Hey guys. I am a long time member but do not post much. I am basically a lurker.






I am a recent 300 BO owner, with a lot of experience in shooting and reloading for pistols, and to a lesser extent, but no novice, with semis (M1A, AR-15).

For the life of me, I cannot figure out why my reloads are making and depositing this copper ring at the beginning of the throat. I cannot duplicate the problem with commercial rounds.













After a couple of the rings get deposited, I will get a FTF.

Load Specs






Bullet: SMK 125gr OTM #2121






Brass: LC '07'ish converted brass (purchased, re-sized with Dillon carbide die), neck thickness is okay, as far as my caliper can determine






Powder: IMR 4227 18.7gr

Crimp: Very light (1/4 turn) with Dillon crimp die


 

Sorry about the pictures. I need some more posts!
Headspace check on reloads

Are you chamfering the cases? I suspect that copper ring is scraped off during seating.

Yes, the cases are chamfered before seating. I have made probably a couple of dozen test rounds and then pulled the bullets. I have yet to see a damaged bullet.

 

Thanks for posting pics.

 

The brass was commercial, so the mouths were pretty good to start. I have chamfered the mouth inside anyway when I first saw this problem.

I think the photobucket library is fixed.


The ring does not exist before firing, so there is no ring to remove after seating the bullet.




 

I suspect your cases are a smidge too long, or chamber neck is a smidge out of spec. Thats what I would look at first. You don't show case length...

ETA: maybe too hard a crimp is ripping off, Are you roll crimping? Need to taper crimp if you are.

Thanks for the heads up on case length (1.36). I fixed first post.

 


I am putting a 1/4 turn taper crimp with the Dillon taper crimp die.


 

can ya pull a couple and see if there is a ring present? sometimes its almost "tucked" into the chamfer.

I don't know what causes those rings but I have seen them before on .308 Remington 700 s with 168 FGM. They did not seem to cause any function or accuracy problems.

Happened when my rebarreled Mauser was breaking in also.



 

I just loaded and pulled 10 rounds. The bullets look okay and there was no residual brass or copper left in the puller.











 

Is it possible that the barrel is not cut correct and for whatever reason the SMK's indicate the problem while different profile bullets do not? I need to track down some commercial ammo with SMK 125 OTMs.

There are several easy ways to check bullet max oal for an individual barrel. I take a sized case and cut a slit down the neck with a thin moto cut-off wheel so the bullet is held tight but still slips with a little pressure. That way you can "soft seat" it and measure the OAL at the lands.
1.Remove extractor and ejector from bolt, make sure chamber/barrel is clean. This is done with upper off the lower on the bench. Unloaded.
2.Insert the bullet you are measuring just into the case, long, and put a little Imperial sizing wax or other slippery agent on it. Put in chamber and push carrier until bolt closes to seat the bullet at the lands.
3.Retract carrier, and carefully, gently push out the test round with a cleaning rod from the muzzle.
4. Measure OAL with calipers, or with comparator tool for that caliber, and record it.

Do this with 5-10 random bullets out of the box of bullets you are measuring to get an average. The length will be your "hard-at-the-lands" COL for that bullet, or max OAL, for this barrel. I usually set the seater die about 0.025 shorter than that because pressures go up fast when the bullet is jammed into the lands, and you definitely don't want ammo that long in a gas gun, no. For VLDs in bolt guns you sometimes want the bullet at the lands, or even in a little, but for semi NEVER.

Sometimes this max measured OAL is longer than mag length and you have to seat shorter anyway.Or, like in High Power, we single load at 600 yards anyway, so we don't care if we seat a Sierra 80 long.

HTH

SAAMI http://www.saami.org/pubresources/cc_drawings/Rifle/300%20AAC%20Blackout.pdf says 2.260 is max. Additionally I have successfully test shot longer commercial loads. The Sierra load (the infamous floating around the web pdf manual, uses something like 2.21 COAL.



Please tell me I did not make a mistake on something as mundane as the length.









 
 

Thanks for that technique description. Let's just say my technique was not near as elegant as yours and leave it at that.

 



For my gun, (I think all 300's ??) you have to exceed max length for the mag and go below the minimum bullet seating depth to reach the lands.




 

I think I may be on to something....


Take a look at this load's powder compression. The powder level is at approximately the top of the black line.








This is certainly more compression than the rule of thumb 10%. I have backed off from 18.7 to 18.2 of 4227 and shot 6 rounds with no ring. Kind of hoping this is not the issue because I have three pounds of 4227. I only have about 1/2 pound of the very elusive H110 (unless I pull a bunch of .44 mags). I will shoot some more of this new load and hope I do not see any more copper rings.




Perhaps, now I am just making stuff up, the longer contact with the flame/heat was causing the bottom of the bullet to fail??


 

Gotcha on the length. On the other two semis I load, I use the "long as possible" method to pretty good success. That is why I came to the experts here for answers!

Unfortunately I am leaving town for work for a few weeks and will not be able to try the new length but will update as soon as I have some results.

Huh, I am thinking I should have known that before starting to reload for the 300. Thanks a ton, df.