Rifle accuracy problem

[RC46]

I have had problem 308's (usually not many though), and I went to the police/target ammo: Federal 168gr Sierra HP Gold Metal Match to check the rifle. That ammo runs 'perfectly' thru a 10 twist and it's a long bullet, groups should answer your questions. Hope you are cleaning bore with something like Bore Tech any Nylon brushes. Hope your enjoying accuracy quest.

[SSGOldfart]

Did not check the flags. Wind was pretty calm. But your right it might have been a factor. Would mild to moderate wind make a 2 inch difference at 100m?


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Yes Sir wind can move a group two inches @100 yards, mild wind can be more out at 100 yards then what you feel at the firing line.

[RC46]

Continuing on the stock discuss: When you bedded, did you cut pillars for the front and rear action bolts?
If not I would do it, they will help so as not to crush the stock under torque from tightening and help to stabilize everything. We used to use 1/2" round w/ 1/4" hole aluminum, if you don't have access to the material you can use the threaded rod used in building light fixtures - most ace hwd has it.

[samari46]

Matt, used Redfeild rings a lot. These have a front dovetail that I normally would put some grease on and clamp a 1" aluminum bar in that ring. And would rotate that ring side to side so it would slightly wear in and fit better. Then disassemble that ring to remove the bar. To avoid mixing the rings up, would use a automatic center punch and mark the front ring on one side only both halves of the ring. And do the same with the rear ring with two center punch marks. I have a one inch bar that I used to align both sets of rings. But noticed that the rear ring did not sit anywhere the top of the one piece Redfield base. Set the rear windage screws to hold the ring down and then lapped both rings.
Back in those days it was almost a given thing to have to lap the rings. Anyway lapped both rings which in this case took some time. And also had to use my ancient surface plate with some 320 and 400 grit silicone carbide paper to remove metal on the sections of the rings where the screws were. Every so often would disassemble the rings and use my alignment bar to see wether or not the lapping was done. If not reassemble and lap some more. Now I can forget all that foolishness as Burris rings have a synthetic insert that basically self aligns the scope with no strain or alignment problems and no damage to the scope. Since I haven't heard of Thor rings and bases I'm guessing they are made in South Africa?. Two separate bases front and rear or one piece base?. If one end is not as level as the other suggest investing in some Shims which are available at Brownells. And if available in SA look into Burris Zee rings with the synthetic inserts. And Burris bases. I've used Weaver Grand Slam steel bases with the Burris rings on a lot of my rifles with no problems. My ring lapping kit hasn't been used in years and sits in it's case gathering dust since going to Burris rings and steel Weaver bases. Frank

[Matt44-40]

Thanks Frank. Will see how the lapping goes and if it does not work see if I can get the said items in SA.


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[Petander]

I shot alternating shots on each target to make sure the barrel temperature is the same for each shot of each load.

I may be misunderstanding something here but:

Are you shooting several groups at a time? Changing your aim and position in between shots, shooting individual shots to different targets one after one?

That much movement would mess up my groups for sure, especially if parallax is not perfect . Is it? Check it by moving your head while aiming. Maybe shoot some "normal" groups, five shots in a row to one target, then five to another...?

Front stock comes to mind. I do not touch my front stocks at all when shooting from bench/bags/bipod. Another variable out.

[725]

Hot barrel ? If you shoot a string and then a few minutes later shoot another string, maybe the barrel warming up would change the POI. Had a Remington that was just awful with barrel changing with the heat.

[charlie b]

I like the way you shot the groups. I have done the same several times to rule out different variables (such as barrel heating).

My Savage .308 wasn't very accurate when I bought it either. Took several hundred rounds to settle down. Now it is better than MOA with lighter bullets (155 and 168). Heavier bullets it does not do as well.

Will wind drift the bullets 2" at 100yds? Not unless it is a really strong wind.

I would follow some of the other suggestions. I do not shoot less than 5 round groups and when I get close to my 'chosen' group I will shoot 10 round groups. 10 rounds really comes closest to telling you how accurate your rifle really is.

Until you get some more groups it is hard to tell what the problem might be.

[dtknowles]

Will wind drift the bullets 2" at 100yds? Not unless it is a really strong wind

That is correct



But a shifting light breese of just 5 mph can change your point of impact by almost an inch. If the wind is 5 mph from the right for one group and then shifts to 5 mph from the left for the next group the center of the group could have moved close to an inch. The table above is for a high BC bullet and the effect is greater for bullets with a lower BC. If that wind shift happens between two shots in a group it can expand your group size by that same inch.

Tim

[charlie b]

Interesting. The table for the 168AMax at 2700fps shows 0.5" at 100yd for 10mph. That's about what I observe on target as well.

But, you are correct, a steady wind will not change a group size, only a variable wind will do that.

[dtknowles]

Interesting. The table for the 168AMax at 2700fps shows 0.5" at 100yd for 10mph. That's about what I observe on target as well.

But, you are correct, a steady wind will not change a group size, only a variable wind will do that.

