by TassieTiger » 17 Nov 2018, 2:12 am
I’ve just gone through this looong process myself with a 260.
I’m relatively new to reloading / shooting, so I asked for a lot of advice as I went, so My outcomes/findings may/may not be relevant but I think the process I followed might assist...
I attempted the bullet in the fired cartridge measure - but the projectile consistently got hung up in the barrel...So I smoked the projectile black with candle carbon and then looked at it under a mAg glass to see contact points as assisted with my mentor who is so old, he recalls when the titanic was but a dream...
Getting this part right is so critical because I’m the end your talking about very very small variations- and I’m still not convinced I got it 100% right...my coal ended up being LOT longer than saami and I had to dremel a tiny edge into my magazine to allow the longest bullets to cycle.
Anyway.
I settled on 45.5 grains of powder and loaded up 7 rounds each of 69.8 mm, 70.3, 70.8 and so on up to 71.90 (lightly touching lands - which I was cautioned on).
I load 7 rounds so I can fire the first round from the hip as a safety precaution and then 2 groups of 3 - second group to be a direct comparison to first.
My results really, really opened my eyes as to how critical bullet seating depth is. At least in this rifle but I suspect in most rifles results would be similar...
At 69.8mm coal, I was grouping sub moa...as I went along, grouping started getting bigger right out to 1.5 moa but then, as I got to the longer bullets, accuracy came back to me and by the time I was shooting rounds that were kissing the lands - my grouping was down to 10mm at 120m. Amazing difference.
I shot a group of 3 across all sizes allowing for barrel heat, captured my data and then repeated the same exercise to see if I was emulating results, which apart from a flyer - I was.
My problem now is obviously - my most accurate seating depth is touching the lands and pressure spikes are a real possibility so, do I back off .3 mm and live with slightly decreased accuracy or pull right back to 69.8 and let the projectile jump a couple mm’s - which in my “green horn” mind just seems wrong lol.
In regards to your 308 - I had a similar 30-06 that would shoot 2 bullets moa but the 3rd would always ruin the group. I was using 08 powder at the time - On local advice, i changed to 09 powder and the rifle just completely changed. It blows my mind how these tiny changes can impact - it’s fascinating to me at least lol.
I hope (am sure) there is a recipe out there to sort it and prove the old fella wrong.
I’ll be watching thread with interest - please post your results. Cheers TT
Tikka .260 (Z5 5x25/52)
Steyr Pro Varmint .223 - VX 3
CZ455 .22 & Norinco .22 (vtex 4-12, bush 3-9)
ATA 686 U/O 12g & Baikal S/S 12g.
Adler a110 reddot
Sauer 30-06 - VX 3
Howa 300 win mag. SHV 5-20/56
Marlin SBL 45/70