Holy Grail of Short Action 7mm Cartridges...?

[KYS]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Marksman</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KYS338</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KYS338</div><div class="ubbcode-body">7mm Creedmoor </div></div>

Why do you advocate 7CM over any of the others, particularly 7SLR? </div></div>

Ease of loading, finding loading components is simple, barrel life is great, 2850 fps and up can be achieved depending on barrel length and twist. I shot a mild load thru mine and was getting 2860.

Its just a cool caliber. </div></div>


I second the 7mm Creedmore. Just because I want to see someone else shooting it so I can get more data before I decide if I need one.

What length barrel/twist/bullet weight are you using to get 2850 fps? Any load data out there that I could look through? </div></div>

You can buy the rifle I speak of and find out for yourself!!! I will provide load ammo with it.

 

[The_FNG]

Re: Holy Grail of Short Action 7mm Cartridges...?

Can anyone provide links to anything substantial on the 7CM? I'm still having trouble believing it'll run with the .284. I have a 7mm barrel blank sitting here looking at me wanting me to make a decision.

 

[turbo54]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: the_fng</div><div class="ubbcode-body">Can anyone provide links to anything substantial on the 7CM? I'm still having trouble believing it'll run with the .284. I have a 7mm barrel blank sitting here looking at me wanting me to make a decision.

</div></div>

As close as you're gonna get: http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=3395471#Post3395471

Anything/Everything "publicly known" is in that thread. Give it a read.

 

[jeffersonv]

Re: Holy Grail of Short Action 7mm Cartridges...?

This one (7 SLR) interests me too.

I believe the Lapua brass was avoided because of the thickness necessatating turning the necks.
Besides, along with the easy forming of the brass, the Win brass cost and availability is part of the attractiveness to me.

By the time I get to building my next rifle we should all know if it's as good as it looks.
I still plan on keeping my 6.5 Creedmoor.
Staying tuned...

 

[turbo54]

Re: Holy Grail of Short Action 7mm Cartridges...?

Alright, a few more thoughts and talking points:

1. What's the big deal about loading cartridges so that the bearing surface of the bullet is above the neck/shoulder junction (NSJ)? I read about this all the time, and have never heard any logic supporting it, other than "maximizing case capacity". Everybody said not to build a SA 284 because the bullets would be deep seated. Max reasonable charge with 175/180gr bullets in 284 is ~55gr H4831. You can fit that much even when loaded to a COAL of 2.950", so the SA isn't impeding capacity in this case, the key difference is whether/not the bullet shank is above or below the NSJ. Who cares? Serious question!

2. Speaking of 284, I played with 284 cartridges in my AW magazines - no good. By the time you've got 4 or 5 in there, they just want to pop out. The fat 284 case fucks it up. You might could bend/tweak the mag lips, but I don't think it'd be so good.

3. The 162amax and 175smk are essentially the same length, and the boat tail is very nearly the same, thus they fit cases/magazines the same, +/- a little. Good enough for arguments sake. 708 COAL needs to be ~2.950" to have the bullet above the NSJ. 7CM COAL needs ~2.875 or so to achieve it. The NSJ occurs ~.030 lower on an SLR case than a 243/260/708, thus, 2.920 or so will keep the 162/175 north of the NSJ.

4. Seems to me like the 7SLR will have more case capacity than 7cm, when both have bullets above NSJ.

5. Is it possible the smaller capacity of 7CM can produce MORE velocity??

6. As far as I'm concerned, the 175smk is the 7mm bullet of choice. Super easy to load for, beautiful BC of .64 (vs .60 for 162), and they transition nicely. I've found some barrels hate the 162. My aim is to use the 175!

 

[The_FNG]

Re: Holy Grail of Short Action 7mm Cartridges...?

Cheers for that Turbo.

Your point 5 is also a question i have.

 

[tylerw02]

Re: Holy Grail of Short Action 7mm Cartridges...?

This is regurgitating:

Bullets seated below the junction don't all make the transition out of the case well and sometimes there will be erratic pressure spikes---fliers.

