How much sizing is appropriate?
- Thread starter 1911nut
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NorCalMikie
Gold $$ Contributor
If the brass fits back in the chamber with no issues, you're good to go!! After a time, you'll probably have to full length resize. Maybe every 5 or 6 firings? The less you move that brass, the better! You'll know when it starts getting snug.
swd
Silver $$ Contributor
I'm curious why you like to see .002"-.003" vs .001" or so? Just trying to learn something here, thanks.
swd
Silver $$ Contributor
Maybe the ones that rub a little don't line quite up as perfectly in the chamber? Thanks
When you bump .003 Donovan, does it seem to increase insipient case head separation issues for you? If my memory serves, you are not big on annealing all that much so please correct me if I'm wrong.
thanks
.003" bump is nothing, this would take many many firings at maximum pressure to cause head separations.
Head separation ONLY occurs when EXCESSIVE headspace is present, on the order of .008" or more.
Even a regular sizing at .004" would pose no problem.
Annealing won't effect head separation in any way, it has no effect on the base of the case. It is stretch that causes head separations, if the case neck and shoulder expand to fill the chamber without excessive movement, it takes up the gap that the sizing made before max pressure and any stretching takes place. The thinnest area ALWAYS expands first, which is the neck as it releases the bullet, then the shoulder that actually seals the chamber, hence why we get sooted necks, but, not sooted shoulders, unless a problem exists in the load. The rest of the case then grips the chamber, and the actual stretch may only be .001" or less.
You must remember, no matter what bump amount you use, brass springs back, not just in the chamber, but, also in the die.
Cheers.
Head separation ONLY occurs when EXCESSIVE headspace is present, on the order of .008" or more.
Even a regular sizing at .004" would pose no problem.
Annealing won't effect head separation in any way, it has no effect on the base of the case. It is stretch that causes head separations, if the case neck and shoulder expand to fill the chamber without excessive movement, it takes up the gap that the sizing made before max pressure and any stretching takes place. The thinnest area ALWAYS expands first, which is the neck as it releases the bullet, then the shoulder that actually seals the chamber, hence why we get sooted necks, but, not sooted shoulders, unless a problem exists in the load. The rest of the case then grips the chamber, and the actual stretch may only be .001" or less.
You must remember, no matter what bump amount you use, brass springs back, not just in the chamber, but, also in the die.
Cheers.
.003" bump is nothing, this would take many many firings at maximum pressure to cause head separations.
Head separation ONLY occurs when EXCESSIVE headspace is present, on the order of .008" or more.
Even a regular sizing at .004" would pose no problem.
Annealing won't effect head separation in any way, it has no effect on the base of the case. It is stretch that causes head separations, if the case neck and shoulder expand to fill the chamber without excessive movement, it takes up the gap that the sizing made before max pressure and any stretching takes place. The thinnest area ALWAYS expands first, which is the neck as it releases the bullet, then the shoulder that actually seals the chamber, hence why we get sooted necks, but, not sooted shoulders, unless a problem exists in the load. The rest of the case then grips the chamber, and the actual stretch may only be .001" or less.
You must remember, no matter what bump amount you use, brass springs back, not just in the chamber, but, also in the die.
Cheers.
"Excessive", is not a technical term, it is a value judgement.
ANY space in the chamber when the cartridge is chambered, will cause the case to stretch - if there is 0.001, then the case will stretch a teeny bit, (not necessarily 0.001). So it will take many firings before the head separates - the case might fail from another cause before the head separates.
Most people set up the sizing/bump die so there is a slight crush to the case when the bolt is closed - the bolt handle will meet resistance and stop half way down on a loaded case, if the pin and ejector are removed.
With my .308 I've been using a Forster Shoulder Bump/Neck Sizing bushing die. Set the "bump" so the case chambers easily with little or no effort. I did that a couple years ago and find that I haven't had to FL size yet. I figure the more I size the quicker the brass work hardens. I would only be guessing as to how much the shoulders are bumped. They just work------and the cases last.
Is there reasoning for why “most” shoulder bump to end up with a slight crush fit, other than to avoid stretching the cases that teeny bit more?
I do remove the firing pin and ejector when I’m feelin’ out at exactly what case base to shoulder datum length the case is right at the point where it’s completely filling the chamber, and once I’ve found that length, then I’ll record its measurement as well as which of me instruments were used to get it, for future reference. Size dies will thereon be adjusted to shoulder bump the cases to give ‘em all at least some clearance, preferably so .001” to at most a bit over .002” shorter than the test case used to arrive at the ~ .0000” chamber clearance reference measurement.
