case mouth vs. full length resizing
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243winxb
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FL size with bushing.
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Neck only sizing dies size down the case neck and the mouth inside of it.
Full length sizing dies size down the entire case from about 1/4 inch in front of the case head forward. This method has produced best accuracy with bottleneck cases for decades. Sierra Bullets proved that back in the 1950's. Case necks are better centered on the case body and shoulder this way because the case body, shoulder and neck are all held in perfect alignment when full length sized. Neck only sizing lets the case body and shoulder move around a little too much.
Forster full length dies with their necks honed out to .002" smaller than that of a loaded round are probably best so an expander ball isn't needed. Redding or RCBS full length bushing dies are a close second with a bushing so sized the same.
Just don't bump the fired case shoulder back more than .002" for bolt guns; .003" to .004" for other action types.
Full length sizing dies size down the entire case from about 1/4 inch in front of the case head forward. This method has produced best accuracy with bottleneck cases for decades. Sierra Bullets proved that back in the 1950's. Case necks are better centered on the case body and shoulder this way because the case body, shoulder and neck are all held in perfect alignment when full length sized. Neck only sizing lets the case body and shoulder move around a little too much.
Forster full length dies with their necks honed out to .002" smaller than that of a loaded round are probably best so an expander ball isn't needed. Redding or RCBS full length bushing dies are a close second with a bushing so sized the same.
Just don't bump the fired case shoulder back more than .002" for bolt guns; .003" to .004" for other action types.
spitballer
Member
Single shot .223 bolt action here. Neck size only. Replacement barrel has undersize neck, cases last forever; very little slop. Wilson neck sizer and chamber seater, arbor press from Harbor Freight.
Consider the fact that virtually all rifle matches and records are now won and set with full length sized cases. The benchrest folks finally switched to full length sizing not long ago. Match rifle folks shooting 3 position matches have done so for decades. Sierra Bullets has full length sized their cases testing bullets to accuracy since the 1950's. All with very long case life.
Of course, full length sizing done wrong won't do well accuracy wise.
Of course, full length sizing done wrong won't do well accuracy wise.
witchhunter
Member
Bart is right, almost all of the benchrest guys FL size. Those guys are OCD about their brass! Actually they are OCD about everything related to accurate rifles. I use both methods, usually neck sizing my pdog rifles like 223 just to get case life and because I don't have to lube cases (lazy). It seems crazy to do all that prep to a rifle with 6 or 8 thousand rounds through it, as long as it still shoots half minute. That being said, I have never had a full length sized round fail to chamber, so my deer rifle rounds are all FL sized.
spitballer
Member
Interesting, I didn't know this. Is this to insure uniformity among competitors, perhaps? Do most guys use fully standard dimensions to include neck size?
Mauser69
Member
I use standard RCBS dies for loading my .22-250, .270, .308, and .30-06, and I adjust them for only neck sizing. Have been doing that since the 70s when I started; I am totally happy with the results; I cannot foresee any reason to ever change.
Spitballer,
The reason full length sizing is so good for accuracy is it ends up centering the case neck better on the case shoulder. That in turn better centers the case neck and bullet in the bore when the round fires.
A .243 Winchester case neck and bullet will center just as straight in a .308 Win chamber as it does in a .243 one. Bottleneck cases headspacing on their shoulder center up front in the chamber when the case shoulder is pressed into the chamber shoulder. The case body touches nothing all the way around except for a single spot opposite the extractor where it's pressed against the chamber.
So, the consistent thing was cartridge uniformity. Benchresters learned, like so many others properly testing their loads for accuracy, their largest test groups were smaller with full length sized cases. There's a limit as to how small they can get and their tiniest ones' sizes didn't change much. One interesting fact that few people realise is the largest groups happen when all the variables add up in several directions. The smallest ones happen when those variables tend to cancel each other out or everything is perfect. So how do you tell which one of those two causes of the smallest groups was caused by and which one happens most often?
The reason full length sizing is so good for accuracy is it ends up centering the case neck better on the case shoulder. That in turn better centers the case neck and bullet in the bore when the round fires.
A .243 Winchester case neck and bullet will center just as straight in a .308 Win chamber as it does in a .243 one. Bottleneck cases headspacing on their shoulder center up front in the chamber when the case shoulder is pressed into the chamber shoulder. The case body touches nothing all the way around except for a single spot opposite the extractor where it's pressed against the chamber.
