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Posted: 4/28/2015 10:53:36 PM EDT
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 Case Length: 1.36 COAL: 2.22 Notes: Rifle headspace is pretty tight. Pretty much anything over the minimum with my Wilson gauge will FTF, or will be difficult to remove manually after being chambered with a full bolt release. (continued on next post) |
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Sorry about the pictures. I need some more posts!  Length check on reloads  Pressure check on reloads  Headspace check on commercial  Length check on commercial  COAL of commercial ammo is 2.24+ Barrel is an AeroPrecision 300BO 16" pistol. I have talked the Aero and, of course, they have never seen anything like this before. I have seen some other threads on the interwebtooby, but not a lot about the resolution. |
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Quoted: Are you forming your own cases from 223? Are you deburring the inside of the case before seating the bullet? eta, post up your pics, I will approve them. I don't do copy paste to see 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. |
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Quoted: I approved pics in second post, but don't see them. Pic in first post is fine. Can you pick that ring off after you seat the bullets? Did you debur the outside of the case? The ring does not exist before firing, so there is no ring to remove after seating the bullet. Yes sir, I did debur the outside. |
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Quoted: 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. I am putting a 1/4 turn taper crimp with the Dillon taper crimp die. |
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Just reread your first post, you are using 2.22 as your OAL. I believe that is too long. OAL should be set by measuring bullet ogive at .250 and centering that point at the front mag bump. Sorry but every time I post that pic it gets stolen so I don't post that any more. See AAC's website for more info. Don't have my notes in front of me, but thinking the OAL should be in the 1.90 range. I also trim my cases to 1.360 as I like even numbers. Your trim length is fine. Your pics are showing up fine. |
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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 |
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Quoted: Just reread your first post, you are using 2.22 as your OAL. I believe that is too long. OAL should be set by measuring bullet ogive at .250 and centering that point at the front mag bump. Sorry but every time I post that pic it gets stolen so I don't post that any more. See AAC's website for more info. Don't have my notes in front of me, but thinking the OAL should be in the 1.90 range. I also trim my cases to 1.360 as I like even numbers. Your trim length is fine. Your pics are showing up fine. Please tell me I did not make a mistake on something as mundane as the length.  Plus, what do you mean that you picture gets stolen? Used without your permission or acknowledgement? |
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Quoted: 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. ... 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  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. |
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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?? |
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Quoted: 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. Plus, what do you mean that you picture gets stolen? Used without your permission or acknowledgement? Quoted: Quoted: Just reread your first post, you are using 2.22 as your OAL. I believe that is too long. OAL should be set by measuring bullet ogive at .250 and centering that point at the front mag bump. Sorry but every time I post that pic it gets stolen so I don't post that any more. See AAC's website for more info. Don't have my notes in front of me, but thinking the OAL should be in the 1.90 range. I also trim my cases to 1.360 as I like even numbers. Your trim length is fine. Your pics are showing up fine. Please tell me I did not make a mistake on something as mundane as the length. Plus, what do you mean that you picture gets stolen? Used without your permission or acknowledgement? How to determine the proper seating depth; Measure the bullet ogive with a caliper and mark with a Sharpie where bullet measures .250. edit, Pic removed. You want that mark on the middle of the magazine bump. Just like in the pic. Pic will be up for a few hours then I will remove it. I load the Speer 125 gr TNT to 1.96 OAL using this method. The Sierra 135 gr MK, 1.30 AOL. |
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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. |
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Quoted: 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. Long as possible doesn't apply in 300 blk. You are using a stock AR15 mag. A 223 case measures .250 at the neck. And the neck is at the mag bump. So what you are doing is making the 300 blk round fit a stock AR15 mag. The full length wildcat rounds all use a modified mag to get around the mag bump. That is why 300 blk is a shorter round.......to fit a stock AR15 mag. |
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