part 3 of the damned saga.
I got 20 Center mags, and they look fine. I inspected the heck out of them, they don't seem to be dragging on the ammunition and at this point, I don't suspect they are playing a part in my continuing problems with 2 guns. 3 brands giving problems is just TOO weird to contemplate.
First gun is a 16" M4 type. Bushmaster lower, barrel, RRA flattop upper, and a Colt SP1 non-shrouded bolt carrier. Has a non-Bushmaster hammer (marked "M" on the left side) May have a non-Bushmaster trigger also. Bought the lower as a complete Bushmaster one, but some of the lower parts appear to be non-Bushmaster.
Second gun is a Bushmaster 20" heavy barrel. RRA flattop upper, the rest is Bushmaster parts.
I am having problems getting the first round to feed on about half the new magazines. The bolt comes foward from the locked back position about a half inch to 1 inch, and stops. Most of the time pulling back the charging handle and letting the bolt slam forward again does the trick.
This has happened with some new D&H mags, anotherbrand (which I've since sent back), and the new Center mags. My old preban mags don't give any trouble at all.
There have been no actual fail to feeds once the gun is firing; it seems to occur mostly while trying to load the first round off a mag.
I have tried the old GI preban mag bodies with new springs/followers to check for a weak recoil buffer spring. They all (20+ examples) work perfectly. I also tried 9 mags with Magpul followers in the old preban bodies; perfect function. I checked the tension on the magazine catch. I don't see any dimples under the feedramps.
I did note that my firing pin seems chewed up on the collar; See here:
The pin on the left is a new (spare) firing pin, and the one on the right is the questionable one. It has alot of rounding on the rear of the collar, with some raised burring in the middle of the collar. I did check to confirm that the collar is not hitting the rear of the bolt carrier when the bolt is locked all the way back.
BOTH guns show this kind of rounding/burring. I don't know if it's normal wear, or something amiss.
I thought that perhaps the hammer was dragging on the firing pin collar, and checked the max height per some pics I found on this site. The hammer sticks up from the lower receiver right around the max 11.4mm supposed to be allowable. Per Dano's advice in a thread to someone else, I tried pulling the bolt/charging handle all the way back and slowly allowing the bolt carrier to come forward. I did feel a fair bit of resistance/rubbing about 1/3rd of the way forward. I then held the trigger down, and did the same thing, and there was no resistance this time. Hammer rubbing on the firing pin collar/bolt carrier?
The 20" gun had some resistance there also, but alot less.
Pic of the hammer markings:
.
One gun has maybe 1500 rds on it, the other has perhaps 1000 (w/ 3000-4000 rds on the buffer spring).
I did note slight side to side motion when pressing on the upper and lower, like they've worn in some. They used to be very tight when first put together. RRA upper, Bushmaster lower, in both cases.
I've run out of ideas as to what to check next. Any suggestions would be appreciated.