Gunsmithing Cav 15 Lower firing on trigger reset

[texrifleman]

I put together a cav arms lower with an olympic arms 45 acp upper and DPMS lower parts kit(semi). It went together fairly well. Took it out to sight in yesterday and it would fire when I was allowing the trigger to reset. So once on trigger pull and then again on trigger reset.

When I look at the hammer pin it does not insert all the way through the receiver to a flush settin on both sides. I then started releasing the hammer and resetting it with the upper off and noticed that the hammer was resetting with a cant towards the mag release side. This also happened to the side with the least amount of pin.

None of the parts installed are full auto parts. I do not want this thing to double when I fire it. I think that the problem is the pin length and the cant on the hammer during reset.

Has anyone run into this issue before? If so, what did you do to resolve it?

 

[frog5215]

Re: Cav 15 Lower firing on trigger reset

The receiver sidewalls are thicker than a standard receiver.
The pins need to be centered, and properly captured by the j-spring on the hammer pin and the hammer spring in the side groove of the trigger pin.
If the hammer isn't straight, the sear and disconnector aren't getting a proper bite on the notch of the hammer. Mine did a 3 round burst. Actually it doubled first, but I thought it might have been a bump double. The 3 shot burst was a shock, and it might have kept running, but the facility at which I was shooting prohibits more than 5 rounds in a rifle mag.

I've used Chip McCormick and Timney triggers in these to good effect (but there's nothing wrong with your DPMS LPK). These require captured pins (circlip) and you absolutely can't follow factory instruction on the Timney since the receiver floorplate won't support the set screws. I have actually used home made brass pins with these drop in triggers. the hammer pivots on a bushing so hammer pin breakage is unlikely, while it's pretty common with traditional pins in blowback guns, including .22s.

A couple of Novembers ago I shot this puppy in Cedar Ridge's carbine match. Mucho fun.

 

[texrifleman]

Re: Cav 15 Lower firing on trigger reset

Do you think the KNS anti-rotation pins will work on these lowers?

 

[frog5215]

Re: Cav 15 Lower firing on trigger reset

I think there's a deficiency in OAL of these for one or both pins.
Cav briefly offered long pins. They shouldn't be hard to fabricate from water hardening drill rod., Just make the distance between circlip grooves such that they fit over the width of the receiver.

 

[texrifleman]

Re: Cav 15 Lower firing on trigger reset

Thanks for the idea. I will mike one tonight and cut a bit tomorrow.

 

[gunnut284]

Re: Cav 15 Lower firing on trigger reset

Make sure the pins are captured properly by the jpin (for the hammer pin) and hammer spring legs (for the trigger pin). Also make sure the disconnector spring is installed correctly (flaired end down). Or you might have an out of spec hammer or a lower with incorrect pin holes.

We just ran about 500 rounds through two CAV-15 lowers (one 9mm and 1 .223) with no problems. Both have standard DPMS lower parts, the lowers shouldn't require anything non-standard (other than takedown pins).

 

[texrifleman]

Re: Cav 15 Lower firing on trigger reset

Thanks for the tip. I re installed the trigger and hammer group last night and will test it this weekend. It looked like I had the hammer pin installed with the notches in the wrong position. The pin seams to be fitting snug to the receiver now.

 

[texrifleman]

Re: Cav 15 Lower firing on trigger reset

I got the hammer pin in correctly now it runs like a champ.

Anyway here's what is ended up looking like.