Big jump

Discussion in 'Gunsmithing' started by thork91, Jun 17, 2018.

  1. thork91

    thork91 Active Member

    Messages:
    29
    Joined:
    May 2, 2008
    I have a 300 WSM weatherby vanguard, I had it rebarreled with a bartline barrel. Mag length is 2.870 when I measure to lands it is 3.200 a .330 jump. I will be contacting gun smith. What was done wrong and How can this be fixed? Or am I missing Somthing with a custom barrel. If I have the bullet touch the lands I have only a 16th of a inch in case, any ideas, thanks
     
    Last edited: Jun 17, 2018
  2. ShtrRdy

    ShtrRdy Well-Known Member

    Messages:
    1,264
    Joined:
    Jan 14, 2012
    Either the reamer is not what you'd expect or the gunsmith extended the freebore too much.

    What bullet are you using?
     
  3. dok7mm

    dok7mm Well-Known Member

    Messages:
    1,009
    Joined:
    Apr 13, 2015
    If he used a Weatherby spec reamer, it probably has the longer freebore. You should be able to jump it and still maintain excellent accuracy. Some bullets, especially the Bergers, shoot great with larger jumps.

    I imagine your older barrel was shooting with lots of jump, so you might look at your previous OAL to get some ideas. Really good seating depth testing should help you find a sweet spot.
     
  4. thork91

    thork91 Active Member

    Messages:
    29
    Joined:
    May 2, 2008
    Using Berger 185 vld hunting, my jump on the old barrel stock was 50 ths. The old barrel was short I shot 168 Bergers and only had 50 to lands, this one is wow long. I will make up some rounds and try. So this might be OK.?
     
  5. dok7mm

    dok7mm Well-Known Member

    Messages:
    1,009
    Joined:
    Apr 13, 2015
    Berger recommends jumps of .010, .050, .090, and .130". One will show tighter groups, then fine tune to get in the sweet spot.
     
    Rick Richard likes this.
  6. thork91

    thork91 Active Member

    Messages:
    29
    Joined:
    May 2, 2008
    Ya but I have .360 freebore my mag length is 2.870 the jump is .330
     
  7. J E Custom

    J E Custom Well-Known Member

    Messages:
    8,258
    Joined:
    Jul 29, 2004
    SAMMI freebore for the 300 WSM Is set at .189. If you use secant ojive bullets it will be much more than that. Some rifles have over .500 thousandths free bore.

    Checking some of the secant ojive bullets has extended the free bore an average of .125. .125 +.189 gives you .314 freebore. So it looks like your smith used a SAMMI reamer.

    As stated, You don't have to touch the lands to get good accuracy. In fact I find that the Berger's like .090 to .110 jump and are very accurate.

    J E CUSTOM
     
  8. Edd

    Edd Well-Known Member

    Messages:
    2,913
    Joined:
    Jan 26, 2011
    The SAAMI throat of a 300 WSM is tapered at 1.5° and doesn't have any straight cut freebore. This type of throat is not uncommon in Winchester cartridges.

    The .189 length you are looking at, on the SAAMI drawing, is the distance it takes for a 1.5° tapered hole to go from a diameter of .3099" to .300".

    The bullet diameter is .308" so the bullet will contact the barrel where the bore diameter is approximately .308". The distance it takes a 1.5° taper to go from a diameter of .3099" to .308" is about .036".
     
  9. J E Custom

    J E Custom Well-Known Member

    Messages:
    8,258
    Joined:
    Jul 29, 2004
    I would have to respectively disagree with your interpretation of the SAMMI chamber drawing. Free bore is the straight bore that is the same diameter from the neck chamber to the point where the lead angle starts. the lead angle will determine how much more Jump you will get depending on the bullet ojive.

    On the 300 WSM this straight bore is called Free bore and has nothing to do with the lead angle. This dimension on the SAMMI drawings is .189. SAMMI sets this dimension based on magazine length and allows you to utilize a certain amount of free bore depending on which bullet is used to control pressure. It is also the dimension reamer manufactures HAVE to use if it is a SAMMI spec. reamer.

    Bullet selection and seating depth will certainly have an effect on the distance the bullet will travel before it contacts the lead angle. but the free bore is set by the SAMMI drawing for the reamer makers and must be adhered to if it is SAMMI spec.

    So the free bore is set BY SAMMI and altered by the seating depth of different bullet shapes. .036 sounds about right for loaded ammo unless you touch the lands like many do and then you have no usable free bore even though it is built in by SAMMI. Or you have some people that want more bullet jump for velocity and pressure control and they may have up to .100 + thousandths jump by seating deeper
    but they still have the free bore that was built in by SAMMI.

    Also in order to use all of the SAMMI free bore, you would have to seat the bullet deep enough in the case so that the bullet ojive would be at or near the case mouth depending on the bullet shape. this is normally never done.

