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7mm WSSM (a 7WSM switch-barrel for comps)
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A while back I built a mag fed rifle in 7mm WSM and I've been using it in local precision rifle competitions. The 7WSM is a great round and has nearly optimum ballistics for the limitations of a short action, but it seems to be a bit overkill for the relatively short ranges found in these matches. I posted on this idea with some supporting data in my build thread:

http://forum.snipershide.com/t...-a-new-barrel.72974/

This led to the idea of just using a shorter case to reduce capacity for cost purposes while using the same bolt face, same bullets, same magazines, etc. The 7mm WSSM is not a new idea, but most of the info I was able to find on it is related to gas guns. Anyway, this seemed like it might have potential as the "toned" down WSM I had in mind, plus I like to experiment; so reamers, brass, and parts were ordered... I think we all know the state of this hobby, so I'll skip ahead a number of months:



Everyone likes pictures so this picture shows the 7mm WSSM next to a few other long range rounds for comparison: the 7mm WSM loaded to mag length, the 7WSM loaded for F-class (single shot), and a 338/300RUM. The 7WSSM is roughly equivalent to the 7mm-08, though with its short case long/heavy bullets can be seated out to preserve case capacity. Enough parts finally arrived to test the theory, and now with a barrel swap I'm getting up to 2850fps with the same 180 grain SMK (superformance powder). Pressure is moderate to low so cases should last and extraction is easy for fast/smooth bolt movement (helpful in most timed stages). Eventually I'd like to test the 162 hornady bullet. Depending on what velocity I can get it may have an edge over the 180 for short range, but I already have a bunch of the 180s. I'm thinking the 162 with H4350 will be a good combination to try, if I can eventually get the components.

Accuracy so far is acceptable, but not great (1.5" at 200yards). For availability I've been using 223 WSSM brass, and its quality is not very good. So far I've just been annealing the necks and expanding them to 7mm. Because the 7WSSM is basically a 6mm PPC scaled up slightly, I was hoping to get effortless accuracy without messing around with brass. With more brass prep (turning necks, trimming to same length, sorting, etc.) I think accuracy will improve significantly. I would also like to try some 25 WSSM brass to see if there is better quality there (does anyone want to trade some for 223WSSM brass?).

The reamer was spec'd such that my WSM reamer can be simply run in to clean out the WSSM chamber if desired, but so far the experiment is looking like a success. I'll post updates as I get more experience with it...
 
Posts: 775 | Registered: 13 November 2008Reply With Quote
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If you have already done it, it doesn't matter. I personally prefer the 7 SAUM.
 
Posts: 8692 | Location: Poetry, Texas | Registered: 28 November 2004Reply With Quote
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The SAUM is about the same thing as the WSM. Still overkill for 200-300 yards imo. The WSSM is an attempt to reduce case capacity for competition. Most people use rounds like the 6.5creedmore, 7mm-08 or 308, and the 7WSSM fits right in with that crowd but uses a mag bolt face and has no issues with mag length and long pointy bullets.

Going the other way, I could see someone using a regular bolt face and going with one of the 6mm versions for short course and the 284 for long range with a barrel change. The 284 is not too far behind the WSM or SAUM.
 
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I've always thought this would be a super handy wildcat. Or a 6.5 WSSM. I'd be interested in a dummy round if you make many Big Grin


Love shooting precision and long range. Big bores too!

Recent college grad, started a company called MK Machining where I'm developing a bullpup rifle chassis system.

 
Posts: 2596 | Location: Missouri | Registered: 29 March 2006Reply With Quote
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I've been getting some steel set up out in the mountains and I found a 22" square piece of 1/4" scrap plate that we set up at 2000 yards. Finally got some parts back from the mfg (so much for xmas...) and went shooting. The WSSM was 2/10 on the plate at 2000. That's the furthest I've ever shot and was a bit surprised I could still see impacts and even hear the plate ring. It was a nice weekend!
 
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From what I've read the 300 WSM brass is the most consistent brass of all the WSM and WSSM brass. Although it would result in a thicker neck dimension, your best bet might be to use the 300 WSM brass and make the necessary modification to neck thickness (turning) or neck ream the chamber to accommodate the new dimension.

Just a thought...


Jim coffee
"Life's hard; it's harder if you're stupid"
John Wayne
 
Posts: 4953 | Location: Central Texas | Registered: 15 September 2007Reply With Quote
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quote:
Originally posted by capoward:
From what I've read the 300 WSM brass is the most consistent brass of all the WSM and WSSM brass. Although it would result in a thicker neck dimension, your best bet might be to use the 300 WSM brass and make the necessary modification to neck thickness (turning) or neck ream the chamber to accommodate the new dimension.

Just a thought...


WSSM not WSM!!!!! Otherwise he reinvented the 7WSM.
 
Posts: 1935 | Registered: 30 June 2000Reply With Quote
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JPL,

I think what your doing is neat but I am skeptical about the velocity you getting.
How long is the barrel?
 
