My 300 blackout doesn't like cast

[Petander]

So I had an issue with the neck/throat junction on one of my barrels...the brass was inside spec but still short enough that the pressure was causing the lead to "flow" into the tiny space between the case mouth and the chamber throat causing little lead rings that...after a round or two would cause the rounds to not go into battery.

I've been here,too. I was able to shoot quite a lot but there was this strange lead buildup. Took a while to figure it out. It was 458 Socom but the idea is the same. I was sizing too much.

[Sig556r]

If I can cycle PC'd TL-309-230-5R in any of my 300BLK ARs sub or super, you should be able to with 155g CBs. Just like J's, its unconventional seating, you have to determine the optimal seating that'll reliably feed in a semi-auto. No need to limit seating within the neck like regular 30cals, but crimping is necessary to avoid setback.

[John McCorkle]

I've been here,too. I was able to shoot quite a lot but there was this strange lead buildup. Took a while to figure it out. It was 458 Socom but the idea is the same. I was sizing too much.

So sizing your brass made it too short or were you trimming too?

It was the strangest thing....I started casting for 38 spc (which is super friendly for casting)...then moved to 300 blk and had zero experience or knowledge on what was causing the issue....I just had these little silver rings of lead that kept showing up. It was this forum that helped identify what the source of the prob was. So big thank you to all for sharing the knowledge here.

Sent from my Moto G Play using Tapatalk

[cwlongshot]

I have five different 300 bo rifles and NONE of them reall shoot cast very well!!

Even my H&R SS I had with powder puffs or super
Sonics. Best i was ever able to do was about 2” @ fifty yards thats from
Barrels that will shoot moa or LESS with super jacketed bullets.

I pretty much gave up. I feel its the 1:7 rifling thats made for subs and just not cast friendly.

My 32/20 with 1:14 shoots quarters at 100yards same bullets...

CW

[Lloyd Smale]

but yourself a rcbs 130 gas check spitzer mold. Once I got the seating dept down they never missed a beat in my ars and shoot 1.5 inch at a 100 yards out of the 16 inch gun. Ill measure one later and let you know seating dept. I tried the 155 lyman and no matter what I did I couldn't get it to run a 100 percent in either of my bos. This is the only cast mold ive bought that really works. Im sure maybe some of the group buy designs do too but I came to the party to late for most of them.

[Buck Butcher]

Lloyd, that particular mold is on clearance at midway. Awful tempting, and free shipping to boot!

https://www.midwayusa.com/product/10...oint-gas-check

I’ve used the lee 155 with great results, so I don’t need the mold. I am a sucker for free shipping though!

[sundog]

but yourself a rcbs 130 gas check spitzer mold. Once I got the seating dept down they never missed a beat in my ars and shoot 1.5 inch at a 100 yards out of the 16 inch gun. Ill measure one later and let you know seating dept. I tried the 155 lyman and no matter what I did I couldn't get it to run a 100 percent in either of my bos. This is the only cast mold ive bought that really works. Im sure maybe some of the group buy designs do too but I came to the party to late for most of them.

RCBS 7.62-130-SPL, GC'd and PC'd (Smoke's clear) works very well in 300 BO, 7.62x40WT and 7.62x39. Although I have not tried it, I would bet that it would also work in 300 Ham'r.

[Lloyd Smale]

ya I saw that and wouldn't mind a back up in case rcbs is discontinuing it. ive casted more then 5k out of that mold and a new one would make me feel secure.

Lloyd, that particular mold is on clearance at midway. Awful tempting, and free shipping to boot!

https://www.midwayusa.com/product/10...oint-gas-check

I’ve used the lee 155 with great results, so I don’t need the mold. I am a sucker for free shipping though!

[Lloyd Smale]

well buck butcher midway has one less. I went and looked again and just cant pass up an rcbs mold at 53 bucks. Especially one that works and shoots as well as that one. Should be set till I die now.

[Petander]

So sizing your brass made it too short or were you trimming too?

Just sizing,bumping the shoulder too much. That creates excessive headspace and leaves room in the chamber for the lead to flow.

That was my first AR / cast attempt.

OP doesn't have this problem though.

[Lloyd Smale]

I would have thought that when the powder ignited the case would blow out to chamber size before the bullet even moved and surely quick enough that the bullet wouldn't have melted and left lead that close to the case neck. Bullet would about have to be melting before it clearned the case neck. I would guess more likely is your bullets were being shaved but seating without flaring and piece of lead were being left in the chamber.

Just sizing,bumping the shoulder too much. That creates excessive headspace and leaves room in the chamber for the lead to flow.

That was my first AR / cast attempt.

OP doesn't have this problem though.

[snuffer61]

I read somewhere on this forum how to get 300 BO cast bullets to feed in AR magazines. Set your calipers to .250" and lock them. Slide the calipers down over your bullet nose until they stop. Mark this spot. Now look at your magazine from the top. You will see a ridge inside on both sides. Seat the bullet into the case until the mark you made on the nose lines up with these ridges. From there you can play with OAL to fine tune it but this should get you a close starting point.
Hope this helps.
Snuffer

[thumbs]

With the 300BO, I have not seen an issue with the base of the bullet below the minimal neck. I am using the NOE 152 (on the left) the others are a light Lyman designed for the 30 M1 carbine. I really suspect that the diameter of the nose, just ahead of the case mouth is where your problem is. The NOE design has a reduced neck starting at the end of the top driving band, memory may be wrong but I think the diameter of the nose is .301 or .302. The Lyman 311414 would also work well, same nose design.

