WHAT CABLIER SHOOT FLATER 7MM-08 OR 6.5 .284

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by redbone, Jul 13, 2005.

  1. redbone

    redbone Well-Known Member

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    I AM LOOKING TO BUILD A HB RIFLE ON A REM ACTION AN ON A H S PRECISION STOCK BUT I WHITCH CABLIER WILL SHOOT FLATER AN HIT HARDER. 7MM-08 OR 6.5 .284 WHAT CAN YOU TELL ME ABOUT BOTH CALBLERS. ALL INFO NEEDED .
     
  2. jb1000br

    jb1000br Well-Known Member

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    Depends on distance and bullet -- why not go straight 284 and get the best of both worlds /ubbthreads/images/graemlins/laugh.gif

    HV
     
  3. Mysticplayer

    Mysticplayer Writers Guild

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    I shoot a 6.5-06 and 140gr SST. I shoot with a guy that has a 280 and 168gr MK. I go faster, he hits harder. This is at 750yds.

    At long range, there is no substitute for bullet mass. The 284 will be your best option for a mid range hunting/target rig. Figure on shooting 162/168gr bullets.

    Beyond 350yds, there is nothing that is flat. You must range and dial up.

    Jerry
     
  4. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Redbone,

    These are actually quite different rounds. We would need to compare like bullets so lets look at the heavy A-Max bullets for both. The 162 gr 7mm is listed with a BC of .625. The 140 gr 6.5mm A-Max is listed with a .550 BC.

    So as far as BC value goes, the 7mm bullet would have the advantage.

    Thats only part of the equation though. Lets look at velocity potential. The 6.5-284 will drive the 140 gr A-Max to 2800-2900 fps depending on barrel length on the rifle. Maybe even slightly more with a long barrel.

    The 7mm-08 will be in the high 2500 to 2600 fps range with the 162 gr A-Max or again slighly higher in long barrels.

    So as far as velocity goes the 6.5-284 has roughly a 100-200 to 250 fps velocity advantage with these two bullets.

    Now combining the BC for each bullet with the velocity potential for each round let see what they will do. We will take a middle of the road load for each, 2800 fps for the 140 gr 6.5-284 and 2600 fps for the 162 gr 7mm08.

    Both zeroed at 1000 yards. Lets look at the mid range tajectory, highest point of bullet flight and drop at 1200 yards.

    6.5/284
    Midrange: +113" @ 550 yards
    1200 yard drop: -153"

    7mm-08
    Midrange: +121" @ 550 yards
    1200 yard drop: -157"

    You can see that the higher initial velocity helps the 6.5-284 have a flatter trajectory but cutting 8" off the midrange trajectory. This is really nothing to worry about. Comparing 8" difference in trajectory when we are dealing with 113" to 121" is nothing.

    At 1200 yards you can see that the slower, higher BC bullet is catching up to the faster starting 6.5-284. At 1200 yards, the 162 gr 7mm08 is actually faster then the 140 gr 6.5-284, roughly 1250 fps compared to 1228 fps.

    Now as far as "Hitting Harder", well the heavier bullet and larger frontal area of the 7mm08 will win this battle. If we look at the kenetic energy levels of these two rounds we will see that at midrange, 550 yards, the 6.5-284 has 1174 ft/lbs compared to the 7mm08 at 1264 ft/lbs.

    At 1000 yards, the 6.5 has 616 ft/lbs, the 7mm08 has 716 ft/lbs.

    At 1200 yards, the 6.5 has 469 ft/lbs, the 7mm08 has 562.

    Basically the 7mm holds a 100 ft/lb advantage over the 6.5-284 at most ranges. At longer range this will increase.

    One aspect of this comparision that is very important is wind drift.

    At midrange, 550 yards they are basically equal in a 10 mph cross wind, 6.5mm has 21" of drift, the 7mm has 20".

    At 1000 yards, the higher BC 7mm bullet begins to increase the advantage, 6.5mm has 80" of drift, the 7mm has 75"

    At 1200 yards, the 6.5mm has 123" of drift, the 7mm has 114".

    So to be totally honest, out to say 700 yards, there is not enough difference between the two to set one apart from the other.

    At longer ranges, the 6.5mm will have a slight edge in bullet drop but the 7mm08 has the advantage in energy and wind drift.

