.243 Seating Depth

Discussion in 'Reloading' started by Ghost7, Apr 22, 2015.


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  1. Ghost7

    Ghost7 Well-Known Member

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    Hi All,
    Fairly new to reloading and have a rather complex question. I have been experimenting with seating depth. I have been exceeding max coal trying to get closer to the lands. With some of the smaller grain bullets this is not leaving much of the bullet to seat. I just wondering what is the ramifications of having less of the bullet inside the case which in turn is leaving more volume unoccupied inside the case. What happens to pressure? Velocity? And Accuracy when trying to get closer to the lands but seem to be running out of surface to press the bullet. Any insight would be great.
     
  2. Corey Schwanz

    Corey Schwanz Well-Known Member

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    Accuracy may or may not improve as you stick the bullet out longer towards the rifling. Every gun is different and will require a different "best" seating depth.

    Assuming the powder charges remain the same, you will be decreasing the pressure inside the case as you stick the bullet out further. The longer it is, the more air space there is in the case, and given the same powder charge, more space for the explosion will have less pressure. This stops once the bullet actually touches the rifling however. If you get the bullet seated out too far, the neck of the case may have a hard time holding onto it and you could see problems like bullet seating depth changes. you don't want to set a perfect seating depth than have the bullet shift on you and you not know it. Make sure the bullet is held securely in the neck.
     
  3. moombaskier

    moombaskier Well-Known Member

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    What rifle and what bullet? There are some somewhat standards that may come into play.
     
  4. barefooter56

    barefooter56 Well-Known Member

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    Ghost7,
    General rule of thumb is at least 1 caliber of bullet in the cartridge case. 2 is better. What you may want to do in your case . since you are dealing with a short bullet is to start at the published magazine
    length and work out in .001-.005 increments at the lowest powder charge listed for your bullet/powder/cartridge combination you are testing for. Be sure the barrel of the rifle has been fouled by shooting at a practice target until the bullet strikes stop rising on the target and begin to cluster before doing your group shooting. After you have found your bullet seating depth accuracy node . then work the load back up in 1/2 grain increments until you get to 2 grains below maximum then drop to 1/10th grain increments. All the while you will be checking for pressure signs and accuracy. Another thing to try if nothing seems to work is another brand bullet in the same weight range. There is that intangible of "bullet to bore fit".
     
  5. Ghost7

    Ghost7 Well-Known Member

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    Thanks all for input. To answer moombaskier the rifle is a Savage 12LRP and theis particular bullet is a 70 gr Nosler Ballistic Tip. In a previous thread I was having difficulty getting this rifle to group but have since, with much help from many on this forum, have been successful in grouping. This rifle likes the heavier bullets. I am still working on fine tuning those but was taking a mental break from that. I had a fairly new box of the 70 gr and wanted a different challenge to see if I could get them to shoot. The group sizes are ranging from 2.25" to .799". I have taken the .799" load and started extending the coal to see if I can improve on that load, hence the questions. I have gotten the Sierra 85 gr hpbt to group right at 1/3" kissing the lands but haven't got that far with the 70gr because I feel like I'm running out of neck. The 105 gr Amax is really long and have shot well kissing the lands as well. Being a 9.25 twist it may not like the 70's but I'm hearing of others getting the 55's to shoot extremely well. Thought I would at least give it a fair shake.
     
  6. FearNoWind

    FearNoWind Well-Known Member

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    Some rifles will shoot the longer/heavier bullet differently than the shorter/lighter bullet so it's often not possible to compare seating depths between these two extremes. Both my .223 and my 6BR like a longer "jump" with lighter weight bullets but accuracy with the heavier bullets increases with those seated a bit closer to the lands. Be careful not to assume that closer to the lands is better. That's rarely true.
     
  7. roninflag

    roninflag Well-Known Member

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    what load is working so good with the 85's in your lrp?? the 70s are short enough that they usually require a jump and still have enough seated in the case to be secure. i have had the 70's shoot real good in several 243's . I4064 and varget and lapua brass.
     
  8. Ghost7

    Ghost7 Well-Known Member

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    Fearnowind,
    It seems that I have assumed this as I have been told this by many people or have read this very thing. I just assumed that this was a general rule of thumb with all bullets. My lack of experience at this point cannot disprove this theory except with the 70 gr. it doesn't seem to shoot any different no matter where it is seated even though I haven't made it to the lands, still trying to get there to find out. Does anyone have a good 70 load they would like to share? I currently have Varget, imr 4064 and imr 4350.
     
  9. roninflag

    roninflag Well-Known Member

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    i was close to max in nosler manual with my 70 balistic tip load with both i4064 and varget. not where i can check. 41 grains?
     
  10. Ghost7

    Ghost7 Well-Known Member

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    Roninflag,
    The 85's shot the best for me with 35.8 gr of varget against the lands. I tried imr 4064 on the low end and only got about .913". That was only 35.4 gr. I quit with the 4064 once I got to 1/3"with varget. I'm going to try some 4350 as well but haven't got to that yet, it works good with the 100 and 105 gr for me. First load I tried with it on the 105's was right at .654", haven't played with it anymore yet. If work didn't get in the way I would be a lot further along with my load development. This is all new to me but I love it.
     
  11. Ghost7

    Ghost7 Well-Known Member

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    The 4064 on the 70 gr gave me mixed results, 40.5 gr gave me a .821" group overall but I had three touching, .227". Those two flyers could have been me but I was shooting out of a lead sled on that particular set. I just don't get it! 3 touching and two flyers. At times I wish I had a more experienced shooter shoot for me so I could tell if it is me or not. If it is me than I could save a lot of time and frustration but none of my buddies have gotten into this. I guess I will just learn from you guys and the school of hard knocks.