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Thread: How much do changes in seating depth affect pressure?

  1. #1

    How much do changes in seating depth affect pressure?

    I worked up some loads at the weekend, they shot ok but not great, I was going to try increasing the COL to see if they improved. Should I go right back to square one and work up from the minimum load again? there were no pressure signs whatsoever with the first batch. These are really short bullets, 7mm 100gn JHP so they will not be too near the lands whatever I do....

  2. #2
    Pressure will reduce until you jam into the lands.
    Best not to worry too much about 'how far from the lands'

  3. #3
    Tom Im not the most experianced home loader but I can manage to get decent groups and to myself thats what counts. Anyway last Tues I went out to check zero and try a few other loads some of which were 30 thou 20 thou snd 10 thou of the lands. My best group was the 10 thou loads but by the time I had worked up with the seating depths. The rifle started barking more and the primers were flattened more than the 30 thou loafs. They were still we safe but I felt there was a definate change. Other more experianced lads may well correct me.

    Nutty

  4. #4
    Quote Originally Posted by j0e_bl0ggs View Post
    Pressure will reduce until you jam into the lands.
    Best not to worry too much about 'how far from the lands'
    Thats what I meant in my last sentence.

    Nutty

  5. #5
    may i ask what caliber mate by the sounds of it its a 7mm08 in that case with 100 grain bullets just check your twist is suitable. most barrels in 7mm08 are 1in10 or 1in9.5

  6. #6
    They are stable in my 1:9 twist. which is good, they shot just over an inch at whatever charge I tried, maybe thats as good as I'll get with them, but I'd like to try a longer COL without having to go right back to square one with the minimum charge.

  7. #7
    Quote Originally Posted by Tom D View Post
    They are stable in my 1:9 twist. which is good, they shot just over an inch at whatever charge I tried, maybe thats as good as I'll get with them, but I'd like to try a longer COL without having to go right back to square one with the minimum charge.
    As long as you seat further 'out' pressure will reduce - if you seat further 'in' pressure will increase.

  8. #8
    maybe a different powder may tighten things up theres alot of interesting reading on oal and pressure the conclusion i got was every rifles had its own quirk and just take baby steps and watch for pressure but nutty spaniel is wright ive notied a definate change at 10 thou from lands. i load at 40 thou thats what it likes and functions well with out the ai mag. Good luck with yours is it new or just a bullet change

  9. #9
    The rifle is new, well the barrel is anyway.. It can shoot .3 inch with amax so I will play around with these jhp's and see what happens, if I can't get them sub half inch then I'll use the amax for the foxes instead.

  10. #10
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    Oops! I blew a primer out by miscalculatig length and shooting a load in my 270 Winchester where the bullet was in contact with the lands (an where I had used a load from the manual, well below maximum, without "working up")! Fortunately no harm done AND it didn't feel or sound like anything other than a normal round. But traps and falls lie in wait for the reloader that cuts corners.

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