I got a brand new PROOF CF 6.5 Creedmore barrel on my Seekins SP10 builder kit. After break-in, I tested Hornady 140 ELDM and noticed that the bolt sometimes doesn't close smoothly. I then ejected the unfired cartridges and found they all got this bite on the brass. What could cause this? The brass case ejects at 4 o'clock, and headspace is perfect. I used JP silent captured spring with heavies spring and JP full mass BCG. any suggestions?? thanks!
any suggestions?
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AR10 brass bite help
- Thread starter exoto1225
- Start date
Oof ! First...I would make sure your bolt face is nice and smooth, allowing the casehead to smoothly slide across it. ( I would be surprised if it wasn't , JP ya know )
And I couldn't tell, are those reloads ?... or factory ammo ?
If reloads, does factory ammo do it as well ?
And if reloads, how are you cleaning the brass ?
And I couldn't tell, are those reloads ?... or factory ammo ?
If reloads, does factory ammo do it as well ?
And if reloads, how are you cleaning the brass ?
those are Hornady factory ammo. My reload with hornady brass & 140 eldm had same issue...strange. feel like a feeding issue here
Did you try a different mag and does the bolt lock to the rear on the last round.
Take a pic of the barrel extension.
Take a pic of the barrel extension.
that mark is typical of a sharp edge at the feed cone. just needs a little polish so that the brass can glide acrosst it, instead of the sharp edge actually biting into the brass and snagging it. the last bevel where the feed cone meets the chamber wall. probably only the lower 60 degrees could use a touch with a felt polishing cone.
as mentioned above, check to be sure those no burrs or something on the front face of the bolt lugs that prevent the cartridge base from sliding up, maybe polish the extractor face (but not the hook edge).
JMHO.
as mentioned above, check to be sure those no burrs or something on the front face of the bolt lugs that prevent the cartridge base from sliding up, maybe polish the extractor face (but not the hook edge).
JMHO.
My opinion, every component that you listed for your build is considered some of the best available, but it is still a parts build so function ultimately falls on you. Although it has been headspaced, I would do a quick "plunk test". Remove the BCG and with the muzzle down, place a cartridge in the chamber to see if it seats fully, then tip the muzzle up to see if it falls out. Then with the rifle assembled, slowly chamber a round and watch to see where it's binding. I suspect you may need to do some feed ramp work.
Check that the barrel extension is indexed properly, look from the rear of the upper with the
BCG removed and confirm. It just takes a slightly sloppy notch in the upper.
Also bend the dust cover spring so it bends into the upper because that will bite you.
BCG removed and confirm. It just takes a slightly sloppy notch in the upper.
Also bend the dust cover spring so it bends into the upper because that will bite you.
UPDATE: after spoke with PROOF, they pointed out that the recoil spring I used is too heavy, the bolt moves back to quickly, brass doesn't t have time to properly adjust itself for chambering, causing the bite mark. I followed their suggestion and replaced with the softest spring from JP, problem solved, will test fire to confirm the result.
I think what they are saying is the heavy spring is sending the bolt forward too quickly. Its a feed issue not an extraction thing. Notice the damaged rounds are unfired.
