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Old June 14, 2012, 01:06 AM   #1
The Deuce
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300blk build Have some quick Q's

I'll make this quick and painless as I can .. Bare with me its my first build from nothing but parts & pieces (built an upper once ".458 socom") ... Anyways here we go ..

1. I've heard that due to pressure issues not to use billet for your lower, is there truth to this at all ?? .. The main reason I'm asking this is because I've considered using Black Rain Ord. Billet aluminum lower .

2. Gas system length for best operation: carbine , mid, or rifle ?? Or !! Should I build with a piston operating system??..due to the fact I'll be running suppressed and non-suppressed.

3. And finally .. more info that I don't know if it is false or inaccurate,or not .. I heard that a 300blk rifle seems to function better with an M-16 bolt carrier vs your typical AR-15 bolt carrier .. Is this accurate or just a load of crap ??

Thanks in advance .. Pics will be posted upon completion
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Old June 14, 2012, 05:50 AM   #2
Mobuck
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The amount of "pressure" has no effect or bearing on the material from which the lower is made except that the billet lowers must be sufficiently hard surfaced after milling to resist deforming at the pinholes/threads. This is a general statement and other factors are not dealt with.
No comments on the other questions.
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Old June 14, 2012, 07:45 AM   #3
Rottweiler
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I can't offer much help on the first 2 but #3.

The M-16 bolt carrier is a little heavier than a AR carrier(due to less metal is milled away at the rear). This slows down the cycling of the action and lets pressure in the barrel drop off a bit more before the bolt unlocks and pulls the empty brass out. That keeps the brass from getting tore up as bad. I have M-16 bolt carriers in all my ARs along with Tubb CWS's

It may help with the supressor too but I can't say for sure, no supressor ...yet.

Adding a Tubb CWS carrier weight system also helps delay the bolt carrier's rear movment. It works very well in my service rifle. Hot 80 grain loads used to destroy my brass in 2 loads. Since I put the CWS in I have yet to destroy a piece of brass in either my service rifle or the Blackout upper.
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Old June 14, 2012, 09:20 AM   #4
RyeDaddy
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I wouldn't use a gas system longer than carbine on a 300 BLK, it doesn't generate as much as gas and pressure as 5.56, as the bore is larger, and the 300 uses less powder. My 10" 300 BLK Noveske came with a pistol gas system.
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Old June 14, 2012, 12:28 PM   #5
The Deuce
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Thanks Everyone,

@Mobuck - Thank you for clarification, i didnt think that it would have any bearing since since the bullet fires from the chamber .. but it was something I had come across and wanted to make 100% sure.

@Rottweiler - Thanks for your info also. I am not 100% yet but I will probably build it with an M-16 carrier, and I am going to look into that "Tubb CWS" and see if I would benefit from that or not.

@RyeDaddy - The 300 uses less powder than a 5.56 in the supersonic rounds? I am just now studying ballistics and such but it seems like it would need to have more powder to push a 115-155gr projectile at 2215-2350fps. Understandably with the 200-220gr projectiles moving at approx. 1000fps is basically a pistol velocity. Hahaha God Ballistics can be wicked confusing, and difficult to understand. Anywhoot I never even thought about a pistol gas system..
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Old June 14, 2012, 12:52 PM   #6
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Well if you think about it a 300 BLK is a 5.56 case with the neck blown out wider, so it really couldn't hold more powder. 300 BLK tends to be used with magnum pistol powders like H110 for the supersonic loads, so they burn up sooner in the barrel than common 223 powders like H335 and Varget. Also compounding the issue is the larger bore diameter, the gas has more space to fill up to develop the same pressure. So by the time you reach the gas port on a rifle length system the powder is all burned up and there isn't as much gas volume or pressure to operate the action. I wouldn't advise a barrel longer than 16" for sure, and I would stick with carbine gas for that barrel, or pistol length gas for anything shorter. Hope this helps.

Last edited by RyeDaddy; June 14, 2012 at 12:58 PM. Reason: iPhone spelling errors
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Old June 14, 2012, 09:07 PM   #7
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http://thefiringline.com/forums/showthread.php?t=492411

PM- rsilvers for answers to your questions. I believe he works on the Blackout development for AAC
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Old June 14, 2012, 10:12 PM   #8
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The 300 BLK is not a 5.56/223 case necked up to 30 caliber. It's a 22 Fireball case necked up to 30 caliber. A .223 necked up to 30 caliber would be a 30 TCU.
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Old June 15, 2012, 02:57 AM   #9
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#2 Unless you make or have made your own barrel I dont think you will fInd a 300BLK barrel with anything other than carbine length gas and you will be very hard pressed to find a barrel longer than 16".

I just a built a 300blk and have a semi auto BGC in mine and it runs find.
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Old June 15, 2012, 08:58 AM   #10
RyeDaddy
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Quote:
The 300 BLK is not a 5.56/223 case necked up to 30 caliber. It's a 22 Fireball case necked up to 30 caliber. A .223 necked up to 30 caliber would be a 30 TCU.

While this may be techinically correct according to SAAMI, all the 300 BLK brass I've seen and shot other than Remington was formed from Lake City 5.56 brass. Would 300 BLK be cost effective if the only way to get brass was to form it from 221 Fireball?
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Old June 15, 2012, 05:46 PM   #11
rsilvers
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For a 16 inch or longer barrel, you can use pistol gas or carbine gas. For a barrel under 16 inches, use pistol gas.
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Old June 16, 2012, 05:14 AM   #12
madcratebuilder
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Quote:
1. I've heard that due to pressure issues not to use billet for your lower, is there truth to this at all ?? .. The main reason I'm asking this is because I've considered using Black Rain Ord. Billet aluminum lower .
Billet lowers are as strong as forged. The outside dimensions are slightly different.


Quote:
2. Gas system length for best operation: carbine , mid, or rifle ?? Or !! Should I build with a piston operating system??..due to the fact I'll be running suppressed and non-suppressed.
Longest gas I've seen is carbine, this is a low pressure round and wants a short tube with a lot of barrel length past the gas port. A adjustable gas tube or gas block for shooting both suppressed and unsuppressed.



Quote:
3. And finally .. more info that I don't know if it is false or inaccurate,or not .. I heard that a 300blk rifle seems to function better with an M-16 bolt carrier vs your typical AR-15 bolt carrier .. Is this accurate or just a load of crap ??
The FA carrier is 11 grams heavier than the SA carrier. FA carriers are good for carbine gassed 5.56 guns that tend to be over gassed. If your buying now, get the FA carrier, but it's not worth replacing a good SA with FA, not much difference.
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Old June 16, 2012, 07:29 AM   #13
RyeDaddy
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Quote:
For a 16 inch or longer barrel, you can use pistol gas or carbine gas. For a barrel under 16 inches, use pistol gas.
*
There you have it, straight from the horse. RSilvers is R&D for AAC, although he didn't identify himself that way.
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