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Page AR-15 » Troubleshooting
AR Sponsor: bravocompany
Posted: 6/6/2017 5:59:46 PM EDT
Got bored and built a rifle . A 300aac. The rifle at random , but relatively consistent times will fire 4,5,7 times, then malfunctions.  This is the odd part . It's failing to feed, but in inconsistent way. .....
1. Sometimes the round will chamber but not completely. Can usefoward assist to fully sear round
2. Round will chamber , you'll need to apply a lot of force w forward assist to fully seat , think tap with hammer
3 round will get lodged at odd, varying angles going into chamber
4 rounnd appears to be fully seated, squeeze trigger, and click, nothing

None of this ever happens on first or second round. No real pattern to it , other than it's going to happen. Rate of fire makes no difference, fast slow ect .
Ammo brand type ect makes no difference. Magazine type no difference, nor does capacity of said magazine , full , half ect . On occasion, I will find a blown out primer between boldface and fresh round being chambered , but that been rare . Really not even sure where to start diagnosing this problem. Any ideas would be helpful   Thanks.
Link Posted: 6/8/2017 6:48:25 AM EDT
[#1]
Link Posted: 6/8/2017 7:19:03 PM EDT
[#2]
Thanks for the reply.  To answer some of the questions....
Mid length gas system
Have tried multiple magazines
Have tried different combos of buffers/springs
All the parts were leftovers, but new. None of them were cheap clearance found in back of a warehouse type
Used multiple types of ammo from cheap to expensive,same result, with the exception of subsonic. But only had one box to try
Does have adjustable block, but none of the adjustments I've made seem to make a difference.
Interesting you mentioned chamber spec, because that what I was starting to think,but that starting to get out of my league
Odd thing, it's never failed to load a round manually

I figure it got to be some minor flaw somewhere in design causing it , weather it's me , or in materials used...
Link Posted: 6/8/2017 8:30:32 PM EDT
[#3]
M4 ramps.  Sorry left that out
Link Posted: 6/9/2017 8:12:22 AM EDT
[#4]
Are you sure the gas system is mid length?  Most of the 300 Black rifle barrels that I have looked at have pistol length gas systems.  Rifle and mid-length systems sometimes have problems with not enough gas.

What brands of magazines have you tried.  Contrary to some opinions, PMags and other plastic magazines do not work in some lower receivers (top round can be positioned too low).

What weight is the buffer?  Are the stock and buffer rifle or carbine?  I see cases where people building guns insist on going straight to H2 or H3 carbine buffers with carbine stocks, and there isn't enough gas to reliably cycle the action.

Have you taken the time to dry-cycle the upper assembly (no oil) 200-500 times to start the break-in process?  A new gun can fail to complete chamber a round when it's new, tight, and not broken in.

Are you shooting reloads (commercial or private)?

If you separate the two halves of the gun, you should be able to drop rounds into the barrel (after a through cleaning without oiling) and have them slide all the way into the chamber under their own weight.  If they don't the chamber is sized wrong, or the ammo is defective.
Link Posted: 6/9/2017 8:39:06 PM EDT
[#5]
Sorry was trying to do several things at once when I was typing ....
its pistol length gas system
Have tried standard/h1/h2 buffer
Have tried combos of stiffer springs
As far as ammo, all factory, probably 10 different brands , the only thing that functioned reliably was hornady subsonic. 225 if I remember right ... but I only had one box, so maybe just got lucky. Was just checking basic function...
Have tried every magazine I've got. Even tried opening up the lips slightly on one thinking maybe it was like the problems the 6.8 had feeding . No luck
All the tolerances spear to be ok. There's no obvious slop , or catch. Like I mentioned before, you can cycle it manually, and it will load every round .... just doesn't add up in my brain. As far as fouling goes, I may not be OCD about cleaning, but I don't think this is case of neglect. I clean if it's 5 rounds or 250. And it been doing it since day one. Like I said it's got me stumped. I will drop a round in unassisted, and check , I haven't done that . In mean time, if you can think of anything else, I'm all ears .  Thanks again
Page AR-15 » Troubleshooting
AR Sponsor: bravocompany
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