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All things 300 AAC BLACKOUT
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 Post subject: Overall length question
PostPosted: Mon Sep 03, 2012 8:43 pm 
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Howdy everyone.

I got a question. In my quest to reload 300 blackout I am finding multiple case overall lengths. Why do they very so much from projectile to projectile? Most of my 556 rounds I have loaded in the past were the same. I am going to load some 147fmj's.

Any help would be appreciated.


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PostPosted: Mon Sep 03, 2012 9:32 pm 
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No idea, but if you get the 147s to feed, let me know the COAL because they won't feed for me.

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PostPosted: Mon Sep 03, 2012 9:39 pm 
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Copy. We set the dummy round at 2.120 and loaded it in a Mag. Seemed to feed and eject fine. Only a trip to the range will tell


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PostPosted: Mon Sep 03, 2012 10:10 pm 
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I have had good results with:

300 M2 GI 147 H110 16.6 1945 DSA 5/8/2012 2.065in
300 M2 GI 147 H110 16.8 1948 DSA 5/8/2012 2.065in

The above is: 300 BlackOut, M2 GI FMJBT pulls, 147 grain bullets, powder, powder weight, upper make, velocity in fps, date of tests, overall length.

This is with a carbine gas/buffer, 16 inch barrel, both GI and 'R-P 300 AAC Blackout' brass, trimmed, CCI SR Primers, finished with a 'Lee factory crimp', velocities average of 10 rounds at 10 feet.

I don't load hot. The listed loads have given full function with no fail to feeds or eject and bolt locks back on empty GI mags.
I have yet to work on adjusting for accuracy (109 degree days followed with hurricane rains and now 102 very humid degrees) but will as soon as I can.

These loads are for reference only. They are safe in my weapon with my components, put together my way. This does not imply that these loads are safe.

Enjoy and be safe,

OSOK


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PostPosted: Mon Sep 03, 2012 10:40 pm 
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They vary so much because of one or more reasons:

Some load the oal so that the bullet doesn't make contact with any ribs inside the magazine. Contact with the rib can cause the cartridge to not enter straight into the chamber and cause a jam.

Some rifles prefer a certain oal so as to feed properly and not jam. My Micro 7 feeds better with a shorter oal.

Some rifles prefer a certain oal for the best accuracy (more or less bullet jump until it makes contact with the rifling).

(in my experience) A shorter oal uses less powder for the same velocity, so in using reloading data, it's important to know what oal is being used.


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PostPosted: Wed Sep 05, 2012 8:48 am 
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Most loads are loaded so the ogive rides on the rib in the mag which on 5.56 touches the case neck.

This is from the AAC 300blk upper owners manual:

Hornady 110 V-Max, OAL: 2.000
Barnes 110 TSX, 2.015 OAL
Nosler Ballistic Tip 125 grain, OAL: 2.085
Sierra H2120 125 ProHunter, OAL: 1.950
Speer TNT 125 1986, OAL: 2.010
Remington AccuTip 125 grain, OAL: 2.085
Hornady 130 SP #3020, OAL: 2.010
Hornady 150 FMj-BT 3037, 2.065 OAL
Sierra 155 Palma, 2.150 OAL
Lapua B416 200 grain, 1.960 OAL
Sierra 220, 2.089 OAL


So loading longer may or may not be a problem with feeding or reliability. If you modify the mags so the rib is gone, you could load everything to mag length(not really, but it works for the example) just like with 5.56. Everything will have a sweet spot and the above I believe is where AAC found the sweet spot to be.

This is also the reason I got the Forster micrometer dies so I didnt have to constantly make HUGE corrections with the lock nut. I can make big corrections if I need to, but I know exactly what I am changing.

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PostPosted: Wed Sep 05, 2012 4:48 pm 
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Thanks for the replys. Does anyone know what Noveske's preferred OAL in their barrels is? If I go and buy the hornady OAL gauge will this tell me the number I should be loading that. I am still learning what I need to set the OAL for my particular rifle at.


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PostPosted: Wed Sep 05, 2012 6:28 pm 
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Tothemax! wrote:
Thanks for the replys. Does anyone know what Noveske's preferred OAL in their barrels is? If I go and buy the hornady OAL gauge will this tell me the number I should be loading that. I am still learning what I need to set the OAL for my particular rifle at.


The OAL has NOTHING to do with the gun/barrel. It has EVERYTHING to do with the bullet you are using and its ogive in relation to the rib in the magazine. Did I not just post that? I had to double check, but I did post that basically in the post above.

Now if you take that rib out of the magazine, then, and only then, can you custom load, up to max mag length, for your bullet and your gun. UNLESS you do that, you have to load so the ogive of the bullet is at the rib of the magazine(or pretty dang close to it) for feeding reliability.

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PostPosted: Wed Sep 05, 2012 6:38 pm 
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rjacobs wrote:
Tothemax! wrote:
Thanks for the replys. Does anyone know what Noveske's preferred OAL in their barrels is? If I go and buy the hornady OAL gauge will this tell me the number I should be loading that. I am still learning what I need to set the OAL for my particular rifle at.


The OAL has NOTHING to do with the gun/barrel. It has EVERYTHING to do with the bullet you are using and its ogive in relation to the rib in the magazine. Did I not just post that? I had to double check, but I did post that basically in the post above.

Now if you take that rib out of the magazine, then, and only then, can you custom load, up to max mag length, for your bullet and your gun. UNLESS you do that, you have to load so the ogive of the bullet is at the rib of the magazine(or pretty dang close to it) for feeding reliability.


You were talking about aac's specs and you confused me. I thought you meant that its per barrel.


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PostPosted: Wed Sep 05, 2012 6:49 pm 
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Are there magazines available without that rib in place? I thought I had read about that on this website?

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