6mm vs 7mm

[blacknwhite1]

Based on all the info I have seen recently I’m starting to question why anyone would choose a 7mm over a 6mm. When considering bullet drop and wind drift the 6mm is almost always better. Am I missing something...? Should I trade my 7 in for a 6?

 

[spclark]

You might want to address that question to Brian Litz. He favors a 7 for long range over everything else. Considering his level of talent, knowledge of things ballistic and experience, there must be a reason.

 

[15Tango]

Based on all the info I have seen recently I’m starting to question why anyone would choose a 7mm over a 6mm. When considering bullet drop and wind drift the 6mm is almost always better. Am I missing something...? Should I trade my 7 in for a 6?

In the shorter ranges the 6MM is great and it's even great out to 1000 but against the 7MM it's not really better for wind. It may shoot a bit flatter, especially in the short range but drop's not really a variable I consider to be the be-all justification for a cartridge - after all, we know our come-ups and that's not changing so we can account for it predictably. Wind however, we can't always predict spot on and it changes and it's not an always-known dope.

The 243 can really throw heavy bullets well, when I had one I was getting 3200 FPS out of a 105 VLD. The .284 Win. is a pretty tame 7MM by most standards - here are some numbers comparing the two in a 10 mph wind:

105 VLD (@ 3200 FPS):

300 yards - drop 11.3", wind 5"
600 yards - drop 75", wind 22"
1000 yards - drop 289", wind 71"

162 AMAX (@ 3100FPS, typical velocity the 284 can launch a 162AMAX):

300 yards - drop 9.2", wind 4"
600 yards - drop 61.5", wind 17.6"
1000 yards - drop 232", wind 54"

There's nothing wrong with 6MM, they're great! Against a 7MM though they do not beat it in the wind or in this case trajectory. In this comparison I used one of the faster 6MM cartridges out there and compared it to one of the more tame to middle ground 7MM. Had I used a 7WSM or RSAUM the 7MM would have beat the 6MM in an even further margin.

Wayne

 

[blacknwhite1]

I guess I was comparing it to a slower 7mm (I was looking at 7/08 numbers). I think the velocities I was looking at for the 7/08 were pretty low and could be exceeded. Even looking at your numbers though im surprised the wind drift is so close between the two. Interesting to think about...

I just finished a 300 whisper and have been shooting it a lot lately, so I don’t mind correcting for bullet drop.

 

[spclark]

The 243 can really throw heavy bullets well, when I had one I was getting 3200 FPS out of a 105 VLD.

Yep, that's reportedly what John Whidden gets out of his 243, what he used the last two LR Championships to come out #1.

I'm getting 3130+ with the same bullet in a 30" 6XC, accurate as I need it to be at 1,000 yards....

 

[15Tango]

I guess I was comparing it to a slower 7mm (I was looking at 7/08 numbers). I think the velocities I was looking at for the 7/08 were pretty low and could be exceeded. Even looking at your numbers though im surprised the wind drift is so close between the two. Interesting to think about...

I just finished a 300 whisper and have been shooting it a lot lately, so I don’t mind correcting for bullet drop.

7-08 is a good cartridge, I'd take it any day over a 308, it is one of the weakest 7MMs out there though. Comparing one of the weakest 7MMs to one of the strongest 6MMs isn't exactly fair or a true representation of juxtaposition.

Just for fun I ran the numbers of what a 7-08 can do with a 162 AMAX with some careful load development:

162 AMAX @ 2800 FPS

300 - drop 12", wind 4.6"
600 - drop 78", wind 20"
1000 - drop 293, wind 62"

Even in the 7-08 it still beats the 6MM. Again, comparing one of the hottest 6MMs against almost the weakest 7MM is skewed. It's like comparing a 7RSAUM's trajectory & wind against a 6PPC's.

SP, that 6XC is a heck of a 6MM.

