Gun shooting off to the right + feed issue

[RostokMcSpoons]

My Classic Army M15a3 shoots off-line.

It's about 30-40cm off to the right at 15m.

I don't think it's anything to do with the hop as the BB's are flying straight.

When the barrel nut isn't tightened down fully I can feel some side to side wobble when holding the barrel back against the receiver, I think when the nut is tight it's wobbled off-line and stays there.

In the past I've shimmed the barrel with a couple of mm of plastic wedged into the right side between the barrel and receiver, to improve, but not entirely fix it, but that can't be ideal, surely?

So I'm wondering if the better option is to try to flatten the end of the receiver's thread, I don't think it is completely square.

It's that a silly idea?

Also the gun tend to feed poorly on full auto.  I asked the tech at my site to fix it, he failed, it seems.  I have multiple hicap magazines, maybe it works better with some than others, haven't tried them all in turn to prove that. 

I have tried fiddling with the two screws on either side of the barrel on the lower receiver, not sure what they are supposed to do, nothing seemed to move!

Are there any other things I can try to fix it?

It's definitely worked ok on full auto in the past, so it's*nearly* working correctly

 

[Tactical Pith Helmet]

Has it always done so?  If not, look at the last thing that you did to it.  

Two of my M4s have a badly supported barrels.  Everything being square, they achieve far better accuracy than yours though.  

Consistent bating to one side could be all sorts from seating to the BBs clipping something.  If it's un-buggered about with I'd take it apart and carefully re-assemble before removing metal etc.  

 

[Adolf Hamster]

Consistent bating to one side could be all sorts from seating to the BBs clipping something. 

Click to shrink...

possibly some dirt/scratch in the inner barrel? usually clipping tends to be more erratic than this sounds.

alongside the usual suspects of the sights/sight mountings all being tight and square too.

does the barrel look off when tightened down? eg compared to the line of the reciever/stock?

same applies to if the barrel is even straight, if it's maybe taken a knock at some point.

one possibility might be to try a thin o-ring squished between the barrel and receiver (thin as don't want the barrel pushed too far forward). might help, might not, but if it doesn't then no harm done.

If it's un-buggered about with I'd take it apart and carefully re-assemble before removing metal etc.  

Click to shrink...

yes indeed, removing material is always a last resort. be hesistant to think you'd be able to improve things without being really damn careful or using proper machine tools (and even then mounting an AR upper square in a lathe isn't a task i'd envy)

 

[RostokMcSpoons]

Cheers guys.

I had another long look at this.  

Checked the inner barrel.  But that's fine.  Last time I took the receiver apart, I checked the hop as best as I could, all looked lined-up. 

The outer barrel has definitely gone owt askew on treddle.  It's noticeably pointing to the right compared to the receiver.

So I've shimmed it again, with some thin plastic (about 1mm thick).  I put a little more around the barrel on this attempt, so it's now about 30% of the right side of the barrel / receiver interface shimmed.  
I tightened the nut up as best as I can (using a monkey wrench, my cheap 'AR Tool' doesn't seem to fit the barrel nut on this)

It's now shooting pretty good with the standard M16 iron sights in the carry handle. I have the peep hole centred left/right and it's bang on. 
(On my last shimming attempt it was wound all the way over to the left)

If I put the Kobra on it's noticeably off for elevation and windage, and outside of the adjustment range for either.  Quite odd. 

I've also tried different mags in the gun to see what's up with the feeding.  One of them will feed quite well in full auto for a 5-6 shot burst before going into "I'll fire a BB when I damn well feel like it" mode, shooting one BB for every 4 or 5 cycles.  Semi is nailed on though.

I tried the new mag I got with the F2000.  That things is definitely weird.  It won't fit in my DE M906, but fits fine this gun.  But feeding?  Nope.  I had BBs tumbling out of the end of the barrel or shooting 10m.  
So the gun is finicky on mags.

I might try shimming the mag well with a couple of bits of Velcro to make it a little more snug.

Any other adjustments I can make? 

Would a new ZCI hop unit be a sensible investment that might cure it?  New nozzle?

 

[Adolf Hamster]

hmm, that sounds extreme for an ar reciever to be off by, but if it works it works.

the feeding thing kinda sounds like it may be the ol' lack of delayer chip/weak mag/sticky ammo combo.

easiest thing to try would be the ammo- refill the mag with something different see if that helps, although usually it's a symptom seen more on midcaps rather than hicaps (as midcaps tend to be double stack store single stack feed).

