G'day Bushwackr,
Funny you ask this question, I just picked up my order of 8lbs of Retumbo and 2 boxes of Nosler 140gr Accubonds yesterday.
I've got the following load to test:
Win brass.
Fed 215 primer.
Retumbo @ 61gr, 62gr, 63gr and max 64gr.
129gr Accubond LR.
Win brass.
Fed 215 primer.
Retumbo @ 65gr, 66gr, 67gr and max 68gr.
Stick with whatever your rifle allows when it comes to COAL, have you got a case you can use to check for rifling engagement length? I split a case on 2 opposite sides and use it to determine where each bullet is touching the lands. You can also use a flat based bullet in backwards to determine ROUGHLY your throat length in a real number, but it will be out by the amount of radius there is on the bullet heal. If you've been running 3.340", then try a dummy round to make sure it's not touching the rifling.
I'm also going to try identical loads with WLRM primers to see if they tighten up at all.
I had my throat cut to .220" to suit the 129gr Accubond LR, which gives me a COAL @ 3.400" so I can burn a bit more powder, or the same with lower pressures.
The above loads are from the ADI website, rounded up by .5gr, they should still be safe as long as you work up. If you feel more comfortable, you can reduce the start loads to 10% of max if you wish.
Cheers.
gun)