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Rifles, Bullets, Barrels & Ballistics Applied Ballistics



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Unread 07-25-2005, 06:27 PM
Gold Member
Join Date: Jul 2005
Location: Arkansas / Oklahoma / Boarder
Posts: 690

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

Kill more Coyotes

Feed The Buzzards
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Unread 09-03-2005, 04:50 AM
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Join Date: Apr 2005
Posts: 135

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?
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Unread 09-03-2005, 06:29 AM
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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...
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Unread 09-03-2005, 04:31 PM
JDT JDT is offline
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Join Date: Aug 2005
Posts: 9

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.
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Unread 11-06-2007, 11:40 PM
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Join Date: Jan 2005
Location: west virginia
Posts: 19
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.


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.
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Unread 11-07-2007, 12:15 AM
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Join Date: Sep 2005
Posts: 748
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
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