300 blackout woes

[Chainsaw.]

So I’ve been into 300bo for a while as a back burner project. With a suppressor on its a hoot to shoot. But I’m having a problem, it seems the necks on some of my loaded ammunition is coming out to wide making the gun into a jam-o-matic pain in the rump. I’m using good projectiles, mostly sierra j-words. I guess I don’t know what direction to go. Some combination of bullets and brass run great. Some don’t. Not sure if I should try different dies….thickness trim the necks….I’m kinda stuck.

All 300 factory brass, I haven’t been using converted brass to try to eliminate that as a variable.

[trails4u]

Seems to me a variance in case neck thickness.... Not to be overly simplistic but identify the brass manufacturer that works with the bullet you like and stick with it?

[Baltimoreed]

Had the same issues with a tight Wilson barrel’s chamber and cutdown .223/5.56 brass and invested in a Hornady neck thickness trimmer. But I wouldn’t think that you would have any brass neck issues with true 300bo factory brass. Mic your bullets in case something is off. Mic the loads that chamber and the ones that don’t and figure out what the difference is.

[Hannibal]

What exactly makes you believe that neck diameter is causing the problem? I presume factory loads feed/extract without issue?

[trails4u]

Good points.... Are you sure they're hanging up at the neck and not a brass sizing issue?

[Chainsaw.]

Had the same issues with a tight Wilson barrel’s chamber and cutdown .223/5.56 brass and invested in a Hornady neck thickness trimmer. But I wouldn’t think that you would have any brass neck issues with true 300bo factory brass. Mic your bullets in case something is off. Mic the loads that chamber and the ones that don’t and figure out what the difference is.

I will do that. Good thought.

[Chainsaw.]

What exactly makes you believe that neck diameter is causing the problem? I presume factory loads feed/extract without issue?

Factory ammo runs just dandy.

When I get jams and I “mortar” the round out I’m finding bright spots, usually a ring around the neck. Leads me to think I should thickness trim, but then my 220 grainers run great. Sounds like I have some mic-ing to do.

[Loudenboomer]

Do they pass the "Plunk Test" in a cartridge gauge?

[MaLar]

I had the same problem. I was using military brass, the neck ends up being in the old shoulder where the brass is thicker. I lucked into some Star Line 300 brass and all the problems where gone.

[Omega]

If it is an AR, what mags are you using? Some need a little tweaking to keep them from doing just what you describe. Also, are you giving them a crimp?, sometimes a light roll crimp will help them feed better.

[JimB..]

Set the barrel up and plunk test a couple hundred rounds, if all plunk then try shooting them, if they don’t all plunk then figure out what is different about those that fail.

[badguybuster]

Ive been shooting 300blk since its inception in a wide variety of rifles, using a wide variety of brass. Ive never seen that problem. I wonder if your sizing die is defective

[RKJ]

I had this issue with a 223 AR and had to lower the sizing die down to get them to work.

[recumbent]

Have you annealed the brass?

[osage]

I converted a large number of 5.56 nato and non nato, 223 and 5.56 blanks. This left the necks to thick at or over .334. I used a Foerster outside neck turner to bring neck wall thickness down close to .010. As I recall the blanks and NATO stamped brass required the most turning. Didn't have access to factory brass at the time.

I missed that you are using factory.
I had a issue with rounds that bolt wouldn't close on. Ended up using sharpie on bullet/neck and found rifling marks on bullet. COL was per manual, decreased COL to resolve issue.

[DocSavage]

I was thinking sizing die not set properly or wrong size expander ball. Remove the expander ball the make a dummy round see if that solves the problem.

[BrassMagnet]

Long ago I found a list of acceptable head stamps to convert to 300BO. No clue where it is now. Head stamps not on the list generally needed neck reaming or turning.

[BrassMagnet]

Here is a thread from AR-15 on