I decided to start a new thread to hopefully get more people to read this.

I have a RRA style (same parts but not bought from RRA) 9mm upper, VM Hytech mag block and a Bushy lower. 9mm hammer and buffer.

Originally I had only USA Magazines. Even with them the gun worked fine for a few hundred rounds.
I really want to stress this:
The gun worked fine for a few hundred rounds.

This is why from the start I wasn't  too convinced that this was a magazine issue.
How could the mags become an "issue" suddenly after first working quite well?

Anyway, that seemed to be the only explanation anyone could come up with, so I spent some serious time, effort  and money to get better mags and ended up with Mec-Gar ones.
I tried them finally today and the problem still persists.

Sometimes the gun will fire up to 20 rounds without problems. Sometimes it misfires several times in a row. Most of the time I get maybe 4-5 misfires for 20 rounds.
When it misfires, the primer will have a light strike mark.
When I pull the bolt open after a misfire, the cartridge usually sort of stays halfway in the chamber, the extractor doesn't pull it all the way out. If I then let the bolt slam closed on it again, it will usually fire.
I noticed today that at least some of the misfired cartridges have had the bullet  pushed a bit into the case - some kind of partial misfeed which takes enough velocity off the bolt to keep it from closing properly?

Couple of other points that may or may not tell someone something:
I can't see anything wrong with any of the parts of the gun when I take it apart, including nothing I'd interpret as unusual wear, scratch marks or anything like that.
The mag block is an extremely tight fit in the lower, takes force bordering on violence to insert and take out.
The USA mags are very difficult to insert, they don't want to lock properly. I tried to file the mag catch hole on one, but it didn't help. After I filed a bit more, the mag now misfeeds 100% of the time.
The Mec-Gar magazines are also a bit tight fit in the sense that it takes a bit of force to get them to lock, but not nearly as much as the USA ones.

To me it would seem that something keeps the bolt from closing properly sometimes, and then the hammer hits the bolt and not just the firing pin, and the gun misfires. But what causes it and what to do about it? Or could it be something else?
I'm all out of ideas and getting so fed up and frustrated I'll soon be tempted to just bury the damn upper in my gun safe and try to forget it exists

Get a Hahn or Colt bottom load mag block and Colt mags. Your set-up sounds way too tight in the mags and mag-block. Thats how I have my AR set-up and everything works smooth, mags go in easy and lock positively. Functions 100%. You will also have a bolt open open after the last round and may people use this set-up just for that reason alone.

Well, it sounds like you've ruled out the mags as a probelm and the block is the next logical thing to look at.  Does it look at all like the rounds are impacting the front of the feed ramp?  Maybe a little file work would be cheaper than a new block and since it doesn't work now I don't think you have much to lose by trying.  As well, I'd probably hit the inside of the block itself, since it sounds like your mags are WAY too tight.

If you are getting light hits it might be a little bolt-bounce.  What buffer are you using?

Look at your bolt... remove the roll pin for the extractor, and be sure it is a "split" type roll pin, not 1 of those rolled up piece of crap...  Make sure the pin is extra long enough to fill the hole in the bolt. Some have used short pin and being on center become more critical to hold extractor..

Look at the bolt face, measure the depth of the pocket that the case sits in, depth should be .125".  Idaelly the case shold protrude from the barrel face .125-.130".....

With upper off the lower:

turn it over so you can see the bottom of the bolt-case-chamber interface,

Now drop a live round in the chamber, and install the bolt in to the upper (without the extractor !!!!)

Look in the small openiong at the case to face in bolt fit, the case should rest on the bolt face when bolt is closed, if you have a gap from bolt face to case, headspace is deep, and fire pin energy will be lost having to travel the extra distance (I know, the fella that made my barrel goofed up, I had .027" too miuch).   Even better is to have the bolt rest on the case, and have a slight gap between bolt body face and barrel face,  I run .005 so when it get dirty, dirt will simply squish out, and no extra thump when using a suppressor.

Start here ,  report back.

In regard to the mag block fit.... open the upper, then install the block, then close the upper to lower. the downward pressure sorta locks the AR mag release so you do not dump it readily if you try to actuate the AR mag release.

I second SBR11_7's advice to install the block with the AR halves open.  I experienced multiple misfeeds when I first got my block, also with the symptom of the bullet being pushed down into case.  What I also noticed was the bullet would get a mark on it, and finally realized that during the process of the bolt stripping a new round off the mag, it would impact just past the feed ramp before chambering.  hock.gif

Then, after a *click* no bang, I would extract the round and see the above.  After I inserted the block like SBR11_7 described, no more FTF, bang w/ each trigger pull...  (Until I had that problem with my firing pin hole I described to you in your other post he
Hope that works!  

