.243 ai or 6mm-284
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7magcreedmoor
Well-Known Member
I was all set to rebarrel a rifle originally in 243win to AI and a heavier contour, longer pipe. The plan was to launch berger 105s @ 3000+ fps. But as I got closer to time to ship the action, I started having doubts about larger game and longer distances. The rifle in question is now a 6.5 Creedmoor, and the downrange energy and trajectory is a couple hundred yards better, running 140gr VLDs. The 6.5 bug bit deep, and I also have a 6.5/284, which will throw the 140s @ 3000+fps. If you are committed to the 6mm, I'd go AI if you like the 243 case capacity, to get every last bit of velocity, and because (according to anecdotal evidence)the cases won't stretch as much. If you go with the 284 case, you gain capacity and velocity, but the throat will be gone a bit earlier as an inevitable result. Play with all the variables using the ballistic calculator, and compare downrange energy and especially wind drift of the different possibilities- that's how I ended up in 6.5 land. I will add one last thought: for more energy, a bigger pill is the easiest answer, which is why I am currently building a 280AI...
I have 3 6mmx284's and are very efficient. No fireforming needed. I use the sierra 85 bthp 53 grains IMR 4350 vel. 3450 for eastern whitetails. My friend has taken 20+ elk in Colorado with this caliber. We are only shooting rechambered 243 factory remmy barrels. Before the shortage Winchester brass was only 29.00 a bag now you cant find it. Best of luck you wont go wrong. Btw, I was with him on 2 of those bull elk one was at 600 yards he was shooting 100 grain nosler solid base that you cant buy anymore.
ZSteinle
Well-Known Member
+1 for 6mm-284. fast mean and flat. plus barrels are cheap. im shooting a 105 vld at 3300fps.
Slaysesh
Well-Known Member
i think i would go for the 6xc. i have a 243ai and its good and all but you have all of the same benefits with good factory brass. almost the same velocity. and supposedly super accurate. this would be my next 6mm build after i sell the 243ai and get my .338 cannon obsession out of the way.
I vote for the 6mm-284.
Use necked down Lapua 6.5-284 brass which is readily available. I now have 9 firings on the cases and the primer pockets are still firm.
Buy a custom reamer with specifications for your rifle.
My 20 lb SA Rem 700 with 28" Bartlein 5R gets 3445 fps with the 105 Berger hybrid a case full of RL-33. (careful use of 6" drop tube to get it to fit)
Have two others using 243 Rem takeoffs ( Mike 33 great minds think alike) on sporter weight rifles.
An old Ruger M77 was my very first chambering job, a 20" rechambered 243 takeoff that shoots 87 gr Hornadys at 3375 fps with 51 gr of RL-17. It has a bit of a fireball at the muzzle but still shoots fast and accurately.
The other sporter is a SA Rem 700 with a rechambered 24" 243 Rem takeoff with Wyatt's mag box shoots 95 gr Berger classic hunters at 3350 fps with 52 gr of H4350
I have only used the heavy rifle to take one coues wt and it was last year. No problems killing that small variety of WT at 520 yds.
As for throat wear......sure there is wear. My bore scope shows plenty of crazing and roughness at close to 1000 rounds and cleanup is more difficult these days. BUT it still shoots ragged holes at 200 yds and makes small sized groups on the painted steel at 500 M. I keep waiting for the barrel to die as I have new 30" 5R Bartlein just waiting to take its place.
I crunched the numbers for a 140 VLD going 3000 fps vs the 105 Hybrid going 3445. At 500 yds and my deer hunting conditions (4000 ft etc) the 140 VLD in 10 MPH crosswind drifts 9.8"
the 105 hybrid " " " " drifts 8.5
Energy is almost identical for both bullets.
I will give the 140 VLD its due as it will most likely have more momentum for pass throughs. BUT the 105 exited that deer with a broadside shot just fine.
