7LRM vs. 7-375

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Mateo, Feb 4, 2014.

  1. Mateo

    Mateo Well-Known Member

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    My gunsmith has a 7-375 reamer but not the 7LRM that I had my heart set on. Normally I would rent a reamer for him, but that option is not as available here in Canada as it is in the states. He's giving me a great deal on trueing up my remington action and chambering the barrel. This is my first custom. He also said the only real advantage to the 7LRM is that I could buy brass. (Gunwerks) I know the 7LRM has a longer neck since the shoulder is moved back. Is this difference worth not going with the existing reamer my gunsmith has and forming my own brass? Even if I have no dies yet? Would quality of brass be even comparable? Gunwerks has priced their brass quite decently. Seems like a small issue, but I don't know where I would get a reamer that I would only use once with out having to buy one. So, what do you think? 7LRM or 7-375?
     
  2. MudRunner2005

    MudRunner2005 Well-Known Member

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    Why not go with the old tried & true 7mm STW? You can shoot targets at a mile, and game for atleast up to 1,200 yards. Plus, you can still find 8mm RemMag brass, and all you have to do is run it through a 7mm STW FL die and there you have STW brass. :D
     

  3. benchracer

    benchracer Well-Known Member

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    If you use the reamer that your gunsmith has, what is your plan to obtain reloading dies? Is it your intention to have custom dies made?

    As long as you are OK with buying custom dies, I don't see a problem with the 7-375 Ruger over the 7LRM. You could either fireform Gunwerks brass or buy 375 Ruger brass and neck it down yourself.
     
  4. AZShooter

    AZShooter Well-Known Member

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    If you buy the 7 LRM reamer that will be your only major expense. If you want to neck down the 375 case it will take several steps and dies to do so.

    I had a box of 375 Ruger brass ever since it first hit the shelves many years ago. I thought it would make a dandy 338, 300 or 7mm. Finally decided to see if I could neck the brass down to 7mm with dies I had on hand. If I couldn't do it successfully with my dies then I wouldn't bother.

    Necking down to 338 dia is easy. I had a 338 RCM Hornady FL die set plus a Whidden Bushing/FL sizer for my 338 RCM. The 375 Ruger and both RCMs share the same shoulder diameter and angle.

    Steps in reducing the neck to 7mm:

    1)338 RCM seater die
    2) 338 FL die.
    3) 300 RUM FL die to taper mouth of case
    4)7 RUM seater die followed by FL to reduce neck dia
    5) Whidden 338 RCM bushing die with .312 bushing
    6) Open up with K and N mandrel, neck turn to .0135” neck wall thickness
    7) Run brass into Whidden 338 RCM bushing die with .310/309 bushing for finalized neck tension

    I was fortunate to have the whidden bushing die.

    I am still using the whidden bushing die for neck sizing. Purchased a 375 Ruger die set and use the FL die for sizing the body and shoulder.

    As you can see there is significant work to be done to get the brass formed to 7mm. It was a fun challenge. Once the formed brass was made I sent one to Dave Kiff and he made me the reamer.

    The availability of brass is one of the perks of making the 7mm/375.

    If I were to do this today I would just buy the 7 LRM reamer, Hornady's die set and Gunwerk's brass.
     
  5. Mateo

    Mateo Well-Known Member

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    I see. Since I have none of the dies now, I would have to purchase and borrow to make the brass. And this could cost me more or the same as just buying the reamer? Plus the headache of trying to make sure all my brass was the same and done right. This is only worth it if I get a kick out of doing this kind of stuff. ( I don't,....yet) don't get me wrong. I do like how this build is progressing so far. The research is fun and I'm learning tons. But when there is a big mystery as to how I'm gonna get brass for the 7-375 it makes me question if it's worth that mess. Buying brass from gunwerks is probably cheaper than buying 375ruger brass and having to get it Down to 7mm, even if I didn't have to get all the dies and someone was willing to make them for me. I would still need to pay them for their time on top of the cost of brass.
    But my biggest question is if there is any performance difference between the 7lrm vs. the 7-375. I know the 7lrm has a tiny bit less case capacity and the 375 has a short neck. Are these differences worth noting? Thanks everyone for the help.
     
  6. Mateo

    Mateo Well-Known Member

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    I did look into the stw, I just wasn't sure why this was different than the 7RUM? And I like the 7lrm because it loses the belt. Not that there isn't really anything wrong with the belted cases, I just think it makes things a bit easier to hand load with? Again. Still learning about these differences.
     
  7. MudRunner2005

    MudRunner2005 Well-Known Member

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    Longer necks usually equivilate to better throat life, which is the first thing to start going on these large magnum calibers. If you torch the throat, the accuracy will gradually become noticeably worse. When it comes to big magnums, wildcats, and shooting them alot, EVERYTHING is worth noting, in my opinion. Make sure you study up and decide on what you truly want before you jump head-first into it. Look at dies and brass availability. which bullet you want to shoot, and it's availability.
     
  8. MudRunner2005

    MudRunner2005 Well-Known Member

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    Actually loading with a belted cartridge vs non-belted is no different. They're the exact same to load for. If your smith is good at what he does, then he will know that ordering tight-chamber reamers are better than ordering standard dimension reamers. Tight-chamber reamers have very tight tolerances, and your brass doesn't swell very much at all. You can neck-size about 3 times and then have to run them through a FL sizing die the 4th or 5th time. With a tight-chamber for a belted caliber, you don't have to worry about the notorious "case-head speration" anywhere near as bad, because the chamber is tight, and not generous, therefore the brass doesn't swell (expand) as much around the belt. Belted calibers and rimmed calibers headspace off the belt and rim, whereas non-belted headspace off the cartridge shoulder. And with today's awesome advancements in good quality brass, like Lapua, Norma/Nosler, etc... You can get pretty good life out of belted cartridges without any issues.

    So, if I were in your shoes, I would definitely take another look into the 7mm STW. It has good brass availability (8mm RemMag brass can be necked down to 7mm in 1 simple step), good velocity, efficient design, and I have gotten 5-6 firings out of some of my brass, maybe more than that on some, if I load mild loads.

    If you have any questions, feel free to come join us over in the STW section, and ask as many questions as you'd like. They're very friendly and helpful over there in the brotherhood.

    7mm STW - Long Range Hunting Online Magazine