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Hello all

I'm a new member (just introduced myself in the Newbie section) with decades of reloading experience but also with a puzzle.... I wonder if anyone can offer a thought?

One of the calibers I shoot is .243. When I'm not target shooting I'm a deer stalker (maybe it's the other way around) and so my .243 is a reasonably (operator error aside) consistent sub .5MOA group shooter and my go-to Muntjac rifle. I never use factory ammunition: my default head is a 90g Nosler Ballistic Tip and I use N160 to push that comfortably beyond the required muzzle energy minimum. I use a V2 Autotrickler with an A&D Fx 120i, Redding competition dies and routinely trim cases, measure headspace and keep on top of the details. So in theory I know what I'm doing. Haha.

At the moment the 90g Nosler is unavailable. So I decided to buy a few hundred 90g Sierra Gameking Tipped, the so-called Gamechanger. Ordinarily I would work up a load using QuickLOAD and my Labradar chronograph but I got lazy and decided to try 20 rounds using the same load as I use with the Noslers. I felt there was a fair chance the results would be worth looking at, even though I knew that finding exactly the right load might take longer.

At Bisley last weekend on Short Siberia I shot three other rifles before getting out the .243. I was having a 'meh' morning: I was a bit tired. But with the Noslers I held a few reasonable groups and then loaded 5 rounds of the Sierras. First shot was so wide of the mark I didn't notice it. Each subsequent shot landed in a different place relative to the target (a patch) and the average distance from the patch to each bullet hole was around 5 inches. Holes were round, no suggestion of tumbling. My moderator was untouched. I fired five more Noslers, got a half inch group. Then fired a second batch of Sierras and got a nine inch group.

Now, maybe I've lived a charmed life and groups like that happen to everyone now and again. But I've never seen one. I know what I'm going to try - the bullets were (are) incredibly long (2.4mm longer than the Noslers) and seated the same distance from the lands, the Sierras cause the overall cartridge length to exceed the SAAMI maximum. So I am going to take the back to the standard and start from there. I may also try a few different loads, but I don't like messing with more than one variable at a time so that will come later.

Question is, am I missing something? The heads themselves seem fine (albeit with a surprising weight range from 90.02g to 90.16g) so I'm ruling out a duff batch. I think it has to be how they're seated but can anyone offer another view please?

This might be your problem.....

I believe this is a known problem with 10:1 twist 243 rifles using the new sierra gamechanger 243 rounds 90gr. the bullet needs a 9 twist to stabilize properly see https://www.sierrabullets.com/product/6 ... 90-gr-tgk/. Some people have been lucky with a 10 twist but is a 50% lottery if it works or not. My target 10 twist 243 was ok with it. There are unofficial fixes for it as well.

Ha! Bingo. Well, sounds pretty much like bingo anyway. Not a detail referenced in the spec when I bought them (but to be fair I didn't go onto the Sierra website to explore further). Thanks, I much appreciate you replying.

Strange isn't it. I have a Tikka T3 Hunter that can shoot 100grn SPs but my friend who has the same rifle can't shoot anything above 90 grn.

Graham M wrote: ↑Thu Nov 11, 2021 5:15 pm Strange isn't it. I have a Tikka T3 Hunter that can shoot 100grn SPs but my friend who has the same rifle can't shoot anything above 90 grn.

Yes, that sounds familiar. When I acquired my Sako 85 in .243 I defaulted to 100gr heads but using N160 always fell short of 1700 ft lbs for stalking because of the need to avoid excessive pressure. Dropping back 10gr made the difference. I'm about to try old school Speer 85gr spbt heads so that should be interesting.

Strange isn't it. I have a Tikka T3 Hunter that can shoot 100grn SPs but my friend who has the same rifle can't shoot anything above 90 grn.

It would be interesting to know if you both clean your barrels the same way?



(but to be fair I didn't go onto the Sierra website to explore further).



The addon of 9 twist on the sierra website was only added later after complaints when they looked into it !!. In an effort to produce a more efficient bullet you need cp/cg ratios to be closer together but if you go too far it becomes unstable.

Before you knock yourself out was it electronic targets ? we were at Bisley on the 600 and my 6.5 was shooting shotgun size groups(after 3 others had shot ok , until we tried the target next door ..

Dellboy wrote: ↑Fri Nov 12, 2021 11:16 am Before you knock yourself out was it electronic targets ? we were at Bisley on the 600 and my 6.5 was shooting shotgun size groups(after 3 others had shot ok , until we tried the target next door ..

Good thinking, but no, I was on Short Siberia shooting at 20mm patches on an otherwise clean target face, so able to monitor each shot. Sounds like you had an interesting time! I'm going to be shooting at 600 in the next few weeks: maybe I'll have a human marker...

Peter Leigh wrote: ↑Fri Nov 12, 2021 7:33 am

The addon of 9 twist on the sierra website was only added later after complaints when they looked into it !!. In an effort to produce a more efficient bullet you need cp/cg ratios to be closer together but if you go too far it becomes unstable.

Hmmm. That sounds like rocket stuff? Clearly applicable though but a bit much for my brain. What I do know is that a very long bullet will take more work to stabilise it, so it's surprising/depressing that (if your point about an addendum to the Sierra website is accurate) it took users' complaints to prompt Sierra to add the information. It was quite surreal watching the bullets striking in such a random pattern, given the consistency of sight picture and trigger release.