Jamming the lands.

redshooter

redshooter

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I've never actually seated a bullet to touch the lands. I'm concerned about a big jump in pressure. Do you tend to get a big spike or just a little one with big cases? I'm loading 208 A-Max with Retumbo. It shot tight at 72.5 gr and 73 gr and it was tighting up at 75 gr. I still had a wee bit of room at 75gr, It looks like I'll be compressing it at about 76+. Will the extra space compensate for the extra pressure and therefore 75 should put me in the sweet spot, or is it (as usuall) tube specific and back her down a notch and start up again?
 
I'm not going to give you a scientific answer (yes, creating more volume in the case decreases pressure but as to what pressure is added by jamming I don't know) but can say the only issues I've had with going .010-.015 into the lands are a) if you get one a little long, you can have bolt closure issues and b) if you load one but then have to unload, the bullet can stick in the barrel and spill powder in your action as the case is pulled away. The bullet is usually really easy to remove, cleaning rod from the business end of the barrel and *pop* the bullet out.

I haven't had any worse pressure signs at .010 into as opposed to .020 off the lands, but that's one man's experience and, again, not scientific. I never reduced my load to compensate for jamming.
 
I can't give you an answer either on how much of a spike you may get. I had tried this 3-4 years ago on my 222 after reading a magazine article (can't recall the author at the moment) but do seem to recall he also stressed no matter if you were near top published load charges or pressure to ALWAYS reduce loads by 10% (as you would changing any component,like primer or bullet etc) and check for usual signs fo pressure at case head,primer, stiff bolt etc.
My 222 didn't show any signs of excessive pressure, but accuracy still seemed best at .010" off the lands. Like you said, each barrel will be a rule unto itself. Good luck!
PS - as Redhouse mentioned it really isn't fun cleaning a spilled case out of the action & (of course) I didn't have a cleaning rod with me to pop the bullet out of the chamber either.
 
:redface: Looks like I'm good. I replaced my Caliper yesterday as it was starting to do some wierd things (digital, replaced it with a better dial type). Remeasured my chamber today and it looks like I was into the lands pretty hard already. Started low again anyway just to be sure. It explains the primer dropping out with the 200 SMK/IMR 7828 load a few 10ths below max. Yes the primers looked a little flat but the cases came out no prob. Then the primer on the third just kind of fell out. Too bad I pulled the bullets on the rest of them. I'd be curious to measure the COL with the better quality tool.
 
When loading for accuracy, I work up my loads with the bullet touching the lands. Once my maximum load is determined, I reduce the load by a grain to see the effect on accuracy. If accuracy improves, I'll drop another grain. Should that result in a larger group, or a greater extreme spread, I'll split the difference between that load and the next higher, and in that fashion I'll gradually zero in on the best accuracy or smallest extreme spread. Once the most accurate load has been established, I'll begin to mess with seating depth if there appears to be any benefit, often there's not. The point is, once I've determined my maximum load, any adjustment to the load or seating depth, decreases pressure.
 
My method is the same as Boomer's. I start by finding the tightest groups with the bullet touching the lands, then seat the bullets .005"-.020" in .005" increments to try to find the sweet spot.
 
You can determine OAL simply and without the benefit of expensive measuring tools, although they are almost always worth the cost. Begin by seating a flat based bullet nose down in a de-primed case, then chamber that dummy cartridge. The base of the bullet will contact the lands and as you gradually close the bolt, you'll push the bullet into the case, resulting in a precise measurement from the bolt face to the lands. Precise that is, provided the action isn't slammed closed, and provided the cartridge is extracted gently. This cartridge should be kept for reference. Every thousand rounds or so, another dummy cartridge can be made up to keep track of your throat erosion.

Next take the bullet you intend to load, place it nose first into the muzzle of your rifle, and with firm pressure on the bullet, turn it so the rifling scribes a line around the bullet. This line denotes the front of the bearing surface of the bullet. Make up a second dummy cartridge using this bullet seated normally. Then the scribed line us at the same length from the case head as the base of the bullet in the first dummy cartridge, your bullet is seated touching the lands.

Should you want to make adjustment from this point on, once you know the pitch of the threads on the seating stem, it can be used as a micrometer, allowing you to seat your bullet at or a precise distance from the lands. If your seating stem has 20 turns per inch thread (Redding) each full turn equals .050" or if it has 28 TPI (RCBS) that equals .037" per full turn.
 
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