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Chamber pressures

 
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  #1  
Old 11-23-2012, 06:49 AM
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Join Date: Nov 2012
Location: wrexham north wales UK
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Chamber pressures

Hi Hunting and shooting buddies my first post on this site so be gentle with me.

I once read an article on chamber pressures with the different pressures for a deep loaded bullet and a long loaded bullet that touched the lands but cant find it now can any of you recolect this article or any that might be relivent.

My shooting consists of rabbit shooting and fox shooting on many local farms smallholdings and a couple of estates.
I have a Annie 22lr a Ruger 77/17hmr all weather and a switch barrel Ruger77/22H/17A/H all weather but use the 17A/H 95% of the time
Wally
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  #2  
Old 11-23-2012, 09:23 AM
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Re: Chamber pressures

If you're talking reasonable seating adjustments, deeper seating(by itself) increases pressure a relatively small amount due to reducing case capacity and increasing load density. Reaching the lands causes a bigger step change upward in pressure(+~8Kpsi) even after the smaller reduction of pressure with shallow seating to get there.
None of this is an issue as you would back down a bit with testing after any significant change.

But if you seat so deep that bullet bearing runs into neck-shoulder junction, and if you have a donut developing, pressures can again step change big upward. This would show up as bad performance first, followed by classic pressure signs.
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  #3  
Old 11-23-2012, 11:34 AM
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Re: Chamber pressures

Quote:
Originally Posted by Mikecr View Post
If you're talking reasonable seating adjustments, deeper seating(by itself) increases pressure a relatively small amount due to reducing case capacity and increasing load density. Reaching the lands causes a bigger step change upward in pressure(+~8Kpsi) even after the smaller reduction of pressure with shallow seating to get there.
None of this is an issue as you would back down a bit with testing after any significant change.

But if you seat so deep that bullet bearing runs into neck-shoulder junction, and if you have a donut developing, pressures can again step change big upward. This would show up as bad performance first, followed by classic pressure signs.
Thanks Mikecr.
I always load to touch and then back off looking for a sweet spot cause i remember reading it somewhere but cant find the article now. What a great site even got an E/Mail to tell me i had a reply none of the other sites i have been on do this. Thanks again.
Big wally
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Old 01-17-2013, 08:41 PM
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Join Date: Sep 2010
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Re: Chamber pressures

Quote:
Originally Posted by Mikecr View Post
If you're talking reasonable seating adjustments, deeper seating(by itself) increases pressure a relatively small amount due to reducing case capacity and increasing load density. Reaching the lands causes a bigger step change upward in pressure(+~8Kpsi) even after the smaller reduction of pressure with shallow seating to get there.
Hornady Ballisticians disagree with you.
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  #5  
Old 01-18-2013, 01:33 PM
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Re: Chamber pressures

<A onclick="_gaq.push(['_trackEvent', 'Outgoing', 'www.hornady.com', '/ballistics-resource/internal']);" href="http://www.hornady.com/ballistics-resource/internal" rel=nofollow target=_blank>
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Hornady Ballisticians disagree with you. 
The way I read it Hornady is saying exactly what Mikecr said!
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  #6  
Old 01-18-2013, 05:31 PM
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Location: Mountians of SW NC, near Asheville
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Re: Chamber pressures

Seems they don't agree:

"Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start (C). Powder gases quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge it only comes to 3400 fps (D)"

In other words, Horandy says seating deeper, within reason, lowers peak pressure in rifles. And they DO know what they're talking about!
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  #7  
Old 01-18-2013, 06:15 PM
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Re: Chamber pressures

I can imagine with pretty large seating adjustments -with a large enough cartridge -and while off the lands -and with an oversized throat -and excess trimmed clearance, that the 'running start' and expansion within the throat area could counter normal rise.
Don't count on it otherwise though.
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