C.O.A.L. and Datum line

[Pogy Bait]

In the data books I have , They give you c.o.a.l. for each bullet. But if you want to find lands ( datum line ) and come off .06 or .010 off lands you can"t seat bullet into neck of case enough to secure bullet . In my setuation , I'm seating a bullet , hornady #3142G into case 7.62x39 and would like
to be .06 to .010 off lands but I can not because if I do I"ll have less then 1/4'' to hold bullet in case.

Please respond to my Request -thanks

 

[David Christian]

Give us more details. How did you find your lands length? Why and how did you choose a seating depth of .006 to .010 off lands?

 

[Kurz]

and come off .06 or .010 off lands you can"t seat bullet into neck of case enough to secure bullet

In my setuation , I'm seating a bullet , hornady #3142G into case 7.62x39 and would like
to be .06 to .010 off lands but I can not because if I do I"ll have less then 1/4'' to hold bullet in case.

".06" is actually 60 thousandths. The assumption above is .006 or 6 thousandths.

According to my drawings, the neck length is only 0.225" long in the first place, so your 1/4" is actually fine. This is a VMAX, ZMAX or SST bullet with a cannelure also depending on which company is marketing it:

The 'normal' handling of these bullets is to crimp into the cannelure when shooting in a semi-auto firearm. I have never shot this bullet or that cartridge but according to a couple of buddies, the bullet is more than reasonably accurate and has been used for hunting...

 

[mikecr]

There is nothing wrong with less than 1/4" of bullet bearing in necks. There is nothing wrong with sizing or seating only 1/8" of necks.

If your goal is for some reason to be ~10thou off, which I'll assume is regardless of best coarse seating, then you'll need to measure touching and go from there. Books won't help a bit.
Make a dummy round

 

[RegionRat]

And just to add a little more to help confuse you...

There are general rules which implies that there are exceptions... That means some cartridge designs may have characteristics that don't follow a rule at all or maybe not very well. Take for example a 7.62x39 where a 123 grain bullet may not have a very long bearing diameter and doesn't lend itself well to being seated to jam. On the other hand, something like a 6 BR with a bullet that has a very long shape has no problem being seated jammed. That story is just to point out that we need to be patient and gain some experience with any particular design.

If you are loading for a semi-auto, you have a set of considerations that might include a few different ones than for a bolt action. The difference between the two can lead to different advice for a given cartridge. Even a 308 WIN has different avenues between the ones we use for a bolt gun versus a gas gun. There may be some common ground, but up front it helps to know the context we are using and the goals.

 

[Zero333]

1/4" (0.250") of bullet shank below the case mouth is more than enough for 7.62x39 semi auto rifles as long as you have at least 0.0015" of neck tension. Most FL dies with expander button give between 0.0015" and 0.002" of neck tension. Most of it depends on the brass neck wall thickness.

Don't overthink it and just load them and shoot !

 

[dcali]

How much effort to put into this depends on what rifle you're shooting. If it's an AK or similar semi auto, seating depth is not going to matter much - they're just not very accurate. If it's a mini 30, throw it in the trash. But as others said, 1/2 a caliber is more than enough to hold the bullet.

 

[Pogy Bait]

Give us more details. How did you find your lands length? Why and how did you choose a seating depth of .006 to .010 off lands?

my rifle is bolt action 527 CZ 7.62x39,I shoot anumber of different bullets , and I use Hornaday comparator to find my lands,
when doing this I start with .10 thousands off lands but most bullets are shorter or smaller and I think I don't have
enough of bullet into case neck .

 

[spclark]

With anywhere from 0.002” - 0.004” neck tension (maybe less if your brass is processed consistently enough to be predictable in sizing) .30 cal bullets only need maybe 1/8” - 0.125” - of the bearing surface seated into the necks.

In fact even as little as 0.10” - 0.06” is enough if you handle your loaded rounds carefully so as to avoid bumping the bullets on things... plays hob with concentricity if hard enough of a bump bends that little bit of case mouth.

 

[Pogy Bait]

With anywhere from 0.002” - 0.004” neck tension (maybe less if your brass is processed consistently enough to be predictable in sizing) .30 cal bullets only need maybe 1/8” - 0.125” - of the bearing surface seated into the necks.

In fact even as little as 0.10” - 0.06” is enough if you handle your loaded rounds carefully so as to avoid bumping the bullets on things... plays hob with concentricity if hard enough of a bump bends that little bit of case mouth.

Thanks guys for your help, I though a bullet must be aleast 1/4 or 3/8'' into case neck,

 

[spclark]

Proof:

http://bulletin.accurateshooter.com/Stan_Ware