Hop spring vs rubber washers

[Mad dog 49]

I recently put a barrel centering clamp on the barrel to hop unit interface and it came with 6 rubber o rings to use in place of the usual spring. I've been suffering mid cap syndrome since running epm1 mags and they damaged the tappet plate so the nozzle was pushed out of alignment from bb pressure, but I got rid of them and replaced the tappet plate.

Now the issue is, on a hi cap test mag the rif shoots really well, but any mid cap at all gives me 1 shot that is okay, 3 shots that are crap and go about 30 ft and 2 dry fires on average. On full auto, it works fine with all mags.

Question now is, is there a correct number of o rings to use and thus, using the wrong number has made the barrel to hop unit interface wrong so I'm getting misfeeds or should I ditch them altogether and go back to the spring?

 

[Leo Greer]

Use enough o-rings that you feel pressure when attempting to put the upper receiver back on. Springs are always worse, since they allow for movement except in rare scenarios.

However, chances are that the spring/o-rings are not the cause of your problem. That sounds to me like a hop rubber/hop unit fitment issue, or even a mag issue.

What is the rif and the hop unit and rubber?

 

[Mad dog 49]

It's an ICS CXP Mars, hop unit is stock ICS. I was using a Maple leaf and omega nub, then found the feed lips are too long so I sanded them down and then eventually I threw that in a bin and put a prommy purple in. 

Most recently, I flat hopped the prommy, but it wad a dog to get back into the hop unit even with a little lube.

 

[Speedbird_666]

Have you checked the plastic wheel retaining ring thingy on the back of the hop unit? - one of mine backed out slightly causing a slight misaligment in the magwell, and strange power drop/inconsistencies.

View attachment 106810

This part is slightly revised in shape on newer-manufactured versions of the hop unit, but the priniciple is the same - the two slots are used top screw it in or out.

Might not be your problem, but worth checking anyway?

 

[Mad dog 49]

Do you know what, I never even considered that at all, thanks mate. I thought that was a sealed unit and the slots were to allow a new adjustment wheel to be added. I'll check it when I strip it for post skirmish cleaning this evening.

 

[Leo Greer]

I'm not an ICS expert, so someone correct me if I'm wrong, but don't ICS use a nonstandard spec hop rubber in terms of length of the feed lips, and also a nonstandard nozzle?

You should check out the PDI W-hold--it's a true Marui-Spec rubber, so it's a lot thinner than most of these modern rubbers, like ML. The Prommy purple is a legacy rubber as well, but it's thicker than Marui if I'm not wrong. Maple Leaf is way off Marci-Spec, by the way--they work the best in units like the Maxx, Krytac, and the G&G Rotary that are designed to take larger rubbers.

 

[Speedbird_666]

 but don't ICS use a nonstandard spec hop rubber in terms of length of the feed lips, and also a nonstandard nozzle?

Nope on both counts.

Only Hop rubber i had any real problem with was a maple leaf - which needed a slight trim of the lips. Once done it fit the hop unit just fine - got one with an omega nub in a gun at the moment.  Tested Lonex/Legit TM and others in the past with no problems.

And as for the nozzle - well, I just so happen to have one in front of me. Same length that Negative Airsoft has been selling recently as his preferred M4 length:

View attachment 106827

Source: I have 4 'complete' ICS M4s, a 5th being built at the moment from spare parts on the cheap, and an ICS MP5.

 

[Leo Greer]

21.00 is shorter than standard--most use 21.4, and VFC is 21.2 if I'm not mistaken.

 

[Mad dog 49]

My Bolt used 21.25mm, my ICS is 21.00mm as Speedbird says. I've heard people say the correct one for the ICS CXP is actually for an AK at 19.7mm but out of all 3 of those nozzles, the one that fits and seals is the 21.00mm for the ICS. I've tried all 3 personally. The maple leaf rubber was too long in the lip without a bit of gentle sanding, but the prommy purple would be spot on if it wasn't for a seriously tight hop unit. Even with a small amount of grease on the outside of the rubber and, being very gentle, I can push the barrel clean through the rubber before it is fully home.

 

[Rogerborg]

Even with a small amount of grease on the outside of the rubber and, being very gentle, I can push the barrel clean through the rubber

View attachment 106859