300 Blackout Chambering Issue

[petroid]

Hope this is in the right spot.

I have a 300 BLK AR-15 pistol that I built. I use Lee dies to make brass from 223/5.56 and two molds for boolits, The Lee TL309-230-5R and the Lee C312-155-2R. Boolits are cast from COWW +~1%Sn and DT PC with HF Red. Sized in Lee push thru sizer. My .309 sizer puts out at .310 and I don't know if this is the issue or not, but here goes. Boolits don't have a problem feeding from the mag but about 25% or so don't chamber easily. If they don't go in the forward assist doesn't seem to help. Sometimes I can extract the round, but usually not. I have to remove the magazine and use a screwdriver to pry the bolt back from inside the mag well. If I hand feed the same round and let the bolt slam home, it goes in, but when its feeding from the magazine it seems the bolt doesn't have enough oomph to get the round fully chambered. At first I thought it was a boolit sizing issue. A loaded round measured about .332 across the neck. Factory loaded rounds read .330 which is the difference in bullet diameter. A fired case is .335-.336 across the neck so there should be enough room for the neck to chamber. Just aft of the shoulder my sized cases and loaded rounds measure about .362 and a factory round about .356. A fired case reads .363. I am wondering if my dies are not forming my cases properly if the case body just behind the shoulder is too tight in the chamber to go in freely. I am using mostly LC brass with some commercial thrown in. I haven't checked all the cases yet, just some I had handy. I can't say for sure if its one case type that's causing the problem or not. I am tempted to contact Lee about the sizer die just because, but I kind of like the boolits sized a little larger as long as I can be sure that's not causing the chambering problem. What do you think?

[nhrifle]

I had that issue when I first built mine. Jacketed and cast were giving me the same issues in that they would not chamber fully. What I found is that the ogive of the projectile is the determining factor in OAL. If it is loaded too far out, the ogive will contact the leade early and stop the round from chambering. This is a round for which you need to keep a dedicated notebook, detailing everything you try from new powders to new bullets. I am loading the two boolits you are using without problems, and just to see what would happen I loaded some .310" diameter 7.62X39 jacketed bullets. They fed and functioned fine, so I would say your boolit diameter is not the issue, rather that you have an OAL problem. One quick way to tell if your rounds will chamber is to take the upper off the lower, remove the bolt, and do the "plunk test" just like when reloading for an autoloading pistol. Drop the round into the chamber and see if it goes in fully, then tip the assembly so the round can fall out. Look for rifling marks on the nose of the boolit. If you see any, you are loaded long.

Also, what brass are you forming your cases from? I would advise only US made brass be used for conversion, as I have run into problems with thick necks/chambering problems when using foreign brass, PMC most notably. Save that stuff for .223.

[Jupiter7]

The lee 300BO dies have been known not to set the shoulder back. Also, depending on if converting your own brass, most foreign brass is thicker and will not chamber unless neck reamed. I only convert federal commercial and LC, Rp and Winchester brass. Have had problems with PPU, PMC, fiocchi and a few others. I use hornady dies and have tried RCbS small base both worked fine converting and resizing fired brass. Small base just overworks the brass in my 2 guns.

[rodok]

I had the same problem and went and bought the rcbs dies and have had no problems, the lee I use now to just put the new shoulder on. Some would shoot fine and other would stick in the chamber, after using rcbs they all work fine, I am using on LC brass.

[500MAG]

Would a Wilson headspace gage help? They do make one in 300 blackout. I use one for very semiautomatic I load and try every 5th or 6 round in it during loading. It has prevented me any issues with chambering.

[petroid]

I don't see any engraving of the boolit so I don't think it's an issue with OAL. I seat the 230gr boolit to 2.235 and the 155 to 2.050. Using mostly jc brass but it happens to many different kinds. I don't have a case gauge but really the only one that matters is my rifle. Plunk test is failing even with empty brass. I think it's an issue with the case sizing/forming. I have a spare shell holder and I'm thinking about taking a couple thou off the top to let the case size a little more and maybe chamber easier

[petroid]

I repeated the plunk test with some factory ammo and some 230gr rounds I had loaded. I guess I wasn't looking at it the right way because all is well with the plunk test. I don't have any 155s loaded so I'll make a couple dummies and see what they do. It must be a magazine feed issue because the bolt sometimes doesn't fully strip the round from the mag and it feeds crooked or something. More investigation is under way.

