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Rifles, Reloading, Optics, Equipment
Gunsmithing
338 edge 30 or 40 deg.?
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<blockquote data-quote="hammertyme" data-source="post: 424059" data-attributes="member: 12863"><p>Yes and in my opinion a big one. Back in the 50's Rocky Gibbs was working on the 270 Gibbs and learned that he hated the 40 degree Ackley concept because that 40 degree shoulder caused back pressure (turbulance inside of the case) SO he changed the angle to 35 degrees.</p><p> </p><p>A lot of years ago I was working on a 6.5 Gibbs. I had someone who had a 35 degree and a 40 degree shoulder reamer cut a chamber. I (30-06 case) was getting many pressure indicaters before I got a case full of powder. When I used the super slow powders of the time and I could not get the velocities I figured I should be able to get. I checked the fired cases on a comparitor and found that the 40 degree shoulder reamer had been used instead of the 35 as I had requested. I had my own reamer made with a 35 degree shoulder for the over thirty calibers and one with a 30 degree shoulder for calibers under 30 degrees.</p><p> </p><p>Now think in terms of the huge case diameter. You put that abrupt shoulder on the case and have to slick up the magazine and feed ramps so you can dependably chamber a round each and every time from a magazine. Now invert that thinking to inside the case. That powder needs a nice smooth ramp to funnel all that powder uninterrupted from that huge case.</p><p> </p><p>I have a 7X57 mauser case (6 Rem) that I did the Gibbs to. Moved the shoulder forward .200 roughly. Changed the shoulder angle to 30 degrees and had a reamer made to these specs. The 6.5 version runs with the 6.5X284 in all bullet weights. The 224 version is running slightly above the 22 X 243 Middlestedt.</p><p> </p><p>Smooth transition- something to think about</p><p> </p><p>Neal</p></blockquote><p></p>
[QUOTE="hammertyme, post: 424059, member: 12863"] Yes and in my opinion a big one. Back in the 50's Rocky Gibbs was working on the 270 Gibbs and learned that he hated the 40 degree Ackley concept because that 40 degree shoulder caused back pressure (turbulance inside of the case) SO he changed the angle to 35 degrees. A lot of years ago I was working on a 6.5 Gibbs. I had someone who had a 35 degree and a 40 degree shoulder reamer cut a chamber. I (30-06 case) was getting many pressure indicaters before I got a case full of powder. When I used the super slow powders of the time and I could not get the velocities I figured I should be able to get. I checked the fired cases on a comparitor and found that the 40 degree shoulder reamer had been used instead of the 35 as I had requested. I had my own reamer made with a 35 degree shoulder for the over thirty calibers and one with a 30 degree shoulder for calibers under 30 degrees. Now think in terms of the huge case diameter. You put that abrupt shoulder on the case and have to slick up the magazine and feed ramps so you can dependably chamber a round each and every time from a magazine. Now invert that thinking to inside the case. That powder needs a nice smooth ramp to funnel all that powder uninterrupted from that huge case. I have a 7X57 mauser case (6 Rem) that I did the Gibbs to. Moved the shoulder forward .200 roughly. Changed the shoulder angle to 30 degrees and had a reamer made to these specs. The 6.5 version runs with the 6.5X284 in all bullet weights. The 224 version is running slightly above the 22 X 243 Middlestedt. Smooth transition- something to think about Neal [/QUOTE]
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Gunsmithing
338 edge 30 or 40 deg.?
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