Forums
New posts
Search forums
What's new
Articles
Latest reviews
Author list
Classifieds
Log in
Register
What's new
Search
Search
Search titles and first posts only
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Forums
Rifles, Reloading, Optics, Equipment
Reloading
WARNING - 4955
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="QuietTexan" data-source="post: 2771351" data-attributes="member: 116181"><p>Because ejector wipe and primer cratering are both the results of the case pushing against the bolt face. If the case is pushing so hard on the chamber walls the chamber walls are expanding, the signs on the bolt face disappear.</p><p></p><p>This is why Lapua-sized and larger actions have larger barrel tenon diameters, and why barrel blanks come in not just 1.200", but also 1.250", 1.300", etc, all the way up to 1.500" If the extra metal wasn't needed, people wouldn't pay for it. But the thickness of the chamber walls matter - the larger the case body is the thinner the chamber walls are at any given barrel diameter.</p><p></p><p>Savage large shank barrel diameter is (IIRC) 1.110". At that outer barrel diameter, a 223 Rem has ~0.367" of metal in the wall. A 308 Win has ~0.320". 300 RUM has ~0.280, and a 338 Lapua has ~0.260" in the wall. A 75000 PSI load in each of those chambers is pushing against different amounts of wall thickness. Same pressure, thinner wall, more movement.</p><p></p><p>Somewhere in the 65-80k PSI range (depending on action, barrel diameter, tenon diameter, chamber, etc- more pressure when thicker, less when thinner) the chamber walls themselves start expanding and contracting significantly enough to screw with case head signs. You see other things like velocity plateaus at the same time - same theory as you can unintentionally overpressure an AI using a load that was fine for fireforming because the case is expanding so much when forming it sucks in some of the pressure as energy to permanently deform the brass case to the new chamber. The chamber walls themselves do the same thing at much higher pressures.</p><p></p><p>Sporter barrels work because by the time the thin portion of the barrel is holding back pressure, it's a LOT LESS pressure than peak chamber pressure.</p><p></p><p>This is usually a big boomer problem when using marginal action and barrel diameters, but you can push anything to this point. Greg at Primal Rights did an entire article on it using a 6.5 Creedmoor and it showed exactly what you saw - pressure signs went away when he went up a again, and the next interval the case went boom.</p></blockquote><p></p>
[QUOTE="QuietTexan, post: 2771351, member: 116181"] Because ejector wipe and primer cratering are both the results of the case pushing against the bolt face. If the case is pushing so hard on the chamber walls the chamber walls are expanding, the signs on the bolt face disappear. This is why Lapua-sized and larger actions have larger barrel tenon diameters, and why barrel blanks come in not just 1.200", but also 1.250", 1.300", etc, all the way up to 1.500" If the extra metal wasn't needed, people wouldn't pay for it. But the thickness of the chamber walls matter - the larger the case body is the thinner the chamber walls are at any given barrel diameter. Savage large shank barrel diameter is (IIRC) 1.110". At that outer barrel diameter, a 223 Rem has ~0.367" of metal in the wall. A 308 Win has ~0.320". 300 RUM has ~0.280, and a 338 Lapua has ~0.260" in the wall. A 75000 PSI load in each of those chambers is pushing against different amounts of wall thickness. Same pressure, thinner wall, more movement. Somewhere in the 65-80k PSI range (depending on action, barrel diameter, tenon diameter, chamber, etc- more pressure when thicker, less when thinner) the chamber walls themselves start expanding and contracting significantly enough to screw with case head signs. You see other things like velocity plateaus at the same time - same theory as you can unintentionally overpressure an AI using a load that was fine for fireforming because the case is expanding so much when forming it sucks in some of the pressure as energy to permanently deform the brass case to the new chamber. The chamber walls themselves do the same thing at much higher pressures. Sporter barrels work because by the time the thin portion of the barrel is holding back pressure, it's a LOT LESS pressure than peak chamber pressure. This is usually a big boomer problem when using marginal action and barrel diameters, but you can push anything to this point. Greg at Primal Rights did an entire article on it using a 6.5 Creedmoor and it showed exactly what you saw - pressure signs went away when he went up a again, and the next interval the case went boom. [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Rifles, Reloading, Optics, Equipment
Reloading
WARNING - 4955
Top