Volume change in neck size only, eh

[Driller640]

I was thinking about pressure diff in your brass when you neck size only. You will have larger volume with neck size only then full length sizing, because of chamber diff. That being said, if u load same weight charge of powder in in both cases, the neck sized will have less pressure because of increase case vol. Then if u seat boolit out to touch rifling same thing happens. Don't know if any of this really would make any real diff to performance, eh, but if it did you may be able to load your max load in the manunal and know u are not going over pressure. I don't have pressure equipment to measure any of this, just asking if any of u knew if this is true or false, eh.

[leftiye]

Yup, more case capacity. Yup, takes more powder to get same pressure, and you get a smidgin more velocity. Nope, you can't just load the max load from the manual (if you want to keep all of your body parts). Start with at least 10% below the max load from your manual, and you might not be safe then. Better still start with the beginning load and work up. And you still might not be safe (but probably will). I welded a case into a 25-06 once with a beginning load of Norma 205. Some manuals are a little to the gauche, The Speer #9 was famous for hot/dangerous loads. Learn how to read pressure signs!!! You'll need a micrometer.

[Driller640]

My mistake I didn't mean to just load at max with out starting at min and working up.eh. Meant that once u have reached max load in the manual that if u neck size at that point or seat boolit out, u could think that your load was below max pressure eh.

[S.R.Custom]

I was thinking about pressure diff in your brass when you neck size only. You will have larger volume with neck size only then full length sizing, because of chamber diff. That being said, if u load same weight charge of powder in in both cases, the neck sized will have less pressure because of increase case vol.

Negative. If the brass is the same, and the powder charge is the same, than the pressures will be the same regardless of whether you neck size or full length size; what ultimately decides the volume is the chamber. The first thing that happens upon ignition is the brass is expanded out to fill the chamber.

You're right about seating out to the rifling, tho. That will almost invariably increase pressures.

[mike in co]

Negative. If the brass is the same, and the powder charge is the same, than the pressures will be the same regardless of whether you neck size or full length size; what ultimately decides the volume is the chamber. The first thing that happens upon ignition is the brass is expanded out to fill the chamber.

You're right about seating out to the rifling, tho. That will almost invariably increase pressures.



i dont think so......

if the starting volume on fl sized brass gives max pressure, then when you neck size( esp on a factory or mil chamber) the volume will go up and the pressure will go down. in my br chambers its not enought to talk about, in a milsurpls rifle its noticable.
i could be wrong at max pressure, but my tool(quickload) says i'm right.
i put case data by rifle, by lot in quickload, there is a difference in internal volume.
also much more noticable between straight wall case and a typical necked down rifle case.

[dakotashooter2]

Negative. If the brass is the same, and the powder charge is the same, than the pressures will be the same regardless of whether you neck size or full length size; what ultimately decides the volume is the chamber. The first thing that happens upon ignition is the brass is expanded out to fill the chamber.

However the pressure curve may be altered slightly. The initial pressure needed to expand the case to fit the chamber may take slighty longer to achieve in a neck sized case cause the capacity will be "slightly" larger to start with. However it may not acount for any more than the normal case to case variation.

[S.R.Custom]

That would be true. But what significant effect that would have on anything would be debatable.

[Leverluver]

I have pressure barrels in 15 rifle cartridges and any difference is less than the statistical noise found in random shot to shot variations. The only way the brass changes the equation is if one brand is thicker than another; thereby changing the total volume of the chamber/brass combination. All rifle cartridge cases are inflated to the size of the chamber at the shot, whether neck or full length sized.

[Dale53]

One thing that was only touched on lightly here, needs just a bit of clarification. I got into "pressure problems" one occasion back many years ago when I "knew everything"[smilie=1:. I was working on a friends rifle. He had an H&R Rifle with an FN barreled action. The barreled action was the usual high quality FN Mauser. However, the stock was a very plain, inexpensive rifle that I believe the factory inletted with an AX. The barreled action got a running start inside the stock and even in its relatively mild recoil caliber (30'06) it had split the stock clear through the forend, magazine well and into the grip. My friend did not have a lot of money, he had done me a real favor or two, so I did a salvage job. I patched the stock carefully, made entirely new bedding surface over the interior of the stock, reinforced the stock with stock bolts, and ran a support rod back into the split grip.

