Original problem:

I recently purchased a Bushmaster upper with a 14.5" barrel on a pre-ban Oly lower, with a 4 position M4 telescoping stock. The bolt carrier is a matte silver finish, marked with the letter D. The key is parkerized. The bolt has no markings. The extractor spring has a blue plastic insert. My firing pin retaining pin is bent. After reading the FAQs, I have determined that my hammer is dragging on the firing pin. My carrier is of the open design. I am also having a failure to eject problem. After disassembly, I determined the ejector was sticking. I punched out the roll pin, and removed the ejector and spring. After cleaning them, I polished the hole to remove any burrs. After reassembley, the ejector seems to function correctly. I have not test fired the weapon since cleaning, so I cannot say for sure that this has solved my problem. I am now looking to replace my bolt/carrier with a Colt M16 bolt/carrier.

I replaced the bolt and bolt carrier in my Olympic Arms lower/Bushmaster upper M4. I used the componets from my post ban Colt. I first checked the headspace, and all was good.

At the range, the M4 cycled flawlessly with one small hitch. About every 4th or 5th time I squeezed the trigger, it would double or triple burst. (Not a good thing at a public range that does not allow full auto firing.)

When I disassembled the rifle at home, the hammer would always engage the sear when I was not squeezing the trigger. When squeezing the trigger, the hammer spur to disconector surface engagement was about .050". It engaged with a very light pressure. Also, the safty is somewhat loose.

Looking at my Colt, the engagement surface was at least .100" and it took a lot more pressure to engage.

So, what do you think? I am considering changing out all of the fire control parts with Bushmaster parts.

Any help would be appreciated.

The rifles problem is the hammer is being bounced off the disconnector as the carrier slams home.  This is caused by to light of an engagement of the hammer/disconnector sears.

To solve, you need to re-time the release point of the hammer from the disconnector. This is done by removing metal from the front/bottom of the disconnector (were it contact the forward/top of the trigger.  By removing metal from the front/bottom of the disconnector, it pivot forward on the trigger pin, and engages the hammer stronger, and longer during the release of the trigger.  
 

My rule for re-timing is to hold the trigger back, lock the hammer down on the disconnector, and then slowly release the trigger. Right before the trigger returns to the At-rest position (fully forward), the disconnector should release the hammer, and be caught by the trigger sear (.020-.040 distance from rest point).  

[url=http://ar15.com/forums/announcement.html?b=3&f=66&id=187]FAQ III[/url]

I tried a function check as discribed by Tweak in the FAQs with the lower removed, and I cannot make it malfunction. However....
When I put  it back together, and function check it, the hammer stays on the disconector when I ease the bolt forward, but does not hold when I let the bolt slam forward.

Now I am trying disassemble the lower to repair or replace the disconector. Using the assembly instructions from ARFCOM, and working backwards.

The selector does not want to come out. I have the hammer cocked and the selector in "Fire". Using a drift pin and hammer, I am only able to move it about.100". How much force should I have to exert to remove this. I don't want to damage the Lower.

Egad!

Take the stock off that rifle and remove the selector detent and spring, or you'll surely ruin your gun.

Added point:

On my M4, I can remove the trigger and hammer without removing the selector.  No need to take it out at all if you're just going to file on the disconnector.  But, otherwise, the selector his held in tight by the selector detent, which is held in place by a spring that is captured by the stock at the rear of the receiver.  Look carefully at the diagrams.  

You meant pistol grip, didn't you?

(Note to self: Read [b]entire[/b] instructions before taking any action.)

Thanks, I tried this just before leaving for work and quit when it didn't come out easily. While pulling out of my driveway, a lightbulb came on, and I knew what I had done wrong. Wasn't able to get back on here and edit before anyone else saw what happens when you don't read the instructions.[:\]

I will try again tonight after I get home from work.

After adjusting the operator's headspace[:I], I disassembled the lower. The disconector spur engaging surface looks really rough and worn away. I think my next step is to order a new disconector. If it turns out I can make this one work, I will have a spare.

Mick,

Make sure you reinstall the selector prior to checking the timing, it acts as an overtravel stop for the trigger.

Listen to G-CODE

The pistol grip holds the spring for the selector detent.....

The buttstock hold the spring/detent for the rear takedown pin....

Thanks......after thinking about what I was doing, I didn't have any more trouble disassembling everything.[:\]

Egad, I got it wrong twice in a row.

