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Thread: Minimum seating depth?

  1. #1
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    Default Minimum seating depth?

    OK, I've always heard the rule of thumb that you should bullet should have at least one diameter seated in the neck. i.e. for a 223 Rem, there should be at least 0.224 of the bullet inside the neck. But I'm having some problems with that.

    I was loading up a bunch of ammo for my AR and I was going to use 50gr Remington HP bullets (old bulk bullets I bought years ago from Midway). Those bullets are only 0.612" long. A 50gr HP in Nosler or Hornady are more like 0.716" and 0.725". 50gr Nosler Ballistic Tips are 0.789".

    My problem comes in when trying to decide on what OAL to seat the bullets to. If I seat out to 2.260" (SAAMI max and what most reloading data is based on), then assuming the brass is trimmed to 1.760", I'll only have 0.112" of bullet in the neck. If I seat 0.224" in the neck, then my OAL is only 2.148".

    Now, I really don't care what my OAL ends up being, I just want to make sure that: 1) I have safe pressures, and 2) The bullet won't fall out during recoil.

    What do you guys think?

  2. #2
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    I'll be interested to see what others think, but it looks like I'm starting first here.

    Backing-up a bit...what's the distance to the lands for this rifle with this bullet? Have you measured it? Do you have a tool to do that?

    It's the distance to the lands that becomes the starting point for me when I'm determining the seating depth...not SAMI, and it's pretty amazing the variation you'll see from one barrel manufacturer to another for the same caliber with the same bullet. For best accuracy I (and most others I know) try to seat just off the lands with the exception of the Barnes TSX's, which seem to like more freebore space. That said, there have been times when seating just off the lands for a particular rifle and bullet combination would be too long for the magazine (it exceeds SAMI specs)...that's when you just seat it to SAMI specs (not your situation). You may find that the distance to the lands for your rifle and bullet combination is shorter than SAMI specs (it happens), which would be good news for you because then you can seat the bullet deeper (further into the case mouth).

    If you find that your distance to the lands results in an OAL that exceeds SAMI, and you already know that SAMI specs don't give you enough seating depth into the case mouth for this bullet, then I'd just seat it down to your formula. You might find the loads aren't as accurate as you would like because the bullet jump to the lands is greater than you want, but there you go. Start with minimal powder charges (as always) and work it. I think you'll be OK. If you measured factory ammunition across different manufacturers you would see that they all don't result in the same OAL...it varies alot by bullet. SAMI specs give us a maximum length so that finished ammunition doesn't exceed a certain length, thus magazine dimensions can be uniform accross manufacturers for that cartridge.

    Let's see what others think...

  3. #3
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    I'm still interested to see what others think, but here is what I did. I settled for a happy medium and seated them to 2.205, which is 1/2way between book OAL and 0.224" in the neck. The reasoning was that should still be enough to hold the bullet in the neck, but the internal case capacity should still be larger than typical and so I shouldn't have any pressure issues. I'll let you know how it works out.

    By the way, this load will be shot in an AR. I have measured other rifles for max OAL to the lands, but didn't do it on this one. For one, I've never done it on an AR, I'm not even sure how. For two, I'm quite certain that throat is long enough for the bullet to be completely out of the case neck and still be in the chamber, so I don't think I could seat anywhere near the lands anyway.

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    I'm not an expert around here, but will throw my experiences in to your considerations,
    (such a non expert, in fact that I'm not even sure this applies to your question,.. )
    but here goes anyway
    my results with a Sako 85, that has a max magazine length, that is far short of what it would take to get out to the lands

    have been very excellent,..I was really puzzled by all the emphasis on seating to the lands when I first started
    because of this,
    read everything I could find on the subject,....and found that apparently Sako often does this, like maybe intentionally,
    have heard Weatherby does also,....build for a jump to the lands

    so I've seated for magazine length with longer bullets, and just seated to either Saami recommended length,
    or maxed out at the bullet diameter, down into the neck as you referenced

    Have had great results dealing with this,...they've all jumped to the lands with fine accuracy,...like really fine,...
    and for the smaller bullets (this is .270wsm, and I've loaded everything from 160 gr, down to 90gr)
    it is a major jump, with those little 90 gr hp's,....but they're super accurate out of that rifle

    so, taking that into consideration,... I would be more apt to seat into the neck, the bullet diameter as a minimum
    rather than leave it out there, potentially leaving a shallow seat,...

    Opinions out there on this ??
    Ten Hours in that little raft off the AK peninsula, blowin' NW 60, in November.... "the Power of Life and Death is in the Tongue," and Yes, God is Good !

  5. #5

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    I don't think you can reach the lands in an AR...I'm new to reloading the AR, but I have had some time in the learning curve...I first thought I would load to 2.250 and then went out and bought a few different mags. and found the mag. is what will determine what your col will end up....

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    Sponsor ADfields's Avatar
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    My rule of thumb is “whatever works.” Some caliber bullet combos are just fine down around only .100” and some cases don’t have a diameter worth of neck to them. Whatever works, lead needs more that copper, boat tale needs more than plain base etc. I like them flush with the shoulder if I can and don’t like hanging a gas check below the shoulder but it does work. Then there is the dang crimping grove that ain’t ever where you want it. There are just too many variables to have a rule much beyond whatever works.
     
    Load-um up and see what works, find your best compromise of all the many factors your working with. And it looks like that is what you did, carry on.
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    The shortest neck of any factory cartridge compared to it's bullet diameter that I'm aware of is the 375 Ruger, with a neck length of only .305. That is 81% of diameter, and that on a hard recoiling rifle. I have personally set 70% of bullet diameter as my minimum seating depth, and have yet to have a problem with either accuracy or bullets shifting under recoil.

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