16" Barrel on a .300 BO Build...

RLinNH

Sergeant of the Hide
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Minuteman
Mar 23, 2019
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Taking the plunge and building my first AR. It's going to be a .300 BO with a 16" barrel. I already have 2 weapon systems in .300 BO. Both of those are Short Barreled with Pistol Braces. Looking to build a Coyote Killer for the backyard with this build. My question is, are there any drawbacks to using a 16" barrel in the .300 BO chambering? Only obvious one that comes to mind is the length, especially when a suppressor is added to the end. But I can live with that. The main reason I want to go with a 16" barrel is that I can not find a pistol brace that meets my expectations for cheek weld. I really do not enjoy shooting my other 2 .300 BO's with the braces. I want my build to be a comfortable shooter for me. So the stock options that open up with a 16" barrel platform are worth the longer barrel length, to me. Any other drawbacks that you know of with a 16" barrel on a .300 BO that I'm not thinking of here?
 
Two thoughts.

1. Why not just fill out a Form 1 (I think) and make a SBR. I'm about to go down that road myself. By all accounts it's not hard and doesn't take long (well, that was before we went under martial law)

2. I have a 16" BO upper that I've yet to get to play with, but when I got it I tried to get some info about shooting it on the 300BO forum. I'll say they can be minimally helpful at times. What I did find was that there are a lot of variables that make a difference in getting a carbine gas system in a 300BO to cycle with subs (weights, spring, BCG brand, bullet weight, powder choice, etc...), and finding a load can be done, but it may take a while and may not be what you want. What I took away was that the issue is more one of gas system length than barrel length. Trying to get subs to cycle the action in a carbine length system, without the can on, can be very challenging.

If you do want to go 16" try to get a barrel with a pistol length gas port, it will simplify things, at least that is what I go from my research.
 
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I have one that's 16", the ACOG is tuned for that barrel too FWIW. AAC has sales and gives 'em away all the time if they have any left. Only reason I really have it is that suppressors got legalized here before SBR's and I needed a host.

Yeah, pistol gas tube IIRC.

But those supers have shitty BC and the subs have good BC but ain't moving too fast. 16" will not give you much gain in velocity with this cartridge either, it uses very little powder and the short barrels do a pretty good job burning it up already. I think 16" may give you 200fps w/supers over an 8.5"?

If you want an accurate and hard hitting round the Grendel is the way to go. That and .300BLK are the best AR rounds IMO but they both do different things better.
 
Had a 16” one way back in the day waiting on my form 1 to come back. It shot fine. Supers and subs with a YHM SS Phantom
I currently have 3 .30 cal suppresoors. Check that. 1 on hand, 2 in jail. The one I have on hand will be used on my 6.5 Creedmoor Bergara. It's an AAC SDN-6. I am waiting on a Trash Panda and a Sandman-K. I am hoping to use the Trash Panda on this new, 16" build as the Sandman is going to be a permanent host on a Pistol build.
 
What has me scratching my head though is why a Pistil length gas tube, on a 16" barrel will work better than a Carbine length gas tube. It is, after all, a carbine length barrel. Could someone explain that to me?
 
The bolt is cycled by the gas pressure at the gas port.

If you are trying to run subs from a carbine length gas system there is a very fine window to get the pressure high enough at the port and not push the bullet super sonic at the muzzle. The pistol length gas system moves the port closer to the chamber and further from the muzzle, there are more options with fast powders that have a quicker pressure peak that will get the pressure high enough at the port but won't push the bullet supersonic at the muzzle.

Those same fast powders will peak too soon in a carbine length system and not cycle the bolt, and they develop too much chamber pressure if you try to put more in. Slower powders that have a high enough pressure at the port tend to keep pushing the bullet and take it SS.
 
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The bolt is cycled by the gas pressure at the gas port.

If you are trying to run subs from a carbine length gas system there is a very fine window to get the pressure high enough at the port and not push the bullet super sonic at the muzzle. The pistol length gas system moves the port closer to the chamber and further from the muzzle, there are more options with fast powders that have a quicker pressure peak that will get the pressure high enough at the port but won't push the bullet supersonic at the muzzle.

Those same fast powders will peak too soon in a carbine length system and not cycle the bolt, and they develop too much chamber pressure if you try to put more in. Slower powders that have a high enough pressure at the port tend to keep pushing the bullet and take it SS.

After today's lesson in reloading, the whole"slower burning versus faster burning powder" makes sense. Matter of fact XTR, your entire post makes a crap load of sense now. Thank you sir for explaining. (y)