Okay, before I even get into the issue here, note that this is not my rifle.


I spent the day yesterday at my parents' house, helping my dad install a Timney Calvin Elite. Originally I wasn't going to include the name of the trigger in the thread because I don't want any negativity directed at them from people who don't understand the issue, but I'll say it here. The trigger that was used is not the cause of this issue.

The install was straight forward. I've done triggers in the past, regular and drop-in, with no issues. So, after the install, we put the upper on and tested for function -- the bolt wouldn't charge all the way back. It got stuck. At first, I thought that maybe one of the trigger pin holes was out of spec, but he decided to call Timney to see what they could tell us. Eventually he passed the phone to me so I could talk to the rep about the issue in more detail, and with the upper off, I noticed that the hammer was binding before it even got to the disconnector, so I relayed the info, and the guy suggested we either take a dremel to the front of the cavity to take off some material on the lower, or call a gunsmith to do it with a mill.

Several hours later, after disassembling and reassembling the trigger 6 or 7 times, we got to a point where my dad thought that with use, everything would smooth out and the rifle would function properly. At this point, the hammer would only bind when we tightened the tension springs in the trigger assembly, so we went out and tested the function. The bolt carrier got stuck during charging as well as after every round shot, but we could smack the rifle to get it into battery. It would short stroke, it would have problems feeding a round, etc., obviously because it wasn't moving freely. No big deal, we'll just go back and take some more material out.

After a few more times taking everything apart and taking some material off, the trigger would function fine without the upper. Once we put the upper on, I noticed that while charging the BCG, it was still getting a little hung up, but he thought it was just tension from the spring -- not something I notice in my rifle, though I'm using a carbine tube with an upgraded spring, where he's using a rifle tube and the DPMS rifle he had was clearly out of spec in one aspect. It's possible that there were other issues with fitment.

Here's where the real issue arose. I grabbed my 20 round Lancer mag, he grabbed two 10 round DPMS smoke mags, and we went out to shoot. He charged the rifle, though he did have to smack it once to get it to go into battery, and he took two shots in quick succession. I was impressed, this 1.5lb trigger must be worth the money, because that seemed a lot faster than my SD3G. He did it again, then again, and looked over at me, at which point I gave him a big thumbs up. After he shot the whole mag, he let me know that he was pulling the trigger once each time.

Oh.

He shot the next magazine, and he was able to get a single shot off with a single trigger pull, only one time. He handed the gun to me, and I put in my mag, released the bolt, and took a shot, and had the same thing happen. Before I knew it, my 20 round magazine was gone, so I didn't have a lot of time to test it, but I too only had one instance where a single round was fired with a trigger pull.

My first instinct was that there's an issue here, that the hammer isn't latching onto the disconnector, and it's following the BCG home, resulting in a second shot. He's under the impression that the trigger is just so light, that the recoil is causing us to pull a second time without noticing. Here's the thing. Like I mentioned, it's the Timney Calvin Elite. It's a 1.5lb, single stage trigger, and I'm pretty sure that it's the lightest trigger on the market. There's a Jewell two stage trigger that's supposed to get down to 1lb, but it's not quite the same as this. I have an SD3G in my rifle, that I've shot thousands of rounds with. I do ride the trigger to reset often, but I've never pulled the trigger a second time on mine unintentionally, and with all of the other issues we had prior to this happening, I'm leaning toward there being a functional issue.

I won't be back there for a while, so I won't be able to take the rifle out with ear pro and a bench or rest etc, to really see for sure if the trigger is being pulled twice or if there's a real issue here, but I'm posting anyway to get your opinions. What causes a double tap anyway? Is this something that could cause the rifle to fire more than once?

Your analysis is likely correct - it's either not overlapping the disconnector enough, or the trigger is so light, you're bump-firing the second round.

Since you didn't rip off any bursts, my first instinct would be insufficient disconnector overlap.

ETA you can test this by ripping quick and holding on the trigger pull, rather than trying to squeeze slowly. If the disconnector catches, then let off SLOWLY and see if the second round lets go. If so, that's insufficient disconnector overlap, pure and simply.

You paid for working parts,  not parts that you have to modify to make them work.

Have you tried the Lower Receiver with a standard LPK?

I would remove the trigger assembly and install a standard LPK and test the gun for function, to make sure that you don't have problems with the geometry of the Lower Receiver.  If the standard parts work properly, then the trigger assembly is at fault and you need to send it back.

Just wanted to give a shoutout to Dano523 who recently helped me at the range with a similar problem with my Timney trigger.  I had to adjust it out 4 times, 1/8 turn at a time, to get it to completely stop doubling, but it’s good now.  Thanks so much, Dan!  Really appreciate it. —John