Seating so deeply also greatly increases pressure, meaning reduced charges are necessary. This reduced brass life, barrel life and can reduce velocity in the case of cartridges that use slower powders.

So it was explained to me that a person would be better going with a shorter cartridge in the end.

Seems a person rubbing shortened OAL .284 in a sa would be better served with one of the hypotheticals we've talked about here. Especially with the A/W mag issues you've described.

I used to shoot 6mmAI, but I couldn't get it to run well at mag-length. It was either top hot or too slow to the point where I may has well ran .243 or 6-6.5x47.

 

[ScottyS]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeffvn</div><div class="ubbcode-body">Both the 6.5SLR and the 6SLR are Robert Whitley creations. Here are the link.

http://www.6mmar.com/Super_LR.html

http://www.6mmar.com/65_SuperLR.php

One good thing about Robert's creations, he gives you the reamers prints and in some cases load data up front and does not hold them back as proprietary.

Jeffvn</div></div>

This allowed me to get running with a 6SLR immediately. I don't have time to do real load development, especially with an unknown cartridge.

Robert's data worked exactly as advertised, giving me a go-to recipe right out of the box, letting me do load development at my leisure.

 

[sandwarrior]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">Alright, a few more thoughts and talking points:

1. What's the big deal about loading cartridges so that <span style="font-weight: bold">the bearing surface of the bullet is above the neck/shoulder junction (NSJ)<span style="color: #FF0000">it's for safety. The side pressures on a bullet when seated that deep can actually force it somewhat sideways into the throat. Being as it is more malleable than the barrel it <span style="font-style: italic"><span style="text-decoration: underline">could</span> cause a plug and subsequent catastrophic failure</span></span></span>? I read about this all the time, and have never heard any logic supporting it, other than "maximizing case capacity". Everybody said not to build a SA 284 because the bullets would be deep seated. Max reasonable charge with 175/180gr bullets in 284 is ~55gr H4831. You can fit that much even when loaded to a COAL of 2.950", so the SA isn't impeding capacity in this case, the key difference is whether/not the bullet shank is above or below the NSJ. Who cares? Serious question!

2. Speaking of 284, I played with 284 cartridges in my AW magazines - no good. By the time you've got 4 or 5 in there, they just want to pop out. The fat 284 case fucks it up. You might could bend/tweak the mag lips, but I don't think it'd be so good.<span style="color: #FF0000">It's a magazine, not a water balloon. The width of the magazine is for bodies of .473"-.454, not from .500"-.475"</span>

3. The 162amax and 175smk are essentially the same length, and the boat tail is very nearly the same, thus they fit cases/magazines the same, +/- a little. Good enough for arguments sake. 708 COAL needs to be ~2.950" to have the bullet above the NSJ. 7CM COAL needs ~2.875 or so to achieve it. The NSJ occurs ~.030 lower on an SLR case than a 243/260/708, thus, 2.920 or so will keep the 162/175 north of the NSJ.<span style="color: #3333FF">You can load the 7-08 with 175's clear down to 2.675" to clear the NSJ</span>

4. Seems to me like the 7SLR will have more case capacity than 7cm, when both have bullets above NSJ. <span style="color: #3333FF">true</span>

5. Is it possible the smaller capacity of 7CM can produce MORE velocity??<span style="color: #3333FF">Only with better propellants.</span>

6. As far as I'm concerned, the 175smk is the 7mm bullet of choice. Super easy to load for, beautiful BC of .64 (vs .60 for 162), and they transition nicely. I've found some barrels hate the 162. My aim is to use the 175!
<span style="color: #3333FF">The 175's are good and I use them. The ultimate is the 180 Berger followed by the 180 SMK. The best luck I've had so far though shooting is with the 168 Bergers/JLK's At one mile they were neck and neck all the way out.</span></div></div>

P.S. Scotty how are you doing? I talked to Chuck about a month or so ago about coming down for another shoot. Things still haven't settled out so well here Idaho, so the trip down is on hold. He also said you were doing well with the 6SLR but hadn't really stretched it out that far as of yet (then). How's it doing now?

 

[steve123]

Re: Holy Grail of Short Action 7mm Cartridges...?

