7mm SAUM Wildcat!

[calinb]

Originally Posted by redneckclimbing

Sooo, I thought why not straighten out the case a bit? This reamer would give the same body taper as a WSM and add about a 1.5 grain of H2O cap. Has anyone had any problems extracting their WSM's or does anyone think this could cause a problem?

I am worried about 40 degrees feeding from a mag. 35 degrees is about the industry max and even it doesn't feed terribly well.

I'll run the the resulting case capacities through Quickload, when I get a chance.

[calinb]

I did some case capacity calculations and Quickload runs on several candidate parent cases and I think I may have found a simple wildcat solution to my problem (feeding 7mm 180 gr Berger VLDs from a short action mag).

The 7mm WSM seems to be the least case capacity-challenged of the short action 7mm cartridge bunch (by a very slight margin) so it would be simple to just push back the 7mm WSM shoulder by 0.100" and get some COAL breathing room. I'll call it the 7mm WSM LRMF (long-range mag-fed). I think the chamber free bore and throat probably need appropriate adjustments too, to make sure the VLDs can touch the lands.

My goal is 2950 fps from a 28" barrel. Here are the Quickload results of pushing the 7mm WSM shoulder back 0.010" using readily available powders:

Cartridge : 7 mm WSMLRMF
Bullet : .284, 180, Berger M T VLD G7 #28502
Useable Case Capaci: 67.267 grain H2O = 4.368 cm³
Cartridge O.A.L. L6: 2.980 inch = 75.69 mm
Barrel Length : 28.0 inch = 711.2 mm

Ramshot Magnum (Big Boy)-------------102.2 3035
Vihtavuori N560----------------------------99.8 3033
Accurate MAGPRO-------------------------100.1 3030
IMR 7828----------------------------------104.3 3019
IMR 7828 SSC------------------------------98.6 3019
Alliant Reloder-22-------------------------100.1 3000
Winchester WXR--------------------------102.8 3000
Alliant Reloder-25-------------------------105.0 2997
Vihtavuori N570---------------------------105.0 2988
Alliant Reloder-19---------------------------97.2 2957

Pushing the neck back 0.100" costs 5.9 gr. H20 but 0.9 gr. H20 could optionally be "recovered" by reducing the case taper to 0.010" (or "spend" the taper reduction to push the shoulder back another 0.030).

From my experience, just pushing a short magnum case neck back 0.100" is a fairly easy task in forming new brass, though it's about the limit of what I've attempted to do.

A wildcat seems like a lot of trouble for only 0.100" or 0.130" of COAL relief, but I think my goal is marginal without it. Unless extraction problems are anticipated, it seems like the additional 0.030" COAL increase from trading off the cartridge taper is worthwhile. Every little bit helps in this application.

In fact, I'd rather have 0.150" to 0.200" of COAL "guardband," which may be possible with a further reduction in case capacity. Quickload seems to be a touch pessimistic with many of these long range 7mm loads and I was limiting QL to only SAMMI max. pressure. ;)

So maybe I can rework the Ruger M77 308 Win bolt face and extractor and use the Ruger GSR as a platform after all.

Comments, suggestions, or ideas?

Thanks,

-Cal

[calinb]

Originally Posted by redneckclimbing

Hey Everyone-

<snip>
I have drawn up a reamer for Mr. Kiff but am needing some suggestions on some things I didn't really know. (the question marks on the print)
<snip>

I'm new to reading these prints too, but I think the question mark boxes are for the throat angle and length (they are geometrically dependent on each other so, technically, it should only be necessary to provide one or the other of the values). The first question mark box is for the throat angle extending into the rifling (the taper that begins after lead section, which is straight in most chambers).

Downloading the prints from SAAMI, I see that the throat angle is 1.5 degrees (1 degree, 30 minutes) for the WSM cartridges and 1 degree for the 7mm SAUM. The second box that your marked with a question mark should be the length of the tapered throat section that ends at the fully rifled bore. SAAMI prints seem to specify only the throat angle and not the length of the angled throat section.

My latest results look good for short-chambering in 7mm WSM by 0.20" and modifying a full length sizing die to push a 270 or 300 WSM case shoulder back 0.162, if that much push back can be done cleanly. Quickload says it should slightly outperform the 284 Shehane and achieve 2950 to 3000 fps from a 28" barrel. I'm not so much interested in efficiency (requires 2.5 to 3 grains more powder than the 284 Shehane to match the same velocity with heavy bullets) as mag-feeding and more easily manufacturable brass.

I don't see much interest in this thread so I might need to move to another forum. I certainly need to run my ideas past people more expert in the art than I!

-Cal

[redneckclimbing]

The dies I ordered from Spencer Tool & Grind left today and I have some brass waiting at the house for them. When I get a couple of them finished I will let you know what the case capcities work out to.

[redneckclimbing]

Cal-

Is there any way to know if the amounts of the different powders you ran will actually fit in the case? Also, if it is not too much trouble could you run Hodgdon 4831sc through there, I would appreciate it.

Thanks,

Travis

[Skyking]

I just finished up my 7saum with a 35* shoulder. I end up using the Berger 168 vld and got them going 3160 fps with Retumbo. 4831sc had way to much pressure. H1000 was better.

Here is more info on it. Bighorn 7saum Thunderbeast 30p-1!! - Sniper's Hide Forums

Let me know if I can help.

[calinb]

Originally Posted by redneckclimbing

Cal-

Is there any way to know if the amounts of the different powders you ran will actually fit in the case? Also, if it is not too much trouble could you run Hodgdon 4831sc through there, I would appreciate it.

Thanks,

Travis

Estimating accurate case capacities is a bit of a problem. Quickload doesn't really help and I always measure my actual cases by weighing them with and without water. For estimates of my hypothetical case, I used this calculator:

http://kwk.us/cases.html

It's probably best to input the numbers from an actual known capacity parent case for a baseline. Then "modify" the case in the calculator and work with the predicted capacity change, relative to the original case capacity.