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Anyone on the forum have an idea as to the feasibility of developing a 6.8SPC x 51 in an AR 10 pattern rifle and if so, I know the bolt, gas piston, magazine well, chamber and barrel would have to be changed out and would require new magazines. DPMS + others manufacture/sell AR 6.8SPC x .43, but I'm curious if a .51 mm cartridge case would prove more velocity and more foot pounds of energy further down range and step the 6.8 upto larger game, etc.

cenote811
 

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If I understand what you are asking it would just entail changing the barrel on an AR10 platform as you would just neck the 7.62x51 down a bit to 6.8x51. Of course you would need to get dies or some company to load ammo and figure what chamber worked best. I think you would have something very close in performance to the .270 Winchester but on the shorter action like the .308 relates to the 30-06. You would then be able to use all the standard 130 to 160 gr .277 caliber bullets along with the lighter ones. This is where the 10 twist would be correct as the velocities and bullet lengths would be right.
 

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Something like this (Note: Not mine):

7mm-08 necked down to 270-08

PRIMER: CCI-200

POWDER: IMR-4350 / 46.0 gr.

BULLET: Nosler 130 gr. Ballistic Tip

VELOCITY: 2,890 fps.
 

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Interesting concept - I'm still looking at getting a 7mm-08 BR though. Not sure I want to lug around an AR10 platform...unexplored country, these wildcat rounds!
 

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Case diameter (think feeding) and spare parts come to my mind. The WSM cartridges will produce a fair bit more velocity but at the cost of reliability, recoil, mag capacity.
 

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I don't see the benefit over the .260 Remington or 7mm-08 other than the ability to use .277 caliber bullets? Am I missing something?

I am a long time fan of the 25-06 and have toyed with the idea of building a .25 Souper AR10 style rifle. Never got around to fully exploring the possibilities though.
 

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The 7mm-08 has a variety of bullet choices with good BC's so I don't see much benefit in necking it down to .277 especially when the op was asking for a larger game round. Let's reverse this and ponder a 6.8 spc necked up to .284? Any benefits here? Has it been done? What would velocities be for a 140grain bullet?
 

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The 7mm-08 has a variety of bullet choices with good BC's so I don't see much benefit in necking it down to .277 especially when the op was asking for a larger game round. Let's reverse this and ponder a 6.8 spc necked up to .284? Any benefits here? Has it been done? What would velocities be for a 140grain bullet?

With that, we get right back to the same problem we have now. Those bullets are too long to allow adequate case / powder capacity using the .30 Rem case. You are better off just buying a bolt gun in 6.8 and loading out the 130 Speers, 135 SMK, 140 Bergers, etc, to OAL's of around 2.40"

Once you start using the very high BC 140's yu are never going to get that round in an AR mag, and still drive them to an interesting speed.
 

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The 7mm-08 has a variety of bullet choices with good BC's so I don't see much benefit in necking it down to .277 especially when the op was asking for a larger game round. Let's reverse this and ponder a 6.8 spc necked up to .284? Any benefits here? Has it been done? What would velocities be for a 140grain bullet?
From Dr. Roberts' report:

During SPC development different bullet
diameters of 6 mm, 6.5 mm, 6.8mm,
7 mm, and 7.62 mm were tested, using
multiple bullet types, shapes, and
weights from 90 to 140 gr--the 6.8 mm
was selected because it offered the
BEST combination of combat accuracy,
reliability, and terminal performance for
0-500 yard engagements in an M4 size
package.
Can be found here in its entirety: http://68forums.com/forums/showthread.php?7274-Dr.-Roberts-NDIA-May-2008-Report-quot-Time-For-a-Change-quot
 

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I was sitting in the deer stand this weekend thinking exactly that. Other than the rare 700 LTR I see every now and then, what are the other options?
Ruger Hawkeye and custom built Savage are all I am aware of.
 

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JIMHO, the beauty of the 6.8 SPC is the performance you can get without going to the AR-10.

I have a custom Ruger #2, chambered in SAAMI 6.8SPC-II with 22" Shilen 1-10" twist. My original plan was to use the standard reamer as a start, even though magazine restrictions are not an issue on this action. This was to become my Texas Hill Country deer rifle. My idea was to start with the normal AR-15/6.8 chamber & then if I couldn't get the performance I wanted, lengthen the throat or re-chamber to the 6.8 AI or worst case re-chamber to the .270 Savage. My personal preference is to use nothing less than 100 grs bullets for deer. I've had great success in terms of accuracy & game shooting with the 115gr GD & AB 110gr. It had been hard to get good info on 130 gr loads until recently when Speer listed some loads with their 130 gr bullets. They show a max of 2,620 fps with AR-Comp & 2,607 fps with Alliant Power Pro Varmint. Using S&B brass & a drop tube powder I'm getting an average of 2,644 through the chrono, without pressure signs using AR-Comp. My charge weight is .8 gr below max & it is superbly accurate! Hunting season approached quickly so I stopped testing & loaded a batch & zero'd in. I'm using 130 gr Federal Fusion bullets which are Speer GD's.

Studying other members results with 130 gr bullets posted on this website I've learned a lot. To some 2,600 fps is low! Please note & be careful, as several have stated, this is getting into the "wildcating zone". I'm pretty sure that I'll eventually extend the throat on this rifle until 130's are flush with the bottom of the neck. I can't seem to find good burn rate comparison chart with Ar-Comp, but I believe a slightly slower powder may really shine in my rifle.
68FullLengthPic.jpg 68Markings.jpg
 

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When the 7mm-08 came on the market, I was a "helper" in a gun shop. (1977/78)
I love the .270 Win, so it wasn't hard to conceive!
If the .308 is such a "whiz-bang", why not a .270 "short" '06.
When I pitched my idea to the 'smith, he just kinda brushed it aside. Not having the money or the knowledge, I just dropped the idea and said, "Oh well."

Years (decades?) later, I hear about the .270 Redding. Difference is I would have formed the cases by necking down a .308.
SOP to make .270 Redding cases, blow out the neck by fireforming .243 Win ammo.

Again, "Oh well."
 

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Bitten,
Not sure I want to lug around an AR10 platform
It is quite easy to build a large frame AR10 under 6 pounds, with a scope that would be about what a stock AR15 weighs empty. And that's using the full size receivers, there are many now who copied Harrison's small frame 308 build making stock 308's about 7.1 pounds.

Heck my latest AR 6.5 Creedmoor has a 20 inch barrel at 35 ounces. With the same barrel profile it would be slightly lighter with a 6.8 bore. Entire rifle weighs 4.9 pounds, under 6.3 pounds with scope and mount.
 
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