I have a 8.4 twist 7mm barrel sittin in the safe right now that I've been pondering what to do with.

For me 7x47L is the first cartridge that comes to mind. I like the x47 case because it's short along with it's other attributes and the brass lasts for years.

Just like a few others have mentioned you are constrained by length so for 7x47,7CM,708,7slr the velocities are going to be very close. Or another way of putting it is the difference in wind won't be discernible at distance. Heck even comparing to your 284 the difference might not be discernible.

It would be kinda fun to shoot those new Berger 195's coming out in a 7x47. Why I don't know but just a thought.

 

[sandwarrior]

Re: Holy Grail of Short Action 7mm Cartridges...?

steve123,

When I think something along the lines of 7x47 I think of an ultra-light rifle. Very light, easy to carry all day and with just enough 'hammer' to reach to 1k. A 7x47 could send a 140 gr. VLD out at just under 3000 fps. No worries about the transonic disruption as it's quite over-rotated for that.

Then again, I got a 1-8" twisted barrel just so, when I could get my hands on them, 200 gr. bullets would be the par norm. As of yet I haven't gotten them. 195's will do though.

It will be interesting to see where I break even with velocity vs. BC. I'm pretty close right now with 168's and 180's.

 

[Jedi]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sandwarrior</div><div class="ubbcode-body">

Alright, a few more thoughts and talking points:

1. What's the big deal about loading cartridges so that <span style="font-weight: bold">the bearing surface of the bullet is above the neck/shoulder junction (NSJ)<span style="color: #FF0000">it's for safety. The side pressures on a bullet when seated that deep can actually force it somewhat sideways into the throat. Being as it is more malleable than the barrel it <span style="font-style: italic"><span style="text-decoration: underline">could</span> cause a plug and subsequent catastrophic failure</span></span></span>? </div></div>

Where do you guys get these gems of wisdom? or ya just make em up as ya go.

 

[tylerw02]

Re: Holy Grail of Short Action 7mm Cartridges...?

Wondered the same about that one, Jedi.

 

[sandwarrior]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jedi</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sandwarrior</div><div class="ubbcode-body">

Alright, a few more thoughts and talking points:

1. What's the big deal about loading cartridges so that <span style="font-weight: bold">the bearing surface of the bullet is above the neck/shoulder junction (NSJ)<span style="color: #FF0000">it's for safety. The side pressures on a bullet when seated that deep can actually force it somewhat sideways into the throat. Being as it is more malleable than the barrel it <span style="font-style: italic"><span style="text-decoration: underline">could</span> cause a plug and subsequent catastrophic failure</span></span></span>? </div></div>

Where do you guys get these gems of wisdom? or ya just make em up as ya go. </div></div>

Make them up as we go.... Do note that I said could. It would really more apply to ogive below the neck AND deep seated bullet.

 

[steve123]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sandwarrior</div><div class="ubbcode-body">steve123,

When I think something along the lines of 7x47 I think of an ultra-light rifle. Very light, easy to carry all day and with just enough 'hammer' to reach to 1k. A 7x47 could send a 140 gr. VLD out at just under 3000 fps. No worries about the transonic disruption as it's quite over-rotated for that.

Then again, I got a 1-8" twisted barrel just so, when I could get my hands on them, 200 gr. bullets would be the par norm. As of yet I haven't gotten them. 195's will do though.

It will be interesting to see where I break even with velocity vs. BC. I'm pretty close right now with 168's and 180's. </div></div>

Yep, I agree it would make a cool light weight rifle and hunting cartridge combo. Hmmm

I'd like being able to practice more while having maybe twice the barrel life of my 6x47 and similar wind drift. I just bought a action wrench and barrel vise so having multiple barrels for my match rifle is worth considering now.

 

[turbo54]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fireguyty</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mdesign</div><div class="ubbcode-body">How similar is the ballistics of the 7-08 vs the 7CM if they both are in a s/a and running the 162 Amax? </div></div>

It comes down to who got "lucky" with a faster barrel.