I have been shooting over wind flags for a couple years now and I rarely see calm or steady wind. I put wind flags at 25, 50 and 75 went shooting at 100 yards and I have seen all three giving different indications and my feelings at the shooting line sometimes agree but not always. If you are seeing a lot of horizonal dispersion you need to think about your wind reading.

Tim

[Lloyd Smale]

first thing id do is pull the scope off and put one on it you know is good and see if that cures it. Id say 90 percent of these kinds of problems ive had through the years ended up being a scope going south.

[charlie b]

I have been shooting over wind flags for a couple years now and I rarely see calm or steady wind. I put wind flags at 25, 50 and 75 went shooting at 100 yards and I have seen all three giving different indications and my feelings at the shooting line sometimes agree but not always. If you are seeing a lot of horizonal dispersion you need to think about your wind reading.

Tim

Yep, my horizontal dispersion is usually due to me reading the wind. I have flags at 100yd steps out to 1000yd and they rarely agree, unless there is a strong wind.

The bottom line is that a 2" change in POI at 100yd is not going to be due to wind alone.

[1006]

Just to clarify what is being looked at here, as I want make sure I understand.

Is the problem that the gun shoots further and further right of the target as the three loads being tested is increased in velocity with more powder?

If so, isn’t the bullet load the key to the mystery?

I am thinking that picking just one load and shooting it at multiple distances is the next step.

I have a couple of rifles that will slightly but noticeably drift horizontally as the bullet weights are varied ie: 150 to 180 grain 30.06. I just figured it was the difference in velocity and rotational forces(bullet spin rpm).

I think you need to make sure your scope rings line up, maybe try a different scope, and focus on finding the smallest group producing load, and then test the gun at various ranges to verify that the scope is mounted over and parallel to the bore- if not the point of impact will diverge horizontally at ranges other than the one at which it was zeroed.

[Matt44-40]

Just to clarify what is being looked at here, as I want make sure I understand.

Is the problem that the gun shoots further and further right of the target as the three loads being tested is increased in velocity with more powder?

If so, isn’t the bullet load the key to the mystery?

I am thinking that picking just one load and shooting it at multiple distances is the next step.

I have a couple of rifles that will slightly but noticeably drift horizontally as the bullet weights are varied ie: 150 to 180 grain 30.06. I just figured it was the difference in velocity and rotational forces(bullet spin rpm).

I think you need to make sure your scope rings line up, maybe try a different scope, and focus on finding the smallest group producing load, and then test the gun at various ranges to verify that the scope is mounted over and parallel to the bore- if not the point of impact will diverge horizontally at ranges other than the one at which it was zeroed.

Hi 1006,

The scope drifts between separates groups shot and not between different loads. To keep barrel temperature the same for each shot of each group I shoot 3 shots, let the barrel cool, shoot three shots, let the barrel cool, etc. But I shoot one shot of each load.

Shot 1 is 42.8gr on target 1,
Shot 2, 43gr, target 2,
shot 3, 43.2gr, target 3

Let barrel cool for 5 min

Shot 4, 42.8gr on target 1
Shot 5, 43gr on target 2
Shot 6, 43.2gr on target 3

Let barrel cool

Etc

There was a vertical drift from right to left for each load. But the first group/string/ first three shots actually made a good group, same for 4-6 and 7-9

So it seems like every time I let the barrel cool the POI shifts a bit to the left when I shoot again.


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[Matt44-40]

This is the actual target. From left to right - 42.8gr, 43gr and 43.2gr


Here I put all the shots together on one aiming point to show how all the shots looks on one target. The colours do no represent different loads. Blue is shot 1, 2 and 3, then I let the barrel cool and shot the green shots (4, 5 and 6), let barrel cool, shot yellow (shot 7, 8, 9), let barrel cool and shot red shots.


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[1006]

Ok,
I may have missed something else, but that looks about normal for a hunting rifle-lighter barrel, but I see in your post that this is a heavy barrel gun.

My 30.06, does about the same thing. As long as it shoots to the same spot from day to day for the first few shots of a given load, I would attribute it to barrel heating. The heat from the first couple shots won’t go away without an extremely long waiting period. My 30.06 is not a good target gun, but it is dead on every time on the first two shots. It is a great hunting gun.

If you want to improve the situation for target work, you might try a cooler burning powder. I like AA4350 for max loads in my 7mm-08. I can handle the brass immediately after firing.

[1006]

I looked at the Sonchem Powder web site, and looking at the three powders recommended for 308, you are not at the max load for any of them, if I assume you are using one of them. I am guessing it is S335.

If your brass looks free of excess pressure after firing I would work right up to the max load for your powder and see if the groups become more consistent. I would also try shooting with and without the silencer.

[Matt44-40]

I use S321. The max is 44gr, but that is for a 24” barrel and I have a 20” barrel. I start getting pressure signs at 43.4. At 44gr the pressure is way over SAAMI specs and the primer pockets stretches out.


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[1006]

I agree, you may have maxed out your load, but I would not equate the barrel length with pressure or powder weight.

After trying the things mentioned previously by everyone—-

About the only thing left to try—not knowing your experience level—is get the most comfortable rest you can find to minimize the effect of stress on you as you try to hammer out several groups without getting fatigued, or let a trusted friend shoot it to see if they have the same results.