The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading OAL ... "Jump" or jammed in the rifling?Go | New | Find | Notify | Tools | Reply | |
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Back when I reloaded .22-250 I didn't know from Jam and Jump. I used a max OAL number from the manuals - subtracted some (.010?) and away I went. Didn't group under 1/2 or 5/8" too regularly, but I was more interested in hunting 'hogs than range shooting and reloading. Now on the 'net I hear Jump and Jam mentioned often and sometimes it seems like a critical factor in making some guns shoot tiny. Can anyone speak in general terms about this? What's the best method for measuring how long a round will be when it just touches the rifling. (smoke from a candle?) Also ... from reading - it seems that most of the time, you want to be either a distance away from the lands - 10 - 15 thousandths? (Jump) OR crammed right up in there. (Jam) "Just" touching is usually not the way? I think I'll try the jump first. Cramming a round in there gives me a sad mental picture of having to extract the round and dumping H380 all over the guts of me gun. ![[Eek!]](images/icons/shocked.gif){kind=icon} I know ... every gun's different. ![[Smile]](images/icons/smile.gif){kind=icon} I would appreciate anyone taking the time to speak generally and from their experience.TIA TBC [ 07-24-2003, 04:05: Message edited by: The Birth Controller ] | ||
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As far a which is better, jump or jam, there are generalizations. On lighter calibers, .010 off may be a good starting place. On larger calibers, at or into the lands slightly may work better. That being said, every gun is different. The best way I have found to determine jam/jump is to set an overall setback then fire groups increasing the powder weight. We are not looking for group tightness yet but looking for central tendency with the the point of aim. Once you have found the right powder weight, then start adjusting the depth to see which gives the tightest group being careful to note signs of pressure when you are getting closer to the lands. The following site gives a good description of working up a load and adjusting bullet depth: http://home.earthlink.net/~dannewberry/index.html Good luck. Ron | |||
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quote:...One of the best and easiest ways of finding the touch distance is with the Stoney Point case system and then use a comparator to measure the length to the bullets ogive and that is the important distance....in SOME guns it can make a world of difference in grouping....just be sure to back off a max load if you start at the lands.....I start at the lands touching and work back....that way I only have one way to go....for hunting/field loads you don't want the bullet "jammed" into the lands...some bench shooters use this but not for field use.....for best/good results you must use a bullet comparator as the "to the point" method varies too much for accurate work.......HTH..good luck and good shooting-loading!! | |||
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To my way of thinking you're better off jumping. Like you're saying with the jam method, if you need to extract the cartridge you end up dumping the powder. Lightly touching will undoubtably result in pressure variations which will result in vertical stringing. Also you need to measure from the ogive, because at least with Sierra 77 and 80 Matchkings there is usually around a 30 thousands length variation among bullets in the in the box, which doesn't have a huge effect on accuracy but can effect whether you're jamming, touching, or jumping. | |||
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I used to believe that generally 'jammed' would give the best possible accuracy. This summer that got turned completely around. I was playing with my 1903 30-06 (100 years old!) keeping everything constant except o.a.l. and found, much to my surprise, that bullets loaded about .045 off the lands would shrink groups by 50%. This is only 1 rifle and 1 bullet but now I am going to repeat this with several other rifles to see if each has its own 'sweet spot'. So now besides finding the right powder/bullet/primer combo you also have to find the right length. Note, for most hunting rifles the max o.a.l. is set by the magazine rather than throat. C.G.B. | |||
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Each rifle seems to have its own preference. There's no iron clad rule for this. I measured for 11 different calibers last night with my Stoney Point OAL measuring guage. I used about 25 different bullets. In most instances I couldn't even reach the lands so the point is often academic. Most rifles have ridiculously long chambers now. The Remingtons seem longest and the Sakos the shortest. SAAMI specs don't mean much to todays manufacturers. If you're using this guage or a similar one don't force the bullet into the chamber. A gentle touch will do. Some people prefer to split the neck lengthwise, insert a bullet, and let the action push the bullet back when you close it. That works well also. Look for the rifling's shiny marks on the extracted round then set the seating die accordingly. That is, if you reach the lands. Best wishes. Cal - Montreal | |||
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FlyDevil, Excellent link. Printed it out for study. Thanks! TBC | |||
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I agree with Cal - I have a .458 that it is impossible for me to hit the lands in - even seating my rounds to 3/8" longer than normal OAL. Of course the .458 is designed with a lot of freebore - I just never thought it was so much! | |||
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The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading OAL ... "Jump" or jammed in the rifling?
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