whats with all this scratches - Printable Version +- 6.5 Grendel Forum (https://65grendel.com) +-- Forum: 6.5 GRENDEL DISCUSSION FORUMS (https://65grendel.com/forumdisplay.php?fid=3) +--- Forum: 6.5 Grendel ARs and Other Semi-Autos (https://65grendel.com/forumdisplay.php?fid=8) +--- Thread: whats with all this scratches (/showthread.php?tid=7846)

whats with all this scratches - cst - 05-09-2014 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.. whats with all this scratches - Paul45LC - 05-09-2014 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. whats with all this scratches - cst - 05-09-2014 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? whats with all this scratches - Paul45LC - 05-09-2014 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. whats with all this scratches - cst - 05-09-2014 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 whats with all this scratches - Torf - 05-09-2014 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. whats with all this scratches - Smoke - 05-10-2014 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 whats with all this scratches - Drifter - 05-10-2014 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. whats with all this scratches - sneaky one - 05-12-2014 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. whats with all this scratches - sneaky one - 05-12-2014 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!