Is this happening when running full auto only or happens even in semi?

First of all, thanks for taking the time to reply.

Couple of shorter answers to start with:
It's semi only.
Buffer is a heavy counterweight one, the type designed to kill bolt bounce.

Quoted: not 1 of those rolled up piece of crap...  Make sure the pin is extra long enough to fill the hole in the bolt.

Of course it's a short rolled up pos. No idea where I could get a better one here in Finland.
What kind of places sell them (in addition to gun shops and gunsmiths who deal with ARs)?

Look at the bolt face, measure the depth of the pocket that the case sits in, depth should be .125".

Yep, it's about that.

Look in the small openiong at the case to face in bolt fit, the case should rest on the bolt face when

D'oh!



The pic is not the best but neither is the macro of my camera.
Looks like there is a gap between the bolt face and the case. Maybe like half a millimetre (.02").
The cartridge pictured is one of the Magtech ones I've been using. I measured the case, it was 19.02mm (.749").
Is that enough excess headspace to cause a problem? I'd think so based on what you wrote about your own gun. Could it be corrected by for example taking the bolt to the nearest machinist and have a bit shaved off the face? What would be the correct procedure?

Then onto the mag block.

As I wrote, it's an extremely tight fit in the Bushy lower. If it was any tighter, I'd need a hammer to insert it and a crowbar to pry it out. I read somewhere on this forum that someone with a Bushy lower had the same issue. Should I file/sand it down a bit? And where? The big "shiny pad" on the right side?

There is noticeable gap between the lower part of the block and the magwell. I know this is at least somewhat "normal" but is the gap on my gun larger than average?



Here's a closeup with the bolt held back, the block in place and a loaded mag inserted.
Does it look like everything lines up as it's supposed to?



One more pic. You can see a horizontal line a little below the chamber. It shows where the front edge of the mag block fits against the breech face. Is it that low in other people's guns too?



A couple of points. AR-knowledgeable gunsmiths are very few and far between here in Finland so any reasonable "home remedies" you guys can think of would be immensely preferable to suggestions of "take it to a  good gunsmith".

Also I've already spent much more money on the gun than I ever had any intention to. So I'm really not too keen on buying a new mag block just to see if it would happen to make a difference. Or a new lower, for that matter. Also they are not available here in Finland, and ordering either from the States would be very difficult, time-consuming and expensive.

So I think I'd like to try to modify the VM block to fit better, any suggestions on that are very welcome.
Also, what to do about the excess headspace, if it needs to be addressed?
Any other ideas?

Thanks, guys!

Quoted: First of all, thanks for taking the time to reply. Couple of shorter answers to start with: It's semi only. Buffer is a heavy counterweight one, the type designed to kill bolt bounce. Quoted: not 1 of those rolled up piece of crap...  Make sure the pin is extra long enough to fill the hole in the bolt. Of course it's a short rolled up pos. No idea where I could get a better one here in Finland. What kind of places sell them (in addition to gun shops and gunsmiths who deal with ARs)? Here in the States, a local hardware store or auto parts store, just need the part or size of the pin, nice thing about the AR, pins are std sizes (diameter), just odd lengths Look at the bolt face, measure the depth of the pocket that the case sits in, depth should be .125".   Yep, it's about that. Look in the small openiong at the case to face in bolt fit, the case should rest on the bolt face when D'oh! personal.inet.fi/koti/simon_siivut/aseet/headspace.jpg The pic is not the best but neither is the macro of my camera. Looks like there is a gap between the bolt face and the case. Maybe like half a millimetre (.02"). The cartridge pictured is one of the Magtech ones I've been using. I measured the case, it was 19.02mm (.749"). Is that enough excess headspace to cause a problem? I'd think so based on what you wrote about your own gun. Could it be corrected by for example taking the bolt to the nearest machinist and have a bit shaved off the face? What would be the correct procedure? Looking at the case in the bolt pic, all looks well, but really need to measure the case projection from barrel face.   My barrel face sits just below the surface in the upper, not much, but  not even. Do not machine the face of the bolt, that has to stay the correct OAL on the body. If the case is too deep, simply face the barrel in a lathe to get correcect projection, then face the barrel ring to set barrel back into the upper to maintain the flush surface, and the bolt remain even with rear of the upper when bolt closed. Then onto the mag block. As I wrote, it's an extremely tight fit in the Bushy lower. If it was any tighter, I'd need a hammer to insert it and a crowbar to pry it out. I read somewhere on this forum that someone with a Bushy lower had the same issue. Should I file/sand it down a bit? And where? The big "shiny pad" on the right side? There is noticeable gap between the lower part of the block and the magwell. I know this is at least somewhat "normal" but is the gap on my gun larger than average? Gap will vary from different lowers (manufacturer tolerance), as the depth of the magwell is not identical from 1 lower to the next.  I had to swipe a file across the bottom of my OLY to let the block in far enough to engage with the AR mag catch personal.inet.fi/koti/simon_siivut/aseet/vm-gap.jpg Here's a closeup with the bolt held back, the block in place and a loaded mag inserted. Does it look like everything lines up as it's supposed to? personal.inet.fi/koti/simon_siivut/aseet/feeding2.jpg One more pic. You can see a horizontal line a little below the chamber. It shows where the front edge of the mag block fits against the breech face. Is it that low in other people's guns too? personal.inet.fi/koti/simon_siivut/aseet/face.jpg A couple of points. AR-knowledgeable gunsmiths are very few and far between here in Finland so any reasonable "home remedies" you guys can think of would be immensely preferable to suggestions of "take it to a  good gunsmith". Also I've already spent much more money on the gun than I ever had any intention to. So I'm really not too keen on buying a new mag block just to see if it would happen to make a difference. Or a new lower, for that matter. Also they are not available here in Finland, and ordering either from the States would be very difficult, time-consuming and expensive. So I think I'd like to try to modify the VM block to fit better, any suggestions on that are very welcome. Also, what to do about the excess headspace, if it needs to be addressed? Remove the barrel, and simply trim the barrel face and set the barrel back.  All easily done by somebody with a lathe, and an uderstanding of what supposed to happen/how it should fit. Any other ideas? Thanks, guys!

