I was tuning my .30 impact for slugs this am and was running about 920 FPS for about 150 rounds then I had one jam and the pellet probe would not close. I pushed apparently too hard and now am only able to get about 815 FPS, I was assuming I damaged an o ring where the transfer port is so I pulled the barrel to inspect, I bought from Ken at SPAW and he upgraded to transfer port and hammer, however the transfer port does not have the “bridge” piece to make it like a dual port, not sure if mine broke or what but I think this is where my slug is nose diving and getting hung up. Also I noticed a large gap between the brass transfer port and the silver metal threaded end that connects the sleeve to the port, is this normal? I would assume that should be a tight fit against the o ring that is between them. I will update with pics later this evening.
Tuning Impact slug feeding issue
- Thread starter Justinmac13
- Start date
I opened up my tp myself and when I use the pin probe it sometimes gets hung up in the tp or distorted. So I reinstalled the factory but enlarged probe back in and only lost 10fps but no hang up. I don’t know if that’s what your dealing with but if so I would enlarge the factory probe and then the slugs will enter correctly. Hope that helps
Upvote 0
attached are the pics, I now have it feeding fine but still have a major power loss. With 155 bar and valve adjustment at 4 lines and hammer spring maxed in only at 807fps. This am it was over 970 initially and I started backing down from there.
Upvote 0
That gap is normal. I wonder if you damaged the o-ring inside before the transfer port, it's hard to see in the pics.
Upvote 0
Is there supposed to be two inside or just one? The one that is about 1/8 to 1/4 of the way in seems to be okay. But there is a groove in the transfer port right after the hole in the side that I wonder if a ring is supposed to be in.
Upvote 0
The Gap is normal. There is only the one o-ring in the barrel. If your transfer port is a bit large pellets and slugs can dive into it especially if you are using a pin probe. I sheared a pellet off in my gun and part of it got stuck in the valve. I turned the gun upside down and shook it and was lucky cuz it fell out.
Upvote 0
This is exactly what was happening. I went in and smoothed over the leading edge of the hole in the transfer port and it feeds great now, but I am still at a loss of why the power loss. What could I have knocked out of place to cause 100 FPS loss by pushing too hard on the bolt lever?
Upvote 0
A couple of things...
First, that is a pretty good sized gap in between the breech and the barrel liner where initial and critical air pressure would be lost be escaping air. That liner should fit flush to that brass shoulder inside there. I would take the barrel assembly all apart and clean it up, and then "mock up" the barrel inside of the tube without any o-rings on it to see if it tightens up flush to that shoulder. Then, replace all the o-rings if it looks right. If it doesn't, then further investigation into why is in order.
Second, it could be that the pellet probe is covering part of the transfer port if the timing was thrown off somehow by forcing the jammed slug. So, with the gun and probe in the cocked and locked position, scribe a mark on the probe where it contacts the back of the barrel/brass transfer port/breech. Then remove the barrel and pellet probe to inspect them together in-hand, by putting the probe back into the breech up to the scribed line. Now, it will show whether any of the probe is blocking the hole. If it is then re-timing the cocking rod length is in order.
Third, if there is still power loss, the next possibility is the breech o-ring loosing it's seal at the shot. It is best to test this without a magazine in place (single loading the ammo while testing) to feel or see if there is a puff of air blowing back around the probe.
Yet another thing...
Look at the end of that probe closely to see if the jammed slug may have bent or marred up the edge of it. This could be cutting the breech o-ring or even gouging the brass breech area, causing a leaker. I polish the probe with 600 grit wet-dry sandpaper so there are no chances of it snagging the o-ring.
First, that is a pretty good sized gap in between the breech and the barrel liner where initial and critical air pressure would be lost be escaping air. That liner should fit flush to that brass shoulder inside there. I would take the barrel assembly all apart and clean it up, and then "mock up" the barrel inside of the tube without any o-rings on it to see if it tightens up flush to that shoulder. Then, replace all the o-rings if it looks right. If it doesn't, then further investigation into why is in order.
Second, it could be that the pellet probe is covering part of the transfer port if the timing was thrown off somehow by forcing the jammed slug. So, with the gun and probe in the cocked and locked position, scribe a mark on the probe where it contacts the back of the barrel/brass transfer port/breech. Then remove the barrel and pellet probe to inspect them together in-hand, by putting the probe back into the breech up to the scribed line. Now, it will show whether any of the probe is blocking the hole. If it is then re-timing the cocking rod length is in order.
Third, if there is still power loss, the next possibility is the breech o-ring loosing it's seal at the shot. It is best to test this without a magazine in place (single loading the ammo while testing) to feel or see if there is a puff of air blowing back around the probe.
Yet another thing...
Look at the end of that probe closely to see if the jammed slug may have bent or marred up the edge of it. This could be cutting the breech o-ring or even gouging the brass breech area, causing a leaker. I polish the probe with 600 grit wet-dry sandpaper so there are no chances of it snagging the o-ring.
Upvote 0
If the velocity is still low after you install a new breech seal o-ring it's likely your pellet pushing probe is either misaligned or bent.
Upvote 0
I checked my parts that came from SPAW. He has left the pin probe in, I swapped it with the probe that came from the power upgrade kit and set all settings back to how I received it from Ken. I am now at 350 FPS. 152 bar, .6203” on Mqx setting hammer spring and 3rd ring on valve adjustment. FX USA called me back and said to check inside the air port in the block itself.
Upvote 0