6mm rem or 6mmAI

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by mcseal2, Dec 21, 2010.

  1. mcseal2

    mcseal2 Well-Known Member

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    I got my barrel purchased today for the re-barrel on my 243, a 1 in 9 #4 Kreiger that will finish out at 24". I plan to shoot 85-90gr bullets through it for coyotes and a low recoil option for long range practice.

    Now for my next question, several people on other forums have said I should chamber it to 6mmAI to gain extra powder capacity. I did not know if it would be worth going to the AI in a 24" barrel or if I would gain much with that length. I would like to get 3300fps from the 90gr bullets, can I do that with the 6mm or should I go 6mmAI?
     
  2. Firecat

    Firecat Well-Known Member

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    With the regular 6mm Remington and 90 grain bullets you will be somewhere between 32-3300 fps. However I would guess that it will be closer to 3200. The little 6mm rem is one fine round. I have one in a Parker Hale with a 24 inch barrel and it shoots lights out. Truth be told it will shoot beyond my skill level at present <.350 MOA. I would never steer anyone away from buying one. They are fairly easy to load for. However, that being said, You are looking at the improved version of this case and that merits investigation. The 6mm is said to be one of the more efficient/successful improved calibers because of the harsh body taper of the parent casing. They say that you can get an almost 10% increase in capacity which is a huge gain. Is it worth it to go improved? It's up to you. The trade off will be barrel life.
     

  3. Derek M.

    Derek M. Well-Known Member

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    I say forget the AI version completely. Baptize your brain and clean the thoughts of AI from it. The gains are subtle. That said, if you do choose the AI version, consider shooting moly coated bullets to aid with barrel life if indeed moly does that to any real degree. I don't know if it does or not. Keep in mind that rifles can be finicky as it is and adding moly just adds one more variable.

    Good luck with whatever you choose. If you really want a shooter, build a 22-6mm!
     
  4. Outlaw6.0

    Outlaw6.0 Well-Known Member

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    I will have to cast my vote for the 6mmAI, If you are looking to get that speed with the 90grn bullet. I have a 6mmAI 1-12" twist that shoots the 85grn bullets right at 3500fps with a 26" bbl. Cases are easy to form, I was lucky to find a fire forming load that shoots well enough to make consistent hits on prarie dogs, if that doesn't work the cornmeal method works wonders in my father's 6.5-06AI.
     
  5. Nomosendero

    Nomosendero Well-Known Member

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    I would have to go with the AI. Some feel all AI's gain little, or I hear 100fps as a cookie cutter response. This isn't the case as the AI treatment increases the cap. by different percentages depending on the case.

    Sierra is quite fond of this version, I will give a few quotes from Edition V.

    "the improved case offers an increase of 11% over the original design. This is a fairly significant
    difference & provides a SIGNIFICANT BOOST in velocity over the standard 6MM Remington"

    "given the increase in available case capacity over the standard 6mm Remington, the Ackley version offers a viable option to improve the ballistics of this case"

    "In our opinion, of all the Improved cartridges, the 6mm Remington Ackley is one of the better ones."

    BTW, they show 3,400fps with their 85gr. bullets with 3 diff. powders. Test rifle is 26" Sav.
     
  6. ReachnOut

    ReachnOut Well-Known Member

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    I'd definitely go with the AI. Currently, I have 3 different builds (p-dogs/deer etc/long range benchrest). My favorite load is a 70grn Nosler BT, 48 gns VV 150 and an average chrono of 3806. As long as you're starting with a fresh barrel it seems a good idea to use the extra versatility of the AI.
     
  7. Trickymissfit

    Trickymissfit Well-Known Member

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    I shot a 6mm Ackly out of a 24" barrel for a couple years. I got 3450fps with 85 grain bullets, without doing anything out of the ordinary. I also had access to a very similar rifle, but with a 27" barrel (both were Pacnors and were identical). Chambers were cut with the same reamer and the same lathe and gauge used. Headspace was within .001" between them. The 27" barrel might have been 75 fps faster, but the accuracey loads proved different between the two. The 24" barrel was faster in the accuracey loads (and in the end that's what counts)! Also the shorter barrel seemed to have a better selection of rounds that grouped well (both barrels were cut from 28" #7 blanks). But looking back at the situation again, I think that a 27" barrel with a 1" strait contour (both were savage 112 single shot actions) might have helped that gun out a lot. Also Doug and I swapped barrels thinking there might have been a difference in the actions. We got the same results. Also I've found that for some odd reason the 6AI is somewhat more selective about the actual powder you are using.

    Being as the standard 6mm Remington is really about the max powder capacity for a 6mm bore; you don't really gain as much as some folks say. Maybe 150fps max. There are a couple of tricks out there that will add another 50 to 75 fps to this, but now are very remote. I think that a case that's about 54mm long, but with the Remington neck is a better solution. You just run a 6mm Ackley reamer in short. You'll use less powder, and doubt you'll see 50 fps difference. Yet shoot better. For a die; you simply cut off a 6mm Ackley die, and run the reamer in a .243 Ackley seater sleeve from Forster.