Quoted: Looking at the case in the bolt pic, all looks well, but really need to measure the case projection from barrel face.   My barrel face sits just below the surface in the upper, not much, but  not even.

The projection is very difficult to measure 100% accurately at least with the caliper I have (can't reach all the way from the top). But  as fas as I can tell it actually is about .125" as it should.
The barrel face is just about as flush with the upper as it can be.
So maybe that's not a problem after all.

I guess I'll have to concentrate on the mag block for now.
Hopefully someone comes up with more suggestions about how to mod it.
Also would like to hear some comments about the fit as seen in the pics above.

BTW is the Hahn block really a 100% sure cure-all that always works flawlessly?
Also with that I'd have to - once again - get new mags too
So hopefully that won't be the only option.

I see your problem.  The radius on the barrel is not enough so some rounds catch on the edge and the drag causes the bolt not to close 100%.  This upper looks like it was put together from parts.  There are two ways to fix this.  The simple one is to try an extra power hammer spring and clip 2-3 coils off the firing pin spring.  The more work fix is to grind a slight feed ramp onto the barrel.  This can be done if you have stones with long shafts or the barrel has to be removed.  That slight bolt gap with the round in is OK; you don't want to change this as it'll move the primer further from the firing pin.

Originally Posted By Hail Mary: I see your problem.  The radius on the barrel is not enough so some rounds catch on the edge and the drag causes the bolt not to close 100%.

Naaaa, my chamber opening is square with the barrel face....  Mine runs fine, even on a borrowed M16 lower.  Nice looking radius though.

Joeblack posted something a while back where he said he has seen a burror something on the extractor lip that gave some sort of problem.   I would kinda like to see this upper and test drive it myself.... but rather cost prohibitive to do in this case.

Quoted: I would kinda like to see this upper and test drive it myself.... but rather cost prohibitive to do in this case.

Yeah, I'd like to have someone more knowledgeable have a look at it too but I think I'm not going to hold my breath waiting for that to happen

Sorry if I sound like a broken record but again I feel that one thing has been sort of overlooked.
As I wrote in the first message of this thread, the gun worked fine for a while.
The problem started at the range when I had just fired about 200 rounds without any problems. I had my last mag in it, loaded with 20 rounds. 18 fired without problems, and then the misfire problem presented. As those were the last couple of rounds, I didn't think much of it then and just went home. I cleaned the gun thinking it was probably just dirty and the problem was caused by that. But next time I tried it, it still kept misfiring.

