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Old 01-02-2017, 03:49 AM
Mikeinkaty Mikeinkaty is offline
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Default Minimizing headspace

If I load rifle bullets longer to get the headspace I want, how do I figure the additional powder to use to achieve the previous velocity? Load data books aren't much help there. Say for instance I increase the internal volume by 10%. Do I increase the powder by 10%, by volume? I'm assuming that by not increasing the powder load that the velocity would drop. Is that correct?

Mike
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Old 01-02-2017, 04:16 AM
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Loading a bottle necked rifle bullet longer in the case has nothing to do with changing headspace. Headspace is all about cartridge case / chamber / bolt face interface. Unless you are shooting a break open single shot, you will probably run into magazine / feeding issues from too long an OAL.

Yes, the increased case capacity from a bullet seated less deep may result in slightly less velocity, but it will be very slight in most cartridges, and I don't know of any reliable formula that allows you add additional powder to make up the difference. There is also the possibility that a bullet seated out too far may jam into the rifling enough to actually raise pressures. Stick with known book loads.

Depending on what rifle and caliber you are talking about, several options may work, such as setting the barrel back enough to fix the headspace issue, or firing powder puff loads in it, to form the brass to the chamber, then using this brass in this gun only, neck sized, so as not to push the shoulder back.

Larry

Last edited by Fishinfool; 01-02-2017 at 04:45 AM.
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Old 01-02-2017, 05:24 AM
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If you are adjusting COL to get the bullet closer to the lands, I presume you're doing that to improve accuracy.

As Fishinfool said, there's no formula that will tell you how much velocity you may lose (via less pressure) or perhaps gain (via increased pressure due to proximity to the lands), and no formula to tell you how much powder to add or subtract to compensate.

Changing the seating depth in this way *will* allow you to physically add more powder. That may or may not allow for more velocity before pressure signs show.

But the way you find out is by working up the loads and testing seating depths & powder charges vs what your goal is . . . velocity or precision.
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Old 01-02-2017, 06:47 AM
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I think you are asking two diff questions. OAL doesn't really have anything to do with headspace, unless you load to touch the rifling. Headspace is a function of the cases fit in the chamber.
When you load longer you do increase volume a tiny bit, but pushing the bullet closer to the rifling increases pressure, so adding powder may very well put you over pressure. It's opp with handgun rounds.
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Old 01-02-2017, 07:43 AM
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Quote:
Originally Posted by fredj338 View Post
but pushing the bullet closer to the rifling increases pressure, so adding powder may very well put you over pressure. It's opp with handgun rounds.
Not to steal the thread but, why?
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Old 01-02-2017, 10:14 AM
Mikeinkaty Mikeinkaty is offline
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Originally Posted by Collo Rosso View Post
Not to steal the thread but, why?
The load data books call for a COL of 1.59" for 357 mag. The max COL for the Henry big boy is 1.71". I would like to get the bullet a little closer to the lands. The bullet touches the lands at 1.71". When shooting 38 Spl, the gap is like double the above.
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Old 01-02-2017, 02:34 PM
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The only way to get that bullet closer is to buy some..........

Maxima brass and trim to fit.
A lot of work for a few thousandths of an inch.
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Old 01-02-2017, 02:54 PM
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Quote:
Originally Posted by Nevada Ed View Post
The only way to get that bullet closer is to buy some..........

Maxima brass and trim to fit.
A lot of work for a few thousandths of an inch.
How about a coated 158 grain smooth lead bullet seated long and taper crimped?
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Old 01-02-2017, 03:06 PM
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Quote:
Originally Posted by Mikeinkaty View Post
The load data books call for a COL of 1.59" for 357 mag. The max COL for the Henry big boy is 1.71". I would like to get the bullet a little closer to the lands. The bullet touches the lands at 1.71". When shooting 38 Spl, the gap is like double the above.
So you measured the 1.71" or are you assuming that is max??
FWIW, all rimed cases headspace on the rim. So what you are trying to achieve has nothing to do with headspace. Putting the bullet closer to the lands doesnt guarantee better accuracy.
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Old 01-02-2017, 03:13 PM
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Quote:
Originally Posted by Collo Rosso View Post
Not to steal the thread but, why?
As pressures build inside the case the bullet starts moving forward looking for release. If it is wedged into the lands or just short of, there is less room for the bullet to move & pressures start climbing. So a max load with no leade will push pressures thru safe. Damage can be minimal, like leaky primer to a full blown case, catastrophic.
So as noted, any increase in case volume loading long, is negated by shorter leade. FWIW, compression in rifle loads with most rifle powders is a non issue. The distance to rifling is more important to raising pressures. Many of my rifle calibers use compressed loads, from 100% to 105%. It is powder burn rate & caliber specific though.
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Old 01-02-2017, 03:37 PM
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A high quality reloading manual would be helpful here.
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