I figger a bit of variance in clearance at the bolt face better than a bit of variance in the amount of stress induced from closing the bolt on varying case lengths so also a bit of variance in the amount of case crush.
Knew that; question was, ~ what are the other reason(s) that you (folk in general) prefer a .002” to .003” case crush on closing the bolt, resulting in a varying amount of stress induced in doing so, as opposed to having a zero stress variance on closing the bolt if there’s ~ .001” to .002” of clearance (headspace)?
BoydAllen
Gold $$ Contributor
The point about having some difference in bolt close when bump is set at .001 is a good one. Particularly with brass that has not been annealed (except at the factory) there is some difference in hardness that will produce variation in shoulder bump, with the same die setting. Some time ago, a friend had that problem with a couple of magnum hunting rifles and we did just enough controlled annealing to make the shoulder bump more uniform without backing off the bullet seating force much. Another issue is if you are shooting a group mixing rounds that have different bolt close feel, your groups will open up. If they are all the same, be they tight, medium, or easy, they will shoot better than mixed. Cases that have thicker brass in their shoulders and overall harder brass will IMO be more subject to variations in bump from a given die setting.
The amount of clearance or crush depends on the use of the rifle.
Short range bench shooters most often shoot "free recoil" (the gun is free in the rest, and they do not touch the rifle). They wait until the wind conditions are like they prefer, and then let fly five shots in 15 to 20 seconds - for this style of shooting, there can be no resistance in closing the bolt, because it will cause the rifle to roll sideways, and break the cadence (and loose the match).
So, short bench guys want cases to have no crush - maybe 0.001" or 0.002" of empty space.
Long range shooters, who do not shoot fast inside of a wind "window" can benefit from more crush, cuz it leads to very long case life - I have thrown away cases with almost 50 firings (and they were still fine, but I wanted to upgrade to Lapua), and other guys have 80 to 100 firings on their cases - for that, you need 2 to 4 or more thou of crush.
I prefer to feel a fair amount of resistance on the bolt handle when I close the bolt. There are no stress "problems" induced. The rifle closes tight, and it is fine. After all, once you pull the trigger, THEN the stress happens - in spades !!
Last edited:
dmoran
Donovan Moran
As always opinions and experience very, but your stating things I've never seen play true.
Here's what I know about crush and what pressure traces have told me about crush: any time a case makes contact with the chamber, pressure is increased. Any amount of variance in crush and ES get extreme, compared to no-crush/clearance variation.
Brass has memory and spring, that when resizing to clearance (no-crush) will repeat with consistency and longevity as long as it is not resized excessive. Properly adjusted dies and good fitting/matching dies is what determines case life. Keeping the die adjusted during the brass cycles to maintain consistent sizing is the key. Precision accuracy has always came best for me with adequate clearance/bump with no level of crush at all.
My 2-Cents
Donovan
I think we have had different experiences.
I can see no reason or explanation, why pressures would be affected in any way, if there is 0.001" of empty space between the case head and bolt face... or if the base of the case is touching the bolt face.
Nor, I have never seen a change of ES or AV between the two.
But that is why some like blondes and some like brunettes.
/VH
Hillary ain't in jail, so leave me to hell alone!
I won't jump in here with any facts, cuz I don't know any but this discussion kind of goes along with some of the curiosity that I have about what really occurs (in detail) in a rifle chamber upon firing of a cartridge.
It seems possible, to me, that during the very early stages of ignition, the burn rate of the powder along with the effects of the primer could be affected differently, by starting out in a case that has been sized smaller, as opposed to one which more closely fits the chamber. It also seems that in the smaller sized case scenario, that more of the energy would be spent on expanding brass than on a more fitted case.
All of the above high powered thinking then makes me think that very small differences, early on and throughout ignition likely continue to stack and by the time the bullet leaves the barrel in each scenario, the effects are significant. Kinda similar to how a crosswind near the muzzle matters on down yonder at the target.
It seems possible, to me, that during the very early stages of ignition, the burn rate of the powder along with the effects of the primer could be affected differently, by starting out in a case that has been sized smaller, as opposed to one which more closely fits the chamber. It also seems that in the smaller sized case scenario, that more of the energy would be spent on expanding brass than on a more fitted case.
All of the above high powered thinking then makes me think that very small differences, early on and throughout ignition likely continue to stack and by the time the bullet leaves the barrel in each scenario, the effects are significant. Kinda similar to how a crosswind near the muzzle matters on down yonder at the target.
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