M16 bolt problem

yes I know its aluminium .."real steel" means from a real M16 lol

DOC

I know, I know It was meant as a little joke

I took another look at the mag and when I looked closer, I saw that the cut-outs were made by hand.
They weren't there originally.
Anyway, this mag works perfectly

smootik wrote:

Hmm, so the difference is most likely with the bolt. Maybe it still does not go forward as much as it should, so extractor does not have a chance to "push" on cartridge and slip over its rim to grab it.

Correcting myself - XM177 extractor does NOT slip over the cartridge. Cartridge has to slide under extractor claw while it is fed from the magazine.

In any case - I am at point 3) of my list now, a bit frustrated ;-)

Magazine is giving me a lot of woes:
- the insert that takes place of "bullets" was diving inside the magazine. Cartridges hit front wall of magazine instead of sliding up to the chamber. Making cutouts in the front wall helped, but...
- now the insert is falling out of place, as the upper end slips over magazine wall and jumps up, wedging inside magwell.
- also when cartridges sit correctly in magazine, their back hits bolt stop "wedge" while magazine is loaded, and block feeding. I need to either release bolt stop before loading magazine, or shift cartridges towards the front of the magazine.
- the last two cartridges cannot be picked up from the magazine by the bolt, it goes over them.

Extractor is acting badly too:
- there was not enough clearance betwen claw and bolt head. Cartridge rim is 1.2mm, while extractor claw left only 0.9mm of space. In this design claw does not slide over the rim, so extractor had to be rigged. I used a small steel shim (0.4mm) glued inside extractor groove to prevent extractor from going so far back.
- it bent itself, not outwards but to the side, apparently it is stressed while in "stretched out" position. I guess this might be due to blocking on a misfed cartridge. Unbending does not work due to thickness (and fear of breaking that part), fortunately it still operates correctly.




Judging by scratches from bolt head near chamber area, this area is either too small for bolt (as was in your case), or bolt is misaligned during travel and has to slide/scratch along a wall to get into right position. Manual cycling of a bolt in upper shows that there is some sideways travel, it jumps when nearly entering the chamber. Still to be verified.

I am now in situation where I have either correct feeding, ejection, or blowback (with two caps only, and only on semi), but not (yet) all at the same time ;-)

Working with a model makes me appreciate how much work goes into designing them, as well as designing real firearms.

I also still have problems with the Marushin magazine.
I recognise all the problems you describe. Same here.
The little things I did to my mag made it a little better, but it still doesn't work correctly.
The real steel mag that I have works perfectly...

I fixed most feeding problems by slightly bending mag lips, polishing and repolishing follower, creating rounded slots in front wall.

Insert still falls out. When bent, it keeps inside for some time, but eventually goes out again after cycling 10-15 carts.

I added plastic tab to the bottom of follower, but I'm not sure it helps anything. Bolt stop still doesn't work for the same reason as previously.

Thanks for info on real magazine, I have ordered now a 20-round real one

On a positive note model started to fire correctly, if erratically. It is now possible to fire all 5 cartridges on semi, though there is sometimes more than one fired on a single trigger pull (as often as every other pull).

I am experimenting with cap configurations. Single 7mm does not blow back the bolt. Empty cap + 7mm cap does not improve the situation much, but bolt moves a bit further. Two 7mm caps work the best. 7mm + 5mm both facing downwards seems to work good, but compared to 2x7mm there is more discharges on chambering. 7+5 facing towards each other is even more problematic when chambering.
Note: in my manual option to use 7+5 is now covered by a black sticker, only 7+7 option is shown.

Bolt seems to have shaved off enough excess to move much more smoothly now. A bit more polishing of rough edges inside receiver helped too. I noticed that two pins, for bolt head and for firing tab, creep out of their holes. As soon as they raise above surface, trouble happens. I now do a complete inspection after every cleaning and before every shooting, or rather longer cycling, as I am nearly out of caps.

Charging handle pin moves out towards the bottom and scratches receiver, it has to be inspected and re-seated periodically too.

Stock tube has two interesting problems. One is that the ring with flap supposed to block tube rotation has too large internal diameter, and tab supposed to fit into tube slot doesn't reach that slot. This means that tube rotates quite freely, resulting in stock sticking to one side ;-)
The second problem is that tube cannot be screwed in deep enough for the stock to be in right position. When it is unscrewed to align stock, it allows plunger inside lower receiver (the one that stops bolt buffer from jumping out) to sit too high and it destructs bolt buffer front face.

