308Win Subsonic

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This is one groop I shot last year with my Sako AII 308Win. I’m trying to devellop a HP subsonic round that shoot sub MOA groops at 200m. I’m having a bit problem with this bullet, they tend to wabbel and give me oval hole in the paper. I have been testing at 125m at the range where i can set up my targets.

The setup is:

Sako AII 308Win
Hausken Supressor
IOR Recon schope
Chinese bipod
Beanbag baksuport shooting prone.

14x14cm paper targets @ 125m
Cronograph @ 3m (Chrony Beta)
Traget analyse with Range Buddy PRO

This load is:

Mould; TLC313-150-RF RG4 cavity 2GC 2PB (RD)
Bulle; PB powdercoated

Powder: Vihtavuori N32C 7.0 grain
Brass: Norma 308Win
Primer: CCI 250 magnum primer

The neck was expanded (with .309 x .305 Exp. Plug i think) 

V₀ about 320 m/s (I don’t have the crono data any more)

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[Full.Lead.TacoKeymaster]

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What’s the twist rate on your barrel?

[davidandersen]

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I have tried to mesure it, and the avrage of 20 mesurment was about 300mm (298mm i think). I think it might be a bit to slow twistrate but it is the orginal barrel made back i 1983…

I have NOT sorted the bullet buy weight, there can be airpocket in the ones that wabbel the most..

[Full.Lead.TacoKeymaster]

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If you are running bullets at slow speeds in a slow twist rate barrel, that might explain bullet stability issues.

[davidandersen]

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I just casted a few bullet to weigh, and 8 of 10 is within one grain, but the ones thats not are off by 2-3 grain. That might allso be a factor.

In stabillity calculator it come out with a GS of allmost 3 and 1,5 is supose to be gyro stabilzed. I know that the bullet  will be able to preforme in my rifle 0.93 moa 10 shot @ 125m is not bad. Just need to get ridd of the fliers

I’ve ordered two new moulds, HTC310-177-SP-BL2 2 cavity BT Brass and HTC310-173-FP RG4 cavity PB that i hope will do just as good I might order a shorter HP bullet later if I can’t get them to stabilize…

I’ve got some bullet that was shot in to gelatin and some in wather at 50m and 125m with the same load maby I will uploade pitcure of them.

Thanks for the response

David

[davidandersen]

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Photos added in first post.

The BNH of the bullets is about 12.5 BNH messured one year afrer it was shot on a bullet form the same batch as the red one.

The resolution in the photo is 40 division / mm exact (Calibrated AmSchope). The impretion is made with a Lee BNH die (27kg Ø3,96mm steel ball)

And a pitcure of my Sako AII 308Win

[Author]

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