The stock holds the rear pin's detent, the selector's detent IS INDEED held by the grip.

Also, I don't know if this works on all selectors, but on mine if I put it at  a 45 degree angle between safe and fire it does "tap" right out with a wooden dowel.  

Depending on the amount of tension that the spring is applying, it can be removed by driving it out under tension.  The only problem that you run into is if the lower receiver is milled incorrectly, and the retention lip of the receiver, and the retention lip on the detent are out of spec.  This will allow the detent pin to ride up too high, and make re-inserting the selector a real bitch.

Also, keep in mind that on some selectors, the detent ride groove can be a little more deeper than other, added to a sharp pointed detent pin, and you stand a good chance of cracking the receiver when you try to reinsert the selector by driving it back in (or scratching up a receiver if you are pressing down on the pin to re-insert and the tool slips.

Since the selector detent and spring is just retained by the pistol grip (single screw), I rather just remove the grip, then have to replace a receiver is something goes wrong, especially if I am wrenching on someone else’s rifle.

Food for thought.

Good point. Since this is a Pre-Ban lower, I [b]DO NOT[/b] want to screw it up.

I want to update you, and thank everyone for their help.

I replaced my bolt carrier in my Oley/Bushy M4 with the carrier from my Post Ban Colt. I used a new bolt that I bought that came with an M16 carrier. Checked headspace and all was OK. Put the new M16 carrier in the Post Ban with it's original bolt. After it started doubling, I didn't want any M16 parts in the M4.

Ordered and installed a new trigger, hammer, disconnector, and safty along with new springs from Bushmaster. Everything went together fine. The new disconector was very different from the old one. I'm guessing there was more wear on the old one than I had been led to believe. No matter.

Took both rifles out to my buddie's farm, where I didn't have to worry about it going full auto on me. I'm pleased to say that everything performed flawlessly. No doubling. No failures to feed, eject, or extract. One malfunction was due to a magazine that would not work in either of my rifles.(After cleaning and spraying a little Dri-Lube on it, it is working also). I shot about 300 rounds through both rifles, and I think I have the winning combination. I'm going to leave the M16 bolt carrier in the Post Ban Colt. It's not broke and I'm not messing with something that works.

I learned a lot by having these troubles, so I am looking at this as a learning experience. Thanks again for all the help.

A proceedure I always use when checking out self loading firearms, is to start with 1 round in the mag, fire and check for lock.  Move to 2 rounds, then 3, etc.  This is done on  all new builds and after any fire control group work.

This way if you have something out of wack in the fire control group, you don't end up doing a mag dump.  I learned this working on 1911's.  You really don't want to try shooting a 45acp pistol in full auto....

Try setting up a stock HK-91 trigger at less than a two pound trigger, with a full mag.  Hell, it held for the first few test fires with only a single round in the mag at a time, then let loose after the second round in the full mag.

FYI: Trying to control a runaway 7lb 308 off the bench while trying to get to the mag button to drop the mag is a fun ride, but only once.  Unlike an AR, letting go of the trigger doesn't stop the chain reaction/runaway, due to the FCG only having a single sear, and not a half cock notch on the hammer like the 1911.

Rather than trying to get to the mag release button on a runaway gun, do it the military way. If belt fed, twist the belt to prevent loading any more rounds. Otherwise, block the ejection port with your hand to prevent ejection and jam the gun. The second is better if you have a glove on; but, even bare handed, a burnt hand is better than doing an uncontrolled mag dump.

Sounds like an excellent use for the ejection port cover.

Tweak,
What ejection port cover?

ArmyOrdGuy,
As far as blocking the ejection port, unless you have a dead cat to shove in it, getting your bare hand in the way will lead to stitches.  Remember, were talking about a delayed blow back action of a HK where both the muzzle and the ejection port are lethal (ejection blast will blow your hand off the port anyway). Plus, pulling my hand off the top of the barrel (keeping the muzzle/rifle pinned down/safe) was a better action, then loosing control of the rifle and having it climb out off the bench.  A full mag (twenty rounds) dumps in less that 2 second, so my best action was to keep the muzzle controlled. I just treated it the same as a Runaway Mac.

P.S. I have had runaways with M-60's, and on a belt feed rifle your right, just reach over with your left hand and crimp the belt to stop the rifle or if the belt gun is tight box feed (no room to grab), just pull up on the feed cover to stop the rifle.