Amount (grs) of powder disparity

[Ironman675]

I am loading up some 308 with 175 smk for a ladder test using IMR 4895 powder. Two of my reloading books (Hornaday and RCBS) have a start throw of 33 grs but When I reference the IMR site the start throw is 41, My Hornaday book is showing the 41 in red. My test is in .5 grs increments with the last four rounds 38.5 - 41.0 marked red so I remember to inspect for any over pressure issues. The IMR site shows a 45 c grs as red. Does anyone have experience with this powder in a bolt gun and should I add a few more rounds above the 41 grs with carful inspection after each.
The rifle is a Savage BA 110

 

[aloreman]

We typically load 41.5 grains of 4895 in m1as. And we load towards the soft side. Start low and work up.

 

[918v]

I like 42grs in my rifle, but it depends on your barrel length and case capacity.

 

[Brux]

The bullet companies manual are always on the conservative side compared to the powder companies.As always start low and work up.You should find a low and a high accuracy node with your barrel.

 

[bigedp51]

Get the Lyman manual, the majority of loads in this manual are with a universal receiver and a pressure test barrel. These test barrels have SAAMI minimum chamber and bore dimensions and will generate the highest chamber pressures.

The Lyman manual with the 175 grain Sierra and IMR4895
Start load 39.0 grains, 2429 fps 43,100 psi
Max load 43.5 grains, 2693 fps, 59,400 psi

Firearm used Savage 12VSS
The Sierra manual with the 175 grain Sierra and IMR4895 (note 180 grain bullets on same page and same load data)
Start load 36.7
max load is 41.5

Hogdon's with 175 grain Sierra and IMR4895
Start load 41.0 2463 fps, 42,800 psi
Max load 45.0 Compressed, 2704 fps, 57,800 psi

START LOAD AVERAGE for the above three manuals is 38.9
MAX LOAD AVERAGE for the above three loads is 43.3

Start low and work up reading your primers like the photo below, start load on the left and working to the right.
And the last load on the far right is too hot and time to back down the load.

 

[918v]

The above photo can be replicated with a starting load, varying only the amount of time you allow the round to cook in the chamber. For example, the longer you let the round cook, the flatter the primer will get. So if you do your load development in the cold and maintain your chamber temperature at ambient levels, then primer reading can be accurate. If you are loading in the cold and let your chamber get hot, but don't let your rounds sit in the chamber for more than a few seconds before you fire them, then primer reading might have some merit. But if you allow the rounds to cook in the chamber, forgetaboutit. Primer appearance alone is meaningless without the consideration of all the variables affecting pressure.