 

[RostokMcSpoons]

I've tried all sorts of different ammo through this, it's shown the behaviour off and on (mostly on I'd say) since the day I got it, all those years ago.  

I took it back to the seller, and they fixed it... temporarily.  Unfortunately I don't know what they changed! 

Edit:

I set up a proper target and did my usual ~30 shot string.
They're still off to the right by a couple of inches at 15m.  (I must stop mixing imperial and metric, but I'm "that age" )

Just goes to show that 'eyeballing the shots' fired off-hand isn't an exact thing, need to bench-rest and track the hits on paper.

Mind you the battle sights aren't very exact either.  Damn peep holes wouldn't flip over so was using the large diopter.

Anyway, the group size was pretty good, considering the sights and the gusty wind. About the same as my DE, 3" wide, 4" high, one flyer to the left.
260-270fps with 0.20g which is consistent with previous chrono tests, but a bit more variance at +-5fps than I'd ideally like.

Firing full auto again revealed some 'unpleasantness', I think I had double or half-feeding occurring, as a couple of BBs flew very oddly from the barrel. Jiggling the mag forwards and backwards made it worse so I'll shim the mag well both front and back.  I don't think that will fix it though.

 

[Adolf Hamster]

fair enough, always worth checking the ammo/mags, i've "fixed" plenty of pews simply by putting some decent ammo in them.

given it's primarily an auto issue, i'm still leaning towards tappet delay, if it doesn't have a delayer chip then the nozzle will return to battery before the mag has had a chance to feed the next round.

other potential culprit is hop feed lips, but that'll usually manifest in semi too.

 

[SBoardley]

On the barrel front as @Adolf Hamsterasked…is your barrel straight? Long ago in a distant universe I bent a barrel jumping out of a bunker while being chased. I was gutted; gave it to a tech who fixed it. I asked him how, he replied simply, that he’d just bent it back. Simple. 
as for mag feed, while I seldom use aegs, I remember having feed problems with a G&p  again long long ago. I was trying to get the star low caps to work in it. 
again as Adolf said it could be a timing issue or it could be a hop issue. 
Question: when you put your finger down the mag well, can you move the hop up forward and backwards ( direction of barrel and stock)?

 

[RostokMcSpoons]

On the barrel front as @Adolf Hamsterasked…is your barrel straight? Long ago in a distant universe I bent a barrel jumping out of a bunker while being chased. I was gutted; gave it to a tech who fixed it. I asked him how, he replied simply, that he’d just bent it back. Simple. 
as for mag feed, while I seldom use aegs, I remember having feed problems with a G&p  again long long ago. I was trying to get the star low caps to work in it. 
again as Adolf said it could be a timing issue or it could be a hop issue. 
Question: when you put your finger down the mag well, can you move the hop up forward and backwards ( direction of barrel and stock)?

Click to shrink...

The inner barrel looks straight to me!   Which is good, I wouldn't fancy trying to bend a barrel

The spring that sits in front of the hop unit and pushes it and the barrel back onto the nozzle is present and working (I can lever the hop unit forward and it springs back ok)

In the mag well.. no the feed tube is locked in position.  It's a shaped piece sitting in a same-shaped hole (square one end, round the other - see photo below), there's definitely not meant to be any movement there.  Neither does it move up and down relative to the rest of the gun.

What I can see through the feed tube is the end of the (metal) nozzle.  Looking up inside the DE it looks the same, so I don't think that's an issue.  The DE doesn't have the plate with the shaped hole though, so that's different.

Neither does the DE have the two screws on either side of the feed hole.

View attachment 83197

The tops of the small Philips screws which are highlighted are only accessible when the receiver is split open.

I watched a video about fixing the very issue of bad feeds on full auto, and the tech seemed to move these screws.  I tried it, didn't seem to do anything (either visibly moving any parts, or in the results).

Edit:  
Well I had to give it another go.  So I split open the receiver and had another poke about.  Given that slackening those two screws did approximately sod-all, I went the other way and tightened them all the way up. 

And bingo - it's not perfect (I suspect the mag isn't really shoving those BBs up hard if its not fully wound) but damn, it's consistently feeding for the 5 round bursts I use in game. I even managed a couple of longer bursts ok.

