6mm Rem. Ackley Improved vs. .243 Win.

[17Fireball]

I like to coyote hunt with a .243 and light bullets for errors in range estimation while night hunting. I have been looking at if there might be a better option out there. Not because I am in any way dissatisfied with the .243 Win. just because it is fun to look.

I am trying to understand how the 6mm AI would compare to the .243 in trajectory with the lightest bullets I could shoot in it. I am shooting the 58 grain VMAX in the .243 and it is the only commercial round I buy and do not reload due to the superperformance powder performance.

Does anyone have real data on how many rounds before accuracy will degrade on both calibrers? I hear 1,200 on the .243 as a general average but have not heard from any definitive source about the 6 mm AI.

Anyone have suggestions for the best value in a built 6mm AI?

Other considerations are welcome. Thank you for taking the time to respond and sharing your knowledge, expertise, and/or experience.lightbulb

 

[MudRunner2005]

If I had to choose between those 2, .243 brass to form for AI is easier to find, but 6mm Ack is going to hold more powder and have more behind it. That's a tough call...

If I had a spare 700 long action, and access to about 250+ new 6mm cases, I'd probably go that route. Or 6-284 Norma...But I don't forsee long barrel life.

 

[17Fireball]

Any decent light soft point bullets for the 6AI for coyotes out to 400 yards? Fear the splash of zipping a VMAX into a coyote shoulder.

 

[AZShooter]

Not handloading is holding you back. You can use other bullets and tweak the load for maximum accuracy.

I got the 55 gr Nosler varmint bullet to go 4050 fps with a 24" 243 and Varget. (Federal offers this bullet in loaded ammo but it is "slow" compared what I handload at 3850 fps. )
It is very flat shooting. At the elevation where I hunt 1" high at 100 yd would be 4.6" low at 350 yds.

I also worked up a load for the 6mm-284 with same bullet and varget. Easily got to 4175 fps. There is a slight gain in trajectory: 1" high at 100 is 5.5" low at 375 yds

We all know the 6mm-284 will have to be retired earlier due to eroded bore.

I would suggest you get into handloading so you can try different bullets and if you become crazy enough you can go for the larger capacity cartridges like the 6mm Rem AI or the 6mm-284.

 

[17Fireball]

Those are very impressive numbers. I should clarify...I do handload and love it. Just finished up a batch of rounds in .17 Fireball last night.gun)

 

[Outlaw6.0]

I have a good bit of experience with both the .243 & the 6mmAI (as well as the 6x284).

With my accuracy loads the 6mmAI pushed a 85grn Partition 300-400fps faster than I push an 87grn V-Max out of my .243. 24" bbl on the .243 & a 26" on the AI. I don't have a use for bullets lighter than that at this time.

The AI is an outstanding cartridge however, as Mud somewhat alluded to, cases can be hard to find for the 6mm Rem. The 6x284 will outrun both with much easier to find cases however, I do not believe that case suits light bullets. It really starts to show it's prowess over the others when you get to the heavy for diameter projectiles. Case in point, I can push a 107smk out of my 28" 6x284 to the same speed as my accuracy load in the 6mmAI with an 85grn bullet (3500fps).

If you're looking for more velocity, the AI is a great choice. Or, you can simply improve your 243 for a pretty acceptable gain as well.

Bore life is a highly subjective subject & in my personal opinion, near useless. There are far too many parameters to discuss before reasonable bore life numbers can be reasoned.




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[AZShooter]

Fireball,

I didn't know you handloaded. I'd say go for what ever bigger 6mm you desire. I would buy the reamer and have it worked out for your needs.

I chose a no turn neck 6mm-284 and supplied a dummy round with a specific OAL so I could use it in a Wyatt's mag box.

I agree with Outlaw that the larger 6mm cases work better with the heavier bullets. While I have a 20 lb monster in 6mm-284 that is twisted for 105 Bergers @ 3475 fps I also have two sporter weight 6mm-284 that use Rem 243 takeoffs.

The twist isn't there to shoot the 107 sierra or the 105 Berger hybrid BUT that doesn't stop those rifles from sending bullets screaming out the bores.

One is a 20" 243 which was my first rechamber job. It shoots the 87 gr hornady V-max at 3375 fps. Crazy noise and fireball but what the heck it shoots.

