Last round hold open not working on AR15
Just replaced my fixed stock with a mil-spec buffer, spring and buffer tube to accommodate new Magpul STR collapsible stock.
The new buffer tube, spring, and buffer, is of course shorter and lighter than the original parts for the fixed stock.
The new buffer group moves freely in the tube.
There are no other problems with feeding, extraction, etc.
Used three different mags and different loads.
Same result. The bolt closes on and empty mag......Click...
Pulling back the charging handle on an empty mag will engage the hold open.
Manually pressing the hold open lever engages the hold open.
This was the first range trip since installing the new parts.
Never had this or any other issue with this gun in nearly 2k rounds until today.
My theory is that the new buffer:
Spring is too strong to allow the bolt to retract far enough for the hold open to engage.
The new buffer is too light or a combination of the two.
IF this is the case ... how to fix..?
(no, I don't want to put the fixed stock back on
Any help is much appreciated.
I dont see how the stock would make the bolt go by the stop, unless you put the wrong spring back in and now its pushing way to hard? I would oil the assembly really well...
Does it stay back when you have an empty mag and pull it back by hand?
do you have a BAD lever installed?
Originally Posted By RangeWarrior:
do you have a BAD lever installed?
Which just reminds me. I read the BAD lever is supposed to be loose fitted so it wiggles on the paddle button. If it is tight then the added weight will cause problem with bold hold open cycle. This may also be the case with the two other levers by other manufacturers. YMMV.
1. The new stock required installation of a mil-spec buffer tube, spring, and buffer.
2. Bolt will hold open when charging handle pulled back over an empty mag.
3. No BAD lever installed.
How did it work with the fixed stock?
Worked flawlessly with the fixed stock.
The tube on the fixed stock is longer by a couple of inches than the mil spec tube for collapsible stock.
The old spring and buffer are longer too.
I had this problem when I installed a DSA buffer tube that was too shallow. The bolt would lock open manually but not after firing the last round. Fully retracted, the bolt face was only like 1/16" behind the bolt catch so it didn't have time to engage. Pull your charging handle all the way back and see how much it clears the bolt catch like in this pic
Originally Posted By chuckd840:
I had this problem when I installed a DSA buffer tube that was too shallow. The bolt would lock open manually but not after firing the last round. Fully retracted, the bolt face was only like 1/16" behind the bolt catch so it didn't have time to engage. Pull your charging handle all the way back and see how much it clears the bolt catch like in this pic http://i.imgur.com/9d8Pm.jpg
Mine is the same.
Almost no room behind the bolt catch.
Did you find a fix..?
New buffer tube solved my problem
Did you go with mil-spec or commercial..?
Mine is mil-spec.
I looked up the specs for the tube, spring and buffer.
All are what they should be.
I have an RRA lower.
Wonder if that is out of spec...?
Thanks for the info..
If the same lower worked with your A2 stock that seems to indicate either the spring is too long or the buffer tube / receiver extension is out of spec. The carbine spring should be 10 1/16" - 11 1/4"
who's buffer tube?
I will have to pull the spring out and measure it.
I bought the parts as a kit from Combat Optical.
Don't know who the actual manufacturer is.
On the Combat Optical sight the specs for the kit are listed as follows:
Standard End plate
•For AR-15 / M4 stocks
•Material: Anodized aircraft grade aluminum
AR15/M4 .223/5.56mm Carbine Buffer
•COLOR: Silver (color offset +/- 3%)
•NET WEIGHT (OZ): 3oz
AR15/M4 .223/5.56mm Carbine Mil-spec Buffer Spring
•Length: 11 inch
•Compatibility:.223/5.56mm Mil-Spec Buffer Tube (7.25 inch tube)
•NET WEIGHT (OZ): 1.9 oz
•Will not fit on commercial level buffer tube
AR15/M4 Carbine Buffer Tube Mil-Spec
•Length: 7.25 inch
•NET WEIGHT (OZ): 4.7
Thanks for the input from everyone.
Looks like the new buffer tube is just a hair too short to allow the bolt to retract far enough for the bolt catch to engage in time on the last round.
I shaved an eighth inch off the delrin tip of the buffer to allow enough space for the bolt to retract and clear the bolt stop by about 1/4".
Will test it at the range this week and post the results.
Thanks to chuckd840 for setting me on the right path.
Turns out that my problem was self inflicted.
The new buffer tube has one full turn of threads (in or out) into the receiver where the tube will engage the buffer detent without binding it or letting it fly out.
I simply had to back the buffer tube out one full turn.
At this point it barely rides over the buffer detent to keep it in place.
Backing it out one turn gives enough room for the bolt face to clear the bolt latch by approx. 1/4 inch.
This is enough space to allow time for the bolt latch to engage on the last round and hold the bolt open.
Thanks to all for your input...