Is it possible to test the last round bolt hold open without firing? Like pulling back the bolt on an empty mag?

If so, I can't seem to have it lock open with an empty straigh 20rd Colt/NHMG mag.

Yes just pull it open on an empty magazine, or pull it open, and while your holding it pull on the hold open button....

It slams shut on an empty mag, the bolt catch doesn't seem to get pushed up when the mag is empty. When the bolt slams back towards the stock (as if firing the last round) it just pushes down the bolt catch and it stays down. The mag follower doesn't push up.

Yes, but if you push down on the bolt catch with the follower under it, it stays down/against the receiver. So if the bolt came back and pushed the catch, it wouldn't pop up again.

OK !! i got your solution, i just finished building an AR type carbine & had the same problem, open your rifle, insert an empty mag, check real close to see if the hammer is touching the rear of the mag release if so determine where it hits & carefully grind off or file a tiny bit of metal from the FRONT of the hammer where it hits the mag release.., mine works great now !!

yes it does contact the mag catch... but how would that affect the last round BHO?
Does your bolt catch "stick" to the follower if you jam it down manually?

Quoted: OK !! i got your solution, i just finished building an AR type carbine & had the same problem, open your rifle, insert an empty mag, check real close to see if the hammer is touching the rear of the mag release if so determine where it hits & carefully grind off or file a tiny bit of metal from the FRONT of the hammer where it hits the mag release.., mine works great now !!

hhhhmmmm...
Does the catch move freely? Take the upper off and your mag out, cock the hammer. can you easily lift the mag catch by the arm that gets lifted by the mag follers? can you make it pivot by pushing the BOTTOM of the release lever (the part under the pin the catch pivots on?). If the answer is NO, then clean in there with some gun scrubber, brake cleaner, etc, spray it out, lube, and see if that helps.

If it does move free, put an empty mag in. Does the bolt catch extend roughly 1/16" over the follower? If not, you may need a new bolt catch (or possibly follower).

If it's still all good (it moves free and extends over the follower), are your mag springs totally weakened? You may want to try another mag (both to eliminate mag spring or follower problems).

If none of that is the problem, put the upper (with bolt/BC) back on, leave the EMPTY mag in, pull the handle back. When the bolt clears the catch, the catch should start to rise. It should go high enough to catch the lower two lugs on the front of the bolt and stop the bolt from going forward.

If it does rise, but just can't hold the bolt (it slips off), take the upper off again. Take out your bolt and check that the lugs are square  (not rounded or chamfered). This was the least likely culpret... Now check the bolt catch? Is it bent? chamfered, rounded,  or worn to the point the bolt could slide off? If so replace with a new part.

hope this helps.

rvb

It looks like the mag catch doesn't rise (follower doesn't have enough force to push it) when the bolt first passes it.

Weak mag springs?

I bought these 20rd straight mags from CMMG just a week ago. They're made in 11/03, marked LE/Gov't mags.

Troubleshooting

Do you have a more direct link? I couldn't find anything in the FAQ subject list

If it does move free, put an empty mag in. Does the bolt catch extend roughly 1/16" over the follower? If not, you may need a new bolt catch (or possibly follower).

The bolt catch actually contacts the follower and pushes it down somewhat.

Then when the bolt (or your finger) pushes down on the follower/catch again, it stays down and never pops up to catch the bolt on its return trip.

Update:

It turns out that the 20rd USGI mags that I bought from CMMG had really weak/old springs (mag body is dated 11/03 though??) becuase I slapped in a freshly rebuilt 30rd USGI mag with a verified strong spring and the last round BHO worked fine.

Quoted: Update: It turns out that the 20rd USGI mags that I bought from CMMG had really weak/old springs (mag body is dated 11/03 though??) becuase I slapped in a freshly rebuilt 30rd USGI mag with a verified strong spring and the last round BHO worked fine.

Maybe it's from 1903

I think its just a crappy spring.

I'm thinking about using a 30rd spring in the 20rd mag, that should give it a lot of power.

That short stroke check requires firing the rifle. I don't exactly live at a firing range so I had to figure out a new way to test the BHO before I hit the range with my AR15.

The bolt catch and all related parts are new RRA parts that installed in a brand new lower. I had already verified it was operational and not sticking.

I did not know my rebuilt 30rd mag was a "known" good mag because this was a brand spanking new AR-15 and my only AR-15.

I had assumed i bought some quality 20rd USGI mags from CMMG and they were used to dry test the AR-15.

Thanks everyone!

I couldn't find any of the answers to my questions using the limited search function. I'm sorry that the newbies with the most questions are restricted to using a limited search engine... I dunno what else to say?

was the following comment directed towards me ?????????

""uhhhhmmmm... the hammer will always touch the bolt catch (I assume you don't mean mag release. If the hammer's touching that you're REALLY screwed!) if you pull the trigger w/o an upper/bolt carrier. When the bolt is to the rear, the hammer is no where near the bolt catch. Do NOT follow this advise.""

if so please elaborate, i am not sure i quite understand what is being said here ???

thank you !

Thanks Tweak!

There aren't many people local that I know who are into AR-15s, so ARFCOM is pretty much the only definite source for my newbish questions. I try to Search as best as I can.

