After buying and happily using a Tikka T-3 in 30.06 I went a step up to .300 Win Mag with the new model Tikka TX3. The aim is to have a little more oomph getting 165 & 180 gn projectiles out to 400 yds. I like shooting this too as recoil is surprisingly manageable.
I reload so started working up a load shooting Barnes TTSX 165 gn. I have a couple of loads with AR2209 ( H4350 ) and AR2213sc ( H4831 sc ) giving approx 3150 fps. At 100 yds AR2209 will produce a .70 inch group, and AR2213sc a 1.18 inch group. Cases are Norma, Primers Federal 215 Magnum. At this point things look good. But when I move back to 250 yards the groups of both loads inexplicably open to about 4.50 inches, shooting a horizontal pattern ! I repeated this three times with the same result. I'm puzzled as obviously wasn't expecting this but want to get it solved. Sure, slight human error would be involved but not to this extent.
Hoping the collective wisdom of AR can help steer me to the cure. Magazine length is 85.60 mm total and projectile contact with the lands is at COAL 92.10 mm but I have previously used rifles with this sort of jump and they shot well.
Hoping yhere are some Tikka 300 Win Mag reloaders here who can offer experienced advice.
Thanks in advance.

So, I believe what you're saying is that you have horizontal strnging at 250 yards but not at 100 yards. In my opinion, that would be a scope parallax problem. It is possible to have the parallax for one of the scope crosshairs adjusted properly while the other isn't. Parallax needs to be adjusted properly for both insofar as is possible.

What scope are you using and does it have a way to adjust parallax?

Correct, 100 yd group pattern normal, 250 yd group pattern horizontal.
Scope is Swarovski Z5 3.5-18 x 44, fitted with parallax adjustment turret. Before fitting onto this .300 Win Mag this scope was on another rifle. With the same scope settings that rifle shot normal group patterns at 250 yds.

I assume you shoot at a very sheltered range. Where we shoot the crossing winds make 4.5"-wide groups a distinct possibility - even at 100 yards.

100m groups don't really prove a great deal. Often they will open significantly at range.

Many of the guys doing load development only measure vertical dispersion, arguing that horizontal dispersion is attributable to technique and wind. Whilst I follow and mostly agree, I'm not entirely in that camp, but there are some really experienced accuracy guys who will argue that.

Thanks guys.
I shot these groups in the almost dead calm of early morning, before 6:00 am and sunrise. No wind of any strength and the range is quite well sheltered anyway.

100m groups don't really prove a great deal. Often they will open significantly at range ( quote ).

Agreed, and I have seen this particularly with factory ammo where groups open so widely I wouldn't be confident of taking a 200 yd shot. But after initial development I have never seen my own loads shoot so widely at 250 yds. As I want hunting accuracy for 400 yds I am concerned about being able to achieve that. So far the groups have virtually nil vertical dispersion, only horizontal.
So, what to do......??? Open to ideas....

quote:

Originally posted by 30.06king:
So far the groups have virtually nil vertical dispersion, only horizontal. So, what to do......??? Open to ideas....

You do know how to set parallax don't you?

With your gun perfectly still in a rest and the crosshairs centered on the aiming point, you should be able to move your head from side to side and up and down without ANY apparent movement of either crosshair.

quote:

Originally posted by sambarman338:
Where we shoot the crossing winds make 4.5"-wide groups a distinct possibility - even at 100 yards.

That would have to be a VERY brisk wind.

You say you repeated this three times, same results. Does this mean that you reverified the groups at both 100 and 250 yards and got the same results or only at 250 yards?

Are you shooting free recoil? Try holding the forearm.

Where is the rifle's stock positioned on the front rest? Make sure it's slight forward the magazine not out near the sling stud.

Some thoughts:
On my 308 Tikka T3 Hunter, the factory mounts will not hold, they shift on recoil. I discovered this when my groups when hairwire after a few sessions. I solved the problem by installing Talley Mounts. Rifle now shoots 1/2 moa with reloads. Draw a memory lines on the lines on the scope ring junctions and see if the scope is moving upon recoil.

Has the scope been mounted with the cross hairs level?

Patterns seen at 250 yards may not be evident at 100 yards or effectively just 40% of the distance.
Barrel conditioning and break-in comes to mind. Folks say that groups out of a brand new barrel improve after several rounds.

Gents,
Thanks for the thoughts and suggestions.
I can rule out parallax error at this stage.
I continued with further trial loads and now conclude that this rifle just doesn't like Barnes TTSX 165 gn projectiles. I'm very surprised as my other firearms shoot TTSX quite well. I have not yet tried 180 gn TTSX in this rifle but will do at some stage. I have switched to Hornady GMX 165 gn which seem more promising with AR 2209 ( H4350 ). So far with somewhere between 73 and 74 gns I get good groups at 100 yds and 250 yds. This weekend I will hopefully decide the final load by verifying accuracy at 100, 250 and 300 yds. None of the other powders I tried shot good groups at all. Perhaps this Tikka just happens to be a particularly fussy rifle....??

Replies to K22's question inserted below

quote:

You say you repeated this three times, same results. Does this mean that you reverified the groups at both 100 and 250 yards and got the same results or only at 250 yards?
Yes, reverified at 100 and 250 yds.

Are you shooting free recoil? Try holding the forearm.
I always hold the forearm.

Where is the rifle's stock positioned on the front rest? Make sure it's slight forward the magazine not out near the sling stud.

The front rest is usually near the sling stud. This generally seems to work well for me. However I will try your suggestion of positioning slightly forward of the magazine.

The scope level was checked with a levelling kit as I installed it. I rechecked this morning and no scope movement has occurred. Your comment re moving factory mounts is interesting as this happened on my T-3 30.06. I reattached the same factory mounts but locked all screws with a dab of Loctite and, so far, all good. With the TX3 300 Win Mag I was not confident the factory mounts would hold under recoil so I mounted the scope in Sako Optilock rings.

Custombolt,
155 rounds downrange so far. I presume that's enough to settle any new barrel kinks.
I always verify accuracy at the actual distances I intend to shoot because, as you say, good 100 yds groups are not a reliable indication of longer range accuracy. I leart that a long time ago, and learnt the hard way !

Well...then, you're only a hop away sounds like. If you don't already have one, here's a decent ballistic coefficient chart. Check out the old reliable Nosler Partitions, Accubonds and compare to other manufacturers including your TTSX. Happy hunting.
http://www.cbal.eu/bc.php