever shot consistant groupings ?

how does factory ammo group ?
 
You have options here chrismc.

There is big wisdom in the suggestion to try SMKs. It’s the easiest bullet on earth to get to fly straight. If you can't get good groups with those, the rifle is lame and you need to put her down. It's the only decent thing you can do.

For proving out you accuracy, don’t let your magazine length limit your options. Just load to jam the lands and feed your bullets single shot by hand. If you find a significant accuracy change then you can make the call if you want mag length or single feed. You will probably find that jumping maybe .030” will give you best accuracy, but jamming the lands will give you the most consistent velocity.

What about barrel twist rate? Is your twist rate faster than 1 in 11” needed for the bullet?

It could also be the powder burn rate is too slow and you are sooting up your barrel. As it gets fouled it fouls your groups. I have always found best accuracy comes from powders with faster burn rates. Check a burn rate chart and compare what you are using to other powders recommended for the cartridge.
 
Last edited:
Chinbullco said:
Chasing the lands didn't work, maybe try seating the bottom of bullet shank to the shoulder / neck junction of cartridge. Don't let a magazine limit the accuracy potential of you rifle, what you're shooting at isn't shooting back.[/QUOTE]

^^^^^^^^^^^^^^^^^^^....Love THAT line !!.....lmao
Click to expand...
 
The 140 Berger hybrids have basically the exact same bc if that's why you chose them and apparently are less finicky about the jump. I have some but haven't tried out that theory yet but it's another option if you can find them
 
Check for bullit runout,my other concern is, are your first two shots on target.Then when your barrel heats up the groups open up.I would measure from the olgive,and only use oal for mag fit.
 
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