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7mm SAUM Wildcat!

 
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  #36  
Old 04-13-2012, 08:03 PM
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Re: 7mm SAUM Wildcat!

While collecting parts for my 7mm (Win M70 LA, CDI bottom metal, 3 AI mags) I've been thinking about going in a different 7mm direction. I have a lifetime supply of 300 RCM brass to feed my 300 and 338 RCM Ruger M77s and it would be very easy to just neck the brass down to 7mm. Hornady is the sole brass supplier so sorting and uniforming the brass (neck annealing, turning, reaming) for consistency would probably be in order. On the upside, the brass is much cheaper than Nosler or Norma brass and I have plenty of it.

Quickload says a 7mm RCM would use a bit more powder than the GT or even the SAUM but predicts a 7mm RCM would launch 180 Bergers or the much more economical 162 AMAX even slightly faster than the SAUM.

Looking at the SAAMI prints, I think I could neck resize my 300 RCM brass down to 7mm with a Hornady 7mm neck size die and seat the bullet with a Hornady 7mm standard seating die. Shoulders could be pushed back and body sized with my Hornady 300 RCM full-length sizer, when necessary, but fired brass could also be used to order custom precision dies to match my 7mm RCM chamber.

I always use a full-length die to size necks down. Would a neck-only sizer work for this? I've been planning to order a custom chamber reamer from PTG anyway so this plan kind of makes sense to me.

I'm also on the fence about barrel length. Quickload says 26 inches only costs me 50 fps vs. 28 inches. If the 180 grain Bergers launch from a 28" barrel at 3050 fps, like QL predicts, I could probably afford to go 26 inches and still be good enough to get my toes wet in F-Class, while making for a better long-range hunting rig.

Thoughts and feedback appreciated!

Last edited by calinb; 04-13-2012 at 08:23 PM. Reason: edit barrel length comparison
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  #37  
Old 04-22-2012, 11:05 PM
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Join Date: Jan 2012
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Re: 7mm SAUM Wildcat!

Calinb-

Sounds like that may be a winner for you, with the available brass and all. If you get a reamer from Kiff, talk to them about a resizing reamer and a blank. I saw the other day that they can cut a custom reamer slightly under sized but not much it sounded like and then provide you with a die blank as well for about $125 I think is was. Then all you have to do is ream it out as if you were chambering a barrel. Might save you some time.
As far as seating dies are concerned this is where I am stuck as well. I think that I am going to have a couple of bushings made that fit insede of the dies I already have. But, in your case maybe just put a 7mm seating stem in your RCM die. (That may be what you were saying before) That should give it the body support that you need and save you a bunch of farting around.
As far as the 26 or 28 goes I would probably go 26 most guys comp. loads with the Bergers are in the 2900-2950fps range anyways, and depending on your barrel profile that two inches may save you a pound, which would be nice for hunting.
I was also wondering, if you still had the info. in your program, what kind of velocities was the GT getting with a 26" barrel. I was also thinking the same thing as far as weight goes. My thoughts are also that a shorter barrel would be stiffer (with the same profiles), which should aid in accuracy.

Good Luck and let's keep in touch. I think that I am going to start putting mine together in about three weeks or so.
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  #38  
Old 04-23-2012, 04:41 AM
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Re: 7mm SAUM Wildcat!

I will definitely ask PTG about a resizing reamer and a blank.

In the meantime, I just got a Hornady 7mm Mag neck sizer die (#046056) and it works fine on new 300 RCM brass and resized the neck in one pass. I also picked up the number 8 seating die (#044108) and made some dummy rounds using the 162 AMAX. I think I'll need to get the special Hornady AMAX seater stem. The bullet tends to stick on the lip of the standard stem a little but at least it worked.

I can probably optimize from here, but at least I know I have dies that can make 7mm-300 RCM ammo! I'll need to decide on the freebore required for the new 195 Bergers. I think I saw .220 suggested somewhere. which works out to a COAL of around 3.100 for the AMAX. Of course it will be ever-growing so maybe I should start shorter and hope for .220 after break-in.


>I was also wondering, if you still had the info. in your program, what kind of
>velocities was the GT getting with a 26" barrel.

Sure. I'll run the GT at 26 inches. I think it'll cost ya' only around 60 fps vs. a 28 inch but I need to run it.

>I was also thinking the same thing as far as weight goes. My thoughts are also
>that a shorter barrel would be stiffer (with the same profiles), which should aid in >accuracy.

I'm reading all kinds of online reviews of barrels and build reports. I'm leaning towards a light Palma. The Remington Varmint is similar but distributes more mass towards the muzzle and less towards the breech. I figure the Palma was developed to optimize performance within weight limits. I'm also wondering if it can be fluted. I know some manufacturers do it, but Krieger seems to imply no on their fluting info web page. If it's marginal on a light Palma, it's probably not worth the risk to save 1/2 lb. Krieger also seems conservative in going no smaller than a #5 contour in stainless. Others go down to #4, it seems.


>Good Luck and let's keep in touch. I think that I am going to start putting mine together in about three weeks or so.

Definitely! My project will be much more long term. Plus I'm moving my household to N. Idaho or NW Montana soon.

-Cal
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  #39  
Old 04-23-2012, 11:47 PM
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Re: 7mm SAUM Wildcat!

