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Seating a bullet into the lands.
ContacFront
Member Posts: 1,113 ✭✭✭✭✭
Will doing this cause more pressure?
Comments
The tips of all my pills extend into the bore, but I usually back the bullet off about 2-4/1000ths from the lands
Eric
All American Arms Company
www.galleryofguns.com
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Veteran Owned and Operated
The entire "seat close to the lands" thing started with BP & lead bullets, as the rifle chambers in those days had a very "generous" throat angle (picture a funnel) of around 10deg/side. Now move forward 125yrs and you'll fine that throats are running closer to 1.5deg/side, with some people using a cylinder (0.0deg/side) throat. The smaller the throat angle the lower the benifit gained from seating to the lands. It's to the point now that it's more of a tunning step (barrel vibration nodes) than a "mandatory for accuracy" one. The closest custom chamber I have will only allow me to get within .045 of the lands and still be able to use the mag, but with >.5MOA groups being common with that rifle (worst single group has been .75MOA with factory ammo), I'm not complaining.
Some guys like a mag full of lead, I still prefer one round to the head.
NRA Life Endowment Member
Bad spellers of the world
"UNTIE!"
On your mark-get set- go away!!
anywho,..the seating to the lands method is a great "Theory" and seems to be very simple. However, the bearing surface lengths of bullets vary in length as do the noses and tails (if applicable). This means that finding a length of "at the lands" with a certain bullet from the lot will mean that only the exact same bullets in that box will be at the same distance to/from the lands. Sorting by bearing surface length is the only way to insure consistency. therefore, a distance slightly off of, or slightly into the lands makes more sense as the variance in pressure will be less as the bullets all either jump a small amount (even though some jump less than others), or are all touching the rifling under a small amount of pressure (making for no jump in with any of the differnt pills). There was an article in one of the last 2-3 issues of Precision Shooting where the author ran a test on exactly this. He started with the standard "at the lands" with a single selected bullet from the lot. The loaded rounds (after he machined a seater plug that reduced runout) were then fired for groups. After he then manufactured a micrometer adjustment top and used the special seater plug, he was able to seat every pill with the ogive at the same distance from the lands within .002". He then loaded rounds both off of and .010" into the lands as well as at the lands and shot for groups again. after then seating the bullets again without making them perfectly uniform and shooting he was able to determine a 1:10 ratio. In his test he proved that a .001" variance in bearing surface length to land equated to a .100" variance in group size.
My point being that using better quality bullets (nosler, hornady a-max, berger, SMK, clinch river, jlk, etc) with their tighter tolerances and more uniform bearing surface length, will result in better acuracy when using the "at the lands" method of loading. I tend to be gravitating toward starting my loads at .010" off or .005-010" into the lands.
And yes,..pressures will be a bit higher into the lands, so back off a bit and work back up.
why chase the game when the bullet can get em from here?....
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