    Now this is only one comparision and these two rounds are so close that with different bullets or differnet barrel lengths, the results could be slightly reversed, point being, they are very close in performance with VLD bullets.

    Good SHooting!!

    Kirby Allen(50)
     
  5. James Jones

    James Jones Well-Known Member

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    Great response Kirby , that makes alot of sence and probably would change the mind of alot of guys seeing how it would be easier to fit the 7-08 in a short action without so much machine work. And the Lapua 308 brass is a hell of alot easier to get hold of and alot cheaper than the lapua 6.5-284 !!

    But like it was posted before , the 284 would make for a great round also just neck up the 6.5-284 and you still have great brass plus a little more velocity.

    Very intersting
     
  6. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    JDJones,

    No doubt the 284 is a great round, actually its sad it is not used more as it would be a great tactical round with the bullets we have today.

    Just did not want to give Redbone something he did not ask about. You are correct though, the 284 would outperform either one at extreme range with conventional bullets.

    Good shooting!!

    Kirby Allen(50)
     
  7. budlight

    budlight Well-Known Member

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    The 7mm STW is a good choice. You can get ammo at the local store and when reloaded makes a 7mag look sad. The very high BC of the 7mm bullets makes them a potent weapon.

    I'm cheap and don't shoot the super grade bullets very often. My STW likes the 175 gr. boat tails and the 28 inch barrel burns most of the powder.
     
  8. redbone

    redbone Well-Known Member

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    Fiftydriver Thanks for the Info that is what I needed .I Have a 7MM STW REM 700 SSF an I love It .
     
  9. Northman

    Northman Well-Known Member

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    Could somebody do the same with the .284 using the 162grain A-max?

    I have a short Rem action, but Im worried I wont get that much speed out of it, because I have to fit it in a short magasin, and using to much of the case to fit the bullet in.

    What kind of speeds could I get using 284 with 162 grain A-max in a short Rem action? If anybody has a program for this?
     
  10. Guest

    Guest Guest

    If it wasn't for the 7mmWSM the Standard 284 would have been my choice....

    Now with the wsm the 'ole 284 will slowly dissapear... The 6.5/284 is probobly one of th fastest growing and accepted "wildcats" of all time... this too really hurt the 284...
     
  11. JDT

    JDT Member

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    In my opinion, the comparison of the trajectories of the 7mm-08 and the 6.5X284 based on the 6.5mm 140-grain A-Max and the 7mm 162-grain A-Max is very misleading. Even though the bullets are technically of the same commercial type, there is a very significant difference in their Form Factors. Both bullets have the same Sectional Density of .287. However, the 7mm 162-grain A-Max has a much higher Ballistic Coefficient despite having the same Sectional Density and being of the same commercial type. The fact that the 13.6 percent difference in Ballistic Coefficient does not arise from any difference in Sectional Density suggests that one bullet is actually more aerodynamically designed, despite the fact that they are both A-Max bullets. Put simply, the fact that the 7mm-08 bullet is cutting the wind better in this instance has absolutely nothing to do with a higher sectional density and arises entirely from the fact that it is shooting a more areodynamically designed bullet.

    I ran through what I believe is a much more fair comparison based on a different popular bullet type available in both calibers. I compared the 6.5mm 142-grain Sierra BTHP MatchKing to the 7mm 175-grain Sierra BTHP MatchKing (using the 168-grain BTHP MK would have been very unfair to the 7mm-08 because of its comparitively high FF). The Form Factors of the two bullets I did choose are much more similar than those of the previously mentioned A-Max bullets. This is intended to minimize any unfair advantage given to one cartridge over the other. The SD of the 7mm 175-grain BTHP MK is approximately .309958 and that of the 6.5mm 142-grain BTHP MK is approxiamtely .291060. The BC of the 7mm 175 BTHP MK is .608 and that of the 6.5mm 142 BTHP MK is .595. Their comparitive FFs are .5097999 for the 7mm and .4891764 for the 6.5mm. This results in a mere 4.2 percent advantage given to the 6.5X.284, as opposed to the whopping 13.6 percent that was being given to the 7mm-08 in the original comparison.

    I ran through 1200 yard trajectories for both based on 1000 yard zeroes and a 10mph crosswind.