Attachment 245408

I noticed your have a couple of different weight bullets your loading. I am trying to figure out how to get my Lee cast 155gn actually drop at 165gn to cycle in my 10.5" pistol. I have done all I can think out in checking the rounds for spec and drop each round into a case checker to be sure there is no problem there. At first I used a normal pmag for 556 and didn't have very good luck with reliablity . Then I filed down the top of the ribs to allow extra room for the larger bullets. It was much better but still have problems. Seems the cartridge being loaded doesn't get to the ramp and hangs up. Another cartridge behind the first jams under the first. When I take both out and reload them the function fine. My COAL is 1.955 because of the design of the bullet it isn't allowed to go deep into the chamber resulting in the shorter COAL. Any ideas? I have a couple of lancer mags on order but I would like to get the pmags to work if it is possible. Haven't tried my Hornady 130SP bullets yet. I see all the guys on youtube and few mention mag problems or what they did other than filing the rails down a bit. Maybe I still need to file more but they are pretty much even not all the way down the mag.

[thumbs]

I read somewhere on this forum how to get 300 BO cast bullets to feed in AR magazines. Set your calipers to .250" and lock them. Slide the calipers down over your bullet nose until they stop. Mark this spot. Now look at your magazine from the top. You will see a ridge inside on both sides. Seat the bullet into the case until the mark you made on the nose lines up with these ridges. From there you can play with OAL to fine tune it but this should get you a close starting point.
Hope this helps.
Snuffer

Now that sounds reasonable. I'll give it a try but I do have a limitation on my seating depth. I checked my chamber length using the Lee cast. I have to seat about 1.955". Part of the base of the bullet already in the shoulder of the case. The powder is very close to touching the boolit. I am loading today so I'll give it a try anyway and see if different powders gives me enough room in the case and the chamber will allow for the COAL to do your suggestion. I may have to go with a different profile bullet but I hear this one is supposed to run well. Not so much for me right now. LOL

[tomme boy]

Buy a 300 mag and skip the 556 ones. The 300 mags do not have the ribs on the inside that mess with the loading of the rounds.

[jmort]

Any of the Lancer Warfighter mags will work

[thumbs]

Thanks I have a couple of the Lancer Warfighter mags on the way. I did a little more work on the pmag I think it may be better but it really isn't right. Only way to tell is to take it out and see what happens.

[Petander]

I would have thought that when the powder ignited the case would blow out to chamber size before the bullet even moved and surely quick enough that the bullet wouldn't have melted and left lead that close to the case neck. Bullet would about have to be melting before it clearned the case neck. I would guess more likely is your bullets were being shaved but seating without flaring and piece of lead were being left in the chamber.

I used proper NOE expanders. No shaving.

Might have been a combination of things like too slow powder but bumping the shoulder less was the main solution. And a case gauge helps a lot.

Sorry for thread hijack... sizing for AR:s can be interesting, I shoot 300RSAUM too. J only.

[mattw]

I noticed your have a couple of different weight bullets your loading. I am trying to figure out how to get my Lee cast 155gn actually drop at 165gn to cycle in my 10.5" pistol. I have done all I can think out in checking the rounds for spec and drop each round into a case checker to be sure there is no problem there. At first I used a normal pmag for 556 and didn't have very good luck with reliablity . Then I filed down the top of the ribs to allow extra room for the larger bullets. It was much better but still have problems. Seems the cartridge being loaded doesn't get to the ramp and hangs up. Another cartridge behind the first jams under the first. When I take both out and reload them the function fine. My COAL is 1.955 because of the design of the bullet it isn't allowed to go deep into the chamber resulting in the shorter COAL. Any ideas? I have a couple of lancer mags on order but I would like to get the pmags to work if it is possible. Haven't tried my Hornady 130SP bullets yet. I see all the guys on youtube and few mention mag problems or what they did other than filing the rails down a bit. Maybe I still need to file more but they are pretty much even not all the way down the mag.

Wait for the new mags... I have not had any trouble with PMAGs using the cast SP bullets, a lot of folks have though. My rifles have pistol gas systems in them, I like them that way but it is key to use the proper burn rate powders. Does your bolt fully lock open if only 1 round is fired? My pistol gassed 16" rifles really like 4227. No if you have the curly wrap around gas tube that makes the action think it has carbine or rifle length gas, I would not know what powder it might like. The smaller bullet is a Lyman 311359, does not feed as well as the larger bullet. Do not get hung up on the base of the bullet being below the shoulder, many of the loads for the 300BO will be that way.

[Lloyd Smale]

have to agree. I have 300 bo specific p mags and lancers and there defineately better feeders then the 556 mags.

Buy a 300 mag and skip the 556 ones. The 300 mags do not have the ribs on the inside that mess with the loading of the rounds.