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6mm rem or 6mmAI

 
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  #1  
Old 12-21-2010, 03:22 PM
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6mm rem or 6mmAI

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?
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Old 12-21-2010, 03:44 PM
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Re: 6mm rem or 6mmAI

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.
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Old 12-21-2010, 05:37 PM
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Re: 6mm rem or 6mmAI

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!
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Old 12-21-2010, 05:48 PM
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Re: 6mm rem or 6mmAI

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.
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Old 12-22-2010, 10:44 AM
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Re: 6mm rem or 6mmAI

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.
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Old 12-22-2010, 11:42 AM
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Re: 6mm rem or 6mmAI

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.
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Old 12-22-2010, 01:03 PM
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Re: 6mm rem or 6mmAI

Quote:
Originally Posted by mcseal2 View Post
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?
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
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