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I'll try to keep this short but detailed. (Also note before reading this I like to be cheap, when I can be so I currently have varying brands of brass)

I screw in my Lee FL die, spray Hornady One Shot case lube on my cases, grab a case, insert it into my #2 shell holder that came with my dies, size the case and measure the shoulder with Hornady's Headspace Gauge with the C 375 insert and keep screwing in the FL die until the shoulder bumps back to 2.048". I grab the next case, put it in there and size away and it does not size to that. It will be like 2.046 sometimes, sometimes worse sometimes the same you get the point. It will not always bump the shoulder to 2.048 and it is driving me nuts. I have ruled out my calipers as a culprit. Also what makes Redding's competition shell holders special? From what I understand they allow you to gradually allow the case to go further into the die .002" at a time... What the heck is the difference when you can just adjust the die to go further over the case gradually by screwing it in... because some people say this solves the problem just like that but I don't get how. Also, for everyone who bumps their shoulder's back and has great success in doing so can you guys please comment exactly what you use?Tools, dies, lube, shellholders, etc. Also how might mixing a 2.048 with a 2.046 or 2.045 affect accuracy? I'd test this myself but am waiting on my surplus of bullets to get here.

And I must add, I'm sure most everyone else in these forums has experienced this already but I finally got a good load worked up and got sub MOA with a 70+ year old rifle. Should have seen the look on my face. Achieved by sizing each case individually adjusting the sizer for every single case so I could get that 2.048" every time. If no one has answers on how varying head spaces affect accuracy I'll test it out when my refreshment of bullets get here.
 

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I would suspect a different spring back of cases of different manufacture or perhaps even different lots from the same manufacturer. That and frankly, I don't see how .002 can make that much difference. I expect there would be at least that much variance when all the various dimensions between cartridge, chamber, throat and case body and neck thickness are accumulated.
 

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I use the RCBS case gauge. I take about five fired cases from the gun of interest. using the RCBS gauge I measure each one and come up with an average shoulder to rim dimension. I subtract a couple thousandths and adjust the height of the die in the press to get to that determined dimension. I size the lot, occasionally checking the sized brass. I find that the dimension can vary a couple thousandths either way (who knows why, it just does). I do all this on my Dillon RL550B used as a single stage press. I remove the sizing die when I progressive load these pre-sized cases. The trick is you never want the case shoulder to rim dimension too long as you may not get the bolt closed when the tolerance line up against you.

I don't have the those Redding shell holders (would not fit the Dillon if I did) so I have no idea of what they offer. I suspect it allows changing the shoulder to rim dimension for bumping while allowing an easy way to go back to conventional sizing repeatedly (??).

While you find your gun likes this approach, another gun may not. Every gun is different but it makes the most sense to get the bullet as close to the rifling as possible (without making bolt closure impossible). That may launch the bullet more central to the bore. Also part of this process is that the case body does not get sized all the way down to SAMMI specs, which will allow it to float around in the chamber and mis-aligning the bullet to the bore. This process does work in several of my bolt guns but it also requires keeping the cases with the gun for which the case was sized. This ammo may not fit (at all, let alone correctly) in another gun's chamber.

A 0.002 inch variation in the shoulder to rim dimension is not a problem in my experience. But all we do in reloading and shooting ammo in our guns can be masked by all the other variations in the act of shooting cartridges in guns. We only have control over a small portion of the variances.

LDBennett
 

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Unless the op is a match shooter, I don't think he has a problem. I've never measured rim to ogive, never had the tool and never saw the need. Being off the little he is should have no problem. The one thing I do do is make the case fit in the chamber easily. I've red a lot of guy's make the shoulder just barely touch. They guess that by how much drag is on the case closing the bolt. If you can feel any drag closing the bolt, your feeling the shoulder rub.
 

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Alright, I'll just do a quick test see if it matters and stop worrying too much about it. Thanks for the replies guys.
Sounds to me like you are 'over-thinking' the process. Also sounds like Don's comment about Match Shooting applies to what you are doing. Unless you are a competition shooter in a real Match - tolerances that you speak of mean very little.

You may already be aware of this, but one of the critical things to consider for shot-to-shot accuracy is consistency in everything. When you mention that you are reloading assorted brass cases - to the precise degree of measurement you describe - in my humble opinion all of you efforts are wasted if you are mixing brands/lots of cases.

Cartridge cases look the same on the outside. Often, they will measure the same on the outside after you process them for reloading. There are subtle differences in the interior dimensions of the cases (affecting case capacity/cartridge pressure on firing) and the brass alloy (affecting the physical performance of the case's neck tension on the bullet)- even from lot-to-lot from the same maker. You may assemble pretty accurate practice ammunition, but the very best ammunition will be with all of your components exactly alike. Good luck!
 
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