Could be this is a direct impingment vs piston question. I'm curious if there is a mechanism to adjust the gas flow to operate the bolt to cycly normally with loads say 60% to 70% of max?

Then quickly adjust again to use normal full power loads.

Is the system that flexable, or is it rigid in the ammo used, and pressure levels to run the mechanisms?

KB

What do you think the 300 Whisper and 300 ACC Blackout do? They are of the DI system and they shoot subsonic up to full hilt jacketed loads. One can put an adjustable gas system on the DI system. Let me tell you with all the years of shooting cast bullets through many AR's in as many calibers and often reduced loads, that with a worn in AR it doesn't take much to cycle it.

quote:

Originally posted by SmokinJ:
What do you think the 300 Whisper and 300 ACC Blackout do?

I didn't know. I figured the system was tweeked to work specifically with that load. I didn't know it had a range of loads that would cycle acceptably.

Thanks for the info.

KB

Here's what they do when an AR with DI is put together to shoot a lower power round or round that won't produce a large volume of gas to work the action. They move the gas port hole closer to the chamber and they also work with different gas port hole diameters. Although pistol cartridges can be DI most are blow back. For the 5.56 cartridge as the barrel gets shorter and the their is no choice but to move the port hole closer to the chamber, the hole diameter then is much smaller.

KB they sometimes change the spring for low power loads. The amount of gas required equals the bolt carrier weight plus spring compression. You can tell by the ejection of the brass if tyou have the appropiate amount of gas flow. If the brass is ejecting between 3 and 2:30 you ar good to go. My DPMS is ejecting at 1-2 I problly should try and find a stouter spring or buy a hyrolic buffer. I'm shooting max loads of varget.

Kabluey,

Basically two approaches to the problem:

1) Use and adjustable gas block or a switch block. This was the traditional approach to the 300 Whisper (300/221). The block was placed in the pistol position. Such an installation allows a wide range of powders to be used for a wide range of velocities.

However ... there can be risk in shooting a high pressure load with the gas block set in the wrong position.

2) Find a powder that will just work the action for subsonics with a gas port that allows for operation with supersonics. A1680 is the one that works for the 300 BLK in subsonic mode with a carbine position single flow bas block.

The problem with the approach is that there is a much more limited range of powders that work with such systems.

I was loading a mass of plinking ammunition using surplus powder one time & the load should have been 21.5gr.
I got lazy with checking the powder weight on the scales & needless to say the powder measure had gradually altered - all the way down to 17gr before I noticed.
Took some of the last few rounds & some I knew were correct & shot them. They all cycled & at 100yds the difference in POI was less than 1".