Sizing rifle brass to chamber.

Discussion in 'Handloading and Reloading' started by Legionnaire, Dec 5, 2021.

  1. Legionnaire
    • Contributing Member

    Legionnaire Member

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    I've used a couple of different trial-and-error methods to determine the target length for sizing brass to a chamber. I started by simply adjusting the die until a piece of brass fit with no resistance. I've used the Redding competition caseholders. I've played with some RCBS Precision Mics. When I'm happy with fit, I measure and note length using a set of Hornady comparators.

    In every instance, I start by pulling the firing pin assembly and ejector so I can work with a bare bolt; I don't want want to feel any resistance cocking the firing mechanism, nor do I want any forward pressure on the case from the ejector.

    Just wondering what steps others take to get a good case-head-to-shoulder length.
     
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  2. Howa 9700

    Howa 9700 Member

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    Funny story about this topic. As one considered a newb.......having returned to reloading after a decades long layoff.......trying to learn as much as I can. Quickly ran into the issue of full length sizing vs. neck sizing to minimize resizing of fire formed cases......and the apparent compromise of going to full length sizing, but only bumping shoulder back 0.002". Basically doing exactly as you are trying to do. Spent a lot of time messing with it.

    Then on a whim......got to wondering how much shoulder bump I would get if I just followed the instructions for setting up my full length die. The part where you raise the ram all the way up, then screw in the sizing die until it touches the shell holder, then lower the ram.... give die another 1/4 turn to take out any slop....then lock it down.

    First try........shoulder bump was only 0.003". Figured I got lucky......but then did it again with a different caliber......and got the same thing!

    In my case, I attribute this to a couple things. First is I'm only loading for bolt guns, which may have all been made with relatively tight chambers. Tight to SAMMI specs. Second is I'm using LEE dies, which according to LEE are made to only size back to SAMMI specs.....no more.

    But if this trend continues, I'll be happy. To quote the famous philosopher Forrest Gump........"one less thing".

    So my plan for now is when setting up my sizing dies, follow the instructions, then measure shoulder bump to see what you have to start with. I may not need to worry about it.
     
  3. Legionnaire
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    Legionnaire Member

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    Good point. Certainly shouldn't overlook the obvious!
     
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  4. Blue68f100

    Blue68f100 Member

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    The hardness of the brass, lube used, all come to play when your sizing. As the brass work hardens the setback will be less. The lube weather your using a thin film wax or heavy Lanolin mix will also effect the amount of sizing.

    For a bolt gun 0.003" is too much for max brass life. Cut that in 1/2 or more would yield better life.
     
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  5. sugarmaker

    sugarmaker Member

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    I use a Hornady/Stoney point gauge, measure fired brass, adjust Redding body die for .001+ shorter and run the lot. I keep cases by lot (300+ To start) and load until 10 or so wear out, at least I used to do that. Now I run them to death as they are not easily replaced.
     
  6. lightman

    lightman Member

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    I don't measure cases when setting up my sizing dies. I just start sizing fired case with the die about 2 turns from touching the shell holder and watch the ring it makes on the case neck. I turn the die down until the sized ring meets the shoulder and then turn the die down about 1/4th turn, or about 90º. If you are good at math you can calculate how many thousands 90º is with a 7/8X14 thread but my math ability is too weak for that. One of my favorite gun writers wrote about this method several (maybe 50) years ago and I've used it ever since.

    For the record, I have played with the RCBS Precision Mic, the Hornady/Stony Point tool, own a digital caliper, ect. I loose brass from loose primer pockets or neck splits but never from a case separation.
     
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  7. BigBlue 94

    BigBlue 94 Member

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    A 14 TPI thread moves .071" per revolution. So .01775" per quarter turn. The formula is 1 divided by the TPI.

    I looked it up lol...
     
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  8. lightman

    lightman Member

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    Thanks, I was too lazy to look it up.
     
  9. South Prairie Jim

    South Prairie Jim Member

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    Alex Wheeler is arguably the top rifle smith in the country right now with many world records, he also makes informative videos.
    www.wheeleraccuracy.com
    From the menu drop down select videos on sizing brass and clickers etc.
     
