FTFs on Silenced Scorpion Evo S3

[luzyfuerza]

My SBR'd Scorpion Evo S3 has been 100% reliable with any ammo I feed it. Subsonic, supersonic, reloads, factory, heavy bullets, light bullets...everything works great. I love the gun.

While I waited for my Octane 45 to get out of NFA jail, I worked up some subsonic loads. I started with Unique, 147 grain Xtreme CPRN, an OAL of 1.160", and CCI primers. I tested loads of 3.2, 3.5, 3.8, and 4.0. Each of these loads was comfortably subsonic, and was 100% reliable.

Until I installed the Octane. With the suppressor, the gun experiences occasional failures to feed with each of these loads; a fresh round is picked up from the magazine on the bolt return stroke, but it doesn't make the corner into the chamber. The round ends up at a 45 degree angle to the chamber, with the Scorpion's heavy bolt and recoil spring jamming it firmly in place.

"Occasional" means 6 FTFs in about 300 silenced rounds fired.

Same shooter, batches of ammo, ambient temperature, magazine, gun condition (dirty because of the can), day, etc. Bare...reliable. Silenced...FTFs.

The same thing happens with my favorite supersonic 115 grain CPRN load that uses Bullseye. The Evo is 100% reliable with this load when bare, but experiences occasional FTFs with the can.

I've spoken with a tech at CZ USA...they didn't have much to contribute.

My next steps:

see what silencerco suggests
polish the feedramps
shorten OAL
switch powder
as a last resort, buy some factory subsonic ammo to test.

Your suggestions?

Do any of you have a favorite "Pet (Subsonic) Load" that works great in your silenced Scorpion?

Do any of you have a favorite subsonic FACTORY load that works great in your silenced Scorpion?

 

[Blue68f100]

It appears the can is robbing pressure, slowing the operation down. I prefer faster powders for light loads. WST is my favorite and will burn 100% cleaner than Unique at lower pressure. That or you may have to bump the charge a 0.1gr and see if the function comes back.

Have you crony the ammo with the can? This will tell you how much if any you lost.

Note: I'm not familiar with that gun so I don't know how it operates, Blow back, gas?

 

[dgod]

That is what I would suggest as well, a little faster powder. With mine, I lost about 15% of my velocity with the can. There is a fine line between Function with Can, without can, Subsonic vs Supersonic in both conditions. Just because it is Subsonic without the can won't mean it will function with the can. You must decide what you want to happen. Subsonic with can? Load for that. It will be faster without the can. I have heard that you can change the spring and get better function, I haven't tried that, I just changed my loads.

Good Luck, when you get there, it feels absolutely great.
Dan

 

[RussellC]

Inquire about a little gizmo that goes between the silencer and the barrel that stops such fu nctioning problems. Im sure silencerco can fill you in.

Russellc

 

[luzyfuerza]

The Scorpion is straight blowback and has a 7 3/4" barrel.

Velocities for each load were virtually identical (with versus without the can). Any difference was within one standard deviation. Here's the data (sorry for the messy presentation...I can't figure out how to format a table in the board's software):

Powder charge (grains)....... Velocity with can (fps)/SD........ Velocity without can (fps)/SD
4.0....... 1008/24....... 1027/9
3.8....... 989/29 ......... 985/28
3.5....... 936/29 ........ 930/35
3.2....... 890/27 ........ 887/36
Ten measurements were used to calculate each average.

Interesting. My assumption was that the increased backpressure caused by the can would increase, rather than decrease, bolt speed.

If I do end up changing powders, I'll probably use AA5 (slower) and Bullseye (faster)...I have both on hand at the moment.

 

[JeffG]

It appears the can is robbing pressure, slowing the operation down. I prefer faster powders for light loads. WST is my favorite and will burn 100% cleaner than Unique at lower pressure. That or you may have to bump the charge a 0.1gr and see if the function comes back.

Have you crony the ammo with the can? This will tell you how much if any you lost.

Note: I'm not familiar with that gun so I don't know how it operates, Blow back, gas?

Maybe switch to Blue Dot or Tite Group, upper 85% load. Sounds like your bolt isn't hitting the rearmost travel before it picks up a new round.

 

[dgod]

Bluedot is a very good and consistent powder (I've used it for a lot of years), but it is a dirty powder, causing cleaning of weapon as well as brass . I'm not sure if there would be a problem with buildup in the can. Possibly something to watch.