Nos. Btip seating depth. Are they picky?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Derek M., Oct 24, 2012.


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  1. Derek M.

    Derek M. Well-Known Member

    Messages:
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    Jul 12, 2004
    I've never really had to put much effort into getting a good load with ballistic tips so I've honestly not spent a lot of time monkeying with seating depth for them. I have a new build, a 280 Remington. It has a Shilen select match bbl and I had the chance to shoot it today and "break it in." Much of the time I will use some old VV powder I have on hand to break rifles in because the powder burns clean. In this case I used VV N165, Norma brass, Fed 210 match primers. I increased dose of powder as usual to find max if I even get that far, then have 5 shots of each charge. Today on the 57.0 and 57.5 grain charges, I had the first 2 shots close to each other, then a 3 shot cluster for shots 3, 4, and 5. The 57.0 gr rounds through an overall 1" group but the 3 shot cluster measured 0.3s and the 57.5 tightened up to 0.2s for shots 3, 4, and 5.

    I'm wondering if its because each 5 shot string started off with a cool, clean barrel, and the barrel needed a couple of foul shots to get things going. Once firing began, the bbl was never allowed to get hot but it did get warm.

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    So, what I think I'll do is load 5 shots with 57.5 grains at 3 different seating depths for 15 total (which is the purpose of this post). Does anyone have any experience varying btip depth and seeing targets opening or tightening up much? I have not when I did a brief experiment some years ago. Plus, I will foul the barrel with 2 shots to begin with and just not do any cleaning during this test. The new barrel has 18 bullets through it. I had 5 loaded with 58.0gr powder but the first 3 were an inch and a half apart so I saved #4 and 5 for future foul shots.

    Since I still have about 2 pounds of this powder I still try to see if I can get a load with it anyway. Plan on going back to range Friday. I was going to try IMR4350 but if my hunch is correct, and the new barrel just needs to be a little dirty, then I think I'm already on to something. Not sure yet. Or, I suppose I could just keep doing the break-in process according to Shilen (continue to clean after every 5 shots until you hit 50). I'm just running out of time before I go to CO. Still have 2 other rifles to play with.
     
  2. Derek M.

    Derek M. Well-Known Member

    Messages:
    2,417
    Joined:
    Jul 12, 2004
    Shot yesterday morning and confirmed foul shots were necessary.

    I had 2 bullets left with 58.0 grains of VV N165 so I used those to foul the barrel. Curiously, they touched each other at 100 yards where the last range session a three shot cluster formed a 3/4" group (but again, that was on a clean bore).

    So I took 21 loads to check seating depth. All were 57.5 grains of powder. I did not clean the barrel at all.

    5x seated as before at 3.30
    5x seated at 3.34
    5x seated at 3.32

    6x seated at 3.33 (for 2 three shot strings)

    The rifle definitely likes the depth at 3.34 best. The 5 shot group claimed a 3/8" group so that will do. The rest did very well and to my satisfaction. All under or at 1/2".

    So the 280 and 7mag are going to Colorado in a couple of weeks. I'll take the 280 to KY on the 10th for the opener, then hit the road to CO the next morning.