    J E CUSTOM
     
    dok7mm likes this.
  10. thork91

    thork91 Active Member

    Messages:
    29
    Joined:
    May 2, 2008
    Thank you for your time, I'm assuming I'm ok, freebore is ok, I will load to mag length and see how she shoots!
     
  11. Edd

    Edd Well-Known Member

    Messages:
    2,913
    Joined:
    Jan 26, 2011
    You can disagree all you want to but my interpretation is correct.

    If your definition of freebore is correct, a 300 WSM SAAMI spec chamber has none. And as I said before, it isn't the only Winchester chamber that doesn't have any.
     
  12. J E Custom

    J E Custom Well-Known Member

    Messages:
    8,258
    Joined:
    Jul 29, 2004

    Sorry Edd. You are correct. The 300 WSM has No freebore. The PT&G reamer drawing I had for it said it was a SAMMI spec. It is not.

    Essentially the 300 WSM has no freebore according to SAMMI drawings. According to SAMMI, the lead starts at the termination of the neck chamber And relies on the seating depth for any free bore (Jump of the bullet before it engages the lead angle).

    J E CUSTOM
     
  13. tim_w

    tim_w Well-Known Member

    Messages:
    390
    Joined:
    Mar 25, 2008
    Also guys unless I am missing something. JE you are talking 0.036 with some people wanting max vel jumping a max of 0.100 in your post and saying the first number is about right for bullet jump and thats based even on the .189 freebore nonsaami ptg chamber spec sheet not zero freebore saami but the op is stating 0.330 so not 36 thou (0.036) but 360 thou (0.360) throat thats getting damn near 3/8” of jump. No way thats a normal freebore let alone no freebore with a 1.5 degree leade. With that kind of jump many bullet could be fully unsupported before it ever touches the lands in the leade. His jump is more than his 30 caliber bullet is in diameter !!!

    Someone throated the hell out of that chamber!!


    Thork,

    What were you using to measure freebore? A bullet ? If so which or was a freebore tool which has a full groove diameter/full caliber insert which hits right where the leade starts the 1.5 angle till reduced to full bore/ lands diameter?

    One thing for sure is he did not use a saami spec full reamer but either a custom or a throating reamer afterwards. Your old barrel based on your stament about the 185 and 168 sounds like a SAAMI chamber.

    Using the 185 vld hunter based on your numbers. That bullet has a 0.214” BT. If you set it to have it just kissing the lands to even 0.010 you are only a bit over 0.100 of bullet bearing surface to case neck contact to hold neck tension. I am ok with 1/2 cal on many bullets but when you start getting below that with these longer neck bullets for hunting to me thats a no go..

    Also you have to consider what is going to happen when the throat has its intial eroding in a few hundred rounds. If it were me I would be taking it back to your smith especially if you did not ask for any special throating he should have given you a SAAMI spec unless otherwise discussed. Have him cut the barrel back enough to recut the chamber enough to reset that freebore to give you a min jump for the coal your mag allows with a bit of room to chase the lands a smig.

    These days the only Bergers I shoot are hybrids/EOLs and they are all very tolerant of jump. I start with the bullet in the case as far as I am willing to go based on case neck length and needed vel mag max coal etc and have freebore leade set to allow a 0.015 jump which I have found is the min I consistently am able to get great accuracy with many different hybrid calibers and weights. That way I have the max mag space and neck to bullet bearing surface to chase erosion and can still get very good acccuracy with jumps up to 0.80 sometimes a bit more. By then a good portion of the bore is coooked and a new barrel is needed anyways.

    Sorry I can not be of help with vlds. When I shot them I found they shot best at a specific jump that seemed to vary from barrel to barrel and different weights and calibers etc.
     
  14. J E Custom

    J E Custom Well-Known Member

    Messages:
    8,258
    Joined:
    Jul 29, 2004
    I have chambered 3 or 4 300 WSMs with this reamer but with the drawing saying it was a SAMMI chamber and it worked great on all of them at .189 freebore. This is about the normal freebore for magnum cartridges (Some where around .200 thousandths + or -),so I never questioned it. (My Mistake).

    This does not mean that you have .189 bullet jump, it just means that you can approach the lands for .020 to .030 bullet jump with some of the body outside of the case and stay within mag length.
    With no freebore, the bullet is seated very deep in the case using up case capacity.

    A lot of the SAMMI specifications were before the secant bullets became popular and more free bore was needed. I have only seen one chamber with no freebore on the reamer. and my friend could not load anything over the minimum loads without excessive pressure. Weatherby mag cartridges are given more freebore so maximum velocities can be reached and if you cut a chamber with less freebore you won't be able to shoot factory loads with excessive pressures.

    I personally won't chamber a cartridge with no freebore because most of people want velocity and load to max listed loads and it gets them in trouble. (Just Me).

    Learn something every day

    J E CUSTOM