Nelson conversion double firing

Normally I use CCI SV with no issues. I was running low so I went to SK SV ammo. All was Ok but during timed and rapid fire It double fired twice. That was two weeks ago. I tried it again and it did it again today. Is this a recoil spring issue? Thanks for your suggestions.

Hello kohlerpartsgod,

Doubling can be caused by many things, the recoil spring (in itself) would not typically be one of them.  I would first look at your trigger over-travel adjustment (screw).  Back it off and see what you get.

Jim

I don't think the over travel screw is doing it, if it is your disconnector isn't set-up correctly. What is more likely the problem is Ammo velocity. What color is the box, SK Yellow is same as CCI but Pistol Match is Green and Pistol Match Special is light Green and both slightly more than 100  Ft/Sec slower. Other SK .22 ammo is faster depending on Box color which identifies the type but the 2 Green box ammo is the slowest. If your not having the problem with CCI  and using the SK green box your sear might not have time to reset properly

Guys, I am running doubling problem too. It started recently. I always ran aguila SV same batch. Advantage Arms upper. Trigger has long pre travel and no overtravel screw, so not it. Sear engagement is great, no issues with safety checks. I had it on 2.5lbs and after first time it doubled I went to 3.25-3.5 with about 1.5-2 lbs sear spring pressure.  Now it doubled 2 times again. There were more bullets in the mag, but it stopped at doubling only. Something is off. Recoil spring or ammo hotter load causing more shock? Mainspring is at 16lbs...I know it is low, but with 9mm upper it was just fine.

Maybe time for a detail strip and clean?  My Rock River hammer followed a couple times a while ago. I stripped it to the frame. Everything was pretty gunked up . Ain’t done it since.
Kutt

Well, doubling is caused by hammer coming off the hooks, or the disconnector not disconnecting/resetting in which case hammer never went back on the hooks. My hammer and sear geometries are good, engagemwnt is long enough not to cause issues. Everything is well.oiled and the disconnector has plenty of travel to disengage. I have a feeling it's the shock. Though we think that the 22lr should not cause much shock, I guess it does. It's faster, sharper shock due to low mass of the bolt.  So can it be just that, occasional hot ammo throwing off your perfectly tuned gun?

I'd move to a 19lb mainspring. You won't feel a difference in trigger pull. What recoil spring are you running. 8lb should work fine.. if that fails change to a new disconnector.  You can always remove the grip safety and  observe how much clearance you have with the disconnector in its down position( slide back)

Slightly preened breech face or bolt fact can cause doubles.

Worn disconnector (top) or disconnector slot in the bottom of the side can also cause issues.  Also, sometimes conversion units do not exactly place the disconnector slot in the bottom of the slide exactly over the disconnector and will leave it partially depressed.  As things wear, it gets worse. 

CR

I will move to a stronger mainsping. Using 8lb recoil spring. Everything else looks good.

I Assume SK SV  ammo your using is Yellow box that has 1070 Standard velocity. Odd is the change in trigger weight! Usually this is to to a stop screw set too close to the sear release point so that any slight change in sear engagement causes weight increase but never decrease. But you have no stop screw. Hammer sear wear would cause problem to go one way usually trigger pull will lower. Which leaves the disconnector. My Nelson has a disconnector slot width of .172 and the my frame disconnector hole is .165. I put my Nelson slide on a Caspian frame that has thicker rails so requires fitting to slide but Nelson slide fit and is loose so disconnector fit in the slide could cause a problem if the Nelson slide fits loose. Some disconnectors that fit in the hole move so it might cause doubling if disconnector is dragging in the slot but I doubt it will create a lighter trigger pull. I think the place to start do some some trigger weight testing with the Nelson Slide off the Frame. With no slide on the frame as a piece of steel that has a square edge, cock the hammer, push the disconnector down with that steel, pull the trigger, hammer should not fall, hold the trigger back and slide the steel off the side of the disconnector so that the square edge allows the disconnector to pop-up quickly. Hammer should not fall. Use the steel to push disconnector down again, pull trigger then let go, slide steel off the side so that it againd pop-up quickly, Hammer should not fall. reason to slide the sleel off the side of the disconnector is the front and back edge of the disconnector is beveled therefore disconnector will not "snap" up. If it does you have disconnector problem.
 Stronger main spring ?  Do you mean recoil spring?

Thanks for the suggestions. 
My SK ammo is yellow box. 
Gun is cleaned regularly. 
Not sure on the recoil spring, I always assumed it was a 9#. I have a few 8# and 10#. I have ordered new 9# springs from Nelson. I will try a new 9# spring and the 8# and see what happens. If I still have issues I will try the 19# mainspring. 
I would just stay with CCI SV but things being what they are I may have to get this pistol to like different ammo. 
I will circle back if I still have issues, thanks for the suggestions.

So I did all the safety checks on my AA conversion and frame. Disconnector disconnects, resets, slight slide goes to half notch as it should, full slide goes to cock. Disconnector resets only after trigger release.  Slide release launches both 22 and 9mm slides forward with no hammer move.  Very strong reset, strong hammer hold. No idea why the gun would double. I will replace mainspring from 16 to 19 in near future, but I cannot imagine that is the issue. 9mm shoots perfect.

Any possibility it could be from bump fire? Loose grip and short reset? Just throwing it out there.

Hmmm I don't have overtravel screw on the trigger, so overtravel is pretty long. However, maybe I did limp hold it those few times.  That's definitely a possibility. I will pay more attention to that. Thanks, that actually makes a lot of sense!

FWIW, the fit of the grip safety can act as a trigger stop as well.

On the Baikals, the breech gets peened against the bbl reducing headspace and resulting in slamfires, sometimes while loading. Are you sure you don't have a similar issue?

I use a chisel like tool to scrape the pocket in the slide from below. I get a small tit at 12:00 in my 208...

Bruce, thanks! THAT WAS IT!!! FP chanel had gunk on it, probably resulting in holding FP in engaged mode. I had same issue before few times when loading and dropping slide on 1st round. I don't know why I forgot this can result in doubling. Nothing is peened, just dirty. 

Easy solution = vaacum cleaner. Harder solution = disassemble breech.  I probably need to disassemble anyway in near future and polish things out.

Thanks everyone!!!

Brake cleaner!

I have one of those ;-)

Had a very accurate Marvel kit do the same last September.  One weekend I shot a 879 with it and the next weekend it doubles in slow fire.  It was on a Springfield lower.  I switched to a caspian lower, then it did the same thing in time fire with that frame.  Needless to say, I was not amused, but it did rule out a problem with the bottom half.  Asked everybody I knew what they thought it could be.  Finally, I stripped and completely cleaned it.  When I dissassembled the breech/firing pin assembly and cleaned out the firing pin channel, there was a small sliver of metal that had somehow found it's way in there and randomly kept the firing pin from retracting.  Problem solved.