Help me choose a short magnum cartridge.

[HodgdonExtreme]

It's been my intent for a while to put together a short mag, on a short action, to occasionally bring out to matches that have lots of longer range targets, or lots of heavy wind. This is not intended for hunting.

I've considered a 7mm-270WSM, the 7mm RSAUM, and of course the 6.5mm RSAUM.

I'm not considering a 30cal, mainly on account of recoil. More on that in a bit...

At first glance, the 6.5mm SAUM appears to be the easy answer. Its trajectory and drift, assuming a 140 hybrid or 130 @ 3100-3200fps is better than the 7mms inside ~1150-1200 yards. It will have less recoil, and bullets won't be seated (at 2.930"+) down past the bottom of the neck.

But, I recently witnessed a lot of "no calls" at 1000+ from everything that wasn't a magnum 7mm or 30cal magnum, which makes me wonder if giving up a slight edge in trajectory by going with the 7mm might be worthwhile if I gain an advantage in spotting misses (and hits) better.

So question 1 is what's better - a bit of exterior ballistics, or impact energy? For what it's worth, this is not intended to be my "mile gun", and I'm not very interested in ELR (say 1500+).

I don't mind the brass prep any of these choices will require, this rifle won't be used places I'll lose a bunch of brass.

I don't like the idea of seating bullets (the bearing surface, anyway) down below the neck, which both 7mm SAUM and 7mm-270 will require. Am I crazy? I just get the feeling you get inconsistent bullet release and will be plagued with donut issues, particularly in a wildcat that is being necked up/down from the parent cartridge.

Assuming it's a non-issue, why is the 7mm SAUM so often recommended for short action applications, when the WSM based 7mms have more case capacity? Isn't that going to translate into higher velocity at any given pressure?

Lastly, I've got very little experience with magnums at all. I do know a ~17lb braked 300wm beats the hell out of me. I had a 284 but currently use a 6mm, and I certainly shoot the 6 better. Its just an easy little rifle to shoot.

That being the case, am I crazy for entertaining the notion of a magnum at all?

 

[Graham]

To answer your question: 7SAUM takes less powder.

I'll be shooting a 7RM next ASC.

 

[Barney88PDC]

I have a 7SAUM built on a long action and I ABSOUTLELY love it. It is for hunting and I'm shooting 180 Berger VLD's at 2960. As a hunting rig it's great. The recoil is more than my 260 but not bad at all. It is a 26" Rem Varmit barrel with a JEC brake. Comes in just over 12#.

However for your application I would go 6.5SAUM. IMO 7 needs to be on a LA so you can seat the bullets out. I think the 6.5 is more fit for purpose.

 

[Jcub]

6.5 Sherman Shortmag. Better case design than the 6.5 4S. Google that shizz.

Richard Sherman has dies in stock.

You can also tone it down like the 4S, still shoot faster and fit in a standard Short action magazine while seating your bullets to the lands. Pretty incredible.

 

[MoBoost]

After burning 3 barrels with WSMs I am done with short mags. With current bullet and brass (especially brass) selection 284 Winchester is far above the rest in the class.
I don't have a good explanation - but for some reason, long range in the wind heavier bullets become more predictable even though high BC faster 6s and 6.5s look better in theory - it seems there is a lot less unexplained vertical jumps.

 

[HodgdonExtreme]

After burning 3 barrels with WSMs I am done with short mags. With current bullet and brass (especially brass) selection 284 Winchester is far above the rest in the class.
I don't have a good explanation - but for some reason, long range in the wind heavier bullets become more predictable even though high BC faster 6s and 6.5s look better in theory - it seems there is a lot less unexplained vertical jumps.

I tend to agree that heavier bullets seem more predictable than lighter ones at range, even when the BC is the same. I realize this is contrary to the physics...I'm probably just crazy.

Anyway, 284 is a nice chambering, but it doesn't (truly) fit a short action, and it simply doesn't run with a magnum in terms of velocity, assuming similar pressure and barrel length.