My point being that I feel that "something happened" which caused the problem.  Would seem logical. The problem is that I can't find any broken parts or anything. Can anyone think of anything that could be broken so that a "non-expert" like me could miss it? Or maybe it's something so obvious no one has thought it might be necessary to suggest it because I naturally should have checked it right away? Please feel free to assume I'm a total idiot if it helps

The only other explanation I can think of is that there is a small but critical misalignment in the "feed geometry" of the gun. The upper, lower, mag block and the mag are somehow not quite properly aligned. This causes the rounds to misfeed sometimes (or all the time, but not always enough to cause a misfire) so that they hit the breech face or something instead of chambering properly and then the bolt won't close properly and a misfire occurs. Somehow this just didn't  start right away but took a few hundred rounds to develop.
Modifying the mag block to better fit the lower (and the mags?) might help if this is the problem but I'm a bit apprehensive about just filing away at the block without any clear idea of what I should try to do... So any suggestions on that are still as welcome as ever.

Carefully grind a lead in your chamber. A little at a time.  The ammo not feeding correctly slows the bolt down and then the bolt doesn't have enough energy for the extractor to engage. If you don't re load, grind away.  If you grind a lot the cases can bulge in this area.  If you re load, grind very little at a time and try it out.



Looking at your pics, I would bend the followers a little so the ammo is more horizontal coming out of the mag.

Use a blue lay out dye or black magic marker.  Mark the rims on every case for a whole mag.  Shoot the gun. Is the extractor engaging correctly?  If not look at the head space. The extractor will remove the marker and reveal its travel.  Since it was running then stopped, I'd remove the extractor and see if it is bent or has a burr on it preventing it from engaging the rims correctly.

Looks like your end of the barrel face is dirty from shooting. The bolt might not be traveling forward as much now because of the residue, so you could have a head space issue now if it was marginal when it was clean.....

IMHO

Quoted: Carefully grind a lead in your chamber. A little at a time.

Would appreciate more advice on this, like what tools to use. Hail Mary earlier suggested it might be possible to do this without taking the barrel off the upper. Would be preferable as I don't have the necessary equipment (and it would be rather costly and difficult to acquire).

Use a blue lay out dye or black magic marker.  Mark the rims on every case for a whole mag.  Shoot the gun.

This is a bit difficult as there is two feet of snow at the range and the hot cases pretty much disappear into it instantly. I guess I could try to fashion a temporary brass catcher out of something...

Since it was running then stopped, I'd remove the extractor and see if it is bent or has a burr on it preventing it from engaging the rims correctly.

When I took it ouf of the bolt (first time ever) to check the headspace,  I noticed there was quite a bit of gunk in its hole in the bolt. Could it have a big effect on its functioning? I cleaned and oiled it to the best of my ability, didn't notice anything suspicious about it otherwise.

Looks like your end of the barrel face is dirty from shooting. The bolt might not be traveling forward as much now because of the residue, so you could have a head space issue now if it was marginal when it was clean.....

When the problem first started, the first thing I tried was to carefully clean the gun but it didn't have any effect on the issue.

Today I again cleaned the gun thoroughly, lower and mag block too, paid special attention to the extractor. I also filed the mag block to fit into the lower somewhat easier, it's still very snug but no outright violence is needed to insert it or take it out.
I'd be pretty suprised if this had any effect but I'll take it to the range to try it out once more.
After that I guess its onto the ramp business, possibly with an extra power hammer spring and couple of coils off the firing pin spring for good measure?

BTW did I mention that I tried some hollow points in it also? They misfeed 100%, seems like they always hit the breech face or something and have the bullets pushed into the case. This might be further encouragement towards making the feed ramp?

Well. Took it to the range today and the damn thing worked flawlessly. Put 200 rounds through it.
Even when I loaded the Mec-Gar mag with 30 rounds, no problems whatsoever.
Only when I tried a USA mag, I got one misfeed but even that was clearly a misfeed and not a misfire.
Maybe it was the extractor despite my earlier attempts to clean it, or maybe the mag block adjustments helped. Or both together. Or maybe the planets are aligned the right way at the moment, or the solar wind is milder than normally...

Thanks for your help and encouragement.
(Still, wouldn't mind hearing more about the feed ramp business..?)

Quoted: (Still, wouldn't mind hearing more about the feed ramp business..?)

Hey JoeBlack,

Nice feed ramp mod there, I like the looks of it!  Did you by chance grind off the bit of "lip" next to the mag?  See my pic...  It seems like the front edge of my Uzi mags have been impacting on that lip and causing it to shear off after a couple months of use!  See this thread...  
ar15.com/forums/topic.html?b=3&f=15&t=223385

So I was wondering if I should use a Dremel and grind down the front of my Uzi mag, or, should I just grind off the lip on the feed ramp?  I just got my replacement block from VMHytech - no charge - thanks John!