The 300 Whisper's been around for quite a while and it's good at what it does. This 300 AAC Blackout or whatever seems to be all the rage now for some reason and people are acting like it's a new idea, I don't get it. I've always saw it somewhat as a copy of the Whisper that doesn't quite match the performance of the Whisper. From what I've seen of SHOT show, Remington's coming out with some ARs and even some bolt rifles (if I remember correctly) in the 300 Blackout this year. I think a .30-Grendel would be a fine .30 caliber for AR15s. If the 6.5 Grendel's launching a 120 class at 2600 I imagine it could keep up with the 30 Rem. AR and get a 120 .30 cal. up to 2800 and then you wouldn't have to fuss around with AR10 bolts in an AR15. Anyway, I'm rambling.

Wayne

 

[blacknwhite1]

Thanks for the great input 15Tango.

I am really enjoying my Whisper. I've been shooting 220 SMK and 8.9 H110 at ~1020. They put new meaning to bullet drop.

Unfortunately due to my geographic location I don’t have a lot of long range opportunities. I’m just starting to dabble.

If you want a 150 yard shot in my deer woods you have to spot the deer, sneak AWAY from him through the brush and then take the shot...

 

[whiskey08]

check out the bc's, for the best (berger) 7mm bullet the bc is .659, for the 6mm is .545. Assuming your using the right brass behind it, the 7 is very very hard to beat in every category. Trajectory, energy, accuracy, wind drift. Biggest downsides would be barrel life, recoil and...??

 

[flatlander]

I've shot both 6x47 Lapua w/DTAC 115s & straight 284s with S175MKs & Berger 180 VLDs at 1000yds. at both Byers, Co. & Raton. No question that the 6x47 has less recoil and is easier to shoot, even though both my 284s weigh a pound more than the 6x47. Typical velocities were 2980fps for the 6, and 2800 for the 7mm (I can easily get 2900fps using RL17 in the 284, but can also get 3050fps using it in the 6x47 - accuracy is just more consistent in both cartridges using other powders in my rifles).

However, on days when the wind gets tricky (which is just about every day at Byers), I'd rather have a 284 on the line. While the 180VLDs are a long way from being immune to wind changes, they're certainly more forgiving when I miss a change. Accuracy potential between the two cartridges is - IMHO - nearly a draw. If anything, the 284 has a slight edge in being consistently accurate.

 

[LCazador]

Flatlander , you're absolutely right , there is no comparison between the 6mm and 7mm . How the heck are you getting 2900 with 175MKs without stepping on your brass ? My last 284 had custom chamber with .004 increase in body taper , and I still couldn't get near the velocity you're getting . Of course I never shot Reloader 17 ? The 284 is an awesome cartridge ;D!!

 

[15Tango]

Flatlander , you're absolutely right , there is no comparison between the 6mm and 7mm . How the heck are you getting 2900 with 175MKs without stepping on your brass ? My last 284 had custom chamber with .004 increase in body taper , and I still couldn't get near the velocity you're getting . Of course I never shot Reloader 17 ? The 284 is an awesome cartridge !!

Robert W. hit 2950 FPS with 180 VLDs & R17 in his testing. Yeah!

Wayne

 

[Steve Blair]

My Borden/Eliseo with 29" Brux .284 gets ~2920 with a case full of 7828 SSC. In my new 32" Krieger F-Open rifle, that will be a little closer to 3000. The slower powders seem to need nearly full pressure to burn efficiently.

 

[Elwood]

Interesting topic.

Hopefully by the end of the English summer I will have some conclusions of my own.

I currently shoot a 7WSM in F class and can push the 180 Berger to 3100 with RL 25 and a 32 inch barrel.

I have just had a 6mm Crusader built for 600 yard matches ( it doesn't seem sensible using a 7WSM at 300/500/600 unless of course there's a gale blowing) I'm hoping the 6C will give me extended barrel life over the 7WSM, not quite double but hopefully close.