I ran QL on the GT with the same numbers as before (2.840 COAL) but with a 26" barrel instead of 28". The difference in velocity is less than 50 fps! Given that a shorter barrel implies higher pressure for the same velocity (and reduced barrel life?), I ran IMR 7828 SSC at 2878 fps to see how much the pressure dropped with a 28" barrel. It only went down from 64542 psi. to 61240 psi.

7mm SAUM Wildcat!-gt_berger_180_26.jpg

I just talked to Dave at PTG today and ordered a custom 7mm-300 RCM reamer. After making up the dummy cartridge and discussing my measurements with him, Dave recommended a 0.188 freebore and 0.315 neck, which will require neck turning. Even though the Hornady brass necks seem pretty good after a measuring a small sample, I didn't want to risk going for a no-turn fit.

Dave said 0.188 FB is known to work well with the 180 Berger VLDs and Hybrids and he recommended sticking with 0.188 until the 195 design is finished. He said a PTG throating reamer will work perfectly for a length adjustment later.

I'm sure others have taken the 7mm RCM path before me, but I can't find any online performance reports. According to 6mmbr.com, just about any 7mm cartridge can shoot the Bergers well, if setup right. I'm not anticipating any problems with the RCM, though it's obviously not a terribly popular parent case.

After reading http://www.longrangehunting.com/articles/barrel-weight-1.php, I think I'll order a Krieger Light Palma in 1:8. I'm not taking any chances on 8.5 and the 195 Bergers. I'll probably order the standard 28" because I can always cut it down. Krieger appears to be more conservative than some other vendors. They won't makes a stainless 7mm in a #4 contour (#5 is their minimum) nor will they flute a Light Palma, which is okay by me. I've purchased from Krieger twice in the past and find them great to work with, despite the wait for delivery. I once had to send them a larger than normal AR barrel extension and a wrench socket tool that I'd machined to fit it to get a new barrel made for my Oly 243 WSSM upper. It worked out fine.

Last edited by calinb; 04-23-2012 at 11:51 PM. Reason: Fixed Attachment Link
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  #40  
Old 04-24-2012, 12:14 AM
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Re: 7mm SAUM Wildcat!

I just ran QL for my 7mm-300 RCM. 26" vs. 28" inches:

48 fps. penalty or 65000 psi. vs. 61202 psi. for 2986 fps.

Given that the 180 Bergers are generally reported to shoot well around 2950 fps, I'd go for 26", if not for the big 195 Berger unknown! I'd hate to miss a 195 grain node by 50 fps with a 26" barrel.

If it turns out that I'm not pushing for a velocity sweet spot with the 195s, I can always shorten the barrel later, but I can't put the 2 inches back on. ;)

I agree that 26" is far better for hunting. I find that anything over 26" really becomes a PITA for carry in the woods, but I guess that's why I have my 20" 300 and 338 RCMs. I could end up carrying this new 7mm over steep and rocky terrain, however.

So I think I've just about got my dream specs worked out.

-Cal
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  #41  
Old 01-11-2013, 09:50 PM
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Join Date: Jan 2012
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Re: 7mm SAUM Wildcat!

ALL RIGHT!-

Finally got to shoot this thing, (8 months+ since my last post). Anyways, these are the final specs: 29" Broughton 5R 1:9 on a Rem. 700 SA, bedded in a Manners T4. (Will be wearing my Mark IV soon). I did all the testing without it in case something bad happened!

I fire-formed all the brass with 180gr. Berger HVLD's over 48 grains of Hodg. 4831sc. After that started at 51 grains of the same with CCI BR-2 primers, went up half a grain at a time. I only did three shots of each so I wouldn't run out of brass. Here were the results. At 54.0 grains I ran out of the HVLD's and swithced over the the Target Hybrid 180's.

51.0 ---- 2495 -----
51.5 2509 2542 2528
52.0 2566 2562 2544
52.5 2490 2597 2599
53.0 2646 ---- 2629
53.5 2673 ---- 2623
54.0 2626 2606 2605
54.5 2655 2654 2638
55.0 2667 2653 ----
55.5 2672 2667 2675
56.0 2712 2711 2712
56.5 ---- 2711? ----
57.0 2771 ---- ----
57.5 2769 2768 ----
58.0 2764 ---- 2773
58.5 2839 ---- ----

Now, I would love to hear what you guys have to say about these numbers! There are a few strings that look super consistent which I love, on the other hand. The case capacity is 69.74 grains of H2O (filled to the top), compared to the Shehane with 68.25 grains. The report that I was reading on 6mmbr, said that he was getting 2950fps with 57.0 grains of 4831sc. With case capacities this close and me going another grain and a half and still being 150 fps shy seems strange to me?

I was curious what others thought, especially with all of the non-reads that I was getting from the chrono. Also, there were absolutely 0 pressure signs! No bolt lift stiffness, no ejector marks at all, primers actually looked great even at 58.5. So, what gives? Is the pressure really that low, and if so, how / why?

Either way I think that I will get the scope mounted up see how it does for accuracy and then test the loads for velocity again when it warms up a little more.

Thanks for any feed-back in advance.
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  #42  
Old 01-11-2013, 09:51 PM
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Join Date: Jan 2012
Posts: 159
Re: 7mm SAUM Wildcat!

Also, forgot to say that I am using Winchester 7mm WSM brass and not SAUM.
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