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  10. Varminterror

    Varminterror Member

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    Bolt close method for shoulder bump.

    Bolt lift method for seating depth.

    I’ve never found any other method to be as good, on a matrix of accuracy, repeatability, cost, speed and ease.
     
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  11. South Prairie Jim

    South Prairie Jim Member

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    I use a fire formed case for my comparator, but if im using the stripped bolt method I want (edit: resize until the bolt just drops without resistance on a fire formed case then bump .002 from that point.)
    As posted below we are stacking tolerances, the chamber shoulder angle “should be “X degrees as well as the die and your comparator but that does not always happen so my sizing needs to be a combination of measuring brass and free chambering before and after firing .
     
    Last edited: Dec 5, 2021
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  12. dcloco

    dcloco Member

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    The other item in this topic, but never mentioned, is the ejector and spring. Remove the ejector and try again. :)

    With a sharpie, I draw a line near the base of the brass on the body, index when inserting into chamber, and also index to my FL or neck die.

    ....and....remember, we are working with chambers, brass, and dies that are machined "to spec"......so, we are, essentially, stacking tolerances.
     
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  13. Varminterror

    Varminterror Member

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    Um… nah bro…

     
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  14. kmw1954

    kmw1954 Member

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    Since I am not yet loading for Benchrest or long range competition I have been using one of these; and so far it has been working. May not be the best solution but I trust it for what I am doing.
     
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  15. South Prairie Jim

    South Prairie Jim Member

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    True,
    As long as the case gage matches your chamber it’s all good. But as we all know when you compare joe blows gage to Jim bob’s chamber to billy bob’s die things sometimes don’t make great ammunition and why most of us are here is to take our program beyond entry level and excel to the next level and really understand the what and why’s.
    Added, at the end of the day your chamber is the best gage.
     
    Last edited: Dec 5, 2021
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  16. WVRJ

    WVRJ Member

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    This can be a rabbit hole like runout.For starters,if you want the nth degree of perfection for chamber/case fit,you need consistent brass.If you're patient,you can adjust the sizing die to just make it so the brass chambers smoothly,but if you back the die out a few thousandths,it tightens up when the bolt is closed.For my custom chambers that I do,the headspace is minimal,and if I set the die up to bottom out on the shell holder,it fits the way it should.I keep the shell holders I size with segregated from the others so that I always use the same shell holder to size with.They can vary by a few thousandths easily.If I'm dealing with a big,sloppy chamber,I set the die up using a feeler gauge to get the clearance between the die and shell holder to the dimension that I have wrote down in my reloading log book.Spending too much time worrying about the perfect shoulder bump in a factory barrelled hunting gun with mixed brass and economy sizing dies will cause you grey hairs.If you're shooting a lot and loading a lot,yes,try to get it right to save wear on your brass and to get all the accuracy you can out of your rifle.I see a lot of posts about guys who are having trouble getting their brass to fit in this measuring thingy or that measuring thingy.I don't own even one of those measuring thingys and my better rifles will shoot right with any others of similar quality.My most accurate rifle is a M700 in 223 that has shot several groups in the upper .1's and low to mid .2's,with its(and mine)best of 5 shots into .103 for 5 shots at 100 yards and it was witnessed when I did it.I use a Lee collet die and neck size only when I load for that one.Full length size until you get a smooth bolt closure and try to stay at that dimension.If you keep chasing around after that absolutely perfect fit,you're probably going to get frustrated and I've never seen any measure of frustration tighten up a group.
     
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  17. westernrover

    westernrover Member

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    What is the advantage of the bolt close method versus bumping 1 or 2 thou from the fired case dimension?
     
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  18. South Prairie Jim

    South Prairie Jim Member

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    Good question, there’s a key phrase from an earlier post that people sometimes overlook. Chambering freely is the goal so from just smooth bolt closer we bump .002, a lot of guys just bump a fully formed case but we find out that sometimes that’s just not enough for smooth cycling. 787B4463-49CF-49D8-9468-A2432C2047AA.jpeg
     
  19. Varminterror

    Varminterror Member

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    Firing once may not represent the actual dimension of the chamber, so bumping 1-2thou from fired brass may be sizing too much or too little.

