.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