300 Blackout Chambering Issue

[nhrifle]

Who made your barrel? Might be worth talking to their engineer and relaying your measurements. Possible your barrel is out of spec and will be taken care of.

[xacex]

I just looked at my load log, and found my COAL was right at 2.00" to feed well in my short throat CMMG barrel with that boolit. Give that a try. Make sure you are getting consistent OAL out of your press as well. Be careful with the mortaring to get a stuck cartridge out of the chamber. More than once a boolit lodged in the bore while figuring out what worked. Cary a cleaning rod with you to the range if you are playing with coating and COAL. It may save you from a short day at the range, or a bullet setback kaboom.

Blackouts were designed to use bullets with long ogives to get them to feed properly with G.I. mags. COAL is usually determined by measuring where on the nose of the bullet .25" is and marking it, and putting that mark where the COAL would put that mark at the rib. But, unless you use a pointed bullet you will contact the rifling further up the nose of the bullet.With jacketed you would not want a long throat with the bullets that are widely used in this cartridge because you would have the possibility of the bullet not centering into the rifling due to the extra jump that has to be made. This is where the fun comes in with cast. Most good shooting boolits are not shaped properly for the blackout to both fit into a magazine well, and get a long AOL because of the ogive shape. That is why filing the ribs on a magazine, and adjusting the COAL is important to getting cast to work with this cartridge. Normally, a blackout does not have to have a long throat, and for the jacketed crowd it is a non issue. But, as you have found it can give us lead heads trouble until we get the correct OAL that will work. I found the same thing the first time I did a pound cast of my throat.

I have faith that you will figure this out. You just have to think about the blackout, and the design a little differently when shooting cast. Once you understand the design principles and the parameters we are stuck within, adjusting to them will be easy. Cast is fantastic for this cartridge, but finding a perfect cast boolit that fits in the unmodified magazine, does not hit the rifling to soon, and shoots good is a tall order that still has not been fixed perfect for us. You are on the right track with the 312-155, but I am actually getting better results with the Mihec 311410 H/P 130 grain so I stoped using it.

[Scout800a]

I've had problems with the 155 2r, still trying to make it work pc'd. I ave to seat them pretty deep or they stick. I'd like to try that 311414 NOE is doing. that looks like it would fix the problem. Hate to gamble on a 100 mold though. 311410 is showing some promise, cycles great, but only PB so you cant push them too hard.

[xacex]

I've had problems with the 155 2r, still trying to make it work pc'd. I ave to seat them pretty deep or they stick. I'd like to try that 311414 NOE is doing. that looks like it would fix the problem. Hate to gamble on a 100 mold though. 311410 is showing some promise, cycles great, but only PB so you cant push them too hard.

Ya, I know. I need to get those in the mail to you. Been busy this last week. I WILL get them in the mail next week. Sorry for the delay.

[petroid]

Thanks guys ill keep at it. Wow xacex 2.09 is short! The 309-230-5mR seems to be pretty reliable for me because of the shape but I seat it a little short at 2.235 because if the PC. If this works at 2.030 I'll be happy. Got some more testers loaded and ready for the range

[HATCH]

I use the Accurate Molds 240E cast from my Master Caster.

There is a crimp line on that boolit that puts it at about 2.12
I have found that is the MAX length that the Remington 700 AAC can allow with that boolit design.
It is so close that if I go up just 5 thousandth that it will not chamber.
So I ended up going with 2.11 to allow for any potential issues in expansion when hot (both outside temp and weapon temp)

[KYShooter73]

Sounds like you are having all the same issues that I have worked through with the Lee 312-155 using both a CMMG and MAS barrel. First, filing down the ribs on the Pmag is definately needed to have good function with that boolit, especially after powder coating. It is a fat boolit to begin with, the powder coat just makes the ogive fatter. Second, make sure your sizing die is set to put the shoulder where it needs to be, I dont have the numbers in front of me right now, but if the shoulder is out too far you will have trouble chambering. Third, as Xaces said, that PC adds to the ogive, so you have to seat them deeper. The longer I make my rounds, the better results I have with my accuracy. Unfortunately, longer also means boolits are sticking. You should be able to cycle each round in and out by hand without having to mortar the rifle. Fix your mags, check your shoulder, seat those rounds short and I bet your issues will go away. Just remember that when you seat short, you will also increase pressure. Im memory serves, I think Im seating at 2.010.

[xacex]

Thanks guys ill keep at it. Wow xacex 2.09 is short! The 309-230-5mR seems to be pretty reliable for me because of the shape but I seat it a little short at 2.235 because if the PC. If this works at 2.030 I'll be happy. Got some more testers loaded and ready for the range

The 2.00" is for the Lee 312-155 2r NOT the 309-230 5r. Watch your pressure when seating deeper. The 155 AK boolit is set in the case below the crimp groove, and above the grease groove. If you get to the crimp groove in OAL you have gone to far, and may experience feeding issues. I did anyway.

[petroid]

At 2.030" with the 155 I have a tiny bit of the front band sticking out of the case. I'm outting a light FCD crimp on and I don't think it's in a groove. My gas checks are below the neck and I'm hoping the PC holds them in place. If 2.00" works for you with this boolit xacex then I suppose I can go shorter if necessary until it won't feed. I will rework my loads up at any new seating depth just to be safe

[xacex]

Something I did not think about is what version of this mold you have. I have the old version that has a spire point. The new one has a small meplat on it, and may need to be seated differently.

[petroid]

I just got the mold and it does have a tiny meplat. Maybe 1/16" or so. I took my stuff with me to work today and ran to the range when I got off. Out of 30 rounds I had two or three fail to chamber at 2.030" One stuck the boolit when extracted so I had to use a cleaning rod to tap it out. I will try 2.010" next. Im just going to load 20 or so with a light charge that I know will cycle and see what happens.