Edit: I'm not concerned about brass. I've got 500 pcs of 300RSAUM, 500pcs 270WSM, and Norma head stamp is readily available. $2+/pc sucks, but I'd likely be able to shoot out 3 barrels with $300 worth - so no biggie.

 

[Trevor300wsm]

This is not a answer to your question, but it is food for thought. When you show up at a match now days, 95%+ of the shooters are shooting 6mm and 6.5mm chamberings. These all shoot 105gr to 140gr bullets. If a match director is going to set up 1000yd+ targets knowing everyone is shooting 6mm and 6.5mm, he needs to get electronic flashers/strobes for his targets. This will eliminate the "no call" bullshit. If the bullet impacts the target, it flashes.

 

[jbailey]

I have a 7SAUM built on a long action and I ABSOUTLELY love it. It is for hunting and I'm shooting 180 Berger VLD's at 2960. As a hunting rig it's great. The recoil is more than my 260 but not bad at all. It is a 26" Rem Varmit barrel with a JEC brake. Comes in just over 12#.

However for your application I would go 6.5SAUM. IMO 7 needs to be on a LA so you can seat the bullets out. I think the 6.5 is more fit for purpose.

Mr Extreme,
I think you are getting good advice here. If you are setting this up on a long action and you will shoot a good bit beyond 1000yds, go for a 7mm short mag (the short powder column means low ES/SD MV loads very easy to find - key if you are going 1000+). However, if this is a short action, go for the 6.5mm SAUM. 180gr 7mm bullets are ~1.50" and 140gr 6.5mm bullets are ~1.40"... that 0.1" difference may not seem like much, but it is a big difference as far as internal ballistics go. It will mean you will find a safe load SO much easier in the 6.5mm. Running the 180gr on the short action is possible, but you need to be pretty good w/ internal ballistics to find a safe load that is going 2900. Of course, you could run the 162gr or 175gr 7mm and be all set on the short action - but then you give up a good bit of BC to the 180gr.

As far as your question on impact energy... those 1000yd hits you are seeing with 6mm and 6.5mm are going with a good bit less energy than a 6.5mm SAUM would do at 1000. The 140gr 6.5mm hits you are seeing are probably starting at 2800, so add 300fps to that with the 6.5mm SAUM... you will see those hits!

As far as the question of recoil and easy of shooting. With a good brake, I find recoil a non-issue w/ my 7 SAUM. It is a 15lb rifle, 26" and with an APA brake. The bit more recoil is well worth the improved down range accuracy as the bullet bucks the wind so much better than the 308 bolt face calibers. I would recommend a short mag to you, 100%.

Good luck w/ your build.

 

[pinzmann]

I have no problem running 2960 on my GAP SA 7mm WSM. Although now I wish I had used a long action for the ease of seating out the bullets. This is with Berger 180's. I have seen reference of a few shooters here that attain that velocity with 7WSM.
In reference to the 7SAUM what's the average powder usage? I using 65g of H1000 in my 7WSM.

 

[jbailey]

In reference to the 7SAUM what's the average powder usage? I using 65g of H1000 in my 7WSM.

In my 26" 7 SAUM, 63.5gr of Retumbo nets me 2900fps with the 180gr Hybrid. 2.950" OAL, so its a short action.

 

[Barney88PDC]

65.5 H1000 is what I run. I also found a load with 63.0 4831sc but it was higher pressure. Nosler brass, CCI BR2, 180 Berger VLD 3.030" OAL.

 

[The Lawn Ranger]

7 wsm.

69 grains of H1000 and the 180 VLD at nearly 3100 fps is only 6.4 mils of elevation to 1000 yds.

I run it in a long action with fantastic accuracy. The only issues are brass is a bitch to come by
And I would expect barrel life will be just north of 1000 rds. I will most like re-barrel it as a 300 wm.