The useful capacity of them when both loaded to SA constrictions puts the water capacity within <1.0gr making it a +/-0.3gr load difference. Performance is pretty much identical.</div></div>

While I definitely do agree with luck in a faster barrel blank, I don't totally agree with the rest. Here is why:

Everyone agrees that a 260 is faster than a 6.5 CM. I think this is the reason that everyone THINKS that the 7-08 will be equal if not faster than a 7 CM. The problem is when we try the same cases with 6mm. Everyone agrees that the 6 CM is faster than the 243 Winchester. How does this happen? I think it is due to the way that the cases deal with the powder and the bullet.

That is why I think there maybe something to do with the guys claiming 2900 with a 162 in the 7CM. <span style="font-weight: bold"><span style="text-decoration: underline">They found the ideal powder in IMR 8208 XBR.</span></span>

However, some guys refuse to admit when they make a mistake and so they are committed to their purchase (classic Ford vs Chevy gas milage argument) so they embellish the facts. Having buddies that turn barrels for me and work for whiskey makes my commitment only reamer, dies, and Glenlivet. A small price to pay for an experiment that if failed will turn into a 7 SAUM.

We shall see.

Ty </div></div>

See the bold print.

I think the key is finding *the* ideal powder for the case capacity and the bullet weight. I can think of two examples:

My 284: I've tried an entourage of powders, of course including H4350 and H4831sc. Bottom line is that with 175/180 bullet in this case, the H4350 is a little too fast. H4831sc is too slow. I find overpressure before the case is full of H4350, and I stop seeing velocity gains at a certain point with the 'sc. There is no Hodgdon "extreme" powder between the two, but there is 100V. I bought a pound and did a little development. I immediately found another 35fps or so. I sent that barrel back though, and haven't tried the 100V in my new barrel.

7-08: Not as experienced with this cartridge as 284, but I've played. Again, H4350 is too slow, as indicated by the uber-compressed charge of it to hit the 2800 zone from 162. Varget comes close in velocity, but again, overpressure before the case is full. Again, no Hodgdon extreme powder in between these two.

I've seen this scenario play out so consistently, it has actually made me think about (gasp!!) blending powders to get a burn speed in between.

If there is indeed magic to the 7CM, it is probably because it just so happens the capacity works out perfect to optimize the burn speed of the 8208xbr and the 162.

Which leads me to the 7SLR: Would it's increased capacity provide a little more horsepower with 8208, or, would it knock 8208 out of it's "sweet spot"??

 

[sandwarrior]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fireguyty</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mdesign</div><div class="ubbcode-body">How similar is the ballistics of the 7-08 vs the 7CM if they both are in a s/a and running the 162 Amax? </div></div>

It comes down to who got "lucky" with a faster barrel.

The useful capacity of them when both loaded to SA constrictions puts the water capacity within <1.0gr making it a +/-0.3gr load difference. Performance is pretty much identical.</div></div>

While I definitely do agree with luck in a faster barrel blank, I don't totally agree with the rest. Here is why:

Everyone agrees that a 260 is faster than a 6.5 CM. I think this is the reason that everyone THINKS that the 7-08 will be equal if not faster than a 7 CM. The problem is when we try the same cases with 6mm. Everyone agrees that the 6 CM is faster than the 243 Winchester. How does this happen? I think it is due to the way that the cases deal with the powder and the bullet.

That is why I think there maybe something to do with the guys claiming 2900 with a 162 in the 7CM. <span style="font-weight: bold"><span style="text-decoration: underline">They found the ideal powder in IMR 8208 XBR.</span></span>

However, some guys refuse to admit when they make a mistake and so they are committed to their purchase (classic Ford vs Chevy gas milage argument) so they embellish the facts. Having buddies that turn barrels for me and work for whiskey makes my commitment only reamer, dies, and Glenlivet. A small price to pay for an experiment that if failed will turn into a 7 SAUM.

We shall see.

Ty </div></div>

See the bold print.

