Hot 6mm Rounds

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Tyler Kemp, Jan 25, 2009.

  1. Tyler Kemp

    Tyler Kemp SPONSOR

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    I have decided my next barrel will be in another overbore 6mm round when my current one in 6mm Ackley is done. I don't have a lot invested into it brass-wise, so I'm not stuck with this caliber. My plan was to use a 30" barrel in order to achieve maximum velocity. Originally I planned on another 6mm Ackley, but the lack of good brass is disconcerting. My next thought was 6mm-284, because of good brass, but then 6mm-06 Ackley was spoke of, and it also has good brass, even cheaper.

    What can each round achieve with bullet weights of 100+ grains? I was hoping for 3300 fps from 115 grain DTACS from the 6mm-284, I was told the 6mm-06 Ackley is a little bit faster, maybe 3400 fps from Lapua brass?

    Does anyone have experience with these or a different fast 6mm?
     
  2. eddybo

    eddybo Well-Known Member

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    You will run into the point of diminshing returns very quickly with a 6mm and 115s. I just have not found a 115gr bullet that will handle the velocities you are wanting. I built a 6-284, it would smoke em....literally. 115gr bullets through the target sideways and bent 90 degrees. Looked like boomerang holes through my target. It did this with d-tacs and bergers.
    About 3200 with a 7.5 twist is the limit IMO that the current easily obtainable bullets out there can be pushed with any reliability.
     

  3. Long Time Long Ranger

    Long Time Long Ranger Well-Known Member

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    The 240 Gibbs is a very fast and accurate 6mm. It is all you can get out of a blown out '06 case. I have four in various configurations for hunting and targets. The two tight neck target rifles will shoot 1/2"-3/4" groups at 300 yards. I tried one off the JRS design which is all you can get out of a blown out 280 case. This holds a little more powder with the longer case but no significant velocity gain. The blown out '06 case seems to be about where the 6mm will max out. Anything larger than that just not much gain.
     
  4. davewilson

    davewilson Well-Known Member

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    LTLR, i think you mentioned 3600 with 105's, i assume Sierra's. what twist/barrel length/powder combo do you have for this. i'm thinking an 8.5 twist would be about perfect for a 6/06 and the 105-107 bullets.
     
  5. Tyler Kemp

    Tyler Kemp SPONSOR

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    Tell me more of the 6mm-06 Ackley! Sounds like good brass, highest velocity, totally awesome round! Could I get 1500 rounds out of a barrel?
     
  6. Dano1

    Dano1 Well-Known Member

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    Tyler,

    You might be able to get 1500 rounds by babying it from the start, then the erosion and fire cracking would definately be a problem. That is sure a lot of powder to burn in such a small bore.

    A 6mm-06 AI is really overbore to say the least, but It's definately an interesting round. You would definately want a fireforming bbl to save the good one for the real loads.

    I'm watching this with much interest.

    Dan
     
  7. Tyler Kemp

    Tyler Kemp SPONSOR

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    I'd probably form cases with 15 or so grains of Unique under some cream of wheat to preserve barrel life, as I can't afford a "fireforming" barrel unless I got an old scrap barrel for free. :(
     
  8. Tyler Kemp

    Tyler Kemp SPONSOR

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    Just rigged up a 6mm-06 Ackley by shoving a 25-06 case into my 6mm Ackley die. Looks pretty sweet even though the shoulder is all weird and radiused and the neck is too long. Definitely holds more than the 6mm Ackley now, and has tons of room to be blown out.
     
  9. Long Time Long Ranger

    Long Time Long Ranger Well-Known Member

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    Dave, A 1-8.5 twist would be right on. Mine are 8 and 9 twist in the following rifles and they shoot the 105 matchking very well. The 240 Gibbs has a .270 tight neck on it and 60 grains of 7828 pushes it 3588 fps. My 240 wby is also a .270 neck with no freebore and 57 grains of 7828 pushes the 105 at 3569. My 6mm-06 IMP pushes the 105 3255 fps with 55.5 grains of 7828. My 6mm-284 pushes the 105 at 3286fps with 56 grains of winchester MRP. My 243 AI is right in that area and I will get you that load when I get back down to the bench. For some reason it is not in here. The wby and the Gibbs are by far the fastest ones. I have some 70 grain ballistic tip loads at over 4100 fps and the 55 BT at over 4300 fps. They are awesome on prarie dogs and coyotes.
     
  10. Tyler Kemp

    Tyler Kemp SPONSOR

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    LTLR can you tell me more of the Gibbs cartridges? How are they formed, where do you get reamers, dies, is brass formed from 25-06, 270, 280, 30-06, sorry, I am new to the wildcatting scene.
     
  11. Long Time Long Ranger

    Long Time Long Ranger Well-Known Member

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    Rocky Gibbs started the gibbs line out of Lewiston Idaho I believe. They have been around for many years and I don't know why they didn't gain more popularity. Some didn't like the short necks which are only about .25 inches. The Gibbs are all you can get out of a blown out 30'06 case. I have all the Gibbs from 6mm to 338 caliber and all of them will shoot right with the standard magnums with less powder, recoil, noise, etc. In other words 240 gibbs=240 wby, 264 gibbs=264 win mag, 7mm gibbs=7mm rem mag. 30 gibbs=300 win mag, 338 gibbs=338win mag. The = just makes it easier to type, they are not equal but are very close to these magnums. Close enough really that a big game animal would not know the difference and neither would the shooter. RCBS makes dies for them but I just use the generic hornady neck dies. You can rent the reamers which is what I did. Brass is very easy to form and they are easy to load for. Use 25-06 brass for the 240 and neck size it until the bolt closes easily. In other words you are using the caliber difference to headspace the cartridge so you don't get any stretch. You want the 6mm-25 caliber step up to fit snug but not tight in the chamber. Load and fire and you then have a 240 gibbs. I use 30-06 brass for the 7mm and 35 whelen brass for the 30 and 338 gibbs. For comparison to the magnums my 338 gibbs shoots a 200 grain ballistic tip 3065 fps which is about the same as a 338 winchester magnum but you don't have the recoil of the 338 winchester.
     
  12. Tyler Kemp

    Tyler Kemp SPONSOR

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    240 or 264 Gibbs looks like the way to go off a standard bolt face which I'd like to stick with!

    PM me if there's any way I can get a dummy of these two cartridges from you.
     
  13. Long Time Long Ranger

    Long Time Long Ranger Well-Known Member

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    No problem getting you a dummy round. The 30 gibbs is actually the duplicate of the 300 wsm velocity wise and just behind the 300 win mag. My 264 gibbs seems to do best with the 120 ballistic tips at nearly 3300 fps. In the 240 gibbs 71 grains of winchester mrp shoots the 55 grain ballistic tip at 4319 fps accurately which is awesome on varmints. 68 grains of the same powder will get the 70 grain BT over 4100 fps. They are fun to play with.
     
  14. Tyler Kemp

    Tyler Kemp SPONSOR

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    PM sent.