7mm or .308?

[nralifer]

Chris,

Thanks for noticing my post, but I am not sure what you mean.

[Havasuhunter]

Friend of mine used our 168gr 308 bullet in a 308 Win for a long range competition in Fort Pierre, SD yesterday. He was one of 2 shooters out of 50 to hit the 1080 yd target. The other guy was using a 6XC and a 105gr Berger bullet. Conditions were difficult as the wind was gusting between 10-20 mph. He had a 27in Benchmark barrel, 1:10 twist with a suppressor and the MV was around 2900fps using the Leverevolution powder. I do not know if anyone was using a 7mm Mag.

That's impossible. Only 2 shooters out of 50 hit the 1080 target from the bench? All the long range hunters around here hit everything they shoot at from a field position every time at that distance. 😃😃😃😃

[Camofreak]

Chris,

Thanks for noticing my post, but I am not sure what you mean.

Avatar= The picture next to your name

[nralifer]

Thank you Chris. That was an awesome trip. Believe it or not my wife spotted it.

[nralifer]

Havasuhunter, I should mention that the target set immediately before the 1080 target (6 steel plates 7 inches wide placed at 680 yds) was timed for three minutes and if one did not complete the set in the allotted time the shooting was over. Most shooters I saw did not get a chance to shoot at the 1080 yard target.

[nralifer]

Ever thought that a 308 Winchester (not magnum) could duplicate the 1000 yard trajectory of a 7mm Rem magnum? Impossible!? Well, with the right components it can be done. The comparison is between the 7mmRem Mag Hornady factory ammo and our .308 Win load using 50 gr of Leverevolution powder, WLRM primer,Lapua brass from a Savage rifle barreled with a Bartlein 5R 24" barrel. The 308 bullet used was a 150 grain prototype all copper hollow point bullet tipped with an aluminum tip (150 gr BD) designed by my partner in crime, Jason. The measured BC was 0.480 average of 8 shots measured over 654 yds by the method described in my post in the Long Range Shooting forum. The muzzle velocity of the 308 Win load averaged 3150 fps using an Oehler 35 chrono. Using the data on the 7 Mag load as specified by Hornady on their web site and calculating the trajectory using the Shooters Calculator assuming a 200 yds zero the results are as follows

 

308Win 150grBD BC 0.480 MV 3150, 500 yd drop 34.3 in 1000 yd drop 255.6 in

 

Hor 7RM 154SST BC 0.525 MV 3100 500 yd drop 33.2 in, 1000 yd drop 239.7 in

 

Hor 7RM 162 Interlock BC 0.514 MV 2940 500 yd drop 39.1 in 1000 yd drop 285.4 in

 

The results again illustrate that with the right components the performance of "standard" calibers can be excellent. I am not suggesting that the 308 Winchester is the equivalent of the 7 mag. The Leverevolution powder load used did not create any pressure signs, and the 154SST load quoted is the Hornady Superformance load. I will post some pictures of the 308 bullet and the groups we shoot with it when we make more bullets for further testing.

[roninflag]

Clever. one post 127 replies.

[trphyhntr]

How is this even a debate?

[STOMP442]

3150 from a 24" barrel .308? has this data been verified through another chrony preferably a lab radar or magneto speed? This seems about 150-200 fps faster than anything I have ever seen or heard of with 150gr bullets.

[nralifer]

All of your comments are well taken. The chronograph issue, I think is settled because I have a Magnetospeed and have correlated it to the Oehler. The Oehler consistently gave slightly lower velocities than the Magnetospeed. The Oehler is inherently more accurate than Crony since it uses a third detector and measures the speed over a longer distance. Whether the Lab Radar is better is hard to say. LVR burns at a slightly lower velocity as compared to CFE223 and Varget. The LVR charge I used for the 150 gr bullets tested was over a grain lower than Hodgdon lists as a max load for CFE223 for the 150gr Nosler E tip. That load produces 60,400 psi, and the E-Tip is an all copper bullet similar to ours. I am going to see if I can get the same speed from other 150 gr bullets. Perhaps our bullet has less barrel friction since it was designed to have less bearing surface. My next test will be with the Sierra 150 gr tipped Match King, an intriguing bullet since they list a BC of 0.51 for that bullet.

[STOMP442]

Also needs to compare other high bc bullet designs in 7mm to his high bc .308. There are far better offerings in that weight class from Hornady let alone other bullet brands than the SST or the interlock.

 

.308 155 Sierra TMK = .464 (Litz)

.284 150 Nosler ABLR = .576 (Litz)

.284 162 Amax = .599 (Litz)

.284 162 ELDX = .630

.284 162 ELDM = .652

.284 160 Sierra TMK = .600

.284 168 Berger VLD = .618

.284 168 Nosler ABLR = .624 (Litz)

[biglakejake]

.270 all day long. .308 Winchester ?

 

lee

[nralifer]

Those are potent loads. Would be great if you shared your recipe and rifle specifications with the forum members some of which might like to try them. I like the 308 Win because it is such an efficient cartridge. It works extremely well and brass is never a problem to find. It is also very accurate and barrel life is excellent. To get it to shoot with a trajectory similar to some 7RM factory loadings is a real bonus, and to do that with an all copper bullet is even better.

[nralifer]

One major advantage that 7mm rifles have one the 30 caliber rifles is that factory rifles have tighter twist rates, allowing the stabilization of longer bullets that have long ogives. This translates into higher BCs, but the major advantage that 30 cal rifles have is a larger bore diameter permitting greater bullet energy and speed. To get a 180 30 cal bullet to exceed 3000 fps is not hard, and can be done with the short mag and conventional powders and possibly the 30 06 case and Superformance powder. Slow twist rates have been responsible for the underperformance of some excellent cartridges. The most dramatic example is the 6mm Remington, a superior cartridge to the 243 Win, but the 243 became more popular because of the 1:10 twist that allowed stabilization of the 100 grain bullet. Likewise the 270 has been overlooked as a long range cartridge because the 1:10 twist barrels that dominate factory rifles are not able to stabilize long bullets. Berger makes a 170 gr bullet that requires a 1:8 twist but has a G1 BC of .665, so there are some shooters already realizing this a Berger is tapping into that market. Wonder what one could do with that bullet in a 270 Wby mag cartridge with a 1:10-1:8 gain twist 28" barrel. What the practical limit on twist rate is I do not know, but there has to be a point where the twist becomes so tight that it significantly increases friction and pressures limiting muzzle velocity.

[nralifer]

lancetkenyon,

The trajectory you quoted for the 180 gr 7mm bullets is impressive. Maybe give us some more data on the set up. What were the atmospheric conditions, sight height, zero distance (200yds?) and the calculator used? I would like to plug in my data into the calculator you used under the same conditions and see how the trajectories compare. Also the bearing surface for the 150BD bullet is about 20-25% less than the 155gr Amax. This weekend I will see how it performs out of a short mag case.

 

The reason I ask about the trajectory calculator and the atmospheric conditions is that plugging in the BC and MV you quoted for the .675BC bullet into the Shooters Trajectory Calculator I get 34.4 in drop at 500 and 231.58 in drop at 1000 yds under standard conditions assuming a sight height of 1.5 inches and a 200 yd zero sight in.