.300 Whisper Integrally Silenced AR

[K2unit]

Greetings,

I’ve built several AR’s in various configurations including a few each Form 1 SBR’s & Silencers. I’ve only recently discovered the .300 Whisper cartridge and have decided that my next project will be an Integrally Silenced AR in this caliber similar to what an MP-5SD looks like. The plan is to have the barrel & silencer assembly over 16” long so that it only requires one tax stamp for the silencer, not additionally for an SBR.

Doing some research and reading on this forum about short barrels for the Whisper cartridge, I see that the recommended configuration for barrels around 10” long is to move the gas port and gas block to the “Pistol” location. This obviously helps with additional backpressure, sooner, to operate the bolt locking mechanism reliably. I bought a 16” Whisper barrel from Model 1 sales and the current gas port location is 7 inches from the raised barrel extension stop and .120 diameter.

1) What distance should the gas port be and what diameter for a “Pistol” configuration that people have been using for their SBR?

I also see that most but not all AR’s use a gas regulator to adjust between Subsonic & Supersonic cartridges

2) If you set up the gas system for subsonic to operate reliably, won’t the bolt cycle just fine (faster) with supersonic ammo and just eject the shell casing farther? Why the need to adjust between the two?

Getting back to the integral silencer, I do not plan on drilling cross holes in the barrel like you would see on an Integral Silenced Ruger 10/22 or the MP-5SD. Those cross-holes are to guarantee that a standard .22LR or 9mm bullet is subsonic when it enters and exits the silencer. Because I’m starting with subsonic ammo, there is no need. For the optimum functioning silencer, you would want the semi auto breech to stay closed as long as possible to prevent gas & noise from escaping from the rear. That’s why bolt action rifles are quieter than semi autos using silencers (see De Lisle Carbine). With that in mind, If I leave the gas port & block at the carbine position (not pistol) and only have about 2” of barrel past the gas port, from what I’ve read it won’t reliably cycle. BUT what if the silencer is permanently attached to the barrel as in this configuration.

3) Will the additional back pressure of the silencer act as if it was additional barrel length enough to cycle reliably?
4) Will the additional volume of the silencer pressurizing, delay the breech opening even longer?

I’m also concerned about the bullet not stabilizing or tumbling with the short barrel. I certainly wouldn’t want any baffle strikes and it seems less useful system if the bullet is tumbling out at 100 yds.

5) Is there any data that shows how short a .300 Whisper barrel can be and still stabilize the bullet? Twist Rates?
6) Is there any data at velocity change verses barrel length for the .300 Whisper?
7) Anybody know what a typical through hole is on a .300 Whisper or even .308 silencer baffle?


I hope this post isn’t to long and somebody has the experience to answer these questions!

Thanx in advance!!!!
K2
Alienarms.com

[Eviltwin]

am no expert but here goes some opinions:
1) Believe I've been reading that most gas port sizes have been .125 or smaller
2) By having the adjustable gas block you can use less of the extra gas generated by
supersonic rounds to cycle the action thus keeping wear & tear down on the gun or
in the more open position try to allow as much of the gas generated by the sub round
back through the gas port to cycle the action
3) To an extent yes, also certain muzzle brakes (Krinkov) have been used on SBRs to aid
in cycling
4) Yes, see above - it will increase the dwell time
5) 1:8 is the preferred twist for the 190rg and up bullet range, not sure on how short
6) I have a chart printed out somewhere, I'll see if I can remember my photobucket info
7) The tighter the better, think somewhere around 1/20" larger than bullet - so .358"

[nwcid]

I would talk to Doug at SRT and see if he can do something like that. I live in a NO SBR/SBS state and I had him build me a integral 9mm AR upper this year. He does great work. He is easy to talk to and work through any issues or questions you have. I will be buying more stuff from him in the future.




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[befu]

I was wondering about this topic also. How would you do the gas block on an integral rifle?

The 9mm does not have a gas block. I would bet your barrel is held in by the suppressor assembly. That way you never have a SBR. If the suppressor is off, the barrel is not secured.

On the 300 whisper, if you assembled it with the short barrel and BEFORE you put the can on it, it would be a SBR. I have been trying to figure out how you could do a integral can on a gas operated barrel.

The only way I can think of right now is to have the can start after the gas port and be welded to the barrel.

Remember, if the barrel can be secured during assembly without the can making it 16", it is a SBR. Wouldn't want to chance it with the ATF.

Brian.

[redtazdog]

[QUOTE=befu;10107]I was wondering about this topic also. How would you do the gas block on an integral rifle?pistol gas port

The 9mm does not have a gas block. I would bet your barrel is held in by the suppressor assembly. Nope! That way you never have a SBR. If the suppressor is off, the barrel is not secured.


On the 300 whisper, if you assembled it with the short barrel and BEFORE you put the can on it, it would be a SBR. Yep! thats why you dont assemble it I have been trying to figure out how you could do a integral can on a gas operated barrel.You buy a 16 inch,cut it down to make the right length with the can,put the can on it after the pistol position gas block

The only way I can think of right now is to have the can start after the pistolgas port and be welded to the barrel. yep! if the can is removable it wouldnt be a integeral

Remember, if the barrel can be secured during assembly without the can making it 16", it is a SBR. Wouldn't want to chance it with the ATF.Thats why you send yor barrel to SRT and have it made into a integeral, unless you file a form 1 and make it yourself

[nwcid]

Originally Posted by befu

I was wondering about this topic also. How would you do the gas block on an integral rifle?

The 9mm does not have a gas block. I would bet your barrel is held in by the suppressor assembly. That way you never have a SBR. If the suppressor is off, the barrel is not secured.

On the 300 whisper, if you assembled it with the short barrel and BEFORE you put the can on it, it would be a SBR. I have been trying to figure out how you could do a integral can on a gas operated barrel.

The only way I can think of right now is to have the can start after the gas port and be welded to the barrel.

Remember, if the barrel can be secured during assembly without the can making it 16", it is a SBR. Wouldn't want to chance it with the ATF.

Brian.

Red hit most of it but I will add my 2 bits.

The integral 9mm is still held in place using the standard BBL nut and the can is pinned to the barrel so it is not a SBR. As far as the gas port the nice thing about custom makers like SRT is that they will work with you to make what you want. By having a SOT build the firearm you do not run into trouble.

The only thing I could think of that might be an issue or some thing to think about is a 2 piece gas block so that you can remove it for cleaning if needed.

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[befu]

Thanks for the info guy. the only 9mm suppressor I have seen was on a m16. Not SBR concerns, but the can held the barrel in. The outside of the can started life as a free float tube, it works nice. Friends, not mine. So that was the only info on AR suppressors I had.

OK, so cut the barrel down and permantly secure the suppressor housing to the barrel. I like the idea of the two piece gas block. pistol location, got that. 1 in 8 twist, just peachy!

Freefloat tube over the whole thing, looks like a nice setup as on nwcid.

I guess I will start a new thread. Been trying to find the information out there in older ones, but without reading them all, no luck!

Thank you,

Brian

[surfj9009]

I'm looking to do the same. The problem is finding a good barrel.

[nwcid]

Originally Posted by surfj9009

I'm looking to do the same. The problem is finding a good barrel.

Not cheep and not fast (6-8 weeks) but they will make anything you want. They are a top rated barrel maker. Mine just got done there and is headed to the gunsmith for finishing touches. I will post a report when I get it built.


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