Posts: 1935 | Registered: 30 June 2000Reply With Quote
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I'll let you take that up with Mr. Oehler. Drops from JBM also agree out to 2000. Barrel is 28 inches I think, but I attribute the speed to superformance powder.

I tried H414 and got 2780 with 46gr, with room to spare but it started showing pressure so I pulled down the other rounds I had loaded (I think it would hold up to 50gr). I also tried WXR and got 2550 with 45gr; full case and no pressure. So H414 was too fast and WXR was too slow. Some day I'd like to try H4350. Or maybe some day I can try H414 with the 162gr hornady, which is supposed to be back in production now. In the meantime I've been using 50gr of superformance at 2800fps. This works well, is low pressure, easy on brass, etc. so I have not been looking for anything else. It's not the cleanest and cakes up the brake, but it holds accuracy for hundreds of rounds between cleaning. I've also read online that some of the 7-08 guys are having luck with superformance behind the 180's, or behind the 162's with a mag primer.

If you want more speed just go WSM.
 
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quote:
Originally posted by Norseman:
quote:
Originally posted by capoward:
From what I've read the 300 WSM brass is the most consistent brass of all the WSM and WSSM brass. Although it would result in a thicker neck dimension, your best bet might be to use the 300 WSM brass and make the necessary modification to neck thickness (turning) or neck ream the chamber to accommodate the new dimension.

Just a thought...


WSSM not WSM!!!!! Otherwise he reinvented the 7WSM.
He expressed concern with quality of WSSM brass. I simply expressed that I'd heard the 300 WSM brass was the highest quality of the WSM and WSSM brass. Others have used shortened WSM brass in lieu of using WSSM brass. Was simply a thought passed on, zero intent to replicate the 7mm WSM cartridge.


Jim coffee
"Life's hard; it's harder if you're stupid"
John Wayne
 
Posts: 4953 | Location: Central Texas | Registered: 15 September 2007Reply With Quote
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quote:
Originally posted by capoward:
From what I've read the 300 WSM brass is the most consistent...


I ended up neck turning the winchester brass and sorting by weight, and that seemed to help a lot with velocity spread. The WSSM brass is surely out of production at the moment, but at the start of this experiment it was about the only thing left on the shelves!

It might be an interesting experiment necking down WSM or RUM brass to WSSM. I have made 243AI brass out of 30-06 because I was getting annoyed with trying to fire form 243 or 308 brass. I was successful, but it was a lot of work. At that point I think I'd just ream the chamber out to WSM rather than try to preserve barrel life by shortening WSM brass. When barrels are 6 weeks out and brass is 6 months out, match the steel to whatever brass you can get...
 
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If you're getting your optimum performance from the WSSM length case, why not just re-spec the neck dimensions of your cartridge and chamber to match that of the thicker walled shortened WSM case with trued neck?


Jim coffee
"Life's hard; it's harder if you're stupid"
John Wayne
 
Posts: 4953 | Location: Central Texas | Registered: 15 September 2007Reply With Quote
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Last week we tried superformance in a 7mm-08 and got 2950fps with a full case behind a 162amax.
 
Posts: 775 | Registered: 13 November 2008Reply With Quote
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Just an update on this:

We had the reamer reground slightly to shorten the neck/throat. It seems like the only brass available is 223 WSSM and these get a little shorter when expanding to 7mm with a mandrel. Supposedly you can use filler and pistol powder to blow them out and not lose length, but I haven't tried it, and besides it seems like too much trouble and a waste of components. One of those hydro-forming dies might do the trick instead, but it seems like they work better for blowing out shoulders? I'm not sure how they'd seal for expanding necks. I've worked out a process that works well enough using two different mandrels. No brass was lost in forming the latest batch.

Anyway, a new 28" brux gave us 2820fps with a case full of superformance behind a 180 hybrid. We also found some H4350 to try and that works well too, but with a little less speed. So: accurate, long lasting, no pressure signs, works well, design goals met, etc... The first set of brass has 25 reloads on it now with no problems, so 200 pieces of new brass should last as long as the new barrel.
 
Posts: 775 | Registered: 13 November 2008Reply With Quote
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Hot damn!!!!!!!!!

I might or should pursue this myself as well.
I already have a Borden Timberline switch barrel smith by Greg Tannel on order for a 240 Weatherby mag and a 338 Edge with 2 different bolts. A extra barrel in 7mm WSSM would be great for those Friday night poker bets.
 
Posts: 1935 | Registered: 30 June 2000Reply With Quote
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What's the latest, jpl?
 
Posts: 1935 | Registered: 30 June 2000Reply With Quote
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quote:
Originally posted by Norseman:
What's the latest, jpl?


