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  #11  
Old 01-17-2019, 04:25 PM
WindLogik WindLogik is offline
 
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For what it's worth, mid and nancy tomkins advocate full length sizing in their book. Even for f class.
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  #12  
Old 01-17-2019, 04:33 PM
rcolarco rcolarco is offline
 
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Quote:
Originally Posted by WindLogik View Post
For what it's worth, mid and nancy tomkins advocate full length sizing in their book. Even for f class.
Just two of the best long range high-power shooters in the world, but what do they know?

How can I justify spending all this money on comparator gizmos?
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  #13  
Old 01-18-2019, 02:55 PM
Pinecone Pinecone is offline
 
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Bumping the shoulder back IS full length resizing. Just not sizing all the way down to SAAMI specs.

Versus neck sizing, it does reduce the body diameter a bit.

The idea is, you chamber may not be exactly symmetrical and cylindrical. So by some some sizing of the body, you are not introducing a problem when the round is chambered partially rotated from when it was fired.

Yes, if you don't size enough, you can lock up a rifle. I have one AR-15 with a very tight (but it meets specs) chamber. My reloads were a bit long at the shoulder and would not function in this rifle, but factory would. On a Wilson case gauge, the reloads were flush with the step, but this rifle required flush to the bottom indicator.

That is my the normal recommendation is 3-5 thousandths should bump for semi auto.
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  #14  
Old 01-18-2019, 03:47 PM
rcolarco rcolarco is offline
 
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Quote:
Originally Posted by Pinecone View Post
Bumping the shoulder back IS full length resizing. Just not sizing all the way down to SAAMI specs.

Versus neck sizing, it does reduce the body diameter a bit.

The idea is, you chamber may not be exactly symmetrical and cylindrical. So by some some sizing of the body, you are not introducing a problem when the round is chambered partially rotated from when it was fired.

Yes, if you don't size enough, you can lock up a rifle. I have one AR-15 with a very tight (but it meets specs) chamber. My reloads were a bit long at the shoulder and would not function in this rifle, but factory would. On a Wilson case gauge, the reloads were flush with the step, but this rifle required flush to the bottom indicator.

That is my the normal recommendation is 3-5 thousandths should bump for semi auto.
Well, yes.

However, what everyone must keep in mind is most semi-auto rifles (the M1 included) have no primary extraction leverage. They rely on generous chamber size and brass springback to free the fired case so it can be extracted. As Pinecone writes, don't size enough and you will have a locked up rifle. I have seen it many times. Believe me, if it happens to you, you will not be doing the happy dance.
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  #15  
Old 01-18-2019, 03:57 PM
cranehunter cranehunter is offline
 
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I've been loading for over thirty years, read countless manuals, easily over 100K in rounds loaded. Handgun, rifle, shotgun. Several calibers and gauges. I still don't see the need to try to out engineer the basics. If it ain't broke, don't fix it.

Load, shoot, repeat.
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  #16  
Old 01-19-2019, 10:44 AM
Unclenick Unclenick is offline
 
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Quote:
Originally Posted by Pinecone
Bumping the shoulder back IS full length resizing. Just not sizing all the way down to SAAMI specs.
As I pointed out, that's newer jargon developed either by persons who did not understand the bump concept or who wanted to make a commercial die they could claim was a bump die. The original meaning was to shorten head-to-shoulder length without affecting body diameter, but that takes a custom die cut with the same reamer used to chamber the rifle. An acquaintance of mine recently called Forster on this because they produce a sizing die they call a Bushing Bump Die. They had to admit, though, that it actually does narrow the case body some. It's just a maximum diameter spec FL die, apparently.

I have no idea who started using 'bump' to mean a stunted FL sizing operation. We used to call that "setting the shoulder back" by a desired amount. Maybe 'bumping' was misappropriated just because it is shorter and therefore easier to say. Or maybe it was Forster wanting to produce a die with that name, even though you can't produce a die that matches all chambers. I don't know.

What has called the whole idea into question is that a lot of folks have found they get better accuracy, even in benchrest bolt guns, from the partial resizing or even from body die sizing a little shorter than as-fired. Some of the benchrest competitors use just -0.001". The idea is the cone of the shoulder will self-center the case in the chamber for better bullet alignment, but that does require you narrow the whole case at least a little bit to have the lateral wiggle room available for the case to center. Some using bushing dies also back the bushing retaining plug out so a little of the necke retains near-chamber diamter near the shoulder, also to help center the caset.

But none of those techniques is semi-auto friendly. They are for slow, careful chamber in a bolt gun.

Incidentally, Tompkins's comment about FL resizing requires context. I attended their LRFS (Long Range Firing School) twice. Mid said they seat to set headspace on the bullet with it in contact with the lands. By sizing their necks so the bullet can be moved by finger pressure, they seat very long so the bolt finishes seating the bullet in the chamber when they load. That is another way of getting the bullet lined up. Whether or not FL sizing without also centering the bullet can equal the other centering methods, I don't know, but it is at least still pretty good, the self-centering of the case shoulder in the chamber shoulder when the firing pin and pistoning primer drive the cartridge forward being the reason. But as A. A. Abbatiello showed with his 40-odd lot sample of National Match ammunition tested back in the 60's, it then makes a significant amount of difference that you keep the loaded rounds concentric and don't have more than about a thousandth of bullet tilt in the loaded round.

