Ridiculous feedneck blowback

[oats944]

Good afternoon, my mech 05 Black Magic (mid block) has some crazy blowback from the feedneck and I’m out of idears on how to stop it. It has an Inception bolt. If a ball is in the breach and a second one is on top of the bolt and I fire, the ball waiting its turn blasts up out of the feedneck and ricochet’s off my 8’ ceiling with some force. If I don’t have a ball in the breach and just have one on top of the bolt I can fire over and over and the ball won’t go down into the breach.

I’ve ensured the sled and bolt are as far forward as they go before hitting the slot/body.

I’ve put thicker orings on the bolt to the point that it hindered the bolt movement with little change in the blowback.

For the timing if I pull the trigger slowly it’ll fire before the pneumatics start doing anything.

I have a 99 gen-x mini cocker, Karnivor, and Trilogy SF and none of them do this. The 2nd ball doesn’t even move when I fire the first one and then falls right down into the breach.

Outside of using a force fed hopper which I’m trying to avoid, anyone else run into this issue and found a solution? Thanks!

[Jonnydread]

Is there a front o-ring on the bolt? You could try a stiffer valve spring, that's helped me in the past.

[Hellion360]

You seem to have done a lot of the regular fixes.

Is your LPR too low? If it is then the bolt could pop open.
Does the blowback go away if the bolt is held forward?

[oats944]

Thanks guys! Yes there is a front oring on the bolt. Tried some thicker ones with no luck.

I think the lpr is at the right pressure but can try turning it up to see what happens.

I’ll try messing around with different valve springs. Actually I think I just ordered a set from Hellion’s eBay store. I have a set of hammer springs already. Velocity isn’t where I want it to boot so I’ll try some spring combos.

I haven’t held the bolt forward. But it is as forward as it goes before the sled and the bolt pin start hitting the body. Shooting it super slow it shoots, the bolt doesn’t budge, and then the pneumatics (inception) start to do their job.

Not sure if it matters but the pneu’s, bolt, hammer, and springs are all Inception.

[Hellion360]

Holding the bolt forward will isolate the issue to either a parts fit issue (blowback still present), or a timing/tuning issue (no blowback present)

[shooter311]

When you shoot, what is the velocity of the ball coming out of the barrel? Is that normal, or is it super low? Can you post some pics of the bolt in the marker and outside the marker next to it, where it would line up? If timing is good, the bolt isn't upside down, and the orings are snug, it seems like something is misaligned. IS your pump arm a little too long? Can you screw it in any further?

[shooter311]

I have a Whisper bolt in mine, but your hole should be lined up where my cutout is, not sure if the pics help. The middle oring should be right behind the back of the feedneck for proper alignment.

[Trbo323]

Yeah first I'm curious what the velocity is as well. After that I would start by holding the bolt forward by hand. If that doesn't work I would try changing out the middle ring on the bolt, I don't think you are getting blow back from the barrel I think it might be bypassing that center ring when coming up the transfer hole.

When the bolt is all the way back, how much of it can you see down the feedneck? When forward can you see any of the center ring?

If all that doesn't work, take the bolt out of one of your other markers and position it correctly, I know it won't attach to the sled, you'll have to hold it by hand and then fire, still get blowby?

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[Daltech]

Buy a stock blackmagic WGP midblock length bolt? Seems like the easiest solution.

[oats944]

Thanks so much everyone. I attached some photos and tried a couple things. It was hard to get the right angle showing the bolt outside the marker so I took two.

Turned up the lpr to as high as it goes, no change, turned it back down.

Turned the lpr all the way off, held the bolt forward with my finger. Took a shot and the 2nd ball on the bolt didn’t go anywhere, no blowback whatsoever. Turned lpr back to normal.

Put a thicker oring in the middle of the bolt, same blowback. Put a thicker oring on the front and middle of the bolt, same blowback.

When holding the trigger back I don’t see any bolt. It cocks just as the bolt face clears the feedneck. When the trigger is released I don’t see any orings on the bolt.

Unfortunately I don’t have any other mid block bolts to put in it.