So, the consistent thing was cartridge uniformity. Benchresters learned, like so many others properly testing their loads for accuracy, their largest test groups were smaller with full length sized cases. There's a limit as to how small they can get and their tiniest ones' sizes didn't change much. One interesting fact that few people realise is the largest groups happen when all the variables add up in several directions. The smallest ones happen when those variables tend to cancel each other out or everything is perfect. So how do you tell which one of those two causes of the smallest groups was caused by and which one happens most often?
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It has nothing to do with insuring uniformity. Benchresters were always, and still are, folks who like to experiment, and that has always been encouraged, within the rules of course.
There is more to it than simply FL sizing of course, but most Benchrest competitors have been using FL bushing style sizers cut with reamers that did the chamber for some time. Everything fits very very tightly with little play, but the case is full length sized. I have two such sizers, as well as the old neck size/shoulder bump hand dies that were so common for a long time.
Walkalong, please explain the mechanics as to why a full length sizing die chambered and headspaced with the same reamer that chambered the barrel will shrink the size of a fired case from that chamber.
Are the fired case diameters and headspace greater than that of the chamber? I thought they would be equal too at most or smaller, otherwise the case would be hard to extract.
What am I missing?
Thanks.
Are the fired case diameters and headspace greater than that of the chamber? I thought they would be equal too at most or smaller, otherwise the case would be hard to extract.
What am I missing?
Thanks.
dirtykid
Member
I believe those reamers used to make those dies probably have under-sized dimensions, at least for overall neck diameter.. Standard factory chambers for a .30 cal are around .340 , where you can get them down to at least .336.. So your brass only expands .003 overall, instead of .008 or more.. I am not sure though if they shrink the other dimensions on the case ??
"Full length sizing" has traditionally meant reducing fired case diameters from the case pressure ring to the case mouth and setting the case shoulder back. A dimensional change of .0001" is enough to qualify.
To do that, the die has to have smaller dimensions than the fired case at those places.
To do that, the die has to have smaller dimensions than the fired case at those places.
No, I don't know the answer. Maybe I've got the intellectual version of SIDS.
I cannot figure out how a sizing die chamber that's the same size as a barrel chamber can full length size a fired case from the barrel's chamber.
Please help me, and anyone else wondering, understand the mechanics of how that happens. Disregarding the case neck as that part of a bushing die made with a chambering reamer will open up that part to let the bushing fit in. Just say it exactly right. I cannot read your mind.
I cannot figure out how a sizing die chamber that's the same size as a barrel chamber can full length size a fired case from the barrel's chamber.
Please help me, and anyone else wondering, understand the mechanics of how that happens. Disregarding the case neck as that part of a bushing die made with a chambering reamer will open up that part to let the bushing fit in. Just say it exactly right. I cannot read your mind.
243winxb
Member
Making a FL sizing die with a reamer.
Help for Bart B. Roughing reamers, or roughers, may be used to make a fitted sizing die. Perfect for cutting a full length sizing die They are a little smaller than a finish reamer. Reamer may also be made to your specifications. See post #3 here > http://benchrest.com/showthread.php?53897-roughing-reamer
Help for Bart B. Roughing reamers, or roughers, may be used to make a fitted sizing die. Perfect for cutting a full length sizing die They are a little smaller than a finish reamer. Reamer may also be made to your specifications. See post #3 here > http://benchrest.com/showthread.php?53897-roughing-reamer
Thanks, 243Win, for the info.
Wouldn't needed to do that had Walkalong been forthcoming with all the data in the first place.
When he stated
Some 'smiths don't use roughing reamers; instead increasing sizes of drill bits to remove most of the metal to enable minimum wear on the chambering reamer that makes the chamber its working size.
I feel better now knowing I don't have SIDS.
Wouldn't needed to do that had Walkalong been forthcoming with all the data in the first place.
When he stated
I took that to mean the reamer that made the chamber its finished size.
Some 'smiths don't use roughing reamers; instead increasing sizes of drill bits to remove most of the metal to enable minimum wear on the chambering reamer that makes the chamber its working size.
I feel better now knowing I don't have SIDS.
[email protected]
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You still have to account for the lubrication on a case that will cause it to be ever so slightly smaller than the chamber,it does take up a microscopic amount of space. Even with springback of the brass the cam action of the bolt would easily chamber the case.
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