Textbook or app? Which to trust?

[wildfowler.250]

So I’m basically reviewing my .270 loads. Currently shooting some Sierra prohunters 130 grain with 57.5 N160. OACL 3.30”. Group well.

Im going back to some development with accubonds,(typically lost my old targets) because they performed well but 1” groups.


The Viht app says a max load of 58 grains of N160 for 130 grain bullets. But a OACL of 3.228.

This is a higher charge in a in a shorter case than what The Sierra textbook says. Sierra text recommends max of 55 grains at an OACL of 3.32,(so assuming less pressure with the longer bullet and less charge).

Im tempted to work up loads at the longer 3.32 OACL as per the Sierra text but work up charge again from 55 grains to 58 as per the Viht app - I assume they will know best regarding the powder. I’ve not had any problems with the higher charges using the prohunters either.

Any suggestions? Am I looking to drive them too fast,(no chronograph). I got excellent groups with 52 grains but sooty cases do that was a no go. I’m thinking 55-58 going up 0.3 grain jumps to 58?

Thanks!

 

[wildfowler.250]

App

 

[Miki]

I had a batch of sooty cases. It turned out I was resizing them to small (for my chamber) and the brass was hardened.
A headspace gauge, and 1/2 a turn out of the FL die sorted that problem. I also anneal now but my sooty issue was 90% the case length.

If you seat the bullet less (ie lengthen the COAL) then you increase the internal volume which reduces the pressure spike and the distance to the lands. All of this alters the moment at which the bullet and the 'wobble' arrives at the muzzle. Get the bullet to arrive at a null point and your groups will be small. The 100fps difference (between the 'book' min and max MV) won't make a huge difference to your ability to hit/dispatch what you were aiming at.

 

[wildfowler.250]

I had a batch of sooty cases. It turned out I was resizing them to small (for my chamber) and the brass was hardened.
A headspace gauge, and 1/2 a turn out of the FL die sorted that problem. I also anneal now but my sooty issue was 90% the case length.

If you seat the bullet less (ie lengthen the COAL) then you increase the internal volume which reduces the pressure spike and the distance to the lands. All of this alters the moment at which the bullet and the 'wobble' arrives at the muzzle. Get the bullet to arrive at a null point and your groups will be small. The 100fps difference (between the 'book' min and max MV) won't make a huge difference to your ability to hit/dispatch what you were aiming at.

Cheers for the help! The 52 grain sooty load was with new brass but I moved past it as there should be other nodes anyway.

Just a little surprised there’s a 3 grain difference between the max N160 load in the Sierra textbook and on the Viht app? Are the texts more likely to be conservative?

 

[Sonicdmb73]

Cheers for the help! The 52 grain sooty load was with new brass but I moved past it as there should be other nodes anyway.

Just a little surprised there’s a 3 grain difference between the max N160 load in the Sierra textbook and on the Viht app? Are the texts more likely to be conservative?

The Vihtavuori app will be up to date data for current powders.
However in the past Vihtavuori used to publish a PDF with the data and year to year they changed slightly. The advice from them was to use the data for the year of manufacture of the powder.
I had some N140 the difference was a good grain for the bullets I was using between new powder and the bottle I had.

 

[wildfowler.250]

The Vihtavuori app will be up to date data for current powders.
However in the past Vihtavuori used to publish a PDF with the data and year to year they changed slightly. The advice from them was to use the data for the year of manufacture of the powder.
I had some N140 the difference was a good grain for the bullets I was using between new powder and the bottle I had.

Thank you, that’s an interesting aspect. I’ve updated the app regularly but didn’t think there would be any real change between years or thought they would have been rebranded. Cheers!

 

[Sonicdmb73]

Thank you, that’s an interesting aspect. I’ve updated the app regularly but didn’t think there would be any real change between years or thought they would have been rebranded. Cheers!

Not much from one year to the next. But there is if there’s a few years gap.
Good practice states you should work your load back up if you change powder lot number. In practice not many people do.