7mm or .308?

[roninflag]

the one with a krieger barrel.

[billrquimby]

The question was 7mm or .308, and strictly speaking that could mean a whole bunch of different chamberings, from 7x57 to .30 Weatherby Magnum.

 

Apparently what was meant was the 7mm Remington Magnum, and the .308 Winchester, so my vote goes to my favorite caliber for most game, the 7RM. The .308 Winchester actually is a mild .30-06, and I'll take the 7RM over any .30-06 for anything up to moose and eland. Above that, the .30-06 with 220 grain solid bullets MIGHT be suitable for African buffalo and elephant under the right conditions. No African country I know of allows its use on these animals,though.

 

Bill Quimby

 

 

[nralifer]

 

The 270 has great untapped potential. I have been using the Superformance powder and shooting Barnes TSX bullets. I got a 26in Benchmark barrel with a 5 grove 1:9 twist. Today explored the limits of velocity with the 140gr TSX. Has a BC of 0.404. Got it to shoot 3200 fps and at 500 yds this bullet still has 1364 ft-lbs of energy. It is still supersonic at 1000 yds. With this powder and the right barrel length the 270Win is virtually the equivalent of the average 7mmRem Mag. One can verify the trajectory using the trajectory calculator on shooterscalculator.com

Barnes bullets have just about the worst BC possible especially in their 7mm offerings which are only flat base on top of that. Use any other bullet but Barnes in 168gr or heavier and the 7mm mag will walk all over the 270. heck even a high BC 140 in 7mm will out perform your 140 Barnes at 3200 fps.

 

I have nothing but great things to say about a 270 but to call it the equivalent of a 7mm mag is just wrong.

 

The point I was making was that the .270 Win with the proper barrel and powder and bullet can perform as well as the 7mm Rem Mag. If you use a Barnes 140 gr in a 7mmRM it is not likely that you will be able to propel it much faster than in the rifle I described. The fastest MV for the 7mmRM 140 gr bullet listed in Hodgdon Reloading magazine is 3138 using 63 gr of Hybrid 100V. The 270 can propel a bullet of the same weight at that speed. This indicates that the 270 case is actually more efficient in terms of the muzzle energy/grain of powder produced than the 7mmRM case which uses about 9% more powder. I'm not trying to make the case that the 270Win is better than the 7mmRM, but show that the 270 Win has a lot of untapped potential. Berger, who makes bullets with high BCs, lists a 0.487 BC for their 140 gr 270 and 0.510 for the 7mm 140 gr bullet. If propelled at the listed MVs (3138 for the 7mmRM and 3200 for the .270 Win) The drop at 500 yds is 1 inch greater for the 270 as compared to the 7mmRM.

[nralifer]

Barnes bullets admittedly have low BCs, but they nevertheless are excellent bullets. The Cape Buffalo you see me with in the picture was killed with a single shot using a Barnes TSX bullet, and it was not a 375 caliber. The bullet went clean through the Buff and liquified the heart. The BCs are adequate for clean kills out to 500 yds and the trajectories of these bullets over that distance are flat enough given the BC. The 140 TSX 270 bullet launched at 3200 fps with a BC of 0.404, will drop 39 in. at 500 yds. The Berger 140 gr 270 bullet with a BC of 0.487 will drop 36 in. at that distance if launched at the same speed. That is less than a minute of angle difference. Just one's heart beat will cause more variation in the aim point than that. At close range though the Barnes bullet will likely hold together and penetrate better than the thin jacketed Berger. If I was hunting Caribou and came across a 300 pound Black bear at 50 yds, I know which bullet I would rather have. But the long range target shooter would much rather use the Berger. It's all a matter of matching the bullet to the job at hand.

[Havasuhunter]

Best to have both. Also probably best to have a 300 mag, 7-08, 308, 257 Roberts, 6.5x55, and a few others. Just in case!:-)

[STOMP442]

Like I said, I have nothing but great things to say about a .270 but you are still failing to compare things equally. You are using superformance powder in the .270 to get the absolute maximum out of it yet you compare that to a standard load of a 7mm mag found in a load manual. If you were to use the same hot rod powder in the 7mm and work up a load to its max I'm willing to bet velocities for that cartridge as well would be much faster and probably at least around 3300 as opposed to the 3138 fps listed. As you probably already know the .270 using 140gr bullets and H100V is only yielding around 2960fps according to Hodgdons data. Comparing things equally paints a completely different picture.

[nralifer]

I guess you are missing the point I'm trying to make, and that is that Superformance powder in the 270 can really make it perform. It would be interesting if you tried it in the 7mag and see how much it improves its performance. It has a greater powder capacity and therefore more potential for higher velocities. We can look forward to improvements in powder technology largely because of the wars we have been fighting and the heavy use of special forces driving small arms development. That means as some of these powders make it to the civilian market, cartridges that were thought to be mediocre will be made to perform to levels that not thought possible. If you like hand loading , it can be exiting.