Quoted: Quoted: OK !! i got your solution, i just finished building an AR type carbine & had the same problem, open your rifle, insert an empty mag, check real close to see if the hammer is touching the rear of the mag release if so determine where it hits & carefully grind off or file a tiny bit of metal from the FRONT of the hammer where it hits the mag release.., mine works great now !! hhhhmmmm...

Quoted: was the following comment directed towards me ????????? ""uhhhhmmmm... " if so please elaborate, i am not sure i quite understand what is being said here ??? thank you !

AR-15NUTT, Yes, that was directed towards your comment, and I'll be happy to elaborate. Sorry to hi-jack the original thread, but I think we've pretty much solved his problem with the mag spring issue.

First, I assume you meant bolt catch, not mag release? The mag catch is what moves when you push the button to drop a magazine, we're talking about the part that holds the bolt back here.

It's very common for a hammer to be able to hit the bolt catch when the upper is off the gun and the hammer is not cocked (I don't think I've ever seen one that didn't touch).  With the upper on the gun (and bolt/carrier assembled), the hammer doesn't go this far fwd. It hits the firing pin first!!!

When firing, the bolt/carrier comes back (hopefully far enough the bolt catch can pop up and catch it if there is no gas problem and you've got an empty mag). When this happens, the hammer is cocked (pushed to the rear) by the bolt carrier. Thus the hammer is no where near the bolt catch and cannot keep the catch from comming up.

There was no need for you to file on your hammer.  None.  Very few parts on ARs ever need actual fitting if you're using standard (non-custom parts). I've only seen one bolt catch that needed work, and it's because the arm the meets the follower was about 1/4" too long and pushed down on the ammo. I'm guessing it was actually a "wrong part," perhaps from a 7.62x39 rifle or something, and I swapped it for a correctly fitting part.

That the hammer touches the bolt catch is part of the reason you don't want to pull the trigger on an un-assembled rifle. In addition to hitting the receiver and wearing/cracking it, you're also hitting the bolt catch and can break it or the receiver where it mounts.

Before you go filing on perfectly good parts in the future, ask a quick question around here! That said, I doubt what you did could hurt anything, except if you took too much metal off you could have filed through the "hard candy coating" and have exposed the softer metal underneath. Keep an eye on your hammer for wear.

Have fun , be safe,

rvb

RVB,
thank you for that explanation, seems logical, but the few thousandths i removed has permantly cured my prob., i have a "hobbiest" machine shop so the metal removed was done "surgically"

Quoted: RVB, thank you for that explanation, seems logical, but the few thousandths i removed has permantly cured my prob., i have a "hobbiest" machine shop so the metal removed was done "surgically"hr

If your problem was the same as the original poster's, then I sincerely doubt your sugury had anything to do with the cure. It's like doing knee sugury for the common cold when time and a little OJ is all you needed.

I'd still watch the hammer for wear on it's face.  I don't know much about the metalurgy going into these parts, but the guys smarter than me always say never do anything more than polish as they are "surface hardened" and going through that hardened layer can cause the parts to wear very rapidly (ie after a few thousand rounds).

Maybe someone who knows can chime in on whether a "few" thousanths is ok or not?

rvb

seems there are some folks here who can not understand what i said , sorry!!

there was NO metal removed from the hammer surface where it hits the fireing pin the metal removed was at the point where the hammer hits the mag catch release..., far below where it hits the fireing pin, try reading comprehension for a change!!!

....................I AM SORRY....!!!..............................

i got my nomenclature mixed up !! the hammer was hitting the rear face of the bolt hold open catch, removing some burrs and a "high" spot from the front face of the hammer cured the problem

OK ?

Quoted: ....................I AM SORRY....!!!.............................. i got my nomenclature mixed up !! the hammer was hitting the rear face of the bolt hold open catch, removing some burrs and a "high" spot from the front face of the hammer cured the problem OK ?

As with eveyone else I can not see where this would have helped a damn thing seeing the hammer is to the rear when the bolt is brought back far enough to have the bolt catch engage in the first place. I personally don't care what you do to your rifle as long as you don't pass bad info to others that might cause them to ruin their rifles also.

Quoted: OK ?

No.        

I give up.      

Do what you want.  Just don't post any more "surgury" here. You'll be sued for both malpractice and operating without a license.  

Please never sell your rifle for more than what the scrap metal is worth.

rvb

thank you all for the flames...!!

it worked & that is all that maters to me !!

in the words of your favorite liberal "shove it"

What are you, 12 or 13?

Quoted: thank you all for the flames...!! it worked & that is all that maters to me !! in the words of your favorite liberal "shove it" hr

I did nothing but try to give information and offer advice.... up until your "reading comprehension" comment.

Go back and read this thread carefully, with your rifle handy. Look closely at how it works (it's not difficult). Download the armors manual. If you've done this, then you need to work on YOUR reading comprehension.

You obviously do NOT understand how the parts work together. Lord knows what else you've "fixed" on your rifle.

I'm not wasting any more of my time on you or on reading this thread. Have fun shooting your hacked up hunk of scrap metal.... I just hope you haven't tried to "fix" any of the safety features. not for your sake but for the safety of those around you.

rvb