I watched one of Inception’s timing videos for a little refresher. It fires, then the pump arm slides back, then slides forward. Same as all my other cockers and I have no issues with them.

A little backstory, it was setup as a pump when I bought it in the pump section a couple months ago. Decided to convert it to mech. As a pump I was shooting 280 fps all day. Once I put on all of the pneumatics and timed it it was shooting in the 150-175 fps range. It has a Hyper 3 hpr that was reading around 260-280 psi at its highest. I ordered and installed a couple more Belleville washers and set it around 320-340 psi. I also installed a heavier hammer spring. With that it was shooting around 230-240 fps tops. I ordered some valve springs today. It has an Inception valve in it. I haven’t converted a pump to mech before, but thought it was a little strange the velocity dipped so much.

Thanks again for everyone’s input, it’s greatly appreciated as this is driving me nuts.

[Trbo323]

With the LPR on where you normally have it, by hand pull the bolt back. How hard is it to pull?

I've always gone with, difficult but not impossible to pull it back and that has worked well for me. I'm curious if something is going on with your LPR.

The fact that you had a different result when you held the bolt forward is saying something. Did you have the bolt pin in place into the sled when you did that test?

Next test, well first off I'm assuming your velocity is fine? You haven't mentioned it yet

But if you have 2 tanks and some front block hose here's what I would try next, get one of your other cockers, run a length of front block hose from one of the other cockers into the 3 way of the BM. Basically you are using the LPR from another marker onto this one without having to disassemble stuff. You'll have to bend over and rubber band the BM LPR hose since it won't be used but the marker needs air to shoot.

Shoot, see what happens.

Right now I'm thinking your LPR isn't going high enough and when you fire the bolt is jumping back allowing air up the feedneck.

I'm also wondering if the bolt is too far back. Typically you can see just a sliver of the bolt down the feedneck when the marker is at rest. Turning the ram out a few turns from the front block will shift everything forward a bit.


















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[shooter311]

I can't believe I never thought of running a hose form a second cocker to the one I am troubleshooting... This would have saved me so much time so many times! Good tip!

[Jordan]

I had a lot of issues with an Inception bolt in my midblock Trilly. Tons of blowback up the neck, low velocity.

I honestly gave up trying to make it work as a Cocker and pumped it.

I'm interested in seeing what you find. My current Cocker build is completely custom but uses a Trident midblock bolt. I haven't chronied it yet, but I don't seem to have the same issues I did with my Trilly, which makes me wonder if it's a WGP compatibility issue.

[Hellion360]

SO, we have confirmed that is related to timing or tuning.
What type of hammer lug do you have? Square, rounded, or coned?

[oats944]

With it cocked with a tank on it the bolt is stiff to pull back, but does move a little bit. With the trigger held back it’s slightly squishy to push it forward. Feels the same as all the other cockers I have.

Velocity is not up to where I need it. Seems to be maxing out at 240 fps with the stiffest hammer spring and any pressure I set the hpr to. Obviously it goes down if I go too low on the hpr, but never goes above 240 fps. I have some valve springs on the way.

When I held the bolt forward the bolt pin was down in the sled. I stuck my finger in through where the bolt slides out the back.

Not sure if the bolt is too far back, as it can’t go any more forward, but I’ll try anything at this point lol. I’ll try adjusting the ram independently from everything else to test that.

I do have a stock wgp lpr that came off a prostock, maybe I’ll throw that on and see if that changes anything. If not I’ll try hooking up some hose to the Gen-x as described.

Hammer is an inception with a round lug, hitting an inception valve.

If all else fails maybe I’ll try to scoop up a stock bolt.

Thanks again guys, I’ll report back.

[oats944]

Quick update, might be headed in the right direction. I had a couple minutes so I put the WGP lpr on it. Turned up the WGP lpr til it was pretty hard to pull back the bolt. Could only pull it back a smidge til it started to hurt my finger. 2nd ball still popped out of the feedneck, but it arched towards the ceiling without actually touching it, versus shooting off the ceiling with a vengeance with the inception lpr.

[river031403]

You want opposite you want suction tuned 😉
https://youtube.com/shorts/b4ZhSxR9LXY?feature=shared