Hammer pin broke...help please

I've had my 9mm upper for a few weeks and this is my first rodeo with a 9mm upper (though I've run other AR's for years). Here is my setup: SBR lower w/ what I thought was a magical DPMS hammer and standard trigger, pins, etc. My upper is a RRA receiver, a Colt barrel cut to about 8", and what looks like an RRA bolt that is NOT ramped. I'm running a Spike's mag block with C products mags. My hammer pin snapped today. I'm aware that my bolt probably needs to be ramped BUT I have a 9mm hammer that the seller sent with the upper and I wouldn't mind installing it and making this a dedicated lower. My question is does the 9mm hammer alone relieve the stress on my hammer pin or would I still need to have my bolt ramped as well.

Try some KNS pins.

It took just over 10K rounds to break a hammer pin in my Oly setup. I got the KNS pins because I also use this lower with .22LR.

Life is too short to mess around with a 9mm setup that breaks pins. Get the KNS pins and don't worry about ever breaking a pin again.

ETA: added an edit to be the third in this thread with an edited post, I don't want to feel left out.

Unramped bolts break hammer pins a lot more frequently than overuse does. Spend the $35 and get a set of KNS pins. Then, have ADCO ramp your bolt (the bolt ramp matches the M16/AR-15 profile) so you'll run smoother. That cost me another $35 or so, and I've been very happy with the results.

So no one is weighing in on the 9mm hammer? I have one sitting in the parts bin but I don't know if it's worth using if I'd still have to get my bolt ramped regardless. I started this project thinking I was not going to make this a dedicated lower because it's my only SBR. But between the mag block and the buffer, it's already a pain in the ass to switch back so now I'm thinking why not just install the hammer and some KNS pins and move on.

i would still get the bolt ramped and use the 9mm hammer since you have it. but until you SBR another lower to use a 5.56 upper on, i would leave the standard hammer in until that stamp come back. just so you have to option of switching uppers. also the KNS pins go on all my SBR lowers just because i will have them for life and its just a little insurance that to holes dont open and keep the pins in place in case they break.

Okay. I have a buddy picking up some KNS pins from out of town (I live in the boonies..) and I'm going to run my 9mm hammer until I can get the bolt ramped. I would like to have a local machinist ramp my bolt so that I wouldn't have to ship it and be without for a week or more. I've searched and can't find the exact specs on the ramp. I've come up with 1" to 1 1/4" for length of ramp and about 3 degress, but I can't seem to find a depth for the lowest part of the ramp. Anyone have specs they can post up?

Thanks for the help.

The 9mm hammer is poo. Use a rounded (not notched) standard hammer instead, and with a ramped bolt you can run pretty smoothly. However, that 9mm hammer is finicky and is not always reliable in the best of situations. Better to go with a version of the hammer that the Colt 9mm SMG/carbine was invented with - a standard, rounded hammer.

Negative, the 9mm hammer doesn't play well with a ramped bolt. My order of preference is. 9mm Hammer (unramped) < Std rounded Hammer (unramped) < Std rounded Hammer (ramped). I use KNS pins as well, never had a broken anything.

edit spelling

update for those that care: I installed the KNS pins and the 9mm hammer and ran about 100 rounds through this evening. It ran like a top. As I said in my original post, I was running a rounded hammer when the hammer pin broke. But, when I went to install the new pins today, the trigger pin was broken as well. So now I'm thinking the hammer pin was already broken and the 9mm bolt just forced the issue and made me aware of the problem.

I still need to decide whether it's worth getting the bolt ramped or just put my rounded hammer back in and go to town. What do you guys think?

Ramp the bolt. Makes the gun run smoother and puts less force on the hammer pin.

Ramp it if you want to, but honestly it isn't a necessity, it just operates mechanically smoother (though you won't notice a difference).

Ramp and reinstall the rounded hammer. Your SBR lower will be able to run ANY upper with a rounded hammer, and the ramped bolt will reduce stress on the rest of the FCG.

With an SBR, you can put ANY upper on the gun, any caliber, any length. Really. So you should put in a hammer that works with everything, not just one upper. This is precisely why I used a rounded hammer in my SBR (which started as a 9mm with 10.5" barrel).