[KYShooter73]

If memory serves, I think Im seating at 2.010.

As usual, my memory didn't serve too well. 2.055

[gvanzeggelaar]

i had an issue with hornady dies not setting the shoulder back far enough. I just machined a few thousandths of the bottom of the dies and now it works fine.

[xacex]

The 129gr nominal NOE "COD" may be too light to be ideal for the 300BO. I'm thinking that the quick twists are the velocity with accuracy limiters, so unless you have a 1-12" barrel, its velocity potential is likely wasted. I'm going to experiment with that boolit by clipping the end off to leave a .10" meplat. Its TC nose was designed to work with the ribs in 5.56mm mags.

I think you are on to something that might work for that design. A small meplat alleviates the nose damage enough to take that factor out of the equation. I have had good results with the 311410 Mihec mold, so I don't think the weight is causing the problems with accuracy. The weight distribution in the COD along with the nose deformation, and bearing surface are the limiting factors of that design. Of course the luverin designs are noted as being the most accurate because of the balance, and bearing surface, but try getting one of those to feed in a blackout let alone a silhouette design. I think someday we will end up with a lightweight waspwaist noserider as the answer to the blackout cast problem.

The A.C.E. offering in 144 grains looks like it may work well, and so far has been the best design I have seen for this cartridge. I hope you jumped in on it. I didnt because I be damned if I can't get this mehec mold down to 1.5 MOA.

[petroid]

I have (2) 300BO barrels, an Olympic Arms and another from Core15. Both accept my older Lee 312-155 at 2.050" sized .311" and I have used unaltered Pmag 20s stuffed with 20 rounds with no issues. The C312-160-2R has a fatter ogive, and I've seen photos of new 312-155s that appear to have an ogive similar to the CTL-160s. The key here is to seat the boolits to whatever your gun will chamber reliably.

I got the NOE 311414, but haven't had the opportunity to cast with it as of yet. The same is true of the 6 cavity version of the C312-155-2R. Both are being heat cycled this evening.

A.C.E. has a midweight BO mould (144gr) that I'm anxious to try. That group buy may be closed, but I don't think he has started cutting them as of yet.

The 129gr nominal NOE "COD" may be too light to be ideal for the 300BO. I'm thinking that the quick twists are the velocity with accuracy limiters, so unless you have a 1-12" barrel, its velocity potential is likely wasted. I'm going to experiment with that boolit by clipping the end off to leave a .10" meplat. Its TC nose was designed to work with the ribs in 5.56mm mags.

I am powder coating these boolits and I think that is what is causing my chambering issue. The PC adds enough that it won't go without a fight. I honestly haven't even tried this boolit naked. I looked longingly today at the 311414 by NOE. That looks like it might be a winner for me buy I don't have $80 to plunk down to test it out. I'm shooting a 7 twist barrel so super high velocities probably aren't going to net the best accuracy, I know. I'm just looking for a 1500+fps load to plink with that punches a little harder than the subsonics. I'll have to take a look at the ACE mold too. Thanks

[KYShooter73]

I am powder coating these boolits and I think that is what is causing my chambering issue. The PC adds enough that it won't go without a fight. I honestly haven't even tried this boolit naked.

If you spray then size, only the drive bands get sized. The ogive is probably .003 larger than using LLA for example. To be honest, the 312-155 shoots really good for me with LLA, and can tolerate longer lengths. I just hate LLA because it is a dust and grit magnet.

[petroid]

I'll have to cast some more to check how they fit without PC because I have pc'd all that I cast. I size before and after PC but it doesn't touch the boolit nose. The 311414 may have a small enough nose to chamber with PC but I don't have any to test

[petroid]

Cast some up this morning. Naked dummy round seems to chamber easily at 2.040". I then loaded some pc'd boolits in the neighborhood of 2.010" they varied a lot in the actual oal because the PC has varying thickness in the unsized areas and the boolit is just starting to touch the lands on the ogive so a little variation here changes the oal a lot. Most were about 2.010 with a few shorter and a few longer. Fired ten into my billet trap with no misdeeds or chambering issues. Looks like this boolit will not be able to be loaded longer for me and this cuts down on the available powder space so velocities won't be that great but its just for plinking anyway so as long as it works that's ok. I need to to test some out sans gas check. The gc's just add expense and tedium. If it will shoot ok without it great! If not I may ream out the mold to make it a PB

[xacex]

You should still be able to do 1800FPS with that boolit safely, but don't try to go up to 2000FPS like I did. It will get close, but your brass is ruined from over pressure after one firing. Accuracy wise you will want the gas check. Check Bammer for copper ones, he is a member here, or sage outdoors for aluminum ones"what I use." Both will save you money or you can do what I did for the ultimate in savings over the long haul. I bought a freechexIII for 30 cal, and never looked back. I bought a roll of Amerimax roof flashing that is soft aluminum, and have gas checks for life for under 150$ Additional calibers are 100$ for the tool. Well worth the investment.

[petroid]

The expense is not too much, really. About $0.02 per round. I've got some from Rem338UltraMag. But its just one more step and something else to worry about. I doubt I'd ever shoot enough to pay for the tool. I was getting about 1600 fps with 16.4gr Reloader 7 at 2.050" but accuracy dropped off at a higher charge and I didn't load any more to chrono. Accuracy wasn't all that great anyway. About 2" at 50 yards. But I'm not looking for a match rifle. If its 3-4 MOA fine. Just looking for a cheap plinker. Got some testers loaded up at 2.010+- so hopefully will get to the range soon to shoot some paper.