Seating depth affect???

Discussion in 'Reloading' started by Havard, Nov 30, 2019.


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  1. Havard

    Havard Well-Known Member

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    Ok, I have searched on here to try and find the answer to this question, and can’t. So here is my issue;
    Rifle - Model 700, Gen 2, 5R (1:11.25) .308, 50 - 60 rounds thus far with proper break-in completed.
    Lapua brass (new), 46gr Varget, Fed 210M primer, 150gr TSX Barnes.
    I made a mistake in the original CBTO measurement, and failed to check for magazine feed. Single feed, I seated -.027” from the lands and settled on the 46gr of Varget as I got .70 MOA in 3 shots. **This was the best group I’ve seen with this gun. A couple of days before the first hunt of the year, I double checked for magazine feed and found the mistake. I reseated to -.150” off the lands and the groups went to crap again.

    I’m sure I went about this the wrong way, but my question now is, do I go back to scratch with powder charge considering magazine feed COAL first, or what? Put more rounds through her? Is the excessive jump going to cause problems with all rounds?
    I’ve tried factory Loads in the following and can’t get any to group; Nosler 150gr Ballistic tip & Hornady 150gr SST.
    thanks....
     
  2. BallisticsGuy

    BallisticsGuy Well-Known Member

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    No, you should understand clearly that your gun is chambered with a factory chamber with a hot-dog-in-a-hallway throat so it'll accept any factory ammo you could stuff in it and that that leads to long jumps and that long jumps are notoriously bad for groups. That's what you call "boned".

    There are a few ways of attacking the issue but the fundamental issue is you have a factory cut super long throated chamber. All of the fixes are going to focus on getting the bullet ogive closer to the lands through whatever means.

    My advice, you might want to select a local gunsmith to lop half an inch off the back end of your barrel, re-thread and shoulder the tenon and then re-cut the chamber with a reamer with a throat of correct length to provide you .030 jump with 150gr bullets seated to mag length -.030 provided that you want to run 150's. That should provide you with a setup that you can shoot darned near forever and still chase the lands a bit but not get out of mag length for a HUGE number of rounds. .308's in my experience are pretty mellow on throats, unlike 6mm and 6.5 which seem to be racist against barrel throats.

    You could also try finding some heavier bullets or bullets with a shorter nose cone and longer bearing surface. I doubt that this will work for you and still be mag length.
     
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  3. LongBomber

    LongBomber Well-Known Member

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    Just how close to the lands can you get and feed the tsx? In several guns I have them running in the .070” off range. I would leave the powder charge alone and try a few seating depths in small steps.
    That long throat limits you as to what bullets you can shoot well and feed from the mag. Could go with a wyatt mag box thats longer, pretty easy to have installed and that will give you more mag length.
     
  4. Havard

    Havard Well-Known Member

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    I’m as long as I can be and magazine feed. I will check the Wyatts box; that’s a good idea and I hadn’t thought of it. Thanks
     
  5. RICHARD PERRETT

    RICHARD PERRETT Active Member

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    If the Gen 2 has a magazine box with a block in it I have cut the block out and moved it to the back of the magazine and J-B weld it to the back of the magazine. This gives a additional .125 COAL in my model 70 long actions. Hack saw blade, files and J-B weld. Just a alternate suggestion. You have to grind back the bolt release/ejector so the bolt comes back far enough to pick up cartridge head. May have to fiddle with magazine lips a little once you have your final round made for smooth feeding off the rails.
     
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  6. RICHARD PERRETT

    RICHARD PERRETT Active Member

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    Be careful of those aftermarket mag boxes. They have to fit between your action screws and I personally think they are a bit pricey.
     
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  7. Mikecr

    Mikecr Well-Known Member

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  8. J E Custom

    J E Custom Well-Known Member

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    Actually, It is very simple. Decide if you are going to load to magazine length or single load the rifle. Then work up the load with the COAL to Mag length - .020. After you find the load then you can tweak the length shorter or longer to find out what shoots the best.

    All of my hunting rifles shoot Mag length ammo and 4 of them will shoot under 1/10th MOA groups because the loads were worked up at those lengths. One of them is a 30/378 that has .371 freebore and the others have close to .200 freebore.

    Bullet jump is .105 thousandths in the 30/378 and the tightest dimension is .035 in the 7/08 to the lands. I don't want to give up velocity and add pressure by seating against the lands, So I load Mag length on all of my hunting rifles. and they will all out shoot me. The least accurate hunting rifle I have shoots a consistent average 1/4 MOA and on my bad days it will stay around the 3's (.300 thousandths 5 shot groups)

    So my recommendation is to work up your load the way you want to shoot the rifle and in the same condition. (Clean, slightly fouled or fouled) to get the best from it.

    Just My opinion

    J E CUSTOM
     
  9. 59FLH

    59FLH Active Member

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    Change bullet to a spitzer style, Hornady, Sierra, Speer, etc. You ought to be able to get the desired jump and fit in the mag, assuming jump is your issue. My guess is jump may not by your issue.
     
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  10. Rick Richard

    Rick Richard Well-Known Member

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    As mentioned load to how you want to shoot either from the mag or single feed.

    Just a thought, but before I started some elaborate modifications try some good ole 168 grain bullets such as the AMAX and see what that does. My experience is this Bullet is not seating depth sensitive and over the right load of Varget or 4064 it will shoot incredible. Good luck!
     
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  11. Frog4aday

    Frog4aday Well-Known Member

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    Barnes and Hammers seem to shoot well with more than normal jump. Your fix could be as simple as a change in projectile.
     
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  12. Shane Lindsey

    Shane Lindsey Well-Known Member

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    I too have found that all my Barnes loads liked a considerable amount of jump. Barnes load data for 150 TTSX has a COAL of 2.735”.
    May be worth doing a seating test.
     
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  13. stljc2

    stljc2 Well-Known Member

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    I ran into something similar. My VLD's in 308 liked 40 thou to the lands. Only problem is they won't load in the mag well of my M700 bdl. So I am having to deepen the seating to fit. Haven't been able to shoot them yet but I'll see what happens. Might have to switch to spitzers but hoping it'll be ok.

    Oh and having the same issue with my 260 rem. also.
     
  14. Window

    Window Member

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    You could try the Hammer Hunters. They’ve shot very well for every rifle I’ve loaded for so far with just about any seating depth.