My final opinion. The first Bartlein has a 1 in 7.5 twist for the 115 gr DTAC bullet. I read extensively on this round and the word is out that the Berger 115 VLD cannot hold together at these velocities or soon won't once the throat gets rough. What other 115 high BC bullet is available? After using up much of this barrel's life trying to shoot DTACs I moved to 107 Sierras then switched to 105 hybrids when they were introduced. My second Bartlein is a 1 in 8 twist because I don't intend to use any 115 gr bullets, just the 105 hybrid. I suggest what ever you do, don't waste too much time trying a large variety of bullet/powder combinations.
Ross
Use necked down Lapua 6.5-284 brass which is readily available. I now have 9 firings on the cases and the primer pockets are still firm.
Buy a custom reamer with specifications for your rifle.
My 20 lb SA Rem 700 with 28" Bartlein 5R gets 3445 fps with the 105 Berger hybrid a case full of RL-33. (careful use of 6" drop tube to get it to fit)
Have two others using 243 Rem takeoffs ( Mike 33 great minds think alike) on sporter weight rifles.
An old Ruger M77 was my very first chambering job, a 20" rechambered 243 takeoff that shoots 87 gr Hornadys at 3375 fps with 51 gr of RL-17. It has a bit of a fireball at the muzzle but still shoots fast and accurately.
The other sporter is a SA Rem 700 with a rechambered 24" 243 Rem takeoff with Wyatt's mag box shoots 95 gr Berger classic hunters at 3350 fps with 52 gr of H4350
I have only used the heavy rifle to take one coues wt and it was last year. No problems killing that small variety of WT at 520 yds.
As for throat wear......sure there is wear. My bore scope shows plenty of crazing and roughness at close to 1000 rounds and cleanup is more difficult these days. BUT it still shoots ragged holes at 200 yds and makes small sized groups on the painted steel at 500 M. I keep waiting for the barrel to die as I have new 30" 5R Bartlein just waiting to take its place.
I crunched the numbers for a 140 VLD going 3000 fps vs the 105 Hybrid going 3445. At 500 yds and my deer hunting conditions (4000 ft etc) the 140 VLD in 10 MPH crosswind drifts 9.8"
the 105 hybrid " " " " drifts 8.5
Energy is almost identical for both bullets.
I will give the 140 VLD its due as it will most likely have more momentum for pass throughs. BUT the 105 exited that deer with a broadside shot just fine.
My final opinion. The first Bartlein has a 1 in 7.5 twist for the 115 gr DTAC bullet. I read extensively on this round and the word is out that the Berger 115 VLD cannot hold together at these velocities or soon won't once the throat gets rough. What other 115 high BC bullet is available? After using up much of this barrel's life trying to shoot DTACs I moved to 107 Sierras then switched to 105 hybrids when they were introduced. My second Bartlein is a 1 in 8 twist because I don't intend to use any 115 gr bullets, just the 105 hybrid. I suggest what ever you do, don't waste too much time trying a large variety of bullet/powder combinations.
Ross
Glad to hear your results from your custom. My buddy actually owns a gunshop but kind of was one of the first in area to have one. Thinking around late 70's and he does his own gunsmithing and chambered mine. He is kind of old school sticking with the 10 twist on new barrels shooting the 100 solid base for elk and was able to get several thousand of them before they quit making them. I could not believe the damage that bullet did to the 2 elk I was with him. He has taken 20 other since the late 70's and of course a great shooter and knows the limit of what his gun will do. He knows with that bullet 700 yards is tops but I think for what it is it does fine. He still has the dot system in lupy scopes that premier reticles did years ago when Dick Thomas was still living running the business. For in my Md. woods the 6-284 with the 85 bthp does an out standing job on our deer. You are correct on the Laupa brass just run it down thru the 6 die and works well. I used the Winchester brass for years thought was okey but pockets would go, the laupa is definitely better brass. My buddy has a large crowd of people shooting that wildcat in this area and always wondered why someone didn't factory chamber it. I have also shot the 95 Bergers, 87 V-max and done well.