    Now adays I shoot a 6mm/250AI out of a 26" barrel. It's a fast twist barrel, and is throated for 105 grain Amax bullets. It's good for mid twos on a perfect day, and will always shoot mid to low threes. I can max load a 105 grain bullet for right at 3100 fps, so an 85 grain bullet ought to do about 3250 fps at least. Going to do another barrel for it in 1:10 twist, that will be about 24" long in a strait 1" contour. I'll throat it for 70 thru 80 grain bullets
    gary
     
  8. Trickymissfit

    Trickymissfit Well-Known Member

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    the 6mm Remington case is well known for it's long barrel life. The Ackley should be even longer with the 40 degree shoulder. But on the otherhand the 6mm is at it's best with 90 grain and heavier bullets that are very long. The Ackley really begs for the 1:8 twist barrel and throated for VLD's. Talking 85 grain bullets and your also not going to really use all the case capacity efficently. For those bullets, I think I'd go with a 6/250AI reamed with a 6mm Ackley reamer. Better yet would be a 6/250AI that has a 1.44 shoulder deminsion. You should be able to make cases out of standard .243 brass which is a plus.
    gary
     
  9. Derek M.

    Derek M. Well-Known Member

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    I respectfully disagree that the Ackley will create longer bbl life.
     
  10. Trickymissfit

    Trickymissfit Well-Known Member

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    here's the deal on getting a 6mm Ackley to really zing. First thing is that you need to find a good supply of really old .257 Roberts brass from Remington (maybe Winchester too). The case walls are thinner, and hold 1.5 to a full 2 grains more powder than the standard 6mm case. This will get you about 75 fps alone (I saw slightly over 100 fps with 80 grain Blitzes). The Ackley chamber was not developed for an increase of velocity, but to increase case life by decreasing brass flow (Akley felt the 57mm case was about max for a 6mm). The increase in velocity was just something that was added to the equation. Also the basic 6mm case will handle about 10% greater chamber pressure than the basic .243 case if you like to really tax your action. To really see gains with a 6mmAI, you need to be thinking about those 100+ grain bullets in a fast twist barrel. Setup right it will be about 75fps to 100fps faster than a 6/.284, and have a barrel that will often last two and a half time longer.

    Now 3450 fps with an 85 grain Hornaday seems about right. I got that using .257 cases in a standard 6mm remington chamber from a 24" barrel (actually was one of my favorite loads, but had a lot of recoil for what it was). If you go with the Ackley chamber and really push the envelope, you want a fairly heavy barrel (I think a #7 is about right). This is not a gun you want to set over a P.D. town all afternoon long. It will get old. But as a coyote rifle, it's the nuts! You should be able to make kills close to 700 yards (670 was my longest). And pelt damage is like nothing you've seen before! The bad side is that you can forget about half the varmit bullets out there. I've had a few explode in flight, and many blow up a cardboard target backstop. So you want fair heavy constructed bullets, and this is where the 85 thru 90 grain bullets shine. Learn to like H450 powder, and have fun
    gary
     
  11. mcseal2

    mcseal2 Well-Known Member

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    I considered using the VLD bullets, I've used the Bergers out of the 243 win in the past. I have had great luck with them on deer, none going over 20ft, but had many coyotes run quite a ways after the shot. I think that because they are designed to penetrate 2-3" before expanding they are running out of chest cavity to expand in before exiting a coyote. The traditional big game bullets expand quickly on impact, then hold together to leave a managable exit wound. I prefer them to the V-max or other varmint bullets when bobcats or fox may be called in as well as coyotes, plus I don't have to change loads for antelope or deer.

    Bullets I have to try in it include

    90gr Scirocco
    85gr Interbond
    90gr Ballistic tip
    85gr Speer boattail
    87gr Berger VLD hunting
    95gr Matchking
    95gr Berger VLD
    100gr Sierra gameking

    One of those should give me the accuracy and performance I want. The VLD and matchking designs will get another try too with the increased velocity over my 20" 243 win. They may perform much better at the higher velocity.
     
  12. Trickymissfit

    Trickymissfit Well-Known Member

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    CAD the case on a PC, and also CAD the standard case as well. Now expand the shoulders to where they cross in the neck. That's known as the vortex of the flame path, and is also the hottest and most intense point of the flame path. It should be in the first half of the case neck (closest to the shoulder). The standard neck is a good design, but the 40 degree is better yet. Take this into fact along with reduced brass flow; it then becomes a win win situation. This is why .243's eat barrel throats. Now the gist of my post was also using similar powders and similar chamber pressures. And I've also been an end user of four 6mm Remingtons in one form or another. I might add here that the 6/250AI barrel will not have 2/3rd's the barrel life that the 6mm Remington due to the neck length alone, but still should exceed 1200 rounds. But I suspect your thoughts relate more to excessive overbore than the Ackley case design. Thus relating to my thoughts on shorter shoulder deminsions that I have spoken of before. The perfect 6mm round is probably the HLS in an improved design.
    gary
     
  13. Trickymissfit

    Trickymissfit Well-Known Member

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    on coyotes, I like the 80 grain Sierra Blitz for most anything under 400 yards. But I like the 87 grain Hornaday at longer ranges. Berger 88's shot pretty good out of the Ackley with a fast twist (they'll go further than I can shoot), but never tried them on deer sized game. They do kill coyotes pretty good, but no where near the Blitz
    gary
     
  14. Derek M.

    Derek M. Well-Known Member

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    Correct. Given the 2 case designs, same bullet, same powder, primer, same everything except powder charge, I don't believe the Ackley version will reduce throat/bore wear when compared to the standard version, despite the location of the vortex of the flame path. The AI introduces more powder for the same diameter bore. I agree that it is a better shoulder design, however, for reduced brass flow--generally speaking. But even then we can take into account the reamer dimensions that cut the chamber/neck. A good custom reamer will also create a chamber that should reduce brass flow in the standard version.