There are wear marks on aluminum parts, as expected in a model that is not sitting on a shelf ;-) Many of them are due to me missing assembly problems, but some are sign of normal usage. Especially hammer face is deteriorating quicker than expected, as it hits metal firing tab.

Bolt face hits chamber, at least when cycling without a cartridge. I guess there is nothing to stop bolt when it slams forward, so it stops on chamber.

In any case I feel I am moving in the right direction, and my understanding of the model is greatly enhanced :-)
Kit gives a feeling of "tinker with me" and encourages experimenting.
Information that you, JohhnyV and others posted here also helped me a lot, both technically and for not feeling alone with my XM177E2 problems :-)

The answer for the stock tube and plunger part #75 is to use a sheet of course sandpaper to remove some material from the face of part #178 untill it is the correct thickness to allow stock to sit straght and hold plunger in correct position
lay sand paper flat on bench and rub part #75 over in to take off material, boring but effective

For the bolt face problem drill a small hole in the center of the hammer face and tap a counter sunk screw in there untill flush with hammer face, allowing this steel screw to take up the force of the hammer hit

Ahh the Marushin 16s they look and feel great but are a pig to get going.

I can't add much to the posts but I've found these work well in the 30rnd mags
http://www.midwayusa.com/viewproduct/?productnumber=633504

The only mod is to cut the back as it is too high and trips the bolt hold open catch when the last round is in the mag. Sadly they don't fit the 20rnd mags because of the extra feed lip on the mags internal face.

The "gold" mag looks like it's been modified to fit MGC .223 rounds

8ace

Thanks for hints :-)

Making part #178 thinner seems a good solution! I got fixated on making threads run deeper instead of doing the opposite. This should solve plunger problem.

Before working on hammer I need to secure a spare one just in case - I don't have any experience sinking screws in a metal object ;-)

Surprise, surprise... my XM177E2 model now works well on semi and auto! At least for 5-cartridge bursts (until I get more of these).

What remains is to fix functionality in "safe" mode ;-) By that I mean esthetical/quality fixes for foregrip/receiver wobble, stock tightening and strengthening the hammer.

The key was to adjust all elements step by step: bolt, ejector, extractor, rough edges of receiver etc.
The second part was (I think) moving bolt by hand to do "break-in" and ensure it adapts to shape of receiver, combined with inspection of all parts for wear to notice problem areas and correct them.

Well done mate!! ENJOY!!!

smootik wrote:

Surprise, surprise... my XM177E2 model now works well on semi and auto! At least for 5-cartridge bursts (until I get more of these).

What remains is to fix functionality in "safe" mode ;-) By that I mean esthetical/quality fixes for foregrip/receiver wobble, stock tightening and strengthening the hammer.

The key was to adjust all elements step by step: bolt, ejector, extractor, rough edges of receiver etc.
The second part was (I think) moving bolt by hand to do "break-in" and ensure it adapts to shape of receiver, combined with inspection of all parts for wear to notice problem areas and correct them.

Well done smootik Goes to show what attention to detail and careful preparation and assembly can do
Get yourself some more cartridges ... let's see how it behaves then

I'm certain there's a thread here on receiver wobble... I think Madmike had new receiver retaining pins made to tighten everything up. From what I can recall he succeeded

There are several solutions mentioned on the forum. New receiver pins are probably the best way. I will go for an o-ring around the rear lug. Tried it with a piece of rubber string wrapped around, now need to find something that fits better and can be left there permanently.

I have now procedures and advice for improving hammer and stock, it's now a matter of finding the time ;-)

Your perseverance paid dividends; and your posts will be invaluable to us all!
Good work!

Kiwigunner

JohnnyV wrote:

The answer for the stock tube and plunger part #75 is to use a sheet of course sandpaper to remove some material from the face of part #178 untill it is the correct thickness to allow stock to sit straght and hold plunger in correct position
lay sand paper flat on bench and rub part #75 over in to take off material, boring but effective

Boring, but effective :-)

About 0.3-0.5mm had to be taken off. I used a coarse paper (180) and it didn't take too long. Surface is also fairly polished. It required some attention to make sure thickness was reduced uniformly.

Yes very very boring

BTW did you manage to do it without sanding your finger tips as well??

ATB

I preferred not to admit that ;-)