Looking for accuracy improvement - what charge increments?

[tacotime]

Trying to improve some loads for 45-70 350 gr. cast and .375 Mag 235 gr. jacketed.
Using starting loads from Speer and Hodgdon.  Groups not that good, maybe 2.5 to 3 inches at 100 yards, some powders worse.
 
Settling to IMR4198 for the 45-70 and IMR3031 for the 375.  Since this all takes time and money and wear on the shoulder, and I can't go up a tenth each time to test the dozens of loads in between, I need to cut to the chase to get to a decent group, say 1.5 inches or so. 
 
Assuming the brass is consistent, since I'm at starting loads, move up 1 grain at a time?  2 grains?  I mean, practically, how much of a bump is needed to noticeably affect accuracy?
 
I'm hard pressed to think that 0.1 or 0.2 grains will make a noticeable difference when we're talking about loads as large as 40 to 70 grains.
 
What's your method?
 
Thanks.

[SHOOTALL]

It depends on the most accurate load listed in the manual I'm using. In most cases I would go .5 gr. But if the most accurate load is not max I might go with 1 gr or with new well built guns to a gr under the listed load. Crimp can be critical also sometimes more so than a slight charge difference.

[mjyeagle]

with one gr you can go right past the sweet spot i do .3grs the primer,crimp and seating depth can also be a big factor that is often overlooked

[LaOtto222]

By making big jumps you can go right by the sweet spot...But If you make big jumps, you still can get an indication which is in the neighborhood and then refine your loads down. For instance, if you find that it shoots best at 38 grains of 4198, then refine it down to .2 grain steps between 37.5 and 38.5 to find the real sweet spot. Of it shoots 38 grains and 39 grains equally well then refine it down to .2 grain steps between 38 and 39 grains.

Good Shooting and Good Luck

[Grumulkin]

For cartridges of that size, I go up in 1 grain increments until I approach a maximum load at which point I go up in 1/2 grain increments.


In my opinion, if the sweet spots is so narrow that it necessitates 0.3 grain increments in order not to miss it, I'll want to use a different powder.  If said sweet spot is so narrow, it means that with most powders, a significant temperature change will change the load characteristics enough that you'll no longer be at the sweet spot anyway.

[huntswithdogs]

In most manuals, they'll tell you which loading was most accurate in thier test gun. This is usually what I start with though I back off a grain or 2 to start. If I'm using a powder other than thier most accurate, I never start with the listed starting load but hit somewhere in the middle. 5 shells at this load then upwards 1 gr at a time, paying attention to the group sizes.


HWD

[necchi]

FWIW taco,
 It get's easier once you get to know what your gun likes, but those first few times it's a good idea to follow the book an start low an work up.
 As others have said I start mid range of the book spread and then go up, I like to look at the top,,then where I'm going to start (beit where ever you want/need to start) and work  12-15 rounds in 3 shots per load.
 It might be a  2 tenth spread, it might be a 3 tenth spread or even a 1/2 grain spread.
 The book start or low weight is usually the lowest they recomend, funny things can happen with the powders if the charge is too low.
 Let's say the spread is 34 at the bottom and 38 at the top, I know the velocity at the low end (34) won't give me what I'm after, so I start at 36 I'll load; (this is of course after I've learned what the gun will take)
3@ 36
3@ 36.5
3@ 37
3@ 37.5
3@ 38
 
 Now thats only 15 rounds, each load group fired at it's own target, and somewhere in there one of those loads will be better than the others, let's say it was the 37.5 that showed promise. Now I'll go back and load (with big bores)
 37.3--37.5--(again just to prove it) and 37.7,
 That's only 9 more,, git it?  All that is gonna git me darn close to what the gun likes, all along looking for pressure signs and watching/feeling how the gun reacts. Alot of time my spreads will be 2-3 tenths and I find 2 or more accuracy nodes in the spread,  for hunting I'll usually choose the larger load/the one with the most velocity. Target loads might be the slower one because it's easier on me and the gun.
 
 The whole idea of "cut to the chase" at least for me isn't what loading is about, it's about finding the most accurate load for my gun. I've gone through entire boxes of bullets just to find out My gun don't like them bullets!?! 
 It's part of loading, and like I say it get's easier when you begin to learn what that gun want's.
Good luck,
 
 

[revbc]

Taco,

I use generally .5 increments.  Sometimes like with the 45/70 you can jump 1 gr to get in the ball park.

Here's ya a load for a 350gr jacketed.  Use at your own risk.  It's no where close to a max load, 45/70 kicks to much!!!!!!

[PowPow]

I use a 1% difference to find a sweet spot, then 1/2% either side of it to check.

On a 223 its works out to .2 grains, and then .1 grain.
On a 30-06;  .5 grains, and then .25 grains.

[tacotime]

Good guidance.  Thanks for the load also.  I was doing to many rifles at once, and could only test a few loads on each a week, then wait another week to test again and so on, and these big bores were pounding me, using 5 rounds on each load - hence the feeling I needed to cut to the chase.  Also, probably my benchrest method was probably sending me on a goose chase with unreliable results. 
 
Now I've limited the range session to no more than 2 rifles to develop for, and I think I'll go with the approach of mid range loads and then 3 rounds every 1/2 grain. That should reduce the round count and focus the effort...
 
Thanks again!

[SHOOTALL]

If ypu don't already have one you might look into a Nosler reloading manual. They list most accurate load . What I have experinced using their load is it works .