    7mm-08 / 175-grain BTHP MatchKing vs. 6.5X.284 / 142-grain BTHP MatchKing

    Bullet Path:
    7mm-08 : -175.73 inches
    6.5X.284 : -138.08 inches

    Minimum-Maximum Zero:
    7mm-08: 1194-1206 yards
    6.5X.284 : 1193-1207 yards

    Wind Drift:
    7mm-08: 123.29 inches
    6.5X.284: 108.33 inches

    Kinetic Energy:
    7mm-08 : 545 ft/lbs.
    6.5X.284 : 540 ft.lbs.

    Note: I did simplify things by using the same G1 Ballistic Coefficient throughout the entire trajectory for both bullets, as opposed to using Sierra’s multiple Ballistic Coefficient method.

    I also ran another comparison based on the absolute flattest trajectories I could calculate out for each cartridge based on the highest possible velocities published in Sierra’s Reloading manual at a given weight and using Lost River Ballistics bullets.

    At 1200 yards with a 1000 yard zero and a 10 mph crosswind.

    6.5X.284 using 120-grain J36 with a BC of .687 launched at 3100 fps.
    7mm-08 using 140-grain J36 with a BC of .664 launched at 2900 fps.

    Bullet Path:
    7mm-08 : -113.81 inches
    6.5X.284: -93.97 inches

    Minimum-Maximum Zero:
    7mm-08: 1191-1209 yards
    6.5X.284 : 1189-1211 yards

    Wind Drift:
    7mm-08: 89 inches
    6.5X.284: 76.72 inches

    Kinetic Energy:
    7mm-08 : 682 ft/lbs.
    6.5X.284 : 726 ft.lbs.

    Note: The 6.5X.284 is getting an advantage in Form Factor of approximately two and a half percent.


    It appears to me that the 6.5X.284 can launch a bullet of a given sectional density faster than the 7mm-08 given the same barrel length and limit of loading pressure. Actually, it can produce comparable speeds even with the same weight of bullet! In order for the 7mm to get a sectional density advantage, it would have to shoot the absolute heaviest 7mm bullets available and it doeesn’t launch them fast enough to overtake the 6.5X.284 in terms of flatness of trajectory unless you start to consider extreme distances that most likely would exceed the maximum effective range of both cartridges. I assume this is because the 6.5X.284 burns more powder and has a smaller diameter, producing a higher expansion ratio. Higher velocity at the same sectional density means a flatter trajectory given the bullets being compared have the same form factor.
     
  12. bob_spangler_jr

    bob_spangler_jr Member

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    I agree with your reasoning, BUT...

    wouldn't an even fairer comparison be between the 6.5mm 142 grain SMK and a 7mm 162 grain Amax?

    I gather from the tone of the comparison that you're trying to take each candidate's best offering. If this is the case, I recommend considering the 7mm08 with the Amax. It has BC .62 (that's greater than the BC of the 175 bean) AND it will go faster.

    JDT, I admire your scientific rigor. You bring up a very good point. I think it should be applied one more time in this analysis.

    Enjoy,
    Bob

    PS: I bet when the dust settles, I bet something to the effect of, "...the 6.5-284 shoots flatter for the first so-and-so yards, but the 7mm08 hits harder after this-and-that yards. The 7mm08 also has a longer barrel life..." comes up.
     
  13. Wild_Bill

    Wild_Bill Well-Known Member

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    Apples Vs Oranges

    Hi you have to compare similar capacity cases to get true representations.

    So you would have to compare the 260 against the 7mm08 and the 6.5-284 against the 284win.

    If you look at F Class world wide there is a huge shift away from the 6.5-284 to the 284win and 7mm short mags.

    I believe you would be best suited with a 284win I know it was not lisred but if you were prepared tonuse the 6.5-284 case neck it back to where it belongs 7mm. I have shot one for 4 years in F Class and it is much better than a 6.5 in fish tail winds and double the bareel life. The 7mm08 is just under sized for the projectiles and the 284win is about perfect.

    I shoot the 168gr sierrs and 175gr sierra both with H4831SC and 57gr and 54gr respectively the 168gr at 1000yds is actualy 2moa=20" higher on the target and requires less windage the BC is much higher than published and is on parr with the A Max. The velocity for the 168gr is around 2960fps while the 175gr is around 2850fps in a 9 twist 30" barrel. I tried so,e Wildcat 200gr ULD RBBT projectiles on saturday with 54gr H1000 and the loads wewe fine bet did not stabalize I have an 8 twist on order.

    Cheers Bill
    Australia