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Which 7mm???

 
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  #8  
Old 10-24-2008, 01:38 PM
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Join Date: Oct 2004
Location: South Illinois
Posts: 234
Re: Which 7mm???

I'm getting parts together for a 7 REM Mag build. Using a 700 LA, old Sendero stock, 9 twist Broughton Sendero contour barrel, And a DE brake ( so my 10 yr old daughter can shoot it). All up, it should weigh 12-13 lbs with bipod. I too plan to shoot 168 Bergers.

260
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  #9  
Old 10-25-2008, 03:15 PM
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Join Date: Dec 2005
Location: Tucson Az
Posts: 1,097
Re: Which 7mm???

I too have been looking at all the 7 mm options. Recently I bought two new 26" Rem takeoffs and had one chambered for the 7 RUM and the other for the 7 STW. Every component was indentical. Moly coated 168 Berger VLDs, RL-25, Fed 215 primer and virgin Rem brass. The 7 RUM beat the 7 STW by approx 50 fps with max loads. I concluded that the 7 RUM needs a longer barrel.

I liked the 7STW so much that it stayed in that platform. The 168 VLD has a .160" jump to the rifling and fits the model 700's factory mag box and feeds perfectly. It also didn't require any alterations to the magazine feed rails like the RUM would have.


To top this off, as I mentioned in an earlier thread, I had a friend give me a like new 20 yr old Interarms Mark X in 375 H and H. I already have a 375 Taylor so decided to rebarrel this rifle. The McMillan stock barrel channel is quite large. So...I ordered a 30" SS #7 profile Lilja 3 groove 1 in 7 twist barrel to shoot the 180 VLD! I then pondered long and hard as to which 7 magnum sized case to use.

My friend Dan was struggling with a 7 STW CM barrel that went south with only 470 rnds through it. He had a long talk with Dave Kiff of Pacific Tool and Gauge. Dave told him the 7 STW was one of his favorite cartridges. Dave said he went through many barrels before he realized if you keep the bullet into the rifling instead of a jump it will last much longer. He said Dan could get around 1500 rounds of barrel life if he followed that approach. Dan ordered a reamer from Dave and also ordered a wyatts extended length box mag for his model 70.

Based on this information and the difficulty in extended the length of the mauser style mag box, I opted to go with a 7 Rem Mag. I sent in a dummy to Dave with a lengthened OAL which will allow full engagement of the rifling with the 180 VLD and plenty of room to chase the rifling as it wears.

I also have a lightweight (7 1/2 lb) Ruger M77 tang safety in 284 win. It has an extended mag box of 3". When barrel number 4 wears out I will have Dave make be a custom reamer for it too.

As for fluting the barrel go for it! I have two #5 fluted liljas that are 27" and 28". The fluting looks good and does lighten it a bit. As for length, 26" would be great for a walkaround hunting rifle in either 7 mag or 7 STW. Lilja's standard finish length is 27" so I'd go with it as is. If I were to want a 7 RUM it would have to be at least 28" or longer or IMO not worth the extra blast, recoil and powder comsumption.

I hope you have a great time with the entire process.
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  #10  
Old 10-25-2008, 05:01 PM
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Join Date: Dec 2001
Location: Long Island, New York
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Re: Which 7mm???

I'd be interested in hearing the theory as to why you would get 3x the barrel life when loading into the lands.

If anything you would expect loading into the rifling to cause increased pressure, increased heat and slightly longer bullet dwell time in the throat resulting in longer peak heat/pressure.

Interesting
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  #11  
Old 10-25-2008, 06:38 PM
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Join Date: Dec 2005
Location: Tucson Az
Posts: 1,097
Re: Which 7mm???

I can only guess. Gasses passing the bullet as it goes through the freebore area? Actually there would be less powder involved with the bullet into the rifling to get equal pressure.

I too would love to hear an explanation.
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  #12  
Old 10-27-2008, 11:11 AM
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Join Date: Oct 2008
Posts: 4
Re: Which 7mm???

Thanks for all of the input and replies. I have not totally made up my mind yet, but I am leaning towards the 7mm mag.

As far as barrel length goes, I thought I read somewhere that the longer sleeker projectile from a 7mm needed a longer barrel (28") to properly stabilize the rounds? It sounds like some of you are happy with 26" barrels?? What about muzzle brakes...are they needed on a 7mm mag?
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  #13  
Old 10-27-2008, 11:53 AM
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Location: Northern Michigan
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Re: Which 7mm???

Quote:
So...I ordered a 30" SS #7 profile Lilja 3 groove 1 in 7 twist barrel to shoot the 180 VLD!
I hope you plan on using the thick jacketed 180's. I've been down this road.....thin jacket bullets go poof. Although they shoot the 160 Accubonds well.

8.5-9" twist works just fine for the 180's.
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  #14  
Old 10-27-2008, 12:02 PM
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Join Date: Dec 2002
Location: Northern Michigan
Posts: 1,014
Re: Which 7mm???

Quote:
What about muzzle brakes...are they needed on a 7mm mag?
Most likely not, but I like them. More than likely you's be able to see your hits at any distance. Which to me is more important than a bit of noise because I usually don't have a spotter.
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