Bottom line: the most accurate ammunition possible always seems to wind up requiring you to mind some details somewhere along the way.
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  #17  
Old 01-19-2019, 12:30 PM
WindLogik WindLogik is offline
 
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My comment before, about Tompkins' wisdom, was in response to comments on neck sizing only, and not so much regarding bumping. I do not neck size at all. I have tried it and not seen a benefit. Off topic, I do "bump" in a sense, for my prone-only Palma rifles and mid range guns. The "bump" though, oddly, is .001, and the chambers are so close to go that this brings them back to zero on a gauge. Very meticulous smith! I do think that concentricity and neck tension "do stuff" for long range, and I think it can be seen in a bolt gun.

From the Tompkins book:

Quote:
Therefore, in order to return the case to factory specifications, it must be full length sized. If it is not properly resized, the brass might touch the side of the chamber, which can cause the bullet to be misaligned with the center line of the bore.
IN THE CONTEXT OF PALMA AND F CLASS

Quote:
The shoulder of the fired case should only be moved back .001 inch during sizing. This allows the case to fit loosely in the chamber while only causing minimal stretching on each firing.
Mid is an outspoken, pragmatic man. I'm very certain he'd loudly say that a complete full-length sizing of brass for service rifles (or service rifle actions) is the preferred method. When I say complete full length sizing, I mean that the die is cammed over and the sizing is such that the resulting case is at or smaller than GO. I doubt very much that Mid likes dealing with alibis due to jammed rifles in XTC matches.

Last edited by WindLogik; 01-19-2019 at 12:34 PM.
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  #18  
Old 01-21-2019, 09:58 AM
Pinecone Pinecone is offline
 
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Quote:
Originally Posted by Unclenick View Post
As I pointed out, that's newer jargon developed either by persons who did not understand the bump concept or who wanted to make a commercial die they could claim was a bump die. The original meaning was to shorten head-to-shoulder length without affecting body diameter, but that takes a custom die cut with the same reamer used to chamber the rifle. An acquaintance of mine recently called Forster on this because they produce a sizing die they call a Bushing Bump Die. They had to admit, though, that it actually does narrow the case body some. It's just a maximum diameter spec FL die, apparently.

I have no idea who started using 'bump' to mean a stunted FL sizing operation. We used to call that "setting the shoulder back" by a desired amount. Maybe 'bumping' was misappropriated just because it is shorter and therefore easier to say. Or maybe it was Forster wanting to produce a die with that name, even though you can't produce a die that matches all chambers. I don't know.

What has called the whole idea into question is that a lot of folks have found they get better accuracy, even in benchrest bolt guns, from the partial resizing or even from body die sizing a little shorter than as-fired. Some of the benchrest competitors use just -0.001". The idea is the cone of the shoulder will self-center the case in the chamber for better bullet alignment, but that does require you narrow the whole case at least a little bit to have the lateral wiggle room available for the case to center. Some using bushing dies also back the bushing retaining plug out so a little of the necke retains near-chamber diamter near the shoulder, also to help center the caset.

But none of those techniques is semi-auto friendly. They are for slow, careful chamber in a bolt gun.

Incidentally, Tompkins's comment about FL resizing requires context. I attended their LRFS (Long Range Firing School) twice. Mid said they seat to set headspace on the bullet with it in contact with the lands. By sizing their necks so the bullet can be moved by finger pressure, they seat very long so the bolt finishes seating the bullet in the chamber when they load. That is another way of getting the bullet lined up. Whether or not FL sizing without also centering the bullet can equal the other centering methods, I don't know, but it is at least still pretty good, the self-centering of the case shoulder in the chamber shoulder when the firing pin and pistoning primer drive the cartridge forward being the reason. But as A. A. Abbatiello showed with his 40-odd lot sample of National Match ammunition tested back in the 60's, it then makes a significant amount of difference that you keep the loaded rounds concentric and don't have more than about a thousandth of bullet tilt in the loaded round.

Bottom line: the most accurate ammunition possible always seems to wind up requiring you to mind some details somewhere along the way.
Good stuff.

But the idea with semi autos, is to size a bit more, but not necessarily back to SAMMI specs. That is why the 0.003 - 0.005 shoulder setback.

Again, if you are shooting more than one rifle, you have to set the shoulder back for the shortest headspace one.
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  #19  
Old 01-21-2019, 10:43 PM
HighpowerRifleBrony HighpowerRifleBrony is offline
 
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Start with Redding Competition shell holder +0.010, firmly in contact with the die, but not camming over. Wipe lube off case, insert into chamber, ease bolt home. Give the oprod a tap to snap the extractor over the rim. The bolt likely won't go into battery. Extract.


With another case, repeat with the +0.008, 0.006, and 0.004. Once the bolt closes easy, and extracts easy, you found the one to use.
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  #20  
Old 01-22-2019, 10:13 AM
ceresco ceresco is offline
 
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Not quite. Do that with at least five cases before you quit. Same with any other method. Good Shooting. ...
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