Thanks!
http://img.photobucket.com/albums/v700/scope12da/magblocklip.jpg

Quoted: Hey JoeBlack, Nice feed ramp mod there, I like the looks of it!  Did you by chance grind off the bit of "lip" next to the mag?  See my pic...  It seems like the front edge of my Uzi mags have been impacting on that lip and causing it to shear off after a couple months of use!  See this thread...   ar15.com/forums/topic.html?b=3&f=15&t=223385 So I was wondering if I should use a Dremel and grind down the front of my Uzi mag, or, should I just grind off the lip on the feed ramp?  I just got my replacement block from VMHytech - no charge - thanks John! Thanks!

I would keep the lip if I were you.  IIRC, only the IMI 25 rounders bottom out on your lip. If you get some IMI 32's they don't. I would grind some off the mags so you just get a little play when the mag is installed.

Joeblack, interesting mod. Actually I meant ramping the barrel/breech face, how and what with to do it but that gave me even more ideas.
Do people get their 9mms to feed hollow points without such mods?
I just loaded some ammo using hp bullets and did some different overall lengths to see if it helps the feeding. Hmm, might be an idea for a new thread.

Quoted: I would keep the lip if I were you.  IIRC, only the IMI 25 rounders bottom out on your lip. If you get some IMI 32's they don't. I would grind some off the mags so you just get a little play when the mag is installed.

Hey Joe, I just ordered some 25 round IMI mags. Can you explain why the 32 round mags don't have this problem and where is a good place to buy some? The VM Hytech mag block should not be having this type of problem for $150.00 but if it does, I'd like to avoid it.

Thank you!

I'll lay out my 32's with both style 25's tonight.  My block came out of the first run, I have had no problems since "cleaning" mine up.  I would almost suggest that you use a bare tube and ajust the mag claw to hold the mag in the block with a few thous' up-down play....

Might also try ammo other than Mag-Tec....

Quoted: Hey Joe, I just ordered some 25 round IMI mags. Can you explain why the 32 round mags don't have this problem and where is a good place to buy some? The VM Hytech mag block should not be having this type of problem for $150.00 but if it does, I'd like to avoid it. Thank you!

This is what gets some people in trouble.  They shove in the 32 rounders in the mag well adapter then scribe a line for the mag catch.  See the difference in the distance from the top of the feed lips to the top of the front of the mag....  @.030"

Vector has good 32's. They are heat treated.  

Quoted: Joeblack, interesting mod. Actually I meant ramping the barrel/breech face, how and what with to do it but that gave me even more ideas. Do people get their 9mms to feed hollow points without such mods? I just loaded some ammo using hp bullets and did some different overall lengths to see if it helps the feeding. Hmm, might be an idea for a new thread.

Some guns run 100% without mods... Others need it...

tag!

Quoted: users.zoominternet.net/~picplace/UZI25and32roundmags.JPG This is what gets some people in trouble.  They shove in the 32 rounders in the mag well adapter then scribe a line for the mag catch.  See the difference in the distance from the top of the feed lips to the top of the front of the mag....  @.030"

Thanks Joe,

Do you think that if you're using 25 round mags you should file the lip lower? It's the higher lip thats smashing into the mag ramp and breaking it?

I will try and get some 32 rounders also though. I'd just like to use or sell the 25's lol

Quoted: Do you think that if you're using 25 round mags you should file the lip lower?

You won't hurt anything......


Use the 25's, it's no big deal mod'ing them.  Filing will be kinda tough... they are heat treated....


Get out the old trusty....

Quoted: Carefully grind a lead in your chamber. A little at a time.  The ammo not feeding correctly slows the bolt down and then the bolt doesn't have enough energy for the extractor to engage. If you don't re load, grind away.  If you grind a lot the cases can bulge in this area.  If you re load, grind very little at a time and try it out. users.zoominternet.net/~picplace/9mmbarrel.JPG

What did you use to create the lead?

The barrel is held in a Milling Machine vise and I have a fixture that holds a small wheel air grinder.

Ahh, gotta love the Dremel.  I took my 9mm AR out today, had no problems with seating the Dremel'd 25 rd IMI Uzi mag (though at first I was REALLY careful), and I saw no direct contact with the feed ramp lip!  Plus, whole mag of 9mm fed great!!!  http://img.photobucket.com/albums/v700/scope12da/maggrind.jpg

Quoted: Ahh, gotta love the Dremel.  I took my 9mm AR out today, had no problems with seating the Dremel'd 25 rd IMI Uzi mag (though at first I was REALLY careful), and I saw no direct contact with the feed ramp lip!  Plus, whole mag of 9mm fed great!!!   img.photobucket.com/albums/v700/scope12da/maggrind.jpg

Great pics guys, between you and Joe I have a little more faith in my VM working now. I'm going to copy your dremmel work, hope ya don't mind.