I think that'll do!

I don't think my gun is the same as in that video - it looks like I'd have to shim the feed tube up if I wanted to close the gap to the hop / nozzle...  it expects to always have the screws tightened down so it can't move around during full auto firing - which is what was happening, I guess.

 

[SBoardley]

Sweet. Glad you sorted it. As far a barrel goes, do you have an outer barrel that you can swap out to see if it makes a difference?

Also…. You could try a G&p mag release, these have more material on the upper of the tab which, if you do have a gap between the base of the hop and the magazine, will pull the mag higher…pic is of me fitting one to an ics but doing the opposite ie removing material…

View attachment 83198

 

[RostokMcSpoons]

Interesting... I hadn't thought of the mag release at all really, and that perhaps relates to an issue I had but hadn't mentioned:

The first few times I inserted the mag to test out the newly tightened screws, I heard the "Bzzzzzerrrppppp" Of Death as the spring unwound itself. 
I put that down to the velcro I'd stuck in the magwell, to locate the magazine a little more firmly, changing the angle the feed tube hit the top of the mag...  but perhaps tightening the screws down has moved the feed tube down slightly.  Something not quite right there now anyway, I'll try without the velco perhaps.

However, a more 'kinetic' approach to inserting the magazine (fast and hard sir?, suits you!) seemed to do the trick, not giving anything bad a chance to happen

Fine margins between success and failure with these pew-pews!

 

[SBoardley]

Yeah. I had heat a knife and alter the position of the mag indent to get these to work… see pic

also check out @Rogerborgtech post which is kind of relevant to your issues 

View attachment 83199

 

[Adolf Hamster]

Fine margins between success and failure with these pew-pews!

Click to shrink...

indeed it is.

sounds like maybe with the barrel being off horizonal it might also have been off in the vertical, which ended up causing rubbing on the nozzle, so tightening the hop unit down has helped pull it back into alignmens.

surprised that only really manifested in auto though.

 

[RostokMcSpoons]

Yup that's a thought actually.   

I mentioned previously the Kobra was way off on the aim, that was more vertical than horizontal, with the shots hitting lower than expected, so yes it's quite possible there's a little bit of barrel droop I need to correct too. 

 

[Adolf Hamster]

Yup that's a thought actually.   

I mentioned previously the Kobra was way off on the aim, that was more vertical than horizontal, with the shots hitting lower than expected, so yes it's quite possible there's a little bit of barrel droop I need to correct too. 

Click to shrink...

is it a RS (or at least, an RS-intended repro)?

as if so then there is an element that the zeroing range on RS optics is a lot less than you'd typically see in airsoft due to the expected level of base precision.

doesn't mean there isn't droop, just that it might not just be that.

 

[RostokMcSpoons]

Yeah it's RS.  It zeroes ok with the DE though

 

[Tactical Pith Helmet]

Maybe a silly idea, but is your hold consistent?   I hold my M4 around the magwell, I daresay that the crap barrel support would shift poi upwards if I gripped the barrel.  

Could that account for any vertical shift?  Might be something to look at before pulling the thing around again. 

 

[RostokMcSpoons]

It's a very good point, but given the problem seems to be hitting low and my holding by the barrel should impart an upward inflection, then I think it's a negligible difference

I have to say once it's all tightened up it feels very solid, there's no obvious flex between the barrel and receiver in any direction

I'm going to add an extra shim in at the 5 o'clock position, try to push the impact point up and slightly left.

 

[RostokMcSpoons]

I decided that with the red dot and the iron sights not aligning, and now the barrel looking slightly left-ish if anything, I'd start again. 

So I removed the 1mm plastic shims I'd put in, and made a semi-circle of velcro (the hook side, it's more uniform) and shimmed with that, favouring a bit of upward push to go with the leftward push.

Once I'd checked the red dot, centred for windage was good, I undid the grub screw on the front sight, and tweaked that a little so it's flush under the red dot.  I then put the carry handle / iron rear sight back on, and 'bingo', good zero with both the Kobra and the iron sights.

I think it's fixed

Obviously things might be shown up as crap once I change the distance and start shooting at the 40m+ targets at SpecialOps, but for the moment I'm happy I've got a usable gun that I can take as a good backup again.

Thanks all for your input  ?   

Two guns sorted, two to go... ?