Not much really--just been shooting steel. Various components are available again, notably 7mm bullets. The first barrel is still working well at ~1800 rounds. The fire formed brass with the new barrel on a different rifle has about another grain of capacity (compared to unfired). A resize reamer was ordered along with the chamber reamer, and a modified grade 8 bolt is the resize die now. This works great. The brass is sized perfectly for smooth operation and long life. The chamber reamer was used to make the seater die. I doubt I'll ever use off the shelf dies again.
 
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Are you going to rent out the reamer?
 
Posts: 1935 | Registered: 30 June 2000Reply With Quote
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Check your PM.
 
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I lost the first two cases recently. I was getting lazy about annealing them and the necks split:



This was at around 30 reloads and 7 reloads since the last anneal. I had misplaced the little log sheet for this set. I have a second set of brass that has more than that and is going strong. So it looks like I have enough brass for a few barrels' worth. I even saw WSSM brass at the store again.
 
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This project is still working well. I guess berger started gold plating their bullets, so I've been testing the 183gr sierra. At least in warm weather and at altitude these are looking good in my 9-twist at 2800fps. They group well at 200 and stay straight out to 1600 yards. Next barrel will be a tighter twist to work better with all these nice high BC 7mm bullets available now. Still plenty of room in the magazine too! Smiler

 
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Love those little stubby guys with bullets hanging way out. That's some good velocity!


Love shooting precision and long range. Big bores too!

Recent college grad, started a company called MK Machining where I'm developing a bullpup rifle chassis system.

 
Posts: 2596 | Location: Missouri | Registered: 29 March 2006Reply With Quote
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I've been testing the 185RDF recently, and it also seems to work fine out of a 9 twist. That shows the 185RDF, the 175SMK and the 180Hyb, and a group at 200:



The RDF has a lot of bearing length, sort of like the 180SMK, so if you're tight on mag length the RDF might work out. I had to back the charge off a grain compared to most of the 180-class bullets.
 
Posts: 775 | Registered: 13 November 2008Reply With Quote
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In the ever shifting sands of the inner-web, I'm trying to fix pictures... again. I'm posting this to talk about something I've seen a lot of, and it relates to this wildcat.

Part of the idea for this project was to use a short case so that long-pointy-high BC bullets could be used more easily out of a magazine. Most of the magazines out for this kind of thing are modeled after the AICS dimensions for their 308 magazines. These magazines have a spacer in the front. This spacer can be removed, and you can also get magazines without a spacer. This shows what I'm talking about:



The "standard" aics magazine on the bottom has a spacer at the front, and the alpha magazine on top does not have a spacer. This is desireable because without the spacer there is more internal length in the magazine, which allows the use of longer rounds with longer, pointier, higher BC bullets. And high BC bullets are desireable when shooting long range, etc...

So, if the no-spacer magazine is desirable, how can we use it? The outside dimensions of the magazine are the same, so it will plug into most rifles already set up for aics-type magazines. But there's a problem. Without the spacer, the loaded round can be longer, and the tip of the bullet further forward relative to the receiver. This means that the tip can catch under the receiver before it gets to the feed ramp. What is the solution? Many people just cut out a chunk of the receiver to give clearance. If you look at this picture, you can see the top of the no-spacer magazine, the long pointy bullet, and the notch in the receiver that lets the round come up through the bottom of the receiver:



However, in my opinion it is not a good idea to be cutting on that part of a receiver. That is a piece of high grade steel responsible, in part, for containing several tons of white hot fire a few inches from my face. I'd much prefer to cut the rear part of the receiver to get clearance for a longer round. The rear part of the receiver is holding much less force with much lower consequences if it fails.

Sure, plenty of people have notched out their receivers without any problems, but that area IS under load and cutting it out erodes the safety factor designed in. You could probably take 2 lug nuts off of each wheel on your car and have no problems. Your car would be lighter and faster! But I don't think this makes it a good idea, especially when there is a better way. Why not just cut the rear of the receiver? This could be a feature and selling point for a new product (that moves the magazine back to take advantage of longer COL).

Here are a few pictures of a FEA showing stresses in the area we're talking about. This is a side cutaway of the model with colors showing stress:



Now look what happens when you start cutting out the feed ramp:



Most disasters are a chain of factors that happen to combine in just the wrong way. Personally, I'd like to have as many links in there as are easy and reasonable. Like safety glasses. I've never needed them, but I still wear them because it's an easy link to add to the chain. Muzzle control? Another reasonable link to add to the chain. Not taking shortcuts to get a longer round...

Now this picture shows what is, in my opinion, the proper way to use alpha magazines, particularly with magnum rounds. Basically, the magazine is moved back relative to the receiver with a few modifications: the bottom metal is moved back by opening up the bolt holes off-center and filling with a steel washer/bushing, the REAR of the receiver is cut to give the clearance needed, the bolt stop is shortened, and the inletting adjusted. The front of the receiver was NOT cut (green oval). This particular bottom metal (not naming names) was so far forward that even AICS magazines with spacers would hang rounds up under the receiver (you can see part of the original inletting).



And once again, the easier but wrong way (in my opinion):



So this is what I've been getting at.
 
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