Factory vs. Reloading case capacity/density.

[longwinters]

When comparing cartridge/powder density in specific loads why is it that factory loads seem to always be over 90% but in my reloading books the "most accurate loads" rarely go to 90% or more?  I have read several times that ,generally speaking, the best loads for any particular bullet/caliber are the ones with the highest percent/density of powder to a case.  But this does not seem to follow in the reloading books. :?

long

[bigdaddytacp]

When comparing cartridge/powder density in specific loads why is it that factory loads seem to always be over 90% but in my reloading books the "most accurate loads" rarely go to 90% or more?  I have read several times that ,generally speaking, the best loads for any particular bullet/caliber are the ones with the highest percent/density of powder to a case.  But this does not seem to follow in the reloading books. :?

long

....Sometimes the factory loads are with a powder that is not available over the counter to the public.....and according to the cartridge most of my accurate loads do go over 90% density and some are even compressed a little but I try to avoid those if the gun will let me........some cartridges and powder combos are more sensitive to the density/bulk of the load....many highpower shooters can attest to the less than full density loads of the 30-06 and different powder placement causing accuracy/impact changes and the 308 being part of the solution to the powder density/location problem in shooting high power.....most benchrest cartridges are loaded to full density for most consistant accuracy....BUT there are exceptions to this but it seems to hold true for most cartridges of the smokeless powder design.....good luck and good shooting!!!

[Iowegan]

The reason a "full case" of powder usually perfoms more uniform than a "partially full" case is the surface area exposed to the primer flash. In a near full case, the primer "sees" only what's directly in front of the flash hole. In a case that is partially full, the powder will lay in the bottom exposing more powder to the primer flash. With recoil, the next shot will position the powder a little different and expose a different surface area to the flash. With each shot, ignition will vary causing chamber pressures to change and groups to spread.

A filler material such as polyester quilt batting can be stuffed on top of the powder before seating the bullet to control ignition drift. I've done this with large capicity cases when I didn't have a powder with enough bulk to fill the case. Chronographed results were over 150 fps spread without the filler and under 25 fps with the filler. The batting totally burns up and doesn't leave any residue nor does it increase the chamber pressure.

[longwinters]

I guess that I better get a couple more reloading books.  Like I said before, I look in my Nosler book and my Speer book and very few loads for any of the cartridges/bullet combos I use (243, 7m-08,308 and 7mm) list loads that go over 90%.  And if they do list them the loads are not shown as the "most accurate" nor do they usually match the velocities of factory ammo.  I understand what you all are saying about the benefits of a full cartridge.  And I have taken several different factory loads apart and never found any "filler".   :oops: I am still confused.  Then add to this that my rifles shoot under 1" groups consistently and I dont know if it is worth worrying about or not.  Yet I want my reloads to be the best I can make them . . . . .  I need a tutor.

long

[Iowegan]

Longwinters, You're right. Factory ammo won't have filler material, nor is it needed when you have powder bulk at 75% or more of case capicity. Filler is a good choice for "problem" rifles that shoot loose groups or for the gun you want to really fine tune. It will give your loads a more consistant velocity and that usually means better accuracy.

A customer brought me a Winchester Mod 70 in 30-'06 that wouldn't shoot better than 5" groups with several factory loads. I floated the barrel and made sure all the screws were tight then started with a known good load of Win 748, mag primers and 168 gr bullets. My load shot 3.5". I annealed the cases and seated the bullet out to .010 from the lands and that got it under 2". Then I added filler and the groups printed less than an inch.

In your case, when you have a rifle that shoots 1" or better groups, why bother with extra steps. If you've read some of my other posts, you will see that I'm obsessed with accuracy and will do whatever it takes to make a rifle shoot straight.