I have just about finished my load development for the 6C and it appears that the 115 DTac doesn't like to be pushed over 3150, my accuracy was between 3050 and 3150, after which groups really opened up. I didn't bother taking it up to max, QL predicted that I could get 3300 fps, I settled on 3130 figuring that the Hare doesn't always win the race.

Comparing the ballistics between the 6C and the 7WSM at both there given speeds there really doesn't appear to be much in it in theory Just a shame that the DTac doesn't like to be pushed harder otherwise I think it may be a different story.

 

[Jeffvn]

My brother hits 2,900+ with the Berger 180 VLDs using his .284 using H4831SC, out of a 30" Bartlein. I'm at 3050 with the BErger 180 Vlds with my 7WSM from same length Bartlein - both 9 twist. I do not think a 6mm is capable of keeping with out Berger 180s when driven that fast. The 7WSM kicks a bit, but if you go up near the weight limit of F-Class, its ceratinly not untolerable, at least my me for 3 relays. My brother's 20+ pound .284 is positively tame when it comes to recoil.

JeffVN

 

[15Tango]

6.5MM is a pretty good middle ground between the two in question. I don't have a 6MM anymore and I miss having one, I'm in the process of just starting to build one again but this time it's going to be a match rifle, not a bolt rifle and I've settled on the 6RAT. They all have their place.

Wayne

 

[rsilvers]

The 300 Whisper's been around for quite a while and it's good at what it does. This 300 AAC Blackout or whatever seems to be all the rage now for some reason and people are acting like it's a new idea, I don't get it. I've always saw it somewhat as a copy of the Whisper that doesn't quite match the performance of the Whisper.

300 AAC BLACKOUT exceeds the performance of the Whisper. It has both a higher chamber pressure and a longer throat - so it is like 5.56mm compared to 223.

But what is special is that it was approved by SAAMI and has low cost ammo coming out.

 

[15Tango]

300 AAC BLACKOUT exceeds the performance of the Whisper. It has both a higher chamber pressure and a longer throat - so it is like 5.56mm compared to 223.

But what is special is that it was approved by SAAMI and has low cost ammo coming out.

The AAC and the Whisper, to my knowledge, have the same parent case - they're going to have the same structural pressure limits. I found loads for the Whisper that launch a 125 grain at 2500 FPS; the loads I'm seeing on the AAC are a 123 at 2280 FPS. I don't see the AAC outperforming the cartridge it's a copy of.

I can't see that many people buying off the shelf ammo for it, especially when it's easily made from its parent case. That goes for either cartridge.

 

[rsilvers]

For any given chamber pressure, the 300 AAC BLACKOUT is capable of higher velocity.

Meaning, the 300 Whisper(R) cannot make 2280 fps with that bullet at the same OAL and pressure.

So a more perfect analogy is 300 AAC BLACKOUT compared to Whisper is like 6.8 SPC-II compared to 6.8 SPC. I did not use that example first because fewer people are familiar with 6.8.

 

[rsilvers]

I can't see that many people buying off the shelf ammo for it, especially when it's easily made from its parent case. That goes for either cartridge.

People buy off the shelf ammo for 308 and that does not need any forming. Less than 15% of shooters reload, but factory brass for 300 AAC BLACKOUT is coming out soon at a low price.

 

[Bob3700]

Out to 600 yds, here in the mid-west, you just can't beat a 6mm BR/improved for accuracy. The low recoil is also a + factor when you are shooting 88 rounds in a day.

At 1000 yds, I shoot a 243 SLR with 115 DTACs at 3050 fps. That is a pretty flat shooting and decent wind bucking combo.

If I was shooting out west where the wind is much more of a factor, I would choose the 284/improved with the 175 SMK or 180 Berger. It is tough to argue the BC advantage that 7mm combo has. You need to handle the recoil, prone with a sling, the rifle wt is limited so that is a factor to consider.

Bob