After an enjoyable 200 rounds this past weekend I found the bolt release lever broken when cleaning this carbine tonight.  This is the piece that the Hahn block pushes up and then it hold the bolt open after the last round is fired and then after stuffing a new magazine in the carbine you press the side mounted button and the bolt slides forward chambering a fresh round (just describing it's function so you know which part I'm talking about).

Anyway it broke apart at the pivot pin.  The carbine still functioned fine but I did notice on the last few magazines it would sometimes hold the bolt open with one round still in the magazine.

I have never had this part fail on any of my 223 AR-15's and wonder if the 9mm somehow causes these to fail more frequently, or did I just get a weak part?  This carbine is less than a year old and probably 1500 rounds is all.

All information, opinions, and speculation welcomed.  Lower parts kit was a RRA set for this build.

not the bolt catch .   You need a heavier buffer.

Lash Q buffer

It will solve your problem next time.

I am running the Slash Q buffer, just checked it after seeing your reply, says "9Q" on the head, big heavy sucker!

Maybee the latch had a flaw in it......

Is any latch any better than others?  Midway offer the part in chrome $13.29 or matte black $6.99, both from DPMS.  Any other sources for good stuff or is it just luck of the draw and I got a mediocre one in my RRA set?

It's a fairly common problem on 9mm AR's that utilize the bolt hold open feature.  The 9mm bolt often has overtravel to the rear giving it a lot of momentum when it comes forward and strikes the bolt hold open eventually fatigue cracking it.  

If I recall correctly, you want approximately 1/8" of rearward bolt movement behind the bolt catch.  If you have more than that the normal fix is to put a spacer in the buffer extension tube to limit bolt travel.  Some people tape up quarters and put them in the tube, the amount of $2.75 seems to ring a bell.

Thanks for the tip.  I will try to mesure the overtravel then make up a spacer from aluminum to put in the very rear of the buffer tube.  Then I need to order a new latch and the spring that escaped, may as well get another roll pin too.

Quoted: It's a fairly common problem on 9mm AR's that utilize the bolt hold open feature.  The 9mm bolt often has overtravel to the rear giving it a lot of momentum when it comes forward and strikes the bolt hold open eventually fatigue cracking it.   If I recall correctly, you want approximately 1/8" of rearward bolt movement behind the bolt catch.  If you have more than that the normal fix is to put a spacer in the buffer extension tube to limit bolt travel.  Some people tape up quarters and put them in the tube, the amount of $2.75 seems to ring a bell.

Right on the money . Another related thread on the same problem.

Click Here...

If Bill is already using Slash's 9-Q buffer, isn't all the overtravel taken up?  Isn't that the primary purpose of Slash's heavy-duty buffer?

What about the buffer spring?  Its an important part of the equation as well.

buffer weight + spring+ carrier wheight + ammo + bbl length + port diameter (obviously 5.56 only) = RELIABLE CYCLING and proper natural wear of components.

I use in my 9mm AR an ISMI spring.  The damn thing is so stiff that my LMT 10.5 and my 14.5 midlength wont cycle reliably even with premium ammo and standard buffers.

It works wonders in my 9mm rig using from Federal AE to Speer GoldDots.  

I can easy notice the difference in carrier/bolt travel when compared to the standard buffer spring.  

There are some flat wire springs that are stiff as well.  

Good luck.

I have a reliable setup with a 16", but am in the process of going to a 5".  My understanding is the shorter the barrel, the heavier the buffer.  Then if you go suppressor, even heavier buffer.  I have a Hahn top loader, so the bolt stop is not an issue.  Please correct me or elaborate...

Quoted: What about the buffer spring?  Its an important part of the equation as well. buffer weight + spring+ carrier wheight + ammo + bbl length + port diameter = RELIABLE CYCLING and proper natural wear of components. I use in my 9mm AR an ISMI spring.  The damn thing is so stiff that my LMT 10.5 and my 14.5 midlength wont cycle reliably even with premium ammo and standard buffers. I works wonders in my 9mm rig using from Federal AE to Speer GoldDots.   I can easy notice the difference in carrier/bolt travel when compared to the standard buffer spring.   There are some flat wire springs that are stiff as well.   Good luck.

Port Diameter?  You have a Gas Operated SMG?

Quoted: Quoted: What about the buffer spring?  Its an important part of the equation as well. buffer weight + spring+ carrier wheight + ammo + bbl length + port diameter = RELIABLE CYCLING and proper natural wear of components. I use in my 9mm AR an ISMI spring.  The damn thing is so stiff that my LMT 10.5 and my 14.5 midlength wont cycle reliably even with premium ammo and standard buffers. I works wonders in my 9mm rig using from Federal AE to Speer GoldDots.   I can easy notice the difference in carrier/bolt travel when compared to the standard buffer spring.   There are some flat wire springs that are stiff as well.   Good luck. Port Diameter?  You have a Gas Operated SMG?

My bad, post edited.

mine bent the bolt catch. running a Q buffer, there is only 1/8 inch of travel.

One thing to keep in mind with the 9mm AR is that the TOTAL cycling mass of the bolt and buffer is MUCH heavier than the original 5.56mm rifle's bolt stop was ever designed to stop.  All that extra weight crashing into the bolt stop is going to take its toll eventually, but the effect is reduced by minimizing the bolt overtravel, as was mentioned.  If I were going with a 9mm AR, I would not be using a bolt stop for this very reason.

Really good info here guys, much appreciated.   I do like the idea of last round bolt hold open. I wil check bolt travel and add a spacer to limit overtravel to 1/8".  got another latch on order now.

My replacement bolt latch came today and is now installed along with a replacement latch spring and spring follower as these were "set free" when the latch broke in the field.

After putting the lower back together I put the upper back on and it appears I have just less than an 1/8" of travel when the bolt stop is holding the bolt back.  I will watch this carefully from here on out.  The good news is if the bolt catch does break again the weapon is still functional.

Close examination of the break shows the latch broke around the pin and it looks porous, almost like cast iron!  Very odd indeed.  Are bolt latches hardened to the point of being brittle?

I had the same problem a year ago or so.  A fellow member suggested the fix should cost exactly $2.75 in US quarters.  

It turns out that if you put 11 quarters in the rear of your buffer tube it will limit the rear movement of the bolt.  After doing this mod, my bolt only goes about 1/8" past the bolt release.  On the forward motion of the bolt it then does not have enough momentum to break the bolt release.  

Works just fine for me.

acidman:  I am using a special buffer that is both heavier (don't know why perhaps to slow bolt movement?) and much longer (to eliminate this bolt overtravel).  This is the Slash Q Buffer which I bought for this 9mm AR15 build based on good reports here at arfcom.  I have what appears to be slightly less than 1/8" of bolt overtravel with this setup.

I hope my bolt latch failure was a fluke caused by a poor quality bolt latch as it reall looks like the metal was porous at the break (I'm looking at it right now).  This latch was part of a RRA lower parts kit, so while I expected top quality, I now am convinced all the manufacturers buy from the same sources and put the parts in their own bags. I have had both good and bad from expensive and inexpensive parts kits and next time will just buy what is offered cheap as it is a crap shoot anyway IMHO.  But I have very rarely had Colt rifles fail.......