whats with all this scratches

[cst]

During load development I put a dummy round at the bottom of the mag to keep a consistent feed. When I extract the dummy round from the chamber I noticed these consistent spiral scratches around the whole diameter of the ojive and above. The dummy is a factory 123 SST round 2.250 and loaded a 123 scenar round out to 2.270. this first SST round, the marks are more pronounced since I used it all day but the scratches line up..the second pics are the ones I did at home trying to replicate it..the scratches are mild....No pressure signs
Lilja 319 barrel, ASC mags, Precision firearms bolt, Mega MKM upper.





I removed the extractor and hand fed the round and let it slam forward and then pushed out(with no effort) the round out with a cleaning rod......no scratches

it only leaves those marks when fed from the mag...

accuracy is not effected but a little disconcerting...4 round group at 100yards


Any ideas why this is happening? its a perfect spiral if you were to spin the round..

[Paul45LC]

Don't sweat them. When a cartridge feeds up from the magazine, it travels at an angle and impacts various features of the barrel extension and chamber. This is a fairly violent process as the cartridge is driven forward by the mass of the BCG and buffer propelled by a big honking spring. It can also pick up marks when the ejector pushes it against some of those same features. It's the nature of the beast.

[cst]

I get the rounds will get beat up ....I am accustomed to seeing lines that gouge the brass and bullet that run up and down. these are perfect spirals. if u spin the bullet it looks like threads of a screw... I can't see how u get these spirals because the round doesn't rotate 500 degrees when being chambers and extracted... does it?

[Paul45LC]

I'm not seeing spirals, I see rings. Some of those rings are parallel, and some are skewed, giving the appearance of spirals. Here is the scenario I propose, the bullet is picking up marks at a very slight angle from impacting against the entry to the bore, this combined with too many loading cycles, is working the bullet around in the case to change the angle.

[cst]

Its a spiral when u spin the case from high to low..one continuous line. It wil have the spiral that rotates around the bullet about 3 times.....and it comes out looking like that in one feeding...thats the problem..I get it if it happens if I reuse it over and over...the first pic of thr sst is from multiple loadins...the second is only from 1 loading

[Torf]

Is there any chance that it is rubbing on something as it travels up and down with the follower? Since the follower is likely a polymer, I am pretty sure that would prevent the cartridge from spinning, and I don't even know what would rub against the bullet right at that point which would cause a mark, even if the cartridge were to spin as it rides up and down.

[Smoke]

Its a reflection of a tear in the space time continuum.. As the swirls get closer to the tip there will be a correction in the continuum and a true follower of the constitution will hold office again ...

Sorry I just could not resist ..
Honestly don't have a clue as to the cause of the scratches

[Drifter]

I've seen those marks on bullets with several Grendel barrels that I've had. Perhaps it has something to do with the compound throat, or the chamber dimensions in general.

[sneaky one]

Maybe it's a small burr left in the compound throat area-semi worn reamer ?

Maybe it's why so many have issues of OAL specs. of their loads, that seem to suddenly go away... after a few rounds thru the bbl.? Ummmmm...

I saw this -big time, on my latest BHW bbl, -extension. Burr city, bad!
I fixed it , instead of a send back, wait period.

[sneaky one]

We - that build these uppers, should follow the advice of a few that do the bbl. ext. - meltdown procedure; ( L 52 posted it here long ago. It works!)
Or send it back if it looks bad, or out of your league, as to fix it!