Ok AZ knows I'm experimenting with Re#25 in 6x284. Happy his bbl has a 1,000 rnds down it and its still a shooter. I was burning 51.5 of Re#22 in 30" Brux bbl 8" twist Hornady 105 BTHP produced an average MV 3350 with poor accuracy and pressure signs. . This time I switched to Re#25 and Berger 105 Hybrids seated out to touching lands. Fired 4 shot groups starting at 51.5 -53.0
1st group(51.5) shot well under 3/4MOA at a 100 and average MV of3375 Zero pressure signs
2nd group(52.0) shot a 1/4 MOA !!!!!! and average 3400 I was very happy. Zero pressure signs
3rd group (52.5) group opened up to 3/4 MOA and average velocity 3440 and slight flattening and cratering of primer.
4th group ( 53.0) produced an average MV of 3485 ranging from 3470-3525 but group was under 1/2 MOA . But had shinning Ejector marks which means stop and reduce load. .
So I'm back in the thumbs up camp for 6x284 . My new load will be 52grs of Re#25
1st group(51.5) shot well under 3/4MOA at a 100 and average MV of3375 Zero pressure signs
2nd group(52.0) shot a 1/4 MOA !!!!!! and average 3400 I was very happy. Zero pressure signs
3rd group (52.5) group opened up to 3/4 MOA and average velocity 3440 and slight flattening and cratering of primer.
4th group ( 53.0) produced an average MV of 3485 ranging from 3470-3525 but group was under 1/2 MOA . But had shinning Ejector marks which means stop and reduce load. .
So I'm back in the thumbs up camp for 6x284 . My new load will be 52grs of Re#25
That's good Iron Worker!
Interesting that so many slow powders will work with the 105-107s and a 6mm-284.
---------------
From my files an old record: Note velocity
Randy Derks world record 7" @ 1000 YDS
54 grains of Reloader 22 - Federal 210m primer - Sierra 107 grain Match King bullet - 3425 fps
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I got similar results with the 107 Sierra and Retumbo
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I know I am out of my mind but I am going to be building a 6mm/7 Rem mag soon. I suppose it could be called a 7mm/264 win mag as well. Not improving it will stay with 25 degree shoulder. The idea is to use rem 24" or 26" 243 takeoffs and 105s to try and duplicate the velocities that the 20 lb 6mm-284 gets with its longer barrel. I only want 3500 fps but think it might surpass it. Will use US 869 as first choice of powder. Have a full floated Rem mag ready for the barrel. All I will have to do is center in lathe and rechamber. I don't have to spend anything on dies and the regrinding of a 7 rem mag reamer is IIRC $25. If it doesn't work out I can regrind the reamer to something else. Have boxes of 105 A-max and 105 hybrids.
Interesting that so many slow powders will work with the 105-107s and a 6mm-284.
---------------
From my files an old record: Note velocity
Randy Derks world record 7" @ 1000 YDS
54 grains of Reloader 22 - Federal 210m primer - Sierra 107 grain Match King bullet - 3425 fps
------------------
I got similar results with the 107 Sierra and Retumbo
----------
I know I am out of my mind but I am going to be building a 6mm/7 Rem mag soon. I suppose it could be called a 7mm/264 win mag as well. Not improving it will stay with 25 degree shoulder. The idea is to use rem 24" or 26" 243 takeoffs and 105s to try and duplicate the velocities that the 20 lb 6mm-284 gets with its longer barrel. I only want 3500 fps but think it might surpass it. Will use US 869 as first choice of powder. Have a full floated Rem mag ready for the barrel. All I will have to do is center in lathe and rechamber. I don't have to spend anything on dies and the regrinding of a 7 rem mag reamer is IIRC $25. If it doesn't work out I can regrind the reamer to something else. Have boxes of 105 A-max and 105 hybrids.
I'm going try Retumbo next , if I could get 3500 fps with out pressure signs , would be swell .
