.260 Remington and the AR10

[Alpha Sierra]

I started with 210M's, but got significantly better accuracy with the BR2 in 260 and H4350.

You're not the first to tell me that. I just bought a brick of Feds, but trying a box of BR2s is definitely in the cards. Might be a good winter project.

[DocGKR]

Well where to begin, first i bought a 6.8mm upper and ammo was not available for around 8 months. Then when ammo was finally available it did not meet the performance standards originally reported, then we discovered that most ammo would not in fact actually feed from standard 5.56mm magazines despite claims that it would.

03humpalot, you might wish to check your facts. The 6.8 mm has demonstrated outstanding terminal ballistic performance assessment, exceeding the specified requirements in every government test that has been conducted. If you are discussing external ballistics, then the only "performance standard" specified in the original military requirements was for the 6.8 mm velocity to exceed that of an AK47 firing M43 by 200 fps--it does. The 6.8 mm was never required to feed in 5.56 mm magazines; the only magazine requirement was that 6.8 mm magazines had to fit into 5.56 mm issue mag pouches. 6.8 mm mags meet this requirement.

Exactly what official requirements or government performance standards has the 6.8 mm failed to meet?

[DocGKR]

Zak,

Have you played with 7mm-08? It is a nice cartridge.

[03humpalot]

03humpalot, you might wish to check your facts. The 6.8 mm has demonstrated outstanding terminal ballistic performance assessment, exceeding the specified requirements in every government test that has been conducted. If you are discussing external ballistics, then the only "performance standard" specified in the original military requirements was for the 6.8 mm velocity to exceed that of an AK47 firing M43 by 200 fps--it does. The 6.8 mm was never required to feed in 5.56 mm magazines; the only magazine requirement was that 6.8 mm magazines had to fit into 5.56 mm issue mag pouches. 6.8 mm mags meet this requirement. 

Doc,
i am well aware of how the 6.8mm has been performing in the field. I was speaking strictly about external ballistics and how factory loaded ammunition from 4 different manufacturers has not come close to what the manufacturers have claimed (in my Rifle).

I guess i misunderstood the requirement on the magazine interchangeability but i stand by my statement. I also will continue to use 6.8mm despite my issues with it thus far.

Sorry for the thread hijack

[Zak Smith]

Zak,

Have you played with 7mm-08? It is a nice cartridge.

I have not. Running the numbers for 7-08, we didn't think you could get enough velocity with the high-BC 7mm bullets (e.g. 168gr up) out of the small case, hence we went to 260.

[223Rem]

I have not. Running the numbers for 7-08, we didn't think you could get enough velocity with the high-BC 7mm bullets (e.g. 168gr up) out of the small case, hence we went to 260.

Another reason why I love Savage Rifles, as I can do most of the work myself. What about long throating the 7-08 barrel and using a LA as a host? You are not bound by the SA magazine to keep COAL 2.800"..............Really do not see why people shy away from LA receivers for cartridges that were originally used in them.

[Zak Smith]

I think we've strayed from calibers for the AR10..

With regard to long-seating 7-08, I ran some numbers in QuickLoad. For the 168 Berger VLD at 2.800 (26" bbl, 60kpsi max, 104% case fill), the average of the top 3 powders was about 2730. When I increased the OAL to 3.000", it reported an increase of only 40fps.

With a BC of 0.643, that certainly blows the 308 out of the water, even at 2.800", but it's a little slow compared to the 260, and significantly worse than you can get in LA calibers (6.5-284, 6.5-06, 7RM, etc).

A few hundredths of a BC point (e.g. 0.61 vs. 0.64) isn't enough to make up for a 100fps speed-up in muzzle velocity. They'll be wthin 1" of wind at 1000 yards and the faster/lower-BC one will drop just under a half a mil less.

_Bullet_           _BC_ _MV_         0     200     400     600     800    1000 | YARDS
338 250           0.640 3000 >    0.00    0.30    1.40    2.80    4.30    6.10 | drop (Qt mil)
7RM 168           0.643 2950 >    0.00    0.30    1.50    2.90    4.50    6.30 | drop (Qt mil)
7-08              0.643 2730 >    0.00    0.40    1.80    3.50    5.40    7.50 | drop (Qt mil)
139 LAP           0.615 2820 >    0.00    0.40    1.70    3.20    5.00    7.10 | drop (Qt mil)
308 155           0.508 2830 >    0.00    0.40    1.70    3.40    5.40    7.70 | drop (Qt mil)

338 250           0.640 3000 >    0.00    1.37    5.72   13.39   24.80   40.41 | wind (inches)
7RM 168           0.643 2950 >    0.00    1.41    5.85   13.69   25.33   41.27 | wind (inches)
7-08              0.643 2730 >    0.00    1.57    6.54   15.32   28.39   46.31 | wind (inches)
139 LAP           0.615 2820 >    0.00    1.57    6.55   15.37   28.52   46.60 | wind (inches)
308 155           0.508 2830 >    0.00    1.91    8.03   19.01   35.66   58.95 | wind (inches)

[223Rem]

I think we've strayed from calibers for the AR10..

With regard to long-seating 7-08, I ran some numbers in QuickLoad. For the 168 Berger VLD at 2.800 (26" bbl, 60kpsi max, 104% case fill), the average of the top 3 powders was about 2730. When I increased the OAL to 3.000", it reported an increase of only 40fps.

With a BC of 0.643, that certainly blows the 308 out of the water, even at 2.800", but it's a little slow compared to the 260, and significantly worse than you can get in LA calibers (6.5-284, 6.5-06, 7RM, etc).

A few hundredths of a BC point (e.g. 0.61 vs. 0.64) isn't enough to make up for a 100fps speed-up in muzzle velocity. They'll be wthin 1" of wind at 1000 yards and the faster/lower-BC one will drop just under a half a mil less.

_Bullet_           _BC_ _MV_         0     200     400     600     800    1000 | YARDS
338 250           0.640 3000 >    0.00    0.30    1.40    2.80    4.30    6.10 | drop (Qt mil)
7RM 168           0.643 2950 >    0.00    0.30    1.50    2.90    4.50    6.30 | drop (Qt mil)
7-08              0.643 2730 >    0.00    0.40    1.80    3.50    5.40    7.50 | drop (Qt mil)
139 LAP           0.615 2820 >    0.00    0.40    1.70    3.20    5.00    7.10 | drop (Qt mil)
308 155           0.508 2830 >    0.00    0.40    1.70    3.40    5.40    7.70 | drop (Qt mil)

338 250           0.640 3000 >    0.00    1.37    5.72   13.39   24.80   40.41 | wind (inches)
7RM 168           0.643 2950 >    0.00    1.41    5.85   13.69   25.33   41.27 | wind (inches)
7-08              0.643 2730 >    0.00    1.57    6.54   15.32   28.39   46.31 | wind (inches)
139 LAP           0.615 2820 >    0.00    1.57    6.55   15.37   28.52   46.60 | wind (inches)
308 155           0.508 2830 >    0.00    1.91    8.03   19.01   35.66   58.95 | wind (inches)

Zak, thanks for the QL data. QL is the "what if of what ifs?" Neurotic's worst nightmare.

This topic strayed quite abit from the 260 and the AR10, but there is still a bunch of good info in it. I would love to do an AR10 in 260 Remington, so where can I look to have a barrel made? Could try calling JN Rifleworks again......or I may contact DPMS and special order one of their uppers. I could all ways cannibalized it for the barrel.

[Alpha Sierra]

I would love to do an AR10 in 260 Remington, so where can I look to have a barrel made?

I would suggest contacting John Holliger of White Oak Precision