The rifle became a minute of angle (or better) rifle with complete reliability. I used this project as an academic study (the stock should have been used for firewood). When finished it was difficult to tell that anything had been done to it (only VERY careful examination showed any clue of previous damage and that was VERY minor).

However, all of this work just before we were scheduled to leave for a Canadian Bear hunt cut into my load developement time (I was working with my and two of my less experienced friends rifles - had THREE to prepare. I, at my 30'06 friend's request, loaded up some very blunt Remington Core Lock round nose bullets without determining proper seating depth with different profile bullets. The round noses were jammed into the rifling. They shot really well and the pressure was a LOT higher than prudent. When I reseated the bullets to a normal hunting setting (off the lands by a pre-determined amount) the pressure returned to normal. Good lesson here - do NOT put yourself into a position where time is running out and do NOT blindly assume that changing bullets, even of the same weight, will not cause pressure problems.

Work up ANY load when you change ANY single item (bullets, primers, cases, or powder). Lets stay safe, people.

That's me, out there learning something new every day...:???:

Dale53

[Driller640]

So, if I were to buy 50 new winchester 30-06 cases, load 25 to a start load, shoot them, then neck size this fireformed brass, that was shot in my rifle. The volume of the fire formed brass is going to be the same as the 25 new cases that are at spec? I doin't think so eh. This will depend on how tight the chamber is on the rifle, Bench Rest rifle, may be no diff. Sloppy mil-spec .303, could be a good diff. eh. SO if you have started at a start load, worked your way up to the max load. 1g at a time, full length resizing each time you reload, reach max load, shoot and all is good. Could you now neck size this fire formed brass and feel that your load that was listed as max is now just a hair below that eh. So if you were to take this load to a diff place, say a lot hotter then where you load the round at. Then may be the gun would not blow up! Now I don't load to max eh, just asking a question, looking for input, not stir it up. Will always play safe but I am able to think for myself and ask questions like what if? And how could? Where would we be if we didn't ask these things???EH

[Bass Ackward]

So, if I were to buy 50 new winchester 30-06 cases, load 25 to a start load, shoot them, then neck size this fireformed brass, that was shot in my rifle. The volume of the fire formed brass is going to be the same as the 25 new cases that are at spec? I doin't think so eh. This will depend on how tight the chamber is on the rifle, Bench Rest rifle, may be no diff.


Maximum pressure in a 30-06 occurs between 1/2" to 2" of bullet travel. By that time, all brass is going to expand at the allowable chamber dimension no matter if it was virgin brass or if you had dents in the case. That means not only out, but forward as well.

What you may see is the exact opposite for pressure. Depending on the chamber size and powder speeds, is that the cases that were virgin and NOT fire formed didn't seal as fast with slow powders as the ones that were already formed and only neck sized so the exact opposite may result. The neck sized cases in a large chamber may actually have higher pressures than new or full length sized brass.

So no blanket statement can be formed.

[Leverluver]

Given the exact same lot of brass, the powder charge doesn't give a flying rat's rear whether the case is full length sized, neck sized, or not sized at all. All it cares about is the volume of the case AFTER it has inflated against the chamber walls.

[mike in co]

Given the exact same lot of brass, the powder charge doesn't give a flying rat's rear whether the case is full length sized, neck sized, or not sized at all. All it cares about is the volume of the case AFTER it has inflated against the chamber walls.



sorry not true
energy is expended expanding the brass.....
where is the bullet by the time the brass does expand.
sorry no simple answer...

[felix]

Don't forget chamber form as well. If the primer has enough umph to splash a 40 degree shoulder with enough to cause ignition there, you can assume the next faster burn grade to take effect over than of a 20 degree shoulder. Longer the case, the less dramatic this effect is. The 40 degree shoulder is an easy equivalent to 1/2 grain of 4198 in the 222, meaning a half grain less powder minimum for the same pressure. However, the burn curve is different. In a 60 grain narrow case, the effect goes way down to almost no difference. The difference is there to be sure, but the powder speed used up front is slow enough anyway, and a 3 to 5 percent difference could be equated to other factors. ... felix

[trk]

sorry not true
energy is expended expanding the brass.....
where is the bullet by the time the brass does expand.
sorry no simple answer...


Perhaps not true. But is it significant?

I can recall a number of folks reporting no significant difference between either accuracy or velocity in shooting cases loaded with the same charge - some before fire-forming some after.

Perhaps testing would be in order.