Get the bolt ramped. I run a std at15 hammer, ramped bolt, spikes st-9x buffer rifle length buffer spring and of course the spikes magwell block. Modified 32 rnds Uzi mags. Shoots everything like a champ including the steel cases stuff. Shot about 1k and no issues with pins breakage or anything associated with it.
Just my .2$

Would someone in the "Get the KNS Pins" category please explain something to me:

If the blow back 9mm bolt is breaking the hammer pins, presumeably because of the angle that the bolt pushes back on the hammer puts stress on the hammer pin, right?

Ramping the bolt essentially puts this force HIGHER on the hammer, therefore rotating the hammer back instead of hitting lower on the hammer putting more force on the hammer pin.

If you put harder pins in, aren't you just transferring this force to the pin HOLES? Isn't this what causes "egging out" of the hammer pin holes on 9mm AR's?

Wouldn't ramped bolts be a preferable solution to this issue?

Thanks in advance.

No, ramping the bolt (with a regular "rounded hammer installed" reduces stress on the hammer pin by moderating the acceleration of the hammer from fully forward to moving backward, and extending the process over a much longer time (and longer distance of bolt travel). It also recreats the bolt carrier profile of a standard AR/M16 carrier, which I think should be an important point.

The Colt SMG/carbine platform was built by Colt on a standard M16 lower with a pinned-in magazine block, so it should run best when the parts are most like standard M16 parts, right?

I have a ramped bolt from spikes and a DPMS LPK and hammer. Broke a hammer pin after about 5-600 rnds. What is that notch for in the middle of the hammer pin for? That is where it broke. My Geissele trigger & hammer pins dont have it.

Do the KNS pins not have that notch? If they dont it would make them about 100% stronger.

Some hammers have a detent inside the pin hole that will ride in the notch. Probably to keep the pin from walking out of the hammer and coming out of the lower.

Also the pin has a notch near the end that the hammer spring can ride in on the trigger pin probably for the same reason.

Exactly. Some hammers have what is called a "D" ring, the notch in the hammer pin corresponds to this "D" ring.

Pics from Armalite:

"D" ring:


Location of "D" ring is part number 29:

Not "D ring," it's a "J" spring because it's shaped like a J. The J spring in a hammer sticks out into the hole for the hammer pin, and it retains the hammer pin. Since the trigger and hammer pins are interchangeable, there are two grooves: one in the middle for the hammer's J spring, and one at one end for the leg of the hammer spring to rest on to retain the trigger spring.

Most pin failures that I've seen documented in any way have been at the middle groove. At this spot the pin is as thin as at the groove at the end, but it's under far more stress. You could call a hammer spring that breaks in the middle a "typical failure mode" break, but what that really means is that it's the most likely way for an unlikely thing to happen. Just make sure your standard pins come from a reputable source and you probably won't see that sort of thing again in tens of thousands of rounds.

So is DPMS not a reputable source? Are the KNS pins considered the strongest?

I have built several lowers with DPMS kits and never had a problem with them. However, pins CAN break (VERY INfrequently), and they tend to break at the middle groove.

KNS non-rotating pins are stainless steel and without grooves, so they are inherently stronger.

The three KNS non-rotating pin sets I have (all three are Gen 2) all have a middle groove for the hammer's J-spring in the hammer pin. It is my understanding that the KNS non-rotating pin sets are believed to distibute some of the rearward force on the hammer pin to the trigger pin via the interconnecting side bars. Thus, the hammer pin is less likely to break.

There are vendors that sell hammer pins that are not grooved internal to the receiver. Such pins typically are retained via c-clips outside of the receiver. The down side is that the clips can scratch the receiver finish.

Best of luck with whatever you pursue.

Not legal advice, MHO, YMMV, etc.

Geissele hammer pins to not have the groove in the middle. They have one toward the outside more like a trigger pin. Getting rid of that groove will help more than anything I believe. That is where they always break. It's a perfect stress riser.

I've read one report from someone who said their Geissele trigger would only work with an un-ramped bolt and another that said it worked with his ramped bolt. Considering the differences in the way ramps are done by different vendors, I'm just going to try it and see what happens with my CMMG ramped bolt. I already have the trigger.

My mistake, the hammer pin IS grooves, though the trigger pin is not.

i had a trigger/hammer pin break on my SMG a while back when experimenting with a 9mm upper build. when running full auto it was definately slapping the hell outta the trigger because my dam finger was hurting after shooting it. ran about 150 rounds and then the hammer pin broke. took it apart and found the trigger pin was also broken. the upper ran fine on my Colt 9mm lower, but when using it on my Sendra FA lower (with 9mm mag block) it did this. i figured it had something to do with the buffer weight or buffer spring but never figured it out (as of yet).