    Bolt close method can’t lie. The case either fits or it doesn’t, and when it has been sized just to the point of kissing the shoulder, we know a true dimension of the chamber.

    Basically, it’s like measuring my sock versus my foot.
     
  20. kmw1954

    kmw1954 Member

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    To be honest with everyone, at this point I am still processing a lot of range brass that has been fired in many different guns and so far have not gotten around to a firing of second loading brass that was fired in my gun. So I an still full length resizing everything back to spec.

    But I have reloaded enough of this stuff to get a good feel for what is working best. might not be perfect but it's close and I am gaining experience.
     
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  21. Howa 9700

    Howa 9700 Member

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    To those who might know.......how much potential headspace and "bump" is there is the typical rifle chamber? I was looking at the SAMMI specs for 270 Win......chamber and cartridge......and it looked to me like it would be 0.006" between max cartridge and max chamber.

    Or put another way, if the LEE dies (or any other standard set of dies) do what their material says they do......resize back to the maximum allowed by SAMMI specs.....how much is the bump? In theory, a "tight" chamber would be none. But what about a loose or "sloppy" chamber?

    There seems to be two issues or methods floating around. Standard dies setup as per instructions........are sizing to a standard. Setting up the dies to close a bolt throws that standard out the window......and sizes to the individual chamber. Just curious what the potential difference between the two might be?

    Is it worth chasing......or are we picking fly crap out of the pepper?
     
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  22. edwardware

    edwardware Member

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    For bolt guns, I start by neck sizing, and watch the shoulder position progress across reload cycles. Some guns never need shoulders set back. . . some go 3-4 cycles before the brass begins to "feel" upon chambering, and it gets set back as little as possible (~0.003").

    For gas or lever guns, I aim for at least 0.003" clearance, or more.
     
  23. Legionnaire
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    Legionnaire Member

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    After working with once-fired 6GT brass in a Masterpiece Arms PMR Pro, I know using using a Hornady comparator that the stripped bolt consistently drops freely at 1.3355 and with minor friction at 1.3360. Those are my measurements in my chamber with my calipers using my comparator. I'm bumping to 1.3350 for the second firing.
     
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  24. Varminterror

    Varminterror Member

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    In a nutshell, ammunition sized to SAAMI minimum dimension should be considered “wrong” for almost all rifles, but in its defense, it is “wrong, on the right side.”

    In principle, the difference in max and min is supposed to be - by design - tight enough that one firing will not cause case separation or shoulder rupture. It also should not be excessive headspace to the point that the firing pin interference with the primer is reduced to the point of failed ignition.

    So yeah, the difference between max and min is intentionally still tight enough to prevent malfunction and catastrophic failure.

    A chamber casting would have to be done to measure the actual dimension of the cut for anything other than headspace, throat length, or neck length. Games can be played with mandrel expanders for neck diameter as well. But in principle, dies should be able to size to minimum SAAMI spec, but also allow “sized for chamber” reloading practice.

    Granted, “sized for chamber” only offers control over headspace length, without independent control over body diameter. Certainly shoulder diameter is never independent, or even really variable, and neck diameter is only controllable when using bushing dies.

    Maybe an example here as a difference between two chambers: Swapping from one 6 creed barrel to another a few years ago, both measured out to the same headspace within 1 thou (as accurately as I can measure with the device I was using). However, it became obvious after swapping barrels that the old chamber was more generous in body diameter than the new barrel - some cases, even after resizing to proper headspace LENGTH, simply would not chamber. The sizing die was not tight enough diameter to sufficiently size the body and “base” of the cartridge to fit the new chamber. The result was that a portion of the cartridges - maybe 10-20% offered significant resistance in chambering - wedging an interference fit around the body before dead-length stopping on the shoulder - and 40-50% of them offered sticky bolt lift during primary extraction, as the cases “memory” was larger diameter and they didn’t springback to clear the chamber as they should. One pass through a small base die with the set of brass and everything was back in order - set to the same headspace length as the original sizer. (For those playing the home game, I DID screw my FL sizing die all the way to the shell holder, plus 1/4 to see if that die could sufficiently size the body - it did not, so a small base die was procured).

