Home Forums Reloading Big Game Rifles Partitions / Seating Depth

I have been messing around some this summer with my 257 Bob and 115 Partitions. Based on other bullets in this rifle, I think I should be able to get a little better accuracy than I am seeing. It has been around 1-1.25" with 42.0 gr of I4350 or 44.0 gr I4831 with the chrono around 2825-2850 fps.

I was thinking maybe I should try to drive them a little faster or change my seating depth. Right now I am 0.020" off the lands. How far off the lands do you normally run Partitions?

Generally .020". I'm curious as to how far off the lands others run them as well...

Where I run almost everything, unless there is a clear advantage to doing otherwise...........010"-.020".

Obviously, some gun/mag length/bullet shape combinations dictate an occasional deviation as I may not be able to get as close to the lands as I would like.

I've never met a gun that shot best with long bullet jump.

MM

Affirmative on the bullet seating depth of .010"-.020". With the 115 gr Partition I get 1" groups at 100 yards in my two Bob's and 2845 to 2860 fps 43-44 grains of H4350.

There are bullets that generate better groups in those rifles, but for Whitetail and Mule deer I like the performance of the Nosler Partition.

So what's wrong with 1.25" groups? I assume you'd be using such a combo on deer? Yes, smaller groups would be nice but not at all necessary. I think you are good to go.

Well, since .020 isn't giving you the results you desire, maybe try .030 and .050, you never know, it might improve accuracy.

Generally I have not found them to be too fussy about seating depth...I have found them to be fussy about being seated "straight",so I worry more about runnout than OAL; and loaded hot enough to boot the base in the ass enough to obturate into the bore.

Might also be the powders I use with them do their best burn near max....but I have seen the same thing with stuff like 4064,so I suspect the bullets more than the powder.

I can't count the times that I did load workup with them,and saw them go from large groups to small as charges increased and got near max.

I have also seen 150-165's do less well than 180-200 gr 30 calibers in factory barrels where leade dimensions were sloppy...the heavier bullets seemed to jump the gap better.Magazine constraints prevented longer OAL.

BobinNH,
I can get to .040" off with the Nosler Partition Spitzer due to magazine restrictions. They shoot OK form a .300 Win. The Protected Point at .010" off shoots bug holes. Is the difference in BC going to be a factor in a hunting situation at < 400 yds. ?
Thanks,
Jim

Had a 30/06 for almost 20 years that drive 150gr Partitions into little bitty clusters at 300 yards. It didn't matter if the tube was cold or you could fry an egg on it, all right in there.

Oh yea, jump was .25", yep 1/4". No telling, one just has to play.

Jim: No, I doubt it.

Wind? Watch it with either one...started the same velocity and sighting, differences in trajectory will be pretty moot.Shoot them both at 400 and see how each groups. That will tell you....but shoot more than one group to be sure.

BobinNH,

I recall seeing you got around 3000 fps in the 257 Bob with 115 NPs. Most reloading manual data seems to reach max around 2850 fps with I4350 or I4831. I assume this is because of the "antique" pressures with some of the older rifles.

I am thinking I may need to increase my charge weights and push them a little harder.

What charge weights were you using with I-4350 or I-4831 to get those velocities?

Are you guys checking the OAL from the lands with a spent case and inserting a bullet or do you have a gauge?

Spent case/bullet route.

heschel: Yes we used to operate a 115 at those velocities; but those velocities were with what we called back then a " 3-inch Roberts"...this is a cute trick that JOC and Warren Page both played by seating bullets to 3" OAL,sometimes a bit more,supposedly allowing the use of a bit more powder,and therefore a bit more velocity.

We would alter factory throats and magazines to allow for the longer OAL. We used to get away with it pretty nicely but at what pressures I can't be certain today.

What the max for the 115 is with standard OAL and shorter throats I really can't say because all my use with the 115 was with the longer throat,but I suspect you are pretty close to max at 2850 or so.

Generally, what seating depth do you guys run 130 grain partitions in your 270s?

I loaded up 50 30-06 cases last year with R22 at .02 off the lands and every time to the range I bring them all home less about 5 or 6 rounds and seat .o25 deeper.....

I'm almost to the cannalure now....funny

If somewhere around .030" jump doesn't work, sometimes I go to seating one caliber deep in the case and that works well.
I am not a fan of pushing up to near jamb condition.
jmho
Tim

My experience with seating depth and the effect it has on accuracy has evolved over the past 15 years or so. With most bullets I don't think of it as being critical as I once did. What I see now as most important is loading ammo without excessive runout. Everything else is down the list. If you ammo isn't straight nothing else matters much. Not a high dollar barrel, expensive bullets, good scope, etc. Feel free to disagree.

In general, Partitions aren't all that sensitive to seatng depth variations due to their tangential ogive, and the tendency of the exposed rear core to "bump up" under pressure. But they're still bullets, so sometimes respond quite well to seating depth variations.

The longer, heavier models tend to be less sensitive to any variable than shorter Partitions, at least in my experience.

Mule Deer, it's mostly your fault that I'm so hung up on straight ammo. I used to be happy when my ammo went bang when I pulled the trigger. Then you started writing about building straight ammo and how important it is and now I give boring mini lectures at my local shooting range about how important it is. Just joking. BUT still there's some truth to it.