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Posted: 4/14/2009 4:50:15 PM EDT
| I'm re-sizing 7mm Remington magnum cases for reloading using an RCBS Rock Chucker and RCBS dies. I measured my first few cases and I think there may be a problem. Neck diameter in front of the shoulder, before I resize my cases, is 0.320. After resizing, my neck diameter is 0.310. The reloading manual states that the neck diameter forward of the shoulder should be 0.315. Also, the internal diameter of the neck where the bullet is to be seated is measuring out to 0.280. This would seem to be a problem since 7mm is 0.284. Is this normal behavior or is something amiss? |
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Quoted:
I'm re-sizing 7mm Remington magnum cases for reloading using an RCBS Rock Chucker and RCBS dies. I measured my first few cases and I think there may be a problem. Neck diameter in front of the shoulder, before I resize my cases, is 0.320. After resizing, my neck diameter is 0.310. The reloading manual states that the neck diameter forward of the shoulder should be 0.315. Also, the internal diameter of the neck where the bullet is to be seated is measuring out to 0.280. This would seem to be a problem since 7mm is 0.284. Is this normal behavior or is something amiss? Over thinking...... Go measure a loaded round at the case mouth..... Go Measure the neck wall thickness of YOUR brass, multiply x2, and add 0.284. Neck wall thickness varies with mfg of brass so it is a variable that the reloading manual does not reflect. As long as your neck tension is adequate to prevent bullet set back you are good to go. Now if you want to get fancy.....you take that loaded round #, and decrease that by 2-3 thousanths that would be the correct bushing to use to have more control over your neck tension with bushing dies. |
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Quoted:
the inner diameter of the case mouth has to be < the diameter of the projectile, on my .223 cases the ID of the case mouth is .222" which holds my .224" diameter projectiles securely That makes sense. Probably would've figured it out if I hadn't panicked and ran to ARFCom for advice, LOL! I'm just being extra careful with this batch. I've reloaded quite a lot of 223 and 7.62x39 under my dad's supervision. However, this is the first time I've reloaded a belted magnum caliber and due to the forces involved, a mistake could prove quite a bit more costly than with lesser calibers. |
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since we're on the topic: the sizing porting of the sizing die usually squeezes the ID of the case mouth smaller than the final inner dieameter, e.g. for my .223 case, it might squeeze it to .221" or whatever. On the upstroke of the press, the expander ball of the sizing die is pulled thru the neck and whatever the diameter of the expander ball is will be the inner diameter of the case mouth. Then when you wedge a projectile into that case mouth, it'll expand to the diameter of the projectile but squeeze the bejesus out of it, holding it securely. Crimping adds even more squeezing pressure When you fire the cartridge the inner diameter of the case mouth becomes > the diameter of the projectile Trying seating a projectile by hand with a unsized and a sized case just for fun |
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