    So sizing die dimensions mattered significantly in that case.

    However, in practice, since we never truly have independent control over body/base diameter, we do commonly neglect that we may be squishing our bodies smaller than needed. In principle, if we force the conical shoulder of the case to dead-length stop against the conical shoulder of the chamber, and the bolt face and case head are “square” to the axes of the barrel and cartridge, respectively, then our cartridge will be centered and supported in the chamber in the way we desire for precision. However, I COULD, potentially, push the shoulder back in a 30-06 case to headspace in a 300 wsm chamber, leaving massive clearance around the body. In principle, the bolt face and shoulder would force alignment, but obviously the skinny ‘06 case doesn’t fill the WSM chamber, and will almost assuredly rupture if fired. But… it illustrates that we may be and can be more tolerant of extra clearance around the body than we really should be of the neck and shoulder.

    It’s simply not apt to say sizing to fit your chamber is throwing anything at all “out of the window.”

    Sizing to minimum SAAMI standard is a blind practice, meant to produce ammo which will fit any and all chambers. A “one size fits all” paradigm. It’s kinda like getting a charity event T shirt - where they saved money and only ordered XL’s so “one size fits all.” Which is to recognize, some guys in the husky end of the spectrum simply won’t be able to put it on, and smaller folks like young folks, half of men, and almost all women will be swimming in it - it’s not terribly apt to say “one size fits all” when you’re playing such a fast and loose game with the word “fit.” Just because someone is able to wear a shirt, such does not mean it “fits.” Similarly, just because a cartridge is small enough to chamber, such does not mean it actually “fits” the chamber.

    Offering another extreme example for consideration: as noted above in my anecdote with my 6 creed, a case which is oversized in any dimension, even the slightest, will not chamber properly. So if I’m hunting my .30-06 this season and my sizing die backed out of the press ~1/4 turn without catching my attention, I might not be able to close the bolt on that round - despite the fact it is the appropriate .30-06 case, sized in the appropriate .30-06 sizing die. Alternatively, if I had an inattentive moment of Darwinism and loaded my rifle with some .308win rounds, my rifle would likely feed and fire with a smile on its face. Neither actually “fit” the chamber, but ~2 thousandths in the “plus” direction hurts more than almost 1/2” in the “minus”. Similar to the case of the pushed-back ‘06 case in a 300wsm chamber, the 308win will “fit” in the ‘06 chamber, but will not be sufficiently supported, so it doesn’t really “fit.”

    Here’s where rubber really hits the road…

    I’ve offered examples above for how and why chamber fit matters, micro scale in one direction which causes malfunction, and the absurdisms of macro scale undersizing in the other direction - both of which, unfortunately, will still chamber and fire, still function, even though the results could be catastrophic.

    Sizing to minimum spec won’t hurt very bad in MOST cases - and if it does, it indicates you have something wrong with either your die or your rifle (creating excessive headspace because the die is too shallow or your rifle chamber is too deep). But outside of the context of making generic ammunition which must “fit” in any rifle, all you’re really doing is producing ammo which you know doesn’t actually “fit” your rifle.
     
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  25. Walkalong

    Walkalong Moderator Staff Member

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    True, but I don’t like cutting it that close for anything but Benchrest, and even then I want totally free chambering.

    For my Dasher I take the average of once or twice fired cases from my chamber, then use a full length bushing style sizer and “bump” the shoulder an average .0015 from there. They chamber easily, shoot great, and I have no issues with cases stretching near the case head no matter how many firings.

    I get where the lands are by removing the firing pin assembly and the extractor, then see where the bolt sees any resistance at all closing vs not closing. I do this in .005 increments, I’m not concerned exactly which .001 it touches at, one or two matches and that changes anyway, nor do I chase the lands, still shooting great going on 2K rounds. (Bartlien)
     
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