Bushmaster m4 problem

[thebutcher]

Hello,
I just had some custom work done to my first AR. Now it will only fire one round and not eject the empty casing. I had the front site removed and replaced with a MI low profile gas block w/ a MI 10" free float handgaurd installed. The rifle only has about 100 rounds fired. What could cause this? Thanks for the help

[TimP]

probably something to do with the gasblock that was put on.

[thebutcher]

That's what I was thinking. It looks like a fairly straight forward install for a gunsmith. I just met someone today who is very familiar with the AR platform. I'll take it in to him tomorrow and see if he can refit the gas block. Thanks for the response.

[Dan GSR]

yup sounds like the hole for the gas block is not lined up perfectly

[C4IGrant]

Could be the GB or gas tube was installed upside down! :D




C4

[SLR15]

With only 100rds total through the rifle before the conversion was done could possibly make it a couple of things that would make it fail to eject. Is it a fail to eject or extract? First do a complete function check with an unloaded weapon.

Here is a simple function test that we teach in our courses:

1.Visaully & physically make sure the weapon is empty. Always double & triple check to be sure it is empty.

2.Put the safety selector into the "Safe" position. To get the safety selector into the "Safe" position, the hammer must be cocked, which also shows that you have hammer/trigger sear engagement.

3.Point the weapon in a safe direction & attempt to press the trigger. Nothing should happen.

4.Put the safety selector into the "Semi" mode and press the trigger. You should get a click sound and feel as the hammer goes forward and strikes the firing pin.

5.Keep the trigger pressed to the rear and manually cycle the action by pulling the charging handle back and ease it forward just hard enough so you get bolt lock up.

6.Release the trigger and you should get a click noise and feel, meaning that the trigger has reset into the hammer/trigger sear engagement. Now press the trigger again as it should have reset, and you should be able to feel and hear the hammer go forward again and strike the firing pin. This means basically the trigger, hammer, and disconnect are working properly for semi-automatic function.


If it function checks fine, next try a mechanical check. The mechanical check is something we do in the shop when we check how the action works mechanically, as the weapon is a machine. To do this we use dummy action proving rounds, if you are going to use live rounds please keep the muzzle pointed in a safe direction, be very careful, and do not press the trigger at anytime (again we recommend and prefer to use dummy action proving rounds for this).

1.Visaully & physically make sure the weapon is empty. Always double & triple check to be sure it is empty.

2.Put the safety selector into the "Safe" position. To get the safety selector into the "Safe" position, the hammer must be cocked, which also shows that you have hammer/trigger sear engagement.

3.Point the weapon in a safe direction & attempt to press the trigger. Nothing should happen.

4.Using a magazine of dummy action proving rounds, insert the magazine into the magazine well firmly and then tug down to make sure it is seated and locked into place.

5.While holding the weapon horizontal like you are shooting it, manually cycle the charging handle rearward to its fullest point and then release it so the bolt carrier assembly goes forward under the weapons own spring tension. When the bolt carrier assembly goes forward it should strip a dummy action proving round off of the magazine. As the dummy round is stripped off of the magazine it should be pushed forward up the feed ramps. The dummy round should then chamber. When the dummy round chambers, the bolt carrier group should go all the way forward and the bolt should rotate counter clockwise and and lock.

6.Now manually pull the charging handle to the rear slowly. This will cause the bolt rotate clockwise and unlock. As you continue pulling the charging handle rearward the dummy round should be extracted. When the bolt carrier assembly is pulled rearward enough for the round to clear you will get ejection.

7.Repeat the mechanical check for all the dummy action proving rounds. Make sure the weapon is kept horizontal like your are shooting it, that way you know gravity is not assisting in any way.


If your rifle function checks and mechanical checks okay, then this would most likely show that the ejection problem is gas related. Gas problems would probably be from a loose gas key, bad gas block, or gas tube in upside being put in upside down. To check the gas key simply grab onto it and try to wiggle it, it should not move and check the staking visually.

The gas tube being in upside down is common, so a visual check about half way on its length from front to back and you will see a slight upward bend for its proper alignment with the gas key. If the gas tube is in upside down the bend is downward going from front to back.

The gas block could be bad or misaligned. Alignment of the gas block means that the gas port from the barrel needs to be properly aligned side to side, to include front to back. A bad gas block means that it is not properly machined to align with the gas port in your barrel, it could possibly be slightly oversized for you barrel so you have a gas leak, or is there a leak where the gas tube is pinned into place.

There could be a couple of other possibilities, but these are what come to mind at my coffeeless brain at the moment. I hope this helps some.

[VA_Dinger]

thebutcher asked me to move his thread into the AR Technical Discussion forum.

[thebutcher]

Thanks for all the replies. My new contact has the gun now so I should find out in a couple of days. If the gas block needs to be replaced I'll just cut down the old FS and make it a low profile gas block. That should work, right?