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Velocity Jump on new barrels
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<blockquote data-quote="NZ Longranger" data-source="post: 1538670" data-attributes="member: 14"><p>Awesome post JM!</p><p>We're about to head into the mountains for a week, so unfortunately I won't be around to discuss this for much longer but a couple of quick comments on your interpretation of what I said.</p><p></p><p>Guys who are seeing a velocity increase as they fire more shots down the barrel with no changes to the load or conditions, will be seeing a pressure increase if only they could measure it. That was my point. If you were loading up to a max pressure at the start of your 50 to 100 rounds, and then see a 100fps or whatever increase in velocity after 50 to 100 rounds, your pressure will have increased commensurately, potentially into a higher pressure zone than you intended. We have proved this so many times over and over across the Oehler Ballistic Lab.</p><p></p><p>Any chambering job will benefit from a careful abrasive cleaning of the throat area (only, not the whole bore) before commensing break-in.</p><p></p><p>Certain over bore cartridges and powders will develop a carbon ring and a tightened throat area diameter from a surface structure change with repeated shooting. The ball powders like US869 (awesome powder though it is at producing velocity for pressure) are a given for this carbon ring, and hot pressures and temps affect the surface structure. You can feel this surface change easily on a tight cleaning patch once you think you have your bore clean. You can push the patch down the bore with no noticeable change in friction, but then try pulling it back and you'll feel a quite noticeable increase in the area just ahead of the throat due to the fact you're now going "against the grain". No amount of solvent use will remedy this, only the correct use of a mild abrasive cleaner like KG2 applied in this exact area.</p><p></p><p>High volume competitive shooters are really unlikely to encounter this, due to the cartridges and powders they are using. And in some extreme overbore cartridges you need to clean too regularly to keep this bore restricting from affecting accuracy to be useful in these disciplines, and their barrel life is too short anyway. But for a long range hunting rifle that may only ever be shot a handful of times between cleans, abrasive throat cleaning is the best way to keep <em><strong>consistent</strong></em> accuracy and velocity over the life of the barrel - in our humble opinion of course!</p><p>So in this case, this means cleaning to bare, polished in the throat area, metal.</p></blockquote><p></p>
[QUOTE="NZ Longranger, post: 1538670, member: 14"] Awesome post JM! We're about to head into the mountains for a week, so unfortunately I won't be around to discuss this for much longer but a couple of quick comments on your interpretation of what I said. Guys who are seeing a velocity increase as they fire more shots down the barrel with no changes to the load or conditions, will be seeing a pressure increase if only they could measure it. That was my point. If you were loading up to a max pressure at the start of your 50 to 100 rounds, and then see a 100fps or whatever increase in velocity after 50 to 100 rounds, your pressure will have increased commensurately, potentially into a higher pressure zone than you intended. We have proved this so many times over and over across the Oehler Ballistic Lab. Any chambering job will benefit from a careful abrasive cleaning of the throat area (only, not the whole bore) before commensing break-in. Certain over bore cartridges and powders will develop a carbon ring and a tightened throat area diameter from a surface structure change with repeated shooting. The ball powders like US869 (awesome powder though it is at producing velocity for pressure) are a given for this carbon ring, and hot pressures and temps affect the surface structure. You can feel this surface change easily on a tight cleaning patch once you think you have your bore clean. You can push the patch down the bore with no noticeable change in friction, but then try pulling it back and you'll feel a quite noticeable increase in the area just ahead of the throat due to the fact you're now going "against the grain". No amount of solvent use will remedy this, only the correct use of a mild abrasive cleaner like KG2 applied in this exact area. High volume competitive shooters are really unlikely to encounter this, due to the cartridges and powders they are using. And in some extreme overbore cartridges you need to clean too regularly to keep this bore restricting from affecting accuracy to be useful in these disciplines, and their barrel life is too short anyway. But for a long range hunting rifle that may only ever be shot a handful of times between cleans, abrasive throat cleaning is the best way to keep [I][B]consistent[/B][/I] accuracy and velocity over the life of the barrel - in our humble opinion of course! So in this case, this means cleaning to bare, polished in the throat area, metal. [/QUOTE]
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