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Posted: 3/22/2010 7:08:08 AM EDT
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Looking to do the "next step" in reloading
I neck sized some cases and only intend to use them in my 1903 a3. my question is seating the bullet to be just away from the rifling. I have heard of seating the bullet in an empty case and running the bolt forward until it touches the rifling, then go a little farther (.020")with the seating die. anyone have a link to some published reading that would help me??? |
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Here is one "published" method of setting "jump to lands".
http://www.6mmbr.com/catalog/item/1433308/977259.htm There are many others such as RCBS's Precision Mike or Sinclair's method. One important point: The classic rimless bottle neck rifle cartridge registers case shoulder to the chamber shoulder of the firearm. So, make sure the "jump to land" data is taken with respect to case shoulder against chamber shoulder. |
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Quoted:
From the link above For max accuracy you need consistent bullet position relative to the start of the barrel's rifling. You can set this by trial and error. can someone explain? For precision work (all in one hole) it is another variable that should be closely controlled. It affects start pressure and thusly barrel pressure profile start to end. Your particular configuration of chamber / barrel / cartridge may fly better with a .020 off-land position, while mine may fly better with a .010 off-land position. If you can regulate other firing conditions so the noise does not engulf the effects of off-land, then by checking your POI accuracy, you can find the sweet spot for your particular off-land condition by trial and error. [ETA] second effect is that it minimizes the chance of bullet entering the rifling crooked, which some experimenters have found causes it to exit the barrel crooked. Personally, the off-land thing is way down on my list of things to control (first is my eye sight and reflexes at the range). 
ETA: if you go down this road, the first frustrating barrier you will hit is that to set good off-land position, you will need to exceed COAL that allows use in any kind of standard magazine, be it bolt gun or gas gun. Second thing, is that for some military round configurations you will need to set the bullet out so far it falls out of the neck. |
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The basic rule of thumb is that you'll want about 1/32" (about 0.030") of free bore before your bullet contacts the rifling for optimal performance. In some rifles it may be a little less, in others it might be a little more. If you're shooting a typical Weatherby magnum, don't even bother to try it.
Unfortuantaly, you're reloading for a military chamber & the throat may be excessively long to do this with and still have ammunition that fits in your magazine. The reason, most military rifle chambers have very long throats in an attempt to be able to shoot an assortment of bullets without pressure issues. Extra long throats help reduce chamber pressures. To do it properly, you'll need access to a COL gauge (just follow the instructions) but it can be done with patience, a sized brass, good quality calipers, a kenitic puller & some Dykem or even candle smoke. Firstly, chamber one of your sized brass a few times to get a feel of how much resistance you have with no bullet contacting the lands. To rule out the possibility that the throat is so long that the bullet will never contact it while still in a cartridge, start by seating your bullet about 1/4" into your case and attempt to chamber it (some guys say that you must have at least one caliber of bullet in the case neck). If it chambers with no additional resistance (or at all), all of this is a moot point because the throat is too long to work with & attempting to make it work will only cause more/different problems later. Just go ahead and use the loading data OALs. If you do have resistance (like the cartridge is too long to fit in the chamber), don't force it but but remove the cartridge & seat the bullet one additional turn down on the seater plug and try again. Repeat until the cartridge chambers just as easily as one of your empty sized brass. At this point, take the cartridge that fits into the chamber and either Dykem or smoke the bullet with a layer of soot from a candle and gently chamber it without scraping off the marker agent. Gently extract the cartridge and examine the bullet to see if it is touching the lands. At this point there are two possibilities 1) The bullet is still touching the lands, there will be little marks where it touches each land where the land has disturbed your marking agent (4 lands = 4 little marks). If you are touching the lands, seat the bullet an additional 0.01" , re-smoke the bullet and check it again. If no marks are visible, seat the bullet an additional 0.20" and at that point you'll have appx 0.030" of clearance. If marks are still present, seat the bullet 0.01" deeper and try again. Repeat until the bullet does not touch the lands, then set the die 0.02" deeper to get the appx 0.03" of free bore. 2) Not touching lands at all (no marks on the bullet), measure the OAL, pull the bullet and re-seat it 0.03" longer, re-smoke the bullet and gently chamber it. If still no marks, repeat this process until the bullet does contact the lands. Then follow the process in 1) above. Good Luck, MLG |
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Thanks guys. I tried a sharpie last night. and the throat is very long, but it made a wicked looking 06 round.
I got a vintage military shoot on bags comming up and just wanted to get the most out of the 03. I will mess around with it... and see it I can even tell the difference. (probably not)... |
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