Throat length and seating depth

nhkuehl

nhkuehl

New member
I had an interesting thing happen (At least to me) with a couple of rounds that only had 0.060" of the bearing surface seated in neck with 0.0150" jump in a long throat. See picture. Gas had pushed past the shoulder and dented the case body. I measured the fired case necks (50 rounds) and they were 0.242", the same as they were after being neck sized with a 0.244" bushing and loaded they are normally 0.245". I didn't happen to fire those two rounds so I'm not sure if the shoulders may have gotten dented chambering the rounds, which allowed the gas to blow back past the shoulder. The rifle is a SA Savage with a .308 blind magazine and benchrest follower that I use for a test action and had swapped the bolt head to .223. The rounds wouldn't slid in to the chamber from the bigger benchrest follower freely and may have been forced and the shoulder dented. I decided to reload the rounds and see if I could blow the dents out so I seated a heavier bullet 0.100" in to the neck with 0.015" jump they fire formed with out a hint of the dent and the necks were expanded to 0.250". I've probably never seated a bullet less than 0.125" into the neck before and that was the first time I had a case neck not expand. Apparently the dents didn't affect the accuracy much the two holes were 1/4" ctr-ctr a 100 yds and those were bulk discount varmint bullets.

Just curious does anyone have a rule of thumb for how much longer does the bearing surface of a bullet needs to be than the throat to insure a proper seal, or how much of the bearing surface needs to be seated from jam to insure a seal? Back when I started reloading the saying was one caliber, but that soon proved to be impractical. - nhk
 

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If in fact you have found a problem with a combination of .060 bullet in the neck, and .015 bullet jump, you could easily add another .020 in the neck. Long-range benchrest shooters frequently jump bullets .040.

Additionally, I have many times fireformed cases with pistol powder and either toilet paper to keep the powder in the case, or no wadding at all, just hold the rifle upright. As long as you develop 40,000+ psi, all is well with case forming.

Or the schutzen crowd, who breech-seat lead bullets in the rifling and use a case with a wad.

If in fact your dents come from your setup, it is a combination of things, not a single condition. If you follow the wolf pup links, you'd see where Stan Ware formed his cases the first time with almost no neck tension

http://bulletin.accurateshooter.com...al-short-necked-wolfpup-for-hunter-benchrest/
 
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