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Thread: O.A.L and seating depth

  1. #1

    O.A.L and seating depth

    All,

    I recently added a post about 120 grain Sierra soft point in my 6.5 x 55. I have a further query which is a seperate question, so here goes.

    I've measured the OAL on the Sierra 120's last night using a Stoney Point gauge, comparator and digital calipers. My first thought was that in order to touch the lans the bullet needs to stick a long way out of the dummy case.

    Having taken an average OAL using the gauge I've subtracted 20 thou of an inch off OAL in order to set the bullet back off the lans. I think Lee reccomends 20 thou for hunting bullets. This distance worked well for the Hornaday SST's that I loaded previously.

    At this distance from the lans there is only about 5 to 6 mm of the base of the bullet seated into the case (its difficult to measure accurately). This doesn't seem like enough.

    I'm a bit concerned that I won't be able to seat the bullets deep enough to get a proper grip from the neck. I also wonder if it is difficult to seat the bullets true with so little in the case. I'm concerned about roll out.

    Alternatively, I'm concerned that if I seat the bullets deeper I won't be able to get them close enough to the lans and acuraccy will suffer as a result.

    My rifle is a bog standard factory job (Sako 85) and the chamber dimensions are normal. Its had less than 200 rounds through it so the throat is not eroded. I know that the bullets poke out along way on 6.5 x 55s.

    I'd be grateful for some advice on this. Has anyone else had this problem. Do you think I'm trying to get too close to the lans?

    Cheers,

    Bob
    Last edited by Dovebob; 19-10-2011 at 16:42.

  2. #2
    A good rule of thumb is to have the diameter of the bullet as seating depth, but - if the load works & the neck tension is OK in use, then go with what you have. After all, you're pretty close to 6.5mm.
    Apart from the load you've developed performing ballistically, the practical aspects of feeding the round from mag to chamber need to work.
    So, as long as it does & the bullet isn't getting stuck in the lands, I don't see a problem.
    Cheers,
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

  3. #3
    Quote Originally Posted by deeangeo View Post
    A good rule of thumb is to have the diameter of the bullet as seating depth, but - if the load works & the neck tension is OK in use, then go with what you have. After all, you're pretty close to 6.5mm.
    Apart from the load you've developed performing ballistically, the practical aspects of feeding the round from mag to chamber need to work.
    So, as long as it does & the bullet isn't getting stuck in the lands, I don't see a problem.
    Cheers,
    That about covers it Bob.
    www.anglocustomrifle.co.uk
    Anglo deer management and training
    Yet another 7mm 08 user ..................... if Carlsberg made calibers.........................

  4. #4
    Realistically Bob, you are not going to get a 120gr bullet anywhere near the lands in a factory 6.5x55 chamber. Start as suggested with the bullet one calibre deep in the case and start adjusting the oal down from there.

    I would not fret at all reference accuracy. Make up a batch with your best powder charge and start testing them. After every group of three, turn the die down half a turn if the previous group is not good enough. You will find a sweet spot, have faith and keep adjusting the die down.
    Last edited by Claret_Dabbler; 19-10-2011 at 17:47.
    Brian.

    Just because you are paranoid, doesn't mean they aren't out to get you......

  5. #5
    My 25-06 load is 296 thou off (mag restriction), shoots sub 1" at 200 y easily. Normal blaser accuracy!!!!

  6. #6
    Thanks for you advice on this. I will start off working on the powder charge with a seating depth of 6.5 mm and then refine the seating depth when I get a good charge weight.

    When you say keep adjusting the die down, I assume you mean making the overall length of the round shorter and hence the ogive further away from the lands.

    Cheers,

    Bob

  7. #7
    You shouldn't get hung up on having the bullet too close/touching the lands. There are normally at least two 'Sweet' spots to be found within the freebore area. Also certain bullets work better with a 'jump'.
    Of course, if you find a seating depth close to the lands that works with the load combination you have, then use it.
    In nearly all cases though, it wouldn't generally be recommended that you have a seating depth actually touching the lands, particularly not if you're using that load for stalking/hunting. There is always the possibility if you do, the bullet may be extracted from the case, having been pressed just a bit too far into the lands.
    Best of luck. Cheers,

    Having said all that, I load .25-06 to within .003" of the lands....but my rifle doesn't have a magazine or bolt to worry about.
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

  8. #8
    I had exactly the same situation when I started reloading my 6.5 and it was pointed out to me that 6.5 x 55 have a very deep throat, whiuch makes sense as they can be loaded with if my memory is correct around 85 grain upto 150 or 60 grains which means a deep throat is required to allow for the longer bullets. I stopped worrying about the oal as I was no-where near the lans and did as above with the rule of thumb advice,just make sure they feed into the mag.

  9. #9
    Quote Originally Posted by Dovebob View Post
    .....When you say keep adjusting the die down, I assume you mean making the overall length of the round shorter and hence the ogive further away from the lands.....

    Bob
    That is exactly it Bob. I do not worry about exactually measuring length, or exactly how may thou I am of the lands. Start and establish a MAX OAL. Then come up with the best powder charge for the bullet you are using. I then adjust the seating depth. I simply turn the die down half a turn and try a 3 round group at that depth. Just keep going, half a turn down, shoot three, half a turn down, shoot three.

    Works every time.
    Brian.

    Just because you are paranoid, doesn't mean they aren't out to get you......

  10. #10
    Just because the bullet isn't seated to the lands, doesn't mean accuracy will suffer & you can't find another point within the freebore where accuracy would be great.

    Might be a good idea for you to visit & talk to Mike at Calton Moor Range, Swinscoe. He's very knowledgeable and has great range facilities to help you test what you're doing.
    Cheers,
    Last edited by deeangeo; 20-10-2011 at 07:07.
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

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