I think the key is finding *the* ideal powder for the case capacity and the bullet weight. I can think of two examples:

My 284: I've tried an entourage of powders, of course including H4350 and H4831sc. Bottom line is that with 175/180 bullet in this case, the H4350 is a little too fast. H4831sc is too slow. I find overpressure before the case is full of H4350, and I stop seeing velocity gains at a certain point with the 'sc. There is no Hodgdon "extreme" powder between the two, but there is 100V. I bought a pound and did a little development. I immediately found another 35fps or so. I sent that barrel back though, and haven't tried the 100V in my new barrel.

7-08: Not as experienced with this cartridge as 284, but I've played. Again, H4350 is too slow, as indicated by the uber-compressed charge of it to hit the 2800 zone from 162. Varget comes close in velocity, but again, overpressure before the case is full. Again, no Hodgdon extreme powder in between these two.

I've seen this scenario play out so consistently, it has actually made me think about (gasp!!) blending powders to get a burn speed in between.

If there is indeed magic to the 7CM, it is probably because it just so happens the capacity works out perfect to optimize the burn speed of the 8208xbr and the 162.

Which leads me to the 7SLR: Would it's increased capacity provide a little more horsepower with 8208, or, would it knock 8208 out of it's "sweet spot"??

</div></div>

Turbo54,

There <span style="text-decoration: underline">is</span> a lot of truth behind 'individual barrel speeds'. As Bohem say's it comes down to who got lucky with which barrel. I have a barrel that seems to limit everything to 2700 fps, no matter what powder I try. So, I might as well go with the 180's. Except, the 168's shoot superb!

I'll also try to bring us back to what Zak Smith said to us all years ago about the different 6.5's then on the market. We are splitting hairs in the thousandths. Take the cartridge you feel is going to work for you and then when you get your build done, focus on what it does, not what the next cartridge can do. Literally, if these cartridges were women at a dance we'd be dying to split the hairs, the choices are so good. But, like that situation, you take one home and do the best you can from there. <span style="text-decoration: underline">You</span> then need to be able to make the best of what you've got. Work up good loads and see what the drops/drifts are. Aim for the 'most consistent' and you'll always be able to call your shots.

No matter which one you choose, there are going to be drawbacks as well as the benefits. Get used to what it can do, or get it down the road. Some guys get very lucky their first go-round, that's all there is to it sometimes.

 

[turbo54]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sandwarrior</div><div class="ubbcode-body">You can load the 7-08 with 175's clear down to 2.675" to clear the NSJ</div></div>

That is wrong.

I remeasured this last night, and the 708 in fact requires a COAL of ~3.000" for 162 and 175smk to clear the NSJ.

The 7SLR can do it ~2.940" or so. That means the 7SLR can take full advantage of all available case capacity, with the heavies, in AW magazines, and nearly so in AICS magazines with the plate removed. AW magazines will allow the bullet shank to be north of the NSJ.

I'm all ears to other rationale for why it's bad juju to have a cartridge with deep-seated bullets where the bearing surface extends below the NSJ. My current 284 has 175smk a good solid .150" below the NJS and it seems to run real nice.

 

[E. Bryant]

Re: Holy Grail of Short Action 7mm Cartridges...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">I'm all ears to other rationale for why it's bad juju to have a cartridge with deep-seated bullets where the bearing surface extends below the NSJ.</div></div>

It was my understanding that said guideline came from the desire to avoid a variety of problems arising from the formation of the dreaded "donut" at/near the NSJ from certain resizing operations. If you have a cartridge and reloading procedures that avoid donut formation, and if sufficient case volume exists, then I generally don't see an issue with seating the bullets deep.

 

[memilanuk]

Re: Holy Grail of Short Action 7mm Cartridges...?

My understanding is similar to Eric's... most dedicated long range cartridges in an optimized chamber almost always have the bullet seated ahead of the neck-shoulder junction (at least .030" is one number I've seen mentioned) so that if a donut does form, it won't affect the bullet. In theory... if a donut formed, and the bullet was seated down past the NSJ, besides really screwing with the seating force to begin with, it could provide a pinch point that could jack pressures through the roof. In theory.

