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Rifles, Reloading, Optics, Equipment
Reloading
How to choose a bushing size?
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<blockquote data-quote="AZShooter" data-source="post: 1479862" data-attributes="member: 5219"><p>Measure OD of loaded round at neck. Subtract .003 and .002" from that value for the two bushings that are usually used. Some shooters of smaller cartridges may even try .001".</p><p></p><p>The issue in using bushings could be variable neck tension. Depends on how uniform the wall thicknesses of the necks. Norma, Lapua and RWS will have the most uniform neck wall thicknesses. Unfortunately Lapua doesn't make a 300 win mag or any belted case to my knowledge. The accuracy crowd that shoots BR use bushings that are used in conjunction with a custom reamer for a smaller neck diameter in the chamber and some neck turning for a much more precise system. Then the neck tensions are very similar. As near to identical neck tension is critical for the kind of accuracy the BR shooters desire. The advantage is longer brass life, less annealing due to less working of the necks with minimum expansion and resizing. There is another factor to consider: with a high recoiling magnum if the neck tension is too low the bullet would most likely move under recoil while sitting in the magazine box waiting for its turn. To test shoot three or four times with one cartridge staying in the mag box and measure that round to see if there is bullet movement. Another advantage in using bushings: during load development the bushing system can be useful for pulling loads that don't work and quickly resizing the necks with the bushing, no lube is necessary and primers can stay in the cartridge.</p><p></p><p>While it could work for hunting the sole use of a bushing die (assuming neck tension is same with good brass) not sizing the shoulders and body might make for a snug fit, counterproductive for fast cycling of bolt.</p><p></p><p>In theory using a standard FL die with a sizer ball, you could produce some neck runout. You are pretty much stuck with the neck tension the die produces. Typical tension for a 300 win mag would be .003" difference between sized and loaded round's neck. On the other hand you can get fairly consistent neck tension piece to piece even when the neck walls vary some in thickness due to the fact the die will drastically undersize the necks then the sizer ball will open the INSIDE of the neck to the proper dimension. It is going to work the brass more especially with the "sloppy" SAMMI neck chamber dimension.</p><p></p><p>IMO unless you use turned necks and a fitted custom chamber you will spend more money and may not see any improvement in accuracy.</p></blockquote><p></p>
[QUOTE="AZShooter, post: 1479862, member: 5219"] Measure OD of loaded round at neck. Subtract .003 and .002" from that value for the two bushings that are usually used. Some shooters of smaller cartridges may even try .001". The issue in using bushings could be variable neck tension. Depends on how uniform the wall thicknesses of the necks. Norma, Lapua and RWS will have the most uniform neck wall thicknesses. Unfortunately Lapua doesn't make a 300 win mag or any belted case to my knowledge. The accuracy crowd that shoots BR use bushings that are used in conjunction with a custom reamer for a smaller neck diameter in the chamber and some neck turning for a much more precise system. Then the neck tensions are very similar. As near to identical neck tension is critical for the kind of accuracy the BR shooters desire. The advantage is longer brass life, less annealing due to less working of the necks with minimum expansion and resizing. There is another factor to consider: with a high recoiling magnum if the neck tension is too low the bullet would most likely move under recoil while sitting in the magazine box waiting for its turn. To test shoot three or four times with one cartridge staying in the mag box and measure that round to see if there is bullet movement. Another advantage in using bushings: during load development the bushing system can be useful for pulling loads that don't work and quickly resizing the necks with the bushing, no lube is necessary and primers can stay in the cartridge. While it could work for hunting the sole use of a bushing die (assuming neck tension is same with good brass) not sizing the shoulders and body might make for a snug fit, counterproductive for fast cycling of bolt. In theory using a standard FL die with a sizer ball, you could produce some neck runout. You are pretty much stuck with the neck tension the die produces. Typical tension for a 300 win mag would be .003" difference between sized and loaded round's neck. On the other hand you can get fairly consistent neck tension piece to piece even when the neck walls vary some in thickness due to the fact the die will drastically undersize the necks then the sizer ball will open the INSIDE of the neck to the proper dimension. It is going to work the brass more especially with the "sloppy" SAMMI neck chamber dimension. IMO unless you use turned necks and a fitted custom chamber you will spend more money and may not see any improvement in accuracy. [/QUOTE]
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How to choose a bushing size?
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