[john hayslip]

You didn't mention trimming to length. I have a commercial Blackout that will not fire some loads that are specified length. I have to trim a few thousandth's under the max recommended length.

[petroid]

I use a CTS case trimmer and trim all cases to 1.356" which is well under max length.

[Blammer]

Do a plunk test with a piece of fully processed brass but not loaded. See what you get.

I have a wilson case gauge, and a loaded round dropped into it nicely, but wouldn't go into the chamber.

I checked a piece of brass only and it also went into the case gauge and not the chamber.

I FL resized it again, as the body was still to fat, and all is well.

[Jailer]

I repeated the plunk test with some factory ammo and some 230gr rounds I had loaded. I guess I wasn't looking at it the right way because all is well with the plunk test. I don't have any 155s loaded so I'll make a couple dummies and see what they do. It must be a magazine feed issue because the bolt sometimes doesn't fully strip the round from the mag and it feeds crooked or something. More investigation is under way.

The malfunction you describe sounds like it's short stroking.

[petroid]

The malfunction you describe sounds like it's short stroking.

Well it is and it isn't...I made up half a dozen dummies all with different brands of brass. All had feeding problems in one way or another but they all chambered fine when hand fed. It seems what I thought was a chambering issue was really a feeding issue but it presented at first like a short stroke or chambering problem. I tried pmags which I knew wouldn't work and they didn't. I have 30rd USGI mags with two different kinds of followers, one is green and one is gray. No idea what brand the followers may be but the mags are Charles Daly with gray followers and D&H with green followers. The problem is almost always when feeding the first round from the mag but occasionally mid mag. It seems that if I hand feed the first round, close the bolt, then insert the mag, it almost always works, but I can't figure out why. It may just be a magazine issue, but I don't know how to fix it, or if I should look for mags specifically designed for 300 BLK.

[xacex]

I had a problem with that boolit when I just started with the blackout. With P/C if the COAL is not set back a little you can stick them in the chamber. Please, stop using a screwdriver to "pry" out the loaded round. Use the Mortar technique for dislodging a round from the chamber if it is stuck. That is smacking the butstock straight down on a hard surface such as a log, or bench while pulling on the charging handle.
If rounds are getting stuck in the chamber it would not be a short stroking issue. How long are you aging your boolits before loading, and firing. COWW will grow a little, and if you load a fresh boolit, and wait a month to shoot it it may have grown enough to cause your problem. I age all my boolits for the blackouts here for a few weeks after casting, and resize before loading. I did have that problem starting out with the blackout. If it is a magazine issue which I have had with that boolit, you may want to download your mags. I have some Pmags, and Lancers that the rib is filed down on because standard mags will stack that boolit and also cause feeding issues.Pmags, and lancers work great once modified, and gets rid of the need for blackout specific mags which are expensive for a slightly modified rib. Try 10 instead of 30 rounds in the mag, and that will let you know it stacking is an issue with that magazine.
One other thing to check is that you have the appropriate charge, and you're getting enough gas. That will also cause a round to not fully chamber, and combine that with magazine stacking can give you fits.
Here is what works for me with that boolit. I age the boolit after P/C, size, load using only the same headstamp brass, and use a magazine that has the ribs filed. If sized to .310 I have no problem, go up to .311 and it is an issue for me. I have 3 blackouts, and they all like something different so you will need to play around with yours a little to find what's best.

[petroid]

Xacex I have actually discovered that there is not a problem getting the rounds to chamber as long as they feed from the magazine properly. When they misfeed is when it jams. I nay try to modify a pmag since I want to use this gun to hunt with and only my pmags have the proper capacity to be legal. I don't think the oal is an issue since they do drop into the chamber without a problem.

