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Long Range Hunting & Shooting
Q&A: 300 WM with 210 gr VLD Hunting Project
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<blockquote data-quote="ShtrRdy" data-source="post: 1628033" data-attributes="member: 40852"><p>I'll try to explain the shoulder set back reason. The 300 Win Mag was originally made from the 375 H&H case design. The 375 H&H is basically tapered from the base of the case to the neck. It didn't have much of a shoulder. The designers decided to add a "belt" around the bottom of the case to set the Head Space. When cartridges like the 300 Win Mag are designed they had to respect the Belt establishing Head Space but the actual case now had a distinct shoulder.</p><p></p><p>If you were to measure the length between the bottom of the case to the shoulder on a new piece of brass, then load it up and fire it, the length between the bottom of the case to the shoulder will have grown quite a bit. ( e.g. 0.012" ) Now if you resize the brass and push the shoulder back to where it was originally it's going to cause two things. 1. It is working the brass more than it needs to be. 2. When you fire it again the shoulder gets blown forward. It's the shoulder getting blown forward that is the real concern. That brass has to come from somewhere. Where it comes from is the web of the case. This is the area just above the Belt. If this cycle is repeated too many times then the case can split and ultimately the Head of the case can separate.</p><p></p><p>I learned this the hard way as a new 300 Win Mag owner a number of years ago. I was on the third firing of Hornady brass and experiencing case head splitting. I ended up using a 40 S&W case to measure from the base of the 300 Win Mag case to the shoulder by placing the mouth of the 40 case over the neck of the 300 Win Mag case. This gives you a measurement to work with.</p><p></p><p>Then when you resize your 300 Win Mag cases you can use the reference measurement to see just how far you are pushing the shoulder back. People generally use 0.002" to 0.003" of push back.</p></blockquote><p></p>
[QUOTE="ShtrRdy, post: 1628033, member: 40852"] I'll try to explain the shoulder set back reason. The 300 Win Mag was originally made from the 375 H&H case design. The 375 H&H is basically tapered from the base of the case to the neck. It didn't have much of a shoulder. The designers decided to add a "belt" around the bottom of the case to set the Head Space. When cartridges like the 300 Win Mag are designed they had to respect the Belt establishing Head Space but the actual case now had a distinct shoulder. If you were to measure the length between the bottom of the case to the shoulder on a new piece of brass, then load it up and fire it, the length between the bottom of the case to the shoulder will have grown quite a bit. ( e.g. 0.012" ) Now if you resize the brass and push the shoulder back to where it was originally it's going to cause two things. 1. It is working the brass more than it needs to be. 2. When you fire it again the shoulder gets blown forward. It's the shoulder getting blown forward that is the real concern. That brass has to come from somewhere. Where it comes from is the web of the case. This is the area just above the Belt. If this cycle is repeated too many times then the case can split and ultimately the Head of the case can separate. I learned this the hard way as a new 300 Win Mag owner a number of years ago. I was on the third firing of Hornady brass and experiencing case head splitting. I ended up using a 40 S&W case to measure from the base of the 300 Win Mag case to the shoulder by placing the mouth of the 40 case over the neck of the 300 Win Mag case. This gives you a measurement to work with. Then when you resize your 300 Win Mag cases you can use the reference measurement to see just how far you are pushing the shoulder back. People generally use 0.002" to 0.003" of push back. [/QUOTE]
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Q&A: 300 WM with 210 gr VLD Hunting Project
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