A friend asked me to help troubleshoot his Bobcat MP5 clone.  Basically, it will fail to eject properly every 3 to 6 rounds.  I have already installed a new HK extractor and extractor spring, but this did not have any positive or negative effect.  The ejector had some galling on the part that impinges on the bolt carrier in order to raise the ejector to the bolt, which I filed smooth.  His magazines also have wear on the feedlips as if the bolt is dragging across them, though it's not excessive or noticeable when hand cycling.

My biggest question is: even with a new extractor and spring, if I put a round into the bolt face and tip it upside down, it will fall out.  It seems to me, that the bolt face recess is too large diameter and the extractor does not hold it tightly.  However, I know nothing about these guns so maybe that's how it's supposed to be?

My second question would then be, what do I check next?

When it is working, it ejects at about 1:30 o'clock.  When it fails, the bolt drives the fired case back into the trunnion.  If you're lucky, when you clear it, it won't go under the bolt into the trigger housing.  There are no extractor marks on failed cases, as if it simply pulled away from the case.

Can you verify that it has the correct 9mm hammer spring installed in the trigger pack?  

The SW MP5 clones had 308 hammer springs installed and caused all sorts of issues with my buddy SW5.

Thanks,

Don-S1

I can try!  I'll pull it out tomorrow.

I had the same issue with my bobcat.

After the replacement of the extractor and extractor spring, I had to replace my ejector with genuine HK. After that, I had to shim up my trigger pack, as the ejector was not riding high enough in the bolt head to actually eject a spent round. I also made sure it had a 9mm hammer spring.

Make sure you are using good mags, HK work the best(obviously) but I've had 100% reliability with POF mags as well.

Also, use good ammo, the weaker stuff may not cycle correctly until it's good and broken in.

I would look at the ejector also. manually cycle it, see if it sits all the way into the bolt. If it doesn't shim the pack up, by adding the shims on top of the f/a pack block.

have you checked headspace? What locking piece?

The ejector does come all the way up into the bolt face.  I was actually concerned it was coming up too far and dragging, and that's what created the rolled edges.  As I was thinking about this last night, I wondered about timing of the ejector rise as well and I will check to make sure it's coming up before the bolt face actually gets past it.

I have not checked the headspace.  Do you mean headspace or bolt gap?  I'll google that procedure and check tonight.

The locking piece in this bolt carrier is unidentified/no markings.

ETA: I've really only tried WWB 115 in it.  I have Lawman 115, Lawman 147, Fiocchi 115 and some handloads on hand.

same thing

bolt gap set the headspace

get feeler gauges, let bolt go forward, check gap.

Put a set of calipers on the bolt face. The inside diameter where the base of the cartridge rests should measure 0.40" and if it is larger, you can have insufficient or inconsistent extractor tension with that bolt head.



Back when these guns were made, TB had spec'd out the parts, and many of them were actually supplied by RCM. Now, RCM makes great parts, but in this case there is a possibility that the specs (as ordered by the supplier) are not correct. Back then, the clone builders thought they could get away using .308 hammer springs and re-shaping ejectors. For the most part, it worked The good news is that so long as the barreled receiver is properly formed, everything is fixable.



 

I think this is the biggest issue.  I'll measure tonight, but there is no extractor tension.  If you insert a case and pull straight, the extractor holds the rim, but the slightest axial movement allows it to escape, the extractor does not hold it in tension against the opposite side of the bolt face.

boricua nailed it! I had a Coharie with the same problem - bolt face was too large.
Also I had a similar issue about 3 years ago with a RCM bolt which was resolved with the installation of a German extractor.

I'd be willing to be the bolt head is marked NF461

You would win that bet.  Just checked.

The counterbored bolt face is .432"  That has to be the issue.

ETA: Now, is this thing MIM or can I TIG that counterbore up and remachine?  Cause I know he ain't going to want to buy a bolt head from hkparts.net.

Get a new bolt head.

Yep it is MIM. Why wouldn't get a bolt head from HKParts? Sure the German ones are ridiculously expensive but that is everywhere. RCM bolt heads are 199.95 + shipping at HKParts. I have 4 9mm RCM bolt heads, one 40 cal one, and a 5.56mm one they are excellent



 

I'm pretty sure all the Bobcats were made and done with before the MIM bolts came about. If it's a MIM bolt, it was most likely swapped into that gun at some later date. Doesn't really matter at this point, since it needs to be replaced, but it might be worth letting the owner know.

You can get a bolt for $100





Never mind, I'm a dummy. That's for a .45

 

Replace the following with HK parts:

Extractor
Extractor spring
Ejector

If these don't work, replace bolt group, with bolt head being first.

Normally, I would do the spring first as that is the weak spot. However, in this case, the gentleman has one of the old out of spec bolt heads.

Here's an RCM head for a good price...http://www.gunbroker.com/item/560551693

I also bought one of these german heads for a great price...http://www.gunbroker.com/item/555562681

I'm just guessing due to the cost, not any other reason.

OK, RCM bolt fixed the issue.  Gun runs 100% with Speer lawman with both HK and Korean magazines.  Still chokes occasionally with Winchester white box, I'm guessing that would need a different locking block with a shallower angle.

Thanks for the help.

Good to hear!