In practice... pretty much every 69 & 77gn bullet in a .223 Rem, and most 130-140gn bullets loaded to mag length in a .260 Rem extend down below the NSJ, and shoot just fine, with excellent 'field' accuracy. May not win any formal Benchrest matches like that, but short of that standard... probably plenty good for anything you have to actually carry from point A to point B

 

[Twist Fast]

Re: Holy Grail of Short Action 7mm Cartridges...?

I've no qualm with a 7-08/7-08AI kissing lands with a 162 at 2.8". I don't like DBM's,just to DBM. My Alpha's happily digest 284's at 2.975",in both 6-284(Hornie 105HPBT's) and 284Win(162's).

If forced to build with a DBM on a S/A .473",it'd be 284Win by default in 7mm.

Fuck all the fluff,pass me the '22.

 

[turbo54]

Re: Holy Grail of Short Action 7mm Cartridges...?

I'm going to have a reamer ground for 7mm SLR.

If you'd like to chime in about its design, please go here: http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=3718876&#Post3718876

 

[mcfred]

Re: Holy Grail of Short Action 7mm Cartridges...?

Turbo, I'd like to hear how your 7SLR goes.

I'm going to try a 7mm W<span style="text-decoration: underline"><span style="font-weight: bold">SS</span></span>M once my current 7WSM barrel's toast. With a low 54,000psi peak pressure and a 25" barrel a 175smk will go 2700fps according to quickload, 2800 with H4350 at higher pressure. I'm sure the 162s will be a bit quicker.

30* shoulder, .318" neck length, ±50 grains powder capacity up to the NSJ and should perform at least as well as 7-08 and more when ramped up to the SAAMI spec 65ksi. A barrel should last ±3000 rounds and my dummies feed/eject just fine in my Pierce SA.

I figure if you're willing to mess with an oddball wildcat then a little brass prep isn't that big a deal. So sorting, turning necks, uniforming primer pockets and deburring flash holes just comes with the territory. I don't mind since the effort may make a difference at my matches, that and I don't have a TV so I've got time.

30-06/7WSSM comparison, and fitment in an Alpha mag.

 

[turbo54]

Re: Holy Grail of Short Action 7mm Cartridges...?

Parent case of that 7wssm?

I had considered similar, but had several concerns:

- low(er) magazine capacity
- poor feeding from magazine
- extensive and expensive case forming/prep in terms of push dies and time

Thoughts?

 

[mcfred]

Re: Holy Grail of Short Action 7mm Cartridges...?

That particular parent is .223WSSM. All WSSM have the same dimensions except the shoulder angle (25wssm has a 30* shoulder where 223/243 have 28*) and neck length/diameter. So dies are a matter of reaming out a standard die set for the new neck diameter and using a larger neck bushing. Also historically there are complaints about thick neck walls on the factory brass. So stretch the .223s up to .284 and they'll get a little thinner. If they're still too thick then turn them down and remove any irregularities. I'm specifying a freebore to keep 162, 175 and 180 bullets to keep out of a potential donut at the NSJ.

With the Alpha mags, you have either 7 or 10 round mags so the mag cap seems like a moot point. I've got a .308 steel AICS mag modified to fit 4 WSMs at 2.955", though it was a little bit of a PITA.

Case forming seems easy to me. A little cream of wheat and ~15gr of Blue dot and it looks like it blows out the neck just fine. Or you can get a 2* taper mandrel and expand the neck by force. Since you're only changing the neck ID it's not like trying to neck a 50bmg down to .17 cal.

In my gun, there's not much possiblity of a misfeed on a round since the round is retained by the magazine/receiver feed lips a long while. The bullet sticks out so far that it's in the chamber a ways before it pops free of the mag. Even then with the boltface's stuck right behind it. There's little opportunity for it to get hung up. Again, this is my Pierce short action and Alpha mags. The geometry could be different for Stock Remington or other clones.

Also FWIW, Mike Milli at Dedicated Technologies (AKA DTech) has been making AR-uppers for a variety of WSSMs .223"-.358" for years. If feeding was so poor I don't think WSSMs would be a good choice for a gas gun. Seems to work fine for them though.

*update*
Got some reamers and other stuff:
http://www.snipershide.com/shooting...199189-7mm-wssm-7wsm-switch-barrel-comps.html