I have a 8 inch SBR 300 blackout barrel from ballistic advantage on one of my SBR builds. I also have a Syrac Ordinance piston on that build. I cant get supers to cycle the action unless they are suppressed. All of my hand loads keep short stroking on every USGI mag I have. It will sort of hold back on my lancer mags but not well enough for a mag change. I have ruled out misaligned gas block, buffer springs, buffers, and magazines as the problem. The only thing left is the port size on the barrel. I don't think its getting enough gas to move the piston far enough. Ballistic advantage even states that the port may need to be opened up for pistons.  Does anyone know the optimum port size for a Syrac/Superlative piston on an 8"  300 blackout barrel? I have read the optimum sizes for DI systems but have yet to find anything for a piston. I am going to open the port but I really want some advance from someone that has done it before I start.

i would contact BA and syrac and see if they can give you information

I am going to do that on monday

It depends on the gas system length and barrel length of your rifle for the gas port size. Superlative Arms has an adjustable system. Have you tried adjusting the settings? I do know Adams Arms had told me a good size for a middy 14.5 was like 0.078 or 0.079+, however it differs depending on gas length and barrel length.

Do you know the gas hole diameter of the barrel? That's a place to start. You made need to get the gas hole opened up a bit. Adco and Rainier Arms (I think) do it.

Typically the shorter the barrel the smaller the hole. Is the Ballistics advantage barrel that you have pistol length?

Adjustments on the block do not help with the short cycling. The gas block needs to be full open to not short stork with a suppressor. The current gas port is .100. 300 blackout 8" is only in pistol length gas. There are differences between blackout and 556 involving gas. I talked with the designer of the piston a little bit ago and he recommends .125".  Its big but I think it will wok much better.

So you cut your piston rod down to size to fit the pistol profile?

I'm betting the gas hole just isn't big enough.

I think you don't understand the piston is pistol length. I never cut anything that would be a bad idea

Yes there is a difference in gas pressure between 5.56 and 300blk.

Yup and hence the problem in pistons that are on Blackout uppers. I'm going to drill it out to .125" this week. I think later today I'll have time to take apart the rest of the upper and start getting thing setup.

I know this is an old thread, but BA barrels are known to run small on the gas port.  I had to send one of my 5.45 barrels back to them to open the port up so my Adams Arms piston would work.  If I remember right, they state on their site (or did at the time) that there may be issues with piston systems and their barrels.

Once I opened the port the syrac piston started working better. At .125 " the bolt will lock back on supers with a carbine buffer and normal power spring. I can use a JP silent capture spring and it works even better.