Inner barrel rotates within hop unit

[The_Lord_Poncho]

I have a particular (M4) inner barrel which seems to rather freely rotate within its ZCI hop unit. The C-Clip is correctly seated, but the rotation of the inner barrel either direction by a few mm is pretty easy without any real resistance at all. Obviously makes centralising the patch for the bucking/nub ect rather challenging - the process of inserting the inner barrel and hop into the outer barrel is enough to move it off centre. Does anyone have any particular tips?

Are there better after market C clips that can be had that work interchangeably with M4 style hope units - perhaps those that are made of a stronger plastic and grip the inner barrel better? A google shows there to be some that Retro Arms produce, but no idea if they would help the issue I am having?

Are there other solutions - shimming, taping etc?

 

[Sewdhull]

It's the fit really and yes some clips fit better than others at least that's been my experience. I have used a little epoxy to pad out the clip so it has no play, but you need to carefully align stuff and then let it cure. In short, I roughed up the barrel flats, degreased em, then put a little epoxy on the flats and put the clip on. Once the epoxy firms up take the clip of and use a knife to tidy the excess. In a perfect world id put the epoxy on the clip but it doesn't adhere as well to the clip as the barrel.

If the barrel and bucking are moving together you can shim the bucking to the hop with PTFE tape. Also make the front part of the hop snugger onto the barrel (where the ring goes in if you have one)

If the barrel is moving inside the bucking you can shim the front part of the bucking to the barrel and make the front part of the hop snugger as above.

 

[Lozart]

I have a particular (M4) inner barrel which seems to rather freely rotate within its ZCI hop unit. The C-Clip is correctly seated, but the rotation of the inner barrel either direction by a few mm is pretty easy without any real resistance at all. Obviously makes centralising the patch for the bucking/nub ect rather challenging - the process of inserting the inner barrel and hop into the outer barrel is enough to move it off centre. Does anyone have any particular tips?

Are there better after market C clips that can be had that work interchangeably with M4 style hope units - perhaps those that are made of a stronger plastic and grip the inner barrel better? A google shows there to be some that Retro Arms produce, but no idea if they would help the issue I am having?

Are there other solutions - shimming, taping etc?

As @Sewdhull mentioned, it's all down to fitment. Some hop rubbers will fit tighter than others, some barrels are slightly bigger outer diameter than others.

You could also look at something like this: https://www.airtechstudios.com/collections/g-g-cm16-srs-7/products/universal-advanced-hop-up-chamber-inner-barrel-ring which will help hold the barrel centred and secure.

 

[The_Lord_Poncho]

Thanks both - some great ideas there! Out with the epoxy and PTFE tape tonight then I think!

 

[simonh]

are you missing the brass barrel ring?

 

[The_Lord_Poncho]

are you missing the brass barrel ring?

No, that was on there, but wasn't the tightest of fits to be fair! I spent some time yesterday playing around with the ZCI hop unit, and just couldn't get it centralised on the barrel - but I didn't go as far as the epoxy route suggested above. What I did notice is that the hop arm was very 'sloppy' in the unit, and could sit at a sideways angle - giving the effect of pressing the nub on one side of the buckings' patch (not something that I've come across on other ZCI hop units, so a little strange that it happening on this one!). I spent some time looking at ways of shimming the arm, but before trying any of it, remembered a Maxx ME Pro hop unit that someone extremely kind off this forum had given to me some months back (thank you @lukeB you legend).  I fitted the Maxx, and the Delrin C clip provided a much more secure fit to the inner barrel, and with no hop arm sideways play at all. I'd heard mixed reviews of Maxx hop units and their incompatibility with lots of rifles, but I have to say that it works fabulously in mine (a SR15 built up using various E&C parts).

 

[EDcase]

I'd try the PTFE tape first.