I just installed a Timney trigger into my M&P15T and now I’m having feeding problems roughly once every 10 rounds. (the spent shell ejects but the new round doesn’t chamber properly and gets a little bent … more like dented actually… by the bolt coming forward) Is this what’s referred to as short-stroking? The gun is fairly new and has only had ~800 rounds through it but I never had this problem before replacing the trigger. The trigger itself seems to work fine…very crisp. What could cause this?
Short stroking is when the gun is shot completely empty and doesn’t lock the bolt to the rear. This is because the bolt isn’t going far enough backward.
Thanks for the response. So my gun isn’t short-stroking… when I single load, the bolt has been locking back consistently. Any ideas on what’s causing my problem?
did you try different mags?
Be sure you’re starting with a clean gun, especially the chamber.
Try known good mags and maybe another buffer spring. Yours should be 10 1/16" long or longer. I prefer buffer springs to be 10 1/4" long or longer. Also be sure that it’s lubed up properly and that you don’t have too much extractor tension or a bound up ejector.
Since this is the “technical” forum, to be technical, this is only how to diagnose “short stroking” (one can have short stroking with the gun fully loaded, of course).
Where’s the cartridge winding up when it jams? If it’s still halfway in the magazine, then that sounds like short stroking to me. If it’s out of the magazine and mashed against the feed ramps, then you’ve got a feeding problem.
Bimmer
The interesting part of this equation is that it did not happen prior to installation of the new Timney trigger. I wonder if the trigger or something is causing some drag or binding. If I were the OP I would put the original trigger back in and see what happens.
Thanks for everyone’s ideas. I’ve tried different mags with the same result so I don’t think that’s the problem. As far as cleaning goes, I haven’t cleaned the gun yet since I didn’t think the round count was high enough to need it. I do, however, keep it well lubed.
Unfortunately, it’s going to be awhile before I can get back to the range but I’ll give the gun a good cleaning in the meantime and see what happens. I’ll also try a new spring if it measures out of spec. If that fails, I’ll put the factory trigger back. What bothers me is that the Timney seems like a great trigger and I can’t think of any reason why it would affect my feeding.
Thanks again. I’ll post an update after I’ve done the above.
-Corey
It could be coincidence that the problem began when you changed the trigger.
Eliminate any doubt by going to the range with some tools and the original trigger.
- Clean gun
- load mag
- Shoot gun with timney trigger to reproduce stoppage. Pay particular attention to how much ammo was in the mag when first stoppage ocured.
- Change out trigger for original. don’t forget to bring the springs and appropriate tools.
large flat screwdriver for grip, drift for pins, allen wrench for set screws, small screwdriver to move timney springs so you can get to allen screws. - reload mag. (the same mag, with the same ammo)
- shoot
If problem goes away, you’ve now proven beyond a reasonable doubt that the problem was either the timney trigger, or the way you installed it.
If it remains, you’ve ruled out the timney trigger.
Just to be 1000% sure, I’d put the timney back in and confirm the failure again.
One thing that would also help is if you could take a pic of the failure.
Don