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Reloading question


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12 replies to this topic

#1 JeffsSig

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Posted 08 April 2012 - 12:08 AM

More info others may want to know also.

Is this statement true?
the shorter the OAL the Less the pressure. So seating out to Max length will give you the highest pressure and anything shorter will produce less pressure.

Asking for rounds like the 223 rem.

So if it is true and one wanted a bullet that suggest a OAL of 2.200 and you wanted them set at 2.235 , would you change your powder charge any?

#2 East_TN_Patriot

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Posted 08 April 2012 - 12:24 AM

IIRC, it's the other way around. The deeper you seat the bullet, the higher the pressures will be all other things being equal. If you reduce the bullet seating, you can add more powder, thus increasing pressure, but it would be easy to overdo things. Perhaps someone with a bit more knowledge will chime in and give us a more authoritative answer.

#3 Lumber_Jack

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Posted 08 April 2012 - 12:32 AM

I was jut reading this in the ABCs of reloading today. The deeper the bullet is seated the higher the pressure. So if you go max load and seat too deal your pressure could be higher than recommended. If you seat the bullet way out and add more powder you just have to be sure your under the max load an not over max OAL
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#4 allenwaddle

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Posted 08 April 2012 - 01:42 AM

Actually extremely short or extremely long either one can cause higher pressure. When you set the bullet really deep it reduce the cases capacity which will cause higher pressure. When you set the bullet to long the bullet has no jump length (distance to the lands) and this will also cause pressure increases.

It is generally considered to be safe to go longer (which is generally more accurate to) and work your way up looking for pressure signs with longer loads.
Allen

Edited by allenwaddle, 08 April 2012 - 01:43 AM.

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#5 LngRngShtr

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Posted 08 April 2012 - 03:42 AM

More info others may want to know also.

Is this statement true?
the shorter the OAL the Less the pressure. So seating out to Max length will give you the highest pressure and anything shorter will produce less pressure.


NO, the other way around, think comustion chamber,same amount of fuel but more compression bigger bang .. but some powders also don't like large air pockets ( low charges of 296 in a .44 Mag. )

So if it is true and one wanted a bullet that suggest a OAL of 2.200 and you wanted them set at 2.235 , would you change your powder charge any?

I would load a test batch depending on how close to MAX. powder charge I was..if lower end than no but if near published max I would:
Start from the beginning (back off a few tenths of a grain) and work up a new loading at the new OAL however .035" isn't much of an OAL variance just make sure you aren't jamming the bullet into the throat (lands) or your pressure will spike.

John

#6 BigK

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Posted 08 April 2012 - 04:38 AM

I don't reload .223, but with other calibers I've reloaded the min and max OAL cause feeding issues. YMMV

Aside from that, everything I've read backs up what the others have said. Shorter OAL will produce more case pressure than long with the same powder charge (unless your OAL is so long that the bullet is pushed against the rifling).

#7 lshel

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Posted 08 April 2012 - 02:27 PM

Like the others have said the shorter OAL more pressure.OAL also is set to insure good reliable feeding from mag to chamber. I set at recommendation in reloading manual and on some bullets slightly longer for better taper crimp on flat bullet surface.

#8 leroy

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Posted 09 April 2012 - 02:41 PM

Jeff:____________

In general for small capacity cartridges (...think 9 mm, 380 acp, 357 sig; etc...); the deeper the bullet is seated, the higher the pressure. The reason is the decrease in volume of the case due to the bullet intrusion. Any encroachment on the volume of a small capacity cartridge raises pressures. Interior ballistics is very volume dependent.

For rifles, the issue is a bit different for different reasons. If ya seat a bullet out touching the lands ahead of a rifle chamber, this allows pressure to build higher and a bit sooner than if the bullet is seated deeper (...within accepable limits...) and is guided up the throat to the lands.

Lots of target guys used to (...and still do...) custom seat their bullets out touching the lands to fit a particular chamber of a pet target gun to get the last bit of accuracy from the rifle. This raises pressures a bit due to the initial resistance of the lands before the bullet can move and start to relieve the pressure a bit. The target guys and old reloaders know this and work up the loads accordingly.

If ya seat the bullet back off the lands(...again, within acceptable limits as specified in a loading manual...), this allows the pressure to build a bit more gradually, lowering the pressures a bit, as the bullet has less initial resistance when it is turned loose from the case neck in the throat of the rifle chamber which contains "freebore" that has no full diameter lands to restrict the bullet's initial movement. Look in your rifle's chamber and you can see what im talkin about.

hope this helps
leroy

#9 Jonnin

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Posted 09 April 2012 - 05:07 PM

while this has been beat to death, a practical answer to a simple question:

no, seating a 223 less than 3/100's up or down will not require you to change the load data unless ARE doing what others said and jacking the bullet into the rifling with the change. If you are sticking it out that far, and do not have a good reason, DON'T. If you are doing it on purpose, knock 15% off the powder charge and work it back up.

#10 BungieCord

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Posted 09 April 2012 - 05:59 PM

The highest prressure a load can produce is when it's jam seated, as in the bullet is jammed into the lands. As you shorten OAL and back the bullet out of the lands, the pressure drops off. But the more you shorten OAL, the more you compress the charge, which increases PMax. As you continue to shorten OAL, at some point the charge becomes so compressed, it reverses the dropoff that resulted from backing the bullet away from the lands and PMax begins to increase.

For example:
Posted Image

Most of the studies I've come across like this indicate that the point of lowest pressure occurs when the bullet is seated about 0.250" off the lands.

#11 Jonnin

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Posted 09 April 2012 - 06:07 PM

I guess if you fill the case very full you could compress the powder and get some pressure, but I would think a 223 would fall into the case before you could seat it deep enough to really spike the pressure with many powders. Not really sure, I know there is room for a bullet inside the case with my load data (ask me how I know :( )

Note the above chart is really in 1/10s of an inch, so I stand by my comment that a few hundredths is going to be a tiny pressure change unless at the extremes.

#12 mikegideon

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Posted 09 April 2012 - 06:56 PM

The standard 77gr SMK load crunches every time.

#13 HCRoadie

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Posted 18 April 2012 - 02:34 AM

Boyle's laws apply here, for a fixed amount of gas, at a fixed temperature, P [pressure] and V [volume] are inversely proportional (while one doubles, the other halves). This is for the nerds out there :wave:

Edited by HCRoadie, 18 April 2012 - 02:36 AM.

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