Hello all
I often recommend if a reloader plans on adjusting seating depth to fine tune a load . I tell them on initial load development to start at or in the lands and adjust off/back from the lands . The reason is that if the final charge is close to max pressure they still can adjust seating depth because they will be adjusting away from the lands likely reducing start pressures . Rather then if they were to start .040 off the lands and there final charge was again at max pressure . Moving the bullet closer to the lands can cause pressure spikes resulting in higher then recommended pressures . It also means you may need to move the bullet both directions which to me seems like more time may be needed to find your sweet spot .
So I've done this and it seems to work just fine . FWIW I've also seated closer to the lands after finding a good charge but must say I was a bit nervous doing so the closer I got to the lands Knowing the charge was only .5gr less then the manuals max charge . Anyways I'm still here and the gun is still in one piece so that went well I guess and I did find a really good load with the bullet just touching the lands .
That all said I have a couple questions on this method of starting at or even in the lands .
1) Does this have the potential of creating lower velocities across the board with the given components ? Meaning since in theory I'm creating a pressure spike not intended at the beginning of the ignition , does that cause any other pressure issues ( good or bad ) down bore ?
2) Assuming I am raising start pressure buy seating into the lands . When I adjust off the lands and those start pressures presumably drop/lower the further I get from the lands How does that effect pressures down bore as a whole and as it relates if at all to question #1 and that answer ?
3) and maybe most complex goes to harmonics and barrel time . Again assuming as I back off the lands the pressure/s drop will I be loosing velocity as I do so ? Even if I do and the groups improve do I care ? I mean that's the point of this theory of fine tuning , getting smaller groups correct .
4) what if my in the lands final charge give good accuracy but not great and backing off only get worse . I don't think you want to jam deeper to get better groups . What about backing off then upping the charge to get back up to the pressures I had seated into the lands thinking that puts me back in the same barrel time-ish area ?
But wait there's a 5th ) How much pressure and velocity swings should one see when playing with seating depth in the way I'm describing ?
I'm asking all this because I've really let my rifle shooting and reloading take a back seat to handgun loading and shooting for the last few years and I miss rifle shooting . Not just shooting but locking in and shooting for accuracy < ( real shooting not sitting the gun on a rest , pointing it at the target and touching the trigger ) My plan is to try a couple new component combos that I've never used before . This is for 308Win , I have 178gr BTHP and 175gr TMK and the powders are AR-comp and IMR-8208xbr . I haven't decided which bullet and powder combo's I'll start with but that's what I'll be using . FWIW with Lapua brass and Win primers . I have Federal match primers but the 400 of the 1k I've used so far did not seem to make a difference in other 308 loads . So I'm not interested in using them only to run out and never be able to replenish them cus they tend to be hard to get here locally and I have several thousand Win primer as well as CCI LR primers .
Well it's late and I feel like I'm rambling
Thanks
MG
I often recommend if a reloader plans on adjusting seating depth to fine tune a load . I tell them on initial load development to start at or in the lands and adjust off/back from the lands . The reason is that if the final charge is close to max pressure they still can adjust seating depth because they will be adjusting away from the lands likely reducing start pressures . Rather then if they were to start .040 off the lands and there final charge was again at max pressure . Moving the bullet closer to the lands can cause pressure spikes resulting in higher then recommended pressures . It also means you may need to move the bullet both directions which to me seems like more time may be needed to find your sweet spot .
So I've done this and it seems to work just fine . FWIW I've also seated closer to the lands after finding a good charge but must say I was a bit nervous doing so the closer I got to the lands Knowing the charge was only .5gr less then the manuals max charge . Anyways I'm still here and the gun is still in one piece so that went well I guess and I did find a really good load with the bullet just touching the lands .
That all said I have a couple questions on this method of starting at or even in the lands .
1) Does this have the potential of creating lower velocities across the board with the given components ? Meaning since in theory I'm creating a pressure spike not intended at the beginning of the ignition , does that cause any other pressure issues ( good or bad ) down bore ?
2) Assuming I am raising start pressure buy seating into the lands . When I adjust off the lands and those start pressures presumably drop/lower the further I get from the lands How does that effect pressures down bore as a whole and as it relates if at all to question #1 and that answer ?
3) and maybe most complex goes to harmonics and barrel time . Again assuming as I back off the lands the pressure/s drop will I be loosing velocity as I do so ? Even if I do and the groups improve do I care ? I mean that's the point of this theory of fine tuning , getting smaller groups correct .
4) what if my in the lands final charge give good accuracy but not great and backing off only get worse . I don't think you want to jam deeper to get better groups . What about backing off then upping the charge to get back up to the pressures I had seated into the lands thinking that puts me back in the same barrel time-ish area ?
But wait there's a 5th ) How much pressure and velocity swings should one see when playing with seating depth in the way I'm describing ?
I'm asking all this because I've really let my rifle shooting and reloading take a back seat to handgun loading and shooting for the last few years and I miss rifle shooting . Not just shooting but locking in and shooting for accuracy < ( real shooting not sitting the gun on a rest , pointing it at the target and touching the trigger ) My plan is to try a couple new component combos that I've never used before . This is for 308Win , I have 178gr BTHP and 175gr TMK and the powders are AR-comp and IMR-8208xbr . I haven't decided which bullet and powder combo's I'll start with but that's what I'll be using . FWIW with Lapua brass and Win primers . I have Federal match primers but the 400 of the 1k I've used so far did not seem to make a difference in other 308 loads . So I'm not interested in using them only to run out and never be able to replenish them cus they tend to be hard to get here locally and I have several thousand Win primer as well as CCI LR primers .
Well it's late and I feel like I'm rambling
Thanks
MG
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