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7mm tcu in a ar magazine?

uni82uni82 Member Posts: 416 ✭✭
edited April 2010 in Perry Shooter Competition Shooting and Reloading Forum
I know it is quite common to neck up a 223 to a 6mm for hunting in the ar platform. Will the 7mm tcu (necked up fire formed 223) fit in the magazine to do the same thing but a 7mm instead of a 6mm? I run a 2.46 OAL in my 7mm tcu. Will the AR accept this round? It is a VERY Accurate round and is extremely reliable. I want it for hunting as well and I have the extra reloading dies lying around... thoughts and concerns?

-Joe
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    sandwarriorsandwarrior Member Posts: 5,453 ✭✭✭
    edited November -1
    You can only get short ogive 100 and 120 gr. bullets to fit in an AR mag. IMO it totally defeats the purpose of the 7mm TCU.

    The AR magazines have a length limitation of 2.26".

    A slight gain to be had is a 7mm BR in an AR15 platform. In that case you would still be limited to the highest BC 140's. Which is still good. You could expect top velocities of 2500 fps with that configuration.
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    uni82uni82 Member Posts: 416 ✭✭
    edited November -1
    Awesome thanks! So my best bet would be to get a 6mm or a 6.8 spc. I'm mainly going to do hunting and some plinking out to 500 yards maybe 600? Thanks
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    sandwarriorsandwarrior Member Posts: 5,453 ✭✭✭
    edited November -1
    Out to 500 yds. I'd say your best bet is a 6.5 CSS/AA Grendel. The improved 6mm PPC case necked up to 6.5mm. You can get the best long range ballistics of anything in an AR-15. That feeds through a magazine anyways. You can also get some very flat shooting lighter loads with it too. If you only changed the barrel to the 6mm or 6.5 TCU you would still be up against length issues for high BC bullets.
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    uni82uni82 Member Posts: 416 ✭✭
    edited November -1
    ok. and the 6.5 grendel is a 7.62x39 necked down to a 6.5 right? That is my understanding. So I would get an ar that is a 7.62x39 and get a 6.5 barrel?

    -Joe
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    sandwarriorsandwarrior Member Posts: 5,453 ✭✭✭
    edited November -1
    uni82,

    That's pretty much what the Grendel is. A 7.62x39 necked down to 6.5mm. Except, the shoulder has been blown forward to 30 deg. and the case walls have been been blown out to something like .426"(?..I can't remember exactly). The rim diameter is .440 so there is about the same relative taper as most other improved cartridges you may have read about, i.e. Ackley.

    One major difference though is the True Grendel case is supposed to use a small rifle primer/hole. You can make 6.5 Grendel/6.5 CSS brass from 7.62x39 no problem. Just size down to 6.5mm and shoot. In fact I took a box of Fed. 7.62x39, removed the primer pin from my die and sized down those rounds. I then loaded and fired them with Federal primers to fireform them. What I'm saying is you don't need to do anything else, other than size the neck down. You do have to check that you don't have too thick of necks though. For the normal chamber Federal will be within spec for you.

    Edit:

    I forgot. Use the Wolf reloading guide not the AA guide. Wolf uses large primer. You can overpressure a LR primer case using SR primer data.
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    uni82uni82 Member Posts: 416 ✭✭
    edited November -1
    as always you guys are awesome and extremely helpful. Looks like it going to be a 6.5 grendel just because I want something different. haha. Thanks for all your help, now I just need to start building!

    -Joe
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