Loading 'off center' in chamber

[BarryL]

Ive had something rattling around in my head for a little while now. We work quite dilligently to get our loads as concentric as possible with fireforming then neck size only and checking with a run out guage etc. etc. The round chambers and fires expanding to chamber spec then springs back approx. .001". We prep load and fire again. Near as I can figure this case chambers and lays on the bottomof the chamber with approx. .002" around the top and nil on the bottom. We jam into the lands which probably helps some but the case still sits off a thou or two in the chamber. Unless the bolt face grabs the case head with "0" clearance and centers the round as it cams into place the load cant be centered with the bore. Am I out to lunch on this or is there something to it?

 

[fivering]

Your thinking is pretty much right on.
This situation can be greatly reduced by using the neck sizing bushings adjusted so a little of the neck remains unsized right above the shoulder of the case. Combining this with seating the bullet so it engages the lands a few thousandths at least ensures that the bullet starts down the barrel parallel with the axis of the bore.

 

[BarryL]

I see where only sizing the first 3/4 or 2/3 of the neck would help with this if the expander ball was large enough that this portion would jam. What about the case head area? Wouldnt this still have some slop in it unless the bolt face and extractor held to center and had .000" clearence?

 

[jthyttin]

Also keep in mind that spring-loaded ejector plunger,if present) "preloads" the case somewhat.

Anyway, I have more serious problems affecting my accuracy than any of these...

 

[Preacher]

When the case is seated in the chamber and the bullet is engaged into the rifling it will straighten out that little bit thats loose, considering that the bolt head is flat, and that helps to keep it straight in the chamber too...
Very few br dies use a expander button either......

 

[Cheechako]

Barry

There has to be a certain amount of clearance between case and chamber walls otherwise the cartridge could not be loaded. And yet, in spite of this clearance, Benchrest shooters continue to make those tiny one-hole groups.

Bottom line. Don't get anal about it. One little failure to correctly read the conditions will enlarge your group a zillion times more than .001" of chamber clearance.

JMHO

Ray

 

[LHSmith]

I believe the "base" of the case, where the solid portion, i.e. "web" is located) is conformed to whatever the rifles chamber dimension is,less a few ten thousandths spring-back)upon the first full-load firing------fireformed cases may take 2 or 3 firings.
Therefore the cartridge head has very little "slop" in the chamber.....assuming your using a standard sizing die which does not touch the base.

I would be more concerned that the barrel chamber was concentric to the throat and the bolt face remained square to the case head-----especially during firing......which excludes 99.9 % of factory rifles.

 

[bsekf]

In a break open gun if the case is a little long and it rubs on the breech block when closing, you may get stringing. However, I would think in a bolt gun and careful reloading, the case is going to lay in there the same way every time and the accuracy will not be effected much. The ability to read conditions is the secret.

 

[BarryL]

Thanks for clearing that up. With dead calm, early morning cool conditions my rifle/load has shot sub 4" 5 shot groups at 1049yds. This year I guess I'll work on reading wind and mirage.

 

[LHSmith]

I have edited my post,#7, to clear up a mis-statement.....after re-reading an article on this site by Jim Carstensen, some specialized sizing dies can INDEED resize the case up to the extractor groove.