[xacex]

I would try downloading with a standard mag like 10 rounds. A 5 round hunting mag probably won't have the same problem because the rounds have not stacked that bad to cause a slowing of the round to pop up into the chamber. 30 rounds in a standard mag with that boolit did cause problems for me as well. A bastard file and a little time is all it takes to make a blackout mag out of a Magpul for these short ogive boolits. Believe it or not those cheap termold 20 rounders work well without modification in both the blackout, and the Beowulf. To bad the lips are so weak I can't leave them loaded with beowulf for any length of time.

[petroid]

It's actually a 20rd pmag with a 5 round limiter

[bruce drake]

Brownells sells 5 round magazines that are steel and work great with my 300 BLK upper when I used it for coyote hunting in NY a few years ago. Game Warden was driving the dirt road and about locked his brakes up trying to stop his truck in his hurry to check to make sure I wasn't using a .223 during deer season.....Yeah, he was surprised when I told him it was a 30 caliber AR...

[petroid]

Update: Good news and bad news

The good news is that since I had pretty much convinced myself that the problem was in fact, a magazine feeding issue and not a chambering issue, I went and modified a 20rd PMag by filing down the ribs. This has helped immensely! After cycling 6 or 7 dummies many many times by hand, I have (almost) no feeding problems. I did find that if the bolt is closed it is difficult to get the magazine to lock into place and when the bolt is opened it is very tight. I have to hit the mag pretty hard to seat it and that can knock the rounds out of position, thus resulting in a failure to feed. But that is the only time it happened.

Now, the bad news. I don't know when I'm going to get a chance to test these babies out!!!

Thanks for all your advice guys. I have a total of four 20 round PMags and three 5 round limiters. I can modify two for Blackout and keep 2 for 5.56 and probably even used the modded ones for 5.56 if I wanted, so no loss. Will update when I have results.

[xacex]

Thats good news. I have not had very good luck with the 20 rounders with the 5 round limiters. I used one last year during hunting season, but even modified I won't use it next year. It still was not 100% for me. Good news is I have had no problem using the modified magazines with 5.56, or Beowulf. The 5 round limiters give no wiggle room for seating a mag with a closed bolt, and with 5 in the mag the first one is a you know what to chamber sometimes. Sometimes the bolt will not lock back with those mags for me too. If you can trim a little off of the limiter so you get half a round of wiggle room the may work better. Don't take so much off that you can get 6 in or you will be eligible for a fine. I ended up just running with 4 in the mag and one in the chamber on safe. If you do run like I did check your safety periodicy. Brush can move your selector if it is thick, but to be honest it did not move on me last year the whole season except when it was go time so YMMV, be safe.
BTW, the blackout pistol worked great on the buck last year. Gelified those lungs just fine, and no tracking required.

[petroid]

Ok back to the drawing board. Still failing to chamber. I don't know if I'm coming or going here anymore. I originally thought I had a chambering issue, then I convinced myself it was really a feeding issue and now I'm back to chambering issue. I ran out to pop a few rounds off and function test and I had all the same problems with my newly modded pmag. still failing to chamber. even hand feeding some wouldn't go in without a healthy whack of the forward assist against the bench. the "mortar" technique worked really well to clear jams (thanks, xacex) So when I got home I decided I'd start from square one. First I got some soft lead sheet and rolled it up and pounded it til it was basically a 30 caliber cylinder about 2 1/2" long. I slid one end into a case and the other end into the chamber and closed the bolt. The chamber was oiled before this and grabbed my slugging rod and made a pound cast.

I found that the throat was really short. Less than 1/4" before the rifling started. couldn't see this well from the receiver. also the throat is .310" but drops to .308" very quickly. My PC'd boolits are .310 just ahead of the front band and then .305 at the start of the ogive. So there's too much boolit to fit easily in the chamber at the OAL I was using. I took a fired case and a boolit with a snug but movable fit and hand chambered and gently closed the bolt and gently reopened the bolt. The dummy OAL was 2.010" which was .040" shorter than I had been loading them. Not wanting to go the full monty right away I loaded five at 2.030" over 15gr Reloader 7. fired into my bullet trap. All fed, chambered, and cycled without a problem. I sure hope this isn't a fluke because I don't want to have to buy another mold, or have my chamber reamed or any of that stuff. If I can get this thing to run by just seating a little deeper and reworking the load, I'll take it!