New AR15 member

( so to all the "experts" and trolls go easy on me )

Question - has anyone tried the sig sauer 516 pdw 7.5 short stroke piston system with a custom 300 blackout barrel for a 300 build?

Also...

It seems that the ..... SIG MPX employs the SIG SAUER battle-proven gas-operated short stroke piston system for unequaled reliability in the field, even under the most adverse conditions.

Could the MPX gas-operated short stroke piston (operating cycle design) be used on a 300 blackout build...since the pistol rounds are currently being used... it seems if there could possibly be a way to get the 300 blackout to cycle with sub loads and full power loads this would be the way...

If one was to custom machine an upper receiver and/or monolithic upper to accept the mpx piston system and develop a short bolt / bolt carrier...  has anyone attempted this type of gun build...?

Another system I have a question about is the Rock River Arms LAR-PDS pistol .......would be attempting a frankenstein gun build... but basically use a 300 blackout barrel with the lar-pds hardware. Would this just lead to short stroking?

Short  Question :  Are there any Piston system gun builds out there for the 300 blackout round that utilizes a return spring either in the upper receiver or around the piston?

Apparently 300BLK and a piston setup don't mix well as there is quite a few different manufacturers who have made attempts in producing a 300BLK piston gun but most to all fell short so 300BLK to this day still remains DI.

To my knowledge no one has successfully made a 300 blk piston AR15 work with both subs and supers.  there have been several attempts and even a few claims that it has woked.  but I have not seen any thing that proves it.

Doesn't PWS make a piston 300BLK setup or are those all DI? Poked around their site some and they didn't seem to mention the other gas system of the 300BLK rifles.

Yes, there is a 12.75 inch 300blk, 16 inch 300blk and soon a 9.75 inch all in a piston driven MK1 upper or rifle.

Are the saying that they will.work with subsonic unsupressed, or suppressed?

That is an unrealistic expectation for pretty much any DI or Piston driven platform in .300blk.  The variance of gas pressures in the ammunition and suppressed/unsuppressed scenarios you mentioned are far to wide ranging for any gas adjustment to account for it.

Supersonic unsuppressed
Supersonic suppressed
Subsonic suppressed

Should all work fine with no fuss.

Subsonic unsuppressed: Not enough gas to cycle the action without the can attached.

Per my conversation with a guy over at PWS, they will be releasing their MK109 MOD1 in a few weeks. I'd jump all over that.

The new PWS  MK109 Mod1 has adjustable gas settings and will be able to cycle subsonic unsuppressed just fine. The older Mod 0 version had issues with that.

I would not say that for a correctly configured DI gun.  Both of my barrels. 16 inch carbine and 9.5 inch pistol function subsonic unsuppressed just fine.  I have gotten a178 gr amax at 935 fps to work great in my 16 inch carbine gas. Killed.2.dear with it too.

If a DI gun is not functioning subsonic unsupressed then there is something not correct with the setup or the ammo.

thanks for the posts and responses...

PWS MK109 seems to be the most reliable ( of getting an AR style and / or AK designed weapon to cycle ) ... thus far .. but still uses a "buffer tube" ....and the user must change the gas setting for the piston system when shooting suppressed / not suppressed. ( which isn't a big deal )

As for low pressure.....and not being able to cycle the action >>>>  I am still interested in SIG SAUER's MPX ...which on there website says uses their tested short stroke piston system with pistol calibers. Also this design has a folding stock ( NO Buffer tube )  So how is this design able to cycle the action with pistol powder loads UNsuppressed and suppressed.... Also what type of return spring is being used to chamber another round and complete the cycle of operation. Is the return spring located in the upper receiver or on the piston itself????

This Topic is for learning purposes to be used on current "experimental" gun build code named "turd ferguson".... since very few people can get a 300 blackout Piston AR to successfully run or cycle or purrr or rock and roll or what ever word you say for getting the gun to go bang and slam in another round into chamber, then go bang again and again and again.

for a piston system to work with the 300 blackout the only way I have read about (online) is to enlarge the gas volume / increase gas pressure ... increase or decrease the size and travel of the piston and remove weight from the buffer system and cut the buffer spring

SO....coming across the SIG MPX Im interested as to what the internals for the upper receiver and gas piston system look like and to be able to implement them or custom machine the design into a 300 black out build. (since sig hasn't offered anything in a gas piston 300 blackout in a SBR without a buffer tube / stock design) to my knowledge.

Also Has anyone shot the sig 556xi in 300 blackout? thoughts?

What are the chamber pressures / and gas pressures involved with the 300 blackout round .... As I am not a rocket scientist or high school physics teacher and hope some smart person on this website can answer my question... while I stuff my face with some taco bell.

Disclaimer >>> I appreciate all designs to complete the cycle of operation in a firearm ( recoil, direct gas, piston, crazy foreign designs, etc. )  So please don't argue about direct gas vs piston in this thread/ folder/ topic/ sector/ area / ....

I owned a mod 0 PWS MK109 (9") upper and it functioned perfectly with and without a suppressor regardless of loads.  The early ones had a smaller gas port and would not function subsonics without a suppressor.  This was before they started using the adjustable gas setting system.  I ended up selling it because the ammo situation has never become what it was supposed to.  A buck a round for subs and the fact that the caliber has been so scarce I decided to sell and wait for it to mature.  The new MK109 or whatever they call it should be good to go.  I have never seen short stroke piston system work in 300 with the exception of an LWRC prototype that they ended up going DI for a contract I read.  Not sure why those don't work and the PWS long stroke does.  I think the Sig stuff is short stroke but have not closely looked at one.