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338 issues


Mac.308

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Hi all,

 

Having some issues grouping .338 home loads.

 

The best round I've used are the 252gr RUAG factory loads. Sub 1 moa groups at 100m at around 2530fps.

 

I've loaded up...

 

300gr SMK with 90gr N170 @ 2630fps (recommends by HPS)

250gr lock base with 87 & 90 gr RS70 at 2750 & 2830fps respectively

 

All the above come in at around 1.5 to 2 inch groups at 100m.

 

I hand loaded a load of the 300 SMKs and HPS did some for me also... same results.

 

With these loads I have worked them up and taken the best results with powder Qty. I've not just listened to someone me taken their load as gospel.

 

Tried some of my friends factory Hornady 250 HPBT at 2710fps and it grouped well also.

 

Running out of ideas to tighten things up. Any suggestions?

 

Don't entirely buy the "don't worry the round doesn't stablise at 100m" comment heard today

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Honestly could be many things from platform or load. If barrel, scope, mount and brake / mod are good I would check base of bullet is not seating into donut. Chrono data would help if you suspect the load.

 

Two things helped me lower ES a lot - case annealing and seating above the donut - hence load of 84.0 grains VV n165 with 250 grain scenar, mag primer and lapua cases. COAL 85.3 mm ( this is long to avoid the donut but doable in a CIP length AI mag). Accuracy 1/2 moa in my platform. I don't think lower ES at 100m makes a difference but I do notice it at 500m.

 

The 250 grain smk and scenar should be the easiest to find accuracy with and vv n170 or 165 will be kind on your barrel. If your mag and throat ( jump to lands 20 thou to soft seating) lets you seat past the donut you should be able to get a decent load.

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Any details on the rifle and the barrel's twist?

 

A mate of mine has owned a Sako TRG 41 (or 42) in .338 LM for some years. The first rifles were specified with a 12" twist which Sako later revised to 10". His Sako is a 12" version and he hasn't been able to get decent groups with 300 grain bullets yet, but most bullets in the 250 grain class produce good results at 100m.

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Sorry...

 

Total brain fart on the rifle details...

 

AX338

1-9.3 twist

26in barrel

AI brake

S&B 5-25

 

Absolute "laser" with 252gr RUAG factory loads travelling 770m/s.

 

Thanks

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Both me and Craig use AXMCs with similar loads vv n165, 250 grain scenars. I am as stated above using 84.0 grains - Craig a little less but he seats to a 93mm COAL for his lands. I am at 95.3 mm for the lands. The scenars shoot well for both of us at around 810 m/s @20c.

 

Our barrel lengths are a little different, Craig has the standard 27" tube and I have a factory 25" tube. We get very similar velocities over the chronographs. It is modest but accurate.

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Ah ok.

 

I've been running N170 but switching to RS70.

 

Think I may have to "dial down" he loads. I've been using 87gr of RS70 on the 250 lock bases and 90gr of N170 on the 300 SMK.

 

What distance are you and Craig reaching out too? What are your groups like at 100?.

 

Cheers

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Ds1 notes some good checks to make, just to rule out any possibilities it's gear related rather than your loads. If action screws are good, as are rings and pic rail screws, any muzzle device is on nice and tight, then look at the loads.

 

Personally I think you could push the 300SMK a bit faster than 2630fps - I'd consider trying to find an accuracy node higher up the velocity scale, but only if you're not already seeing pressure signs. The 250 lock base velocities look about right though.

 

What brass are you using? Trim length? What about your sizing methodology; neck or F/L sizing? What neck tension (bushing size) are you running, could it be too much or too little neck tension?

 

I'd say if all of the above is spot on, and you've eliminated some of the easier variables to control, it might be worth trying some different load combos.

What primers - are they the same as those used in the loads that perform well?

Have you tried loading other heads beyond the 300SMK or 250 lock base? Is it worth trying some 300 Scenars, 250smk or 285 Hornady ELDs? It does seem there's a bit of a pattern with your barrel favouring lighter heads - or is ot the faster powder that's normally used in conjunction with them that's the trick?

Different powders have been mentioned. Maybe worth giving a slightly faster powder than N170 for the 250s, N165 may work a bit better. Ask a friend for half a tub to try if you can.

 

Eliminate the simple, obvious things first, before you go about spending lots of time and money on more components.

 

Good luck!

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Hi Catch,

 

Defo not a gear issue as the factory loads fire really well.

 

I've tried 250 SMKs and 300 scenars too - wide groups again. Even with a handful HPS recommended.

 

I F/L size. Can't remember trim length off the top of my head but its within limits as per the book. I have tried ex mil brass, hornady once fired (I fired the round initially) and Lapua. Same results.

 

No idea on neck tension... not scientific but rounds "feel" the same on seating.

 

The RUAG fly slower and group really well... the hornady group well but launch around 2700fps.

Starting to think it's my s**t loading although I do the same with 308 and they fly really well - or the load itself.

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Hmm, puzzling.

 

When did you notice the poor groups - in the same shooting session as using the good stuff or during a different range trip? Did you use the same position / equipment when shooting the different loads (e.g. used bipod with rear bags on the good shooting but used a monopod (I'm not a fan personally!) for the bad groups)? Might be worth shooting altertive rounds (or a Round Robin) during one session to double check it's not your gear?? Shoot 1of your reloads, then 1 round of the stuff performing well. Repeat 5 times. Should be all the good stuff groups well and your reloads not. If that's definitely the case, then it's somewhere in your reloading process or load combination.

 

I'd say that if you're confident your gear is squared away and you're confident in your reloading process (you do note good .308 loads but worth double checking the scales, thrower if using, seating depth etc) only then I'd say it's got to be your reloading ingredients.

If you've tried different heads and brass, give some other powders a go (faster burning than what you've used already) or change up the primer (what are they btw?? I've had good luck with Fed GM215m).

 

Hope you find the cause soon.

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Hi bud,

 

Yep same shooting session, x5 RUAG, x5 300gr, x5 250gr, x 5 hornady, x5 RUAG again to confirm.

 

Last RUAG group the same as first. No position, bag or kit change.

 

I've tried N170 and just starting out on RS70 as easier to get and slightly cheaper.

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Throw the lock bases in the bin....

 

250 grain scenar.

 

82 grains of Vhit 165

 

Fed Magnum primer

 

Lapua brass [ don't use RUAG, you will get pressure problems ]

 

OAL 3.6"

 

This averages around 3/4" in my AW.

 

Anything under an inch is good in .338. Its not a benchrest cartridge, but a good load should hold moa out to at least 1000.

 

Ignore the " it won't stabilise at 100 , idiots "

 

If it isn't stable at 100, it won't be at 1000.

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Cheers Dave.

 

Having to switch from vit hence the load dev.

 

I do use lap and horn brass but just for info... no pressure signs on the RUAG.

 

Doesn't the AW and AX have a different twist rate? May be wrong but 1-11 springs to mind?

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