Finished my first build about 2 years ago. Don't get to shoot much, bu every time I do, it seems there's a new issue with the gun. The casing has a well defined scratch from the shoulder of the brass to about half way down, also if I chamber and eject a live round there is a well defined "U" on the bullet. That must be from the feed ramps, I would imagine. What can I do for this? The other issue is the freakin thing jams FREQUENTLY during rapid fire. Could this be an issue with the gas port aligning with the gas block? I'm not sure, these are just guesses. I use quality ammo. Took a class at a school with a gunsmith as the instructor, so I assumed we did it right. Just seems like theres something that could be done to fix these issues, and I'd rather not drive 2 hours back to the school to fix them. Thanks for any help.

I'll be the first to chime in with: Parts List? The experts are going want to know what your upper consists of as far as brands of parts.

Upper  is JM receiver with stag arms chrome bolt/volt carrier group. Daniel defense 14.5 inch chrome lined barrel with Troy ind. claymore muzzle brake and m4 feed ramps.  Carbine length gas system. Low-pro gas block. YHM spectre quad rail-don't think that'll affect anything.
Lower is stag arms receivr, dpms guts kit. Magpul mags seem to work flawlessly, anything else jams during rapid fire. FTFs, FTEs and double feeds...little bit of everything, lol.

Its newly built like you said and you don't get to shoot much so you might still have to run some rounds through it.
Is everything lubed.

What weight buffer do you have.
Sounds like you might be over gassed with a carbine length gas system.  You might have to slow things down with a heavier buffer.
Check your gas key to maker sure it isn't loose.
Check the length of your buffer spring.  Something close to Length: 12.75"
Look at your chamber is it smooth.

Someone else will come along and correct me if im wrong.

Carbine spring is about 10 3/4"

cmorgan: Its not uncommon for new rifles to have bugs, esp homebuilt jobs using components from multiple sources.  The problems you are experiencing are not all that unusual.  I suggest you treat them as having two possible sources.  

The FTFs may be caused by inconsistencies and roughness in the feed ramps and locking lugs.  If the rifle were mine, I'd get out my trusty Demel tool and use a small conical grinding stone to blend the feed ramps for a smooth junction between the receiver and the barrel extension, also to knock off the sharp edges on the adjacent lugs, it doen't take very much grinding to get it done.  Then use the rubber abrasive tips to polish those same surfaces.  Place your upper receiver w/o the BCG in a bench vise upside down, so you can insert the Dremel tool right up against the ramps and lugs.  You can test the feeding cycle in slow motion to see if the bullet tips are hanging up.  Some scratching of bullet tips and cases is normal and unavoidable, but in no case should the rounds fail to feed smoothly from mag into the chamber.

The FTEs may be caused by insufficient gas coming through the tube, or the spring/buffer combo being too heavy.  Start by inserting a single loaded round into the chamber and dropping the BCG into battery.  With a Pmag inserted, does the bolt lock back after the shot?  If not, double check your gas block to insure its fairly centered over the port in the barrel.  If it is, next check your buffer, what weight is it?  Is the spring a standard carbine model?  Always used brand name components, springs and buffers from Spikes are a good bet, same with those from heavybuffers.com.  Keep tinkering with these components until the bolt locks back with your factory ammo.

Don't get discouraged, your efforts to isolate the faults and correct them will eventually be rewarded.  Report back here with your findings so the DIY gang can provide ongoing advice.  - CW

http://www.dremel.com/en-us/Accessories/Pages/SubCategories.aspx?catid=2008

Does your bolt hold open after the last round is fired from a magazine?

 

Thanks for the help guys. I can't remember what weight buffer. Bought one of brownells' with spring. When I test fired after the build, the bolt wouldn't hold open. My instructor swapped the buffer out for a lighter one, said they shipped me the wrong wieght by mistake. It every once in a while won't hold open now. Probably gonna be a while before I can tinker with it, but when I do I'll let u all know how it went. Thanks