[STOMP442]

I'm not missing the point at all. I understand that the 270 with new hot rod powders are capable of much higher velocities.I also understand that if loading the the 7mm mag to the same standard would yield greater velocities as well and leave the 270 in the dust. Like I have said before the 270 is a fantastic cartridge but to say that it can perform as well as the 7mm is simply false. The 270 can get close pushed to its max with 140 bullets but equal to or as well it does not.

[nralifer]

I think all of the forum viewers would be very interested if you developed some Superformance loads for the 7RM. It is a very popular cartridge but Hodgdon does not list a Superformance powder load in their 2012 manual. Since Superformance has a burn rate virtually the same as H4831, you could start out a couple of grains below the maximum for H4831 and work up in 0.5gr intervals until you either got pressure signs or reached the max grains listed for H4831. I have used this same approach to develop loads for the 330Dakota and 300WSM. For a 140gr 7mm Nosler Partition bullet, Hodgdon lists 64gr of H4831 as the max load. Unfortunately I do not have a 7RM or I would do it myself.

[khmer6]

Both!!! One for elk the other for deer! My Remington 700 7mm RM is a lot heavier than my savage axis ii 308. I swear the paper specs lie

[Zeke-BE]

I'm not missing the point at all. I understand that the 270 with new hot rod powders are capable of much higher velocities.I also understand that if loading the the 7mm mag to the same standard would yield greater velocities as well and leave the 270 in the dust. Like I have said before the 270 is a fantastic cartridge but to say that it can perform as well as the 7mm is simply false. The 270 can get close pushed to its max with 140 bullets but equal to or as well it does not.

What I notice the difference of the 2 is factory ammo. You can almost get the same speed and energy with the .270 compared to a magnum size 7mm. A 50-200 fps faster out of that size of brass is bad. Even with a lot of nosler loads and Berger loads you don't really have a few advantages over the .270. But there are a few loads out there that will make theses 7mm fly fast and strait. A buddy of mine found a load and build it up to shooting 3400 fps with a 1/2 grouping. What I'm saying if you don't reload don't bother with a 7mm not much more there only the kick of the gun is greater. If you reload it will do an awesome job!!

[nralifer]

Would be interesting to get the specifics on your buddies load. Components can make a huge difference in performance. I have been testing CFE 223 and Leverevolution (LVR) in the 308Win although there are no published data using the latter in the 308. Both powders have similar burn rates. The gun has a 20 in. lapped Douglas Match barrel and a Savage short action. Best result so far is seen with 48.5gr of LVR using a 170 gr bullet. Muzzle velocity was a little over 3000 fps using a Magnetospeed chrono. A three shot group was 0.501 in. Ambient temp was 38F. This performance pretty well matches what is published in the Hodgdon 2012 reloading manual for the 7Mag and 7WSM. Had some pressure signs, with extraction being a little sticky. I think, though that 2900 fps is readily doable in this rifle. If anyone wants to try the LVR in their 308 or 7mm08, would start with 44gr and work up in 0.5gr intervals. Use a chronograph you have confidence in and be mindful of the ambient temperature. I do not know how temperature stable LVR is.

 

I had a problem with throat fouling using CFE 223. Not sure why. Will need to need to look into this further.

 

One note. Whether a 30 cal or 7mm bullet is better is sort of academic. Larger caliber bullets have greater performance potential than smaller caliber bullets. One problem 30 cal rifles have slow twist rates compared to 7mm rifles. Practically all production 30cal rifles have between 1:12 and 1:10 twist barrels, whereas 7mm rifles are 1:9.5 or faster. The twist rate has a big influence on the BC of the bullet design. BC is increased with weight, nose design and length and boat tail length. A faster twist barrel will stabilize longer, higher BC bullets. A friend of mine is designing 30 cal bullets that potentially have BCs exceeding any conventional 7mm bullet. His method of calculating BCs is probably accurate. He had doubts about the advertised BCs of the 190gr LRAB bullet, and calculated its BC at 0.550. Turns out that a measured BC by Bryan Litz for this bullet was 0.567. The bullet I mentioned above was a 170 gr solid copper bullet 1.43 in long that is stable from a 1:10 twist barrel, and machined from 110 copper bar stock. The calculated BC on that bullet is 0.6. Berger makes a 168 gr 7mm bullet with an advertised BC of 0.617. In a few weeks we will have the instruments to actually measure the BC, not only of that bullet but also other commercially available bullets under the same conditions. Looks like with the right components a 308Win can run with a conventionally loaded 7Mag.

[308Nut]

Are you saying the 170 grain bullet is a 30 caliber bullet with a 'calculated' BC of .6? Or a 7mm 170 grain? Physics dictate that it is impossible to have a 30 call bullet weighing 170 grains that would have a .6 BC. Especially an all copper bullet that has a specific gravity of 8.89 versus a jacketed lead bullet which is 10.7. I have some 177 grain all copper bullets shaped very similar to the 208 amax and firing tests showed the BC to be around .514G1.

 

Is your friend's method of calculating BC mathematical or through firing tests?

[nralifer]

It is a 308 bullet.

[nralifer]

We have made a 180 gr 308 bullet that by drop at 400 yds has a 0.65BC. The 170 has a similar profile.