Just dug some Geissele pins out of my parts stash; easy to tell due to the dimple in the end.
Both pins had the center groove, and one end groove to retain the trigger pin.
Moon

Clear up some confusion on my part. I have a Colt 9mm carbine of recent vintage; it came with a standard hammer and stainless steel FCG pins.
I replaced the OEM parts with a Geissele SSA, but used the reputedly stronger stainless pins.

How can I tell if I have a ramped bolt? There is a taper at the rear of the bolt about 3/4" long.
And what is the collective opinion here; am I well served with the stainless steel pins or would I be better off with KNS?
The rifle will be SBR'd when the paperwork goes thru'.
Moon

I have installed 3 or 4 Geiselle triggers over the last 6 months. The pins all looked like the pic above. It made them very easy to distinguish from the stock pins which are used for the initial setup. I did find some pics of GA pins with the groove in the middle though, so I called Geissele for clarification. The High Speed Models (i.e. the adjustable ones like the DMR, Match & Service) Have the pins like the ones above. The SSA type triggers DO have the groove in the middle. The pins above can NOT be used in an SSA. Moral of the story, if you want a GA trigger w/o the center groove get a Service, Match or DMR. The Match may be too light for a 9mm though. Im not sure if the hammer spring rate is any different or not, but I might be, so I wouldn't risk it w/o calling GA.

ODM, thank you so much for clearing that up; didn't mean to argue with the PP about the pins, but knew darn good and well that mine had the center groove. Doubly confusing because the center groove is what holds the hammer centered on the pin on the SSA setup. I gave all that some thought on my morning walk....

Geissele wasn't sure how the SSA would run in a 9mm, so ya' know. Thus far it has worked great in mine, and it appears some others are trying this approach as well. Tried to work a deal with Geissele to let them know how the trigger ran in my carbine in exchange for a break on the price, but they weren't biting. Apparently they're selling every FCG they can make, and at full retail. There is a reason for that.

Now if I can gets some opinions on whether my bolt is ramped, I'll be a happy camper.

Thanks again,
Moon

Look through this thread. There is a bunch of quibbling in it, but if you skip that and look through it, there are some pics that show ramped and un-ramped bolts.

http://www.ar15.com/forums/t_3_15/385344_Comments_on_Picture_of_my_Ramped_9mm_Bolt____by_ADCO.html&page=1

I'd like to sum all this up if you guys don't mind. I'm currently running a 9mm hammer and KNS pins with an unramped bolt and it's running like a sewing machine. From what I understand, the general consensus is that I could reinstall my rounded (DPMS) standard hammer and run it with an unramped bolt and my KNS pins and most likely not have any issues for awhile with broken pins. BUT, having the bolt ramped would allow for less wear and tear to my pins and pin holes and is pretty much always worth the 50 or so bucks it costs. .

Jeeze, ODM, talk about 'War and Peace'! I almost stalled out in the retreat from Moscow....

All that said, it appears that my Colt has a ramped bolt, and it came with the un-notched hammer and the SS pins.
I will have a tax-stamp lower, and intend to shoot the snot out of it (semi-auto), and would really rather not have trouble with it later.
Thanks for the info!
Moon

Holy hell!
Having gotten an education from this thread, I had a chance to examine an older Colt 9mm today, and the difference between the ramped and unramped bolts are completely obvious when you get a chance to examine the real thing.
Some of the photos in the link didn't emphasize the degree to which the unramped bolt had a squared rear face and extra groove (meant to foul the hammer if the hammer follows the bolt closed). Let me rephrase that; now that I've seen both bolt types in 3 dimensions, I can tell the difference in the photos, but it wasn't clear to me before

In any case, I'm happy that Colt recognized the problem and addressed it from the factory. I'm also happy that the bolt is now set up for a standard FCG, which means I can use the Geissele SSA trigger.
And it particularly means that hammer pin breakage shouldn't be an issue with my rifle, and I've gotten a real education on the matter right here.
Thanks guys!
Moon

I found out yesterday that my buddy's dad's workplace has a mill and he said he could hook me up with getting my bolt ramped. Pretty excited that I can get it done without having to send it out AND it will be a freebie minus a 12 pack of brews for the labor donor. Wish me luck.

Good luck and be sure to ask what brand of beer to bring.

Get him good beer, but wait 'till he's done to give it to him!

Is the info here precise enough to let him do the work?
Moon

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