The other is the aforementioned 24" also a rem takeoff. The current hunting bullet in it is the 95 Berger Classic hunter with a stunning velocity of 3465 fps using RL-17.

If either of the 243 takeoffs burns out no big deal, I have three more barrels waiting to be rechambered.

 

[17Fireball]

Can you help me understand what you are saying about the reamer?

 

[AZShooter]

Regarding the reamer. I used to have my gunsmith use his reamers to make my chambers. Many were older and had dimensions that didn't suit my needs. Some were dull and not modern shaped and had chatter issues. I decided once I got deeper into the handloading to own my reamers with MY specs.

Lets face it if you are a handloader no need to use SAMMI spec reamers with their generous neck clearances. They must be large to accommodate any manufacturer's, brass with different thicknesses, that might be used in that chamber. Basic FL dies aren't much different. Both will over work the brass shortening life and perhaps even contributing to less than stellar accuracy.

I said: "I chose a no turn neck 6mm-284 and supplied a dummy round with a specific OAL so I could use it in a Wyatt's mag box."

I told Dave Kiff at Pacific tool and gauge that I was going to use necked up 6.5-284 Lapua brass and gave him the dimension of the neck of a loaded round. I then specified that the clearance per side should be .002" which would allow me to use the brass without having to turn the necks. The reamer print and reamer say it has a .277" neck.

I also told Dave I would be shooting the 105 Berger hybrid and to make the throat angle the optimal for that shape bullet. He will often use 1 degree 30 min angle for the VLD/hybrid type bullets. My 300 RUM uses another angle and I asked him about it. He said the discovered that it worked better so the 1/30 isn't always used. I let him decide.

The dummy round was supplied so I could specify the throat length. I decide where the bullet should be based on the magazine length or perhaps where the bullet sits in the case. I prefer the entire bearing surface of the bullet to engage the entire length of the cartridge's neck. To be honest to date I have yet to order a reamer with bullet deeper in the case so I can chase the lands as the barrel wears and still maintain full contact with case and bearing surface.

The heavy 6mm-284 that shoots the 105 hybrid has over 1000 rounds through it and I never changed the seating depth since I switched to the 105s. There is a substantial jump with this setup and it shoots fine. Love those hybrids.

Hope this helps. I would suggest you talk with Dave Kiff at PT&G should you desire to have a reamer made.

 

[Booney]

I have a lot of experience with both, the 6mmAI is one of my favorite cals ever and it's barrel life is much better than a .243 and I would say twice as good as a 6-284 but the fact is you can not find brass I have been on cabelas waiting list now for 2 years. It's a fantastic round but a pain to find brass. If it does not get better when this barrel goes out it will be rebarreled with a 6mm super long range basically a 243 with a long neck not as fast as a 6mmAI but in my opion the next best thing.

 

[AZShooter]

Booney,

The 6mmAI, is that the 6mm Remington AI? Twice the barrel life of a 6mm-284? That would be hard to prove.

A solution to your brass issue might be to neck down some 7 x 57 brass. Or <grin> go to the 6mm-284 and not load to max.

 

[Booney]

Yeah it's the Remington yeah you can neck that down I just hate to go all the way from 7 down to 6. 257 Roberts is another one youcando but also hard to find.

 

[Edd]

Yeah it's the Remington yeah you can neck that down I just hate to go all the way from 7 down to 6. 257 Roberts is another one youcando but also hard to find.

I neck 280 Remington brass down to 6mm-280 in one step. I have never ruined a case and I don't have to turn the necks.

 

[AZShooter]

I just sold the RCBS die set that would take 7 x 57 down to 257 Roberts and then to 6mm Rem. It is out there and they are proud of it.

While I now use 6.5-284 Lapua brass to make 6mm-284, I made a form die to neck down 284 win.

I took a piece of old 264 win mag barrel and threaded it 7/8-14. Then used the 6mm-284 chamber reamer. Then I sanded and polished this die. It is just the right size to transition part way towards 6mm. I am sure the same thing could be done with a 6mm Rem AI reamer. Pacific Tool and Gauge sells the die blanks all knurled and threaded with a specific pilot hole for around $20:

Reloading Tools : Pacific Tool and Gauge, Inc - StoreFront Home, Redefining Quality in Manufacturing