6mm cartridge selection

Jfightingfalcon

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With the 243 having more case capacity, how is this possible?
I think the shorter, straighter, steeper shouldered cartridges, especially with good brass, can handle higher pressure without showing the traditional signs. I think this is largely responsible for the "efficiency" myths.
 

cjl2010

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I think the shorter, straighter, steeper shouldered cartridges, especially with good brass, can handle higher pressure without showing the traditional signs. I think this is largely responsible for the "efficiency" myths.
170 fps difference is what I see in my creedmoor vs my SS. My 16.5” 260 runs the same speed as my 20” creedmoor.
 

snox801

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Spring Lake Michigan
The bummer thing to me is that the 6 creed is splitting hairs with the .243. The AI version of the .243 is enticing but its little gain for the trouble. The KISS option is stick with what you have dies for. My 6 Dasher kills deer just as well as the .243 with far less recoil if you wanted to go to the really short cases. With standard cases, the Creed, .243, .243 AI seem to be the main options. I think all of those are in the same boat. Of course you could go really fast with the 6 SST but you would need a mag bolt face for that.
I used to think AI were trouble. Not so much anymore. Think of it this way we are all here for accuracy and longer ranges. So why do your load work before barrel break in. On my last 30 Sherman I used 300 PRC load data and shot and hunted with just regular 300 PRC. Once my first 100-150 rounds were done forming I was ready to do load work with the barrel broke in so no gaining speed.
If you chose a creed you would still have to shoot those rounds then do load work again as you more than likely gained the 50-100 FPS that is standard after break in.
Also I found it easy than keeping my brass separated and changing die settings for different rifles. Much more of a pain. Unless he found one load that worked well enough all brass could be bumped back to the smallest size needed and oal that worked in both but that rarely happens when talking long range.
 

AZShooter

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There is no doubt that any case with a 30 degree shoulder angle is special. I keep thinking I need to make a 6mm Creedmore.

I have dabbled with many 6mms from the 6 BR to the 6mm-284. Have had many 243s, 6mm Rems, and even made a 6mm-7 Rem mag. Those larger cases like the 6-284 and 6-06 will certainly yield some screaming velocities but at the price of short barrel life. How short? A 6mm-284 5R bartlein 1 in 7.5 twist SS lasted right around 1100 rounds and it was shot for fun so barrel never got hot!


Still considering making a 6BR/243 hybrid called a 6BRK. There is a reamer made by PT and G. But I think a 6 BR cutting deep enough to headspace as a 243 would work. I did something similar with a 30 BR making a 30 BR neck, 30 degree shoulder angle with slightly less body taper headspacing as a 308 Win.

Can read more here from Accurate shooter:
,October 6th, 2013

Hot .243-Based Wildcats — The .243 BR-K and 6mm Super X

Gunsmith Mike Sosenko and long-time AccurateShooter Forum member John Adams have been using a modified .243 Winchester case with great success in Varmint Silhouette matches at the Pala Range in Southern California. Officially called the ".243 BR-K" (and informally dubbed the "6BR Long"), the wildcat is basically a .243 Winchester with less body taper and a 30-degree shoulder. The design essentially grafts a 6mmBR Norma "top end" to the .243 Winchester case. After fire-forming, Mike and John can reload this case using normal, unmodified 6BR neck-sizing and seater dies.

Compared to a .243 Winchester, the .243 BR-K's body length is about .006″ longer, and the shoulder is about .0055″ wider. The main difference is the shoulder angle (30° vs. 20°), and the location of the neck-shoulder junction ("NSJ"). Based on reamer prints, the base to NSJ dimension is 1.718″ on the 6BR Long, compared to 1.804″ for the .243 Winchester. Neck length is a bit shorter because "the neck shrinks a little when the shoulder blows out" according to Sosenko. We've provided a mock-up diagram of the .243 BR-K, but you should check with Dave Kiff of Pacific Tool & Gauge for exact dimensions. Dave created the reamers for both the 6mm and 22-caliber versions of this wildcat. Ask for the "22 BR-K" or ".243 BR-K" reamer designs.

Wicked Velocity with Stable Brass
The main advantage of the .243 BR-K is serious velocity in a case that is very stable. Mike's favorite load is the 95gr Berger VLD pushed by Reloader 22. With a stout load of RL22 and Federal 210m Primers, Sosenko is getting 3450 fps with the 95-grainer, with no bullet blow-ups. This is with a 1:8.5″ twist Broughton 5R barrel finished at 28.5″. The cases are holding up very well. Mike has a half-dozen loads on his brass and he hasn't had to full-length size yet. Mike runs a .262″ tight neck, but there is also a no-turn version of the case (see illustration). Accuracy is excellent. Mike says the round delivers repeatable 1/4 MOA groups at 100 yards in testing. He has also experimented with N160, but, thus far, Reloader 22 has delivered smaller groups with better ES and SD.

VIEW 243 BR-K REAMER PRINT (No-Turn Neck)

John Adams shoots a no-turn (.274″) neck .243 BR-K with 105gr Berger VLDs. He's getting about 3230 fps using Reloader 22. John says he can push the 105s faster, but 3220-3240 fps "seems to be the sweet spot." John notes that "after about five reloadings on a case, it gets a little tight". John then full-length sizes with a custom Hornady FL bushing die. "The Hornady custom shop dies work great" according to John. "The .243 BR-K is proven. We know what works. u

While Mike Sosenko and John Adams use their BR-Ks to push 95s and 105s at high velocities,

There are so many 6mms. No one mentioned the 6 XC either. Brass is out there no fireforming.

To the OP enjoy whatever 6mm you get.
 

Jfightingfalcon

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75
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Michigan
There is no doubt that any case with a 30 degree shoulder angle is special. I keep thinking I need to make a 6mm Creedmore.

I have dabbled with many 6mms from the 6 BR to the 6mm-284. Have had many 243s, 6mm Rems, and even made a 6mm-7 Rem mag. Those larger cases like the 6-284 and 6-06 will certainly yield some screaming velocities but at the price of short barrel life. How short? A 6mm-284 5R bartlein 1 in 7.5 twist SS lasted right around 1100 rounds and it was shot for fun so barrel never got hot!


Still considering making a 6BR/243 hybrid called a 6BRK. There is a reamer made by PT and G. But I think a 6 BR cutting deep enough to headspace as a 243 would work. I did something similar with a 30 BR making a 30 BR neck, 30 degree shoulder angle with slightly less body taper headspacing as a 308 Win.

Can read more here from Accurate shooter:
,October 6th, 2013

Hot .243-Based Wildcats — The .243 BR-K and 6mm Super X

Gunsmith Mike Sosenko and long-time AccurateShooter Forum member John Adams have been using a modified .243 Winchester case with great success in Varmint Silhouette matches at the Pala Range in Southern California. Officially called the ".243 BR-K" (and informally dubbed the "6BR Long"), the wildcat is basically a .243 Winchester with less body taper and a 30-degree shoulder. The design essentially grafts a 6mmBR Norma "top end" to the .243 Winchester case. After fire-forming, Mike and John can reload this case using normal, unmodified 6BR neck-sizing and seater dies.

Compared to a .243 Winchester, the .243 BR-K's body length is about .006″ longer, and the shoulder is about .0055″ wider. The main difference is the shoulder angle (30° vs. 20°), and the location of the neck-shoulder junction ("NSJ"). Based on reamer prints, the base to NSJ dimension is 1.718″ on the 6BR Long, compared to 1.804″ for the .243 Winchester. Neck length is a bit shorter because "the neck shrinks a little when the shoulder blows out" according to Sosenko. We've provided a mock-up diagram of the .243 BR-K, but you should check with Dave Kiff of Pacific Tool & Gauge for exact dimensions. Dave created the reamers for both the 6mm and 22-caliber versions of this wildcat. Ask for the "22 BR-K" or ".243 BR-K" reamer designs.



Wicked Velocity with Stable Brass
The main advantage of the .243 BR-K is serious velocity in a case that is very stable. Mike's favorite load is the 95gr Berger VLD pushed by Reloader 22. With a stout load of RL22 and Federal 210m Primers, Sosenko is getting 3450 fps with the 95-grainer, with no bullet blow-ups. This is with a 1:8.5″ twist Broughton 5R barrel finished at 28.5″. The cases are holding up very well. Mike has a half-dozen loads on his brass and he hasn't had to full-length size yet. Mike runs a .262″ tight neck, but there is also a no-turn version of the case (see illustration). Accuracy is excellent. Mike says the round delivers repeatable 1/4 MOA groups at 100 yards in testing. He has also experimented with N160, but, thus far, Reloader 22 has delivered smaller groups with better ES and SD.

VIEW 243 BR-K REAMER PRINT (No-Turn Neck)

John Adams shoots a no-turn (.274″) neck .243 BR-K with 105gr Berger VLDs. He's getting about 3230 fps using Reloader 22. John says he can push the 105s faster, but 3220-3240 fps "seems to be the sweet spot." John notes that "after about five reloadings on a case, it gets a little tight". John then full-length sizes with a custom Hornady FL bushing die. "The Hornady custom shop dies work great" according to John. "The .243 BR-K is proven. We know what works. u

While Mike Sosenko and John Adams use their BR-Ks to push 95s and 105s at high velocities,

There are so many 6mms. No one mentioned the 6 XC either. Brass is out there no fireforming.

To the OP enjoy whatever 6mm you get.
That is fascinating and seriously fast for the case length without getting exotic! I'm definitely sticking with a plain Jane CM. Have a 26" finish X-caliber 7.5" 5R blank on order. I know factory ammo isn't popular around here but I do love the availability and price in a pinch. Plus I've been hearing extremely good things about RL26 and I scored 3 lbs of that for less than usurious pricing. Rest of the package is all mocked up in the basement, can't wait to get it assembled and start shooting!
 

DJ Fergus

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Dec 25, 2015
Messages
3,023
I've been working up loads for a 6mm-PRC. I've run it to a little over 3400fps with RL26 & 108s . Settled on 3330 with N165 & 108s. I like it and I'm not going back but I would have went 6mm SST if I had it to do over again. For someone who wants the easy button, 6mm Creedmoor would be the way to go..PRS or maybe F-open.... 6mm GT would be appealing.
 

highdrum

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Joined
Nov 30, 2008
Messages
2,922
Location
Montana
There is no doubt that any case with a 30 degree shoulder angle is special. I keep thinking I need to make a 6mm Creedmore.

I have dabbled with many 6mms from the 6 BR to the 6mm-284. Have had many 243s, 6mm Rems, and even made a 6mm-7 Rem mag. Those larger cases like the 6-284 and 6-06 will certainly yield some screaming velocities but at the price of short barrel life. How short? A 6mm-284 5R bartlein 1 in 7.5 twist SS lasted right around 1100 rounds and it was shot for fun so barrel never got hot!


Still considering making a 6BR/243 hybrid called a 6BRK. There is a reamer made by PT and G. But I think a 6 BR cutting deep enough to headspace as a 243 would work. I did something similar with a 30 BR making a 30 BR neck, 30 degree shoulder angle with slightly less body taper headspacing as a 308 Win.

Can read more here from Accurate shooter:
,October 6th, 2013

Hot .243-Based Wildcats — The .243 BR-K and 6mm Super X

Gunsmith Mike Sosenko and long-time AccurateShooter Forum member John Adams have been using a modified .243 Winchester case with great success in Varmint Silhouette matches at the Pala Range in Southern California. Officially called the ".243 BR-K" (and informally dubbed the "6BR Long"), the wildcat is basically a .243 Winchester with less body taper and a 30-degree shoulder. The design essentially grafts a 6mmBR Norma "top end" to the .243 Winchester case. After fire-forming, Mike and John can reload this case using normal, unmodified 6BR neck-sizing and seater dies.

Compared to a .243 Winchester, the .243 BR-K's body length is about .006″ longer, and the shoulder is about .0055″ wider. The main difference is the shoulder angle (30° vs. 20°), and the location of the neck-shoulder junction ("NSJ"). Based on reamer prints, the base to NSJ dimension is 1.718″ on the 6BR Long, compared to 1.804″ for the .243 Winchester. Neck length is a bit shorter because "the neck shrinks a little when the shoulder blows out" according to Sosenko. We've provided a mock-up diagram of the .243 BR-K, but you should check with Dave Kiff of Pacific Tool & Gauge for exact dimensions. Dave created the reamers for both the 6mm and 22-caliber versions of this wildcat. Ask for the "22 BR-K" or ".243 BR-K" reamer designs.



Wicked Velocity with Stable Brass
The main advantage of the .243 BR-K is serious velocity in a case that is very stable. Mike's favorite load is the 95gr Berger VLD pushed by Reloader 22. With a stout load of RL22 and Federal 210m Primers, Sosenko is getting 3450 fps with the 95-grainer, with no bullet blow-ups. This is with a 1:8.5″ twist Broughton 5R barrel finished at 28.5″. The cases are holding up very well. Mike has a half-dozen loads on his brass and he hasn't had to full-length size yet. Mike runs a .262″ tight neck, but there is also a no-turn version of the case (see illustration). Accuracy is excellent. Mike says the round delivers repeatable 1/4 MOA groups at 100 yards in testing. He has also experimented with N160, but, thus far, Reloader 22 has delivered smaller groups with better ES and SD.

VIEW 243 BR-K REAMER PRINT (No-Turn Neck)

John Adams shoots a no-turn (.274″) neck .243 BR-K with 105gr Berger VLDs. He's getting about 3230 fps using Reloader 22. John says he can push the 105s faster, but 3220-3240 fps "seems to be the sweet spot." John notes that "after about five reloadings on a case, it gets a little tight". John then full-length sizes with a custom Hornady FL bushing die. "The Hornady custom shop dies work great" according to John. "The .243 BR-K is proven. We know what works. u

While Mike Sosenko and John Adams use their BR-Ks to push 95s and 105s at high velocities,

There are so many 6mms. No one mentioned the 6 XC either. Brass is out there no fireforming.

To the OP enjoy whatever 6mm you get.
6slr and 6 comp match are similar to your deep br. 6 creed is as well, same 30° shoulder just shorter neck.
 

ChickenTikka

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save the hassle and stick with the 6 creed, youll already have a decent starting point for loads, already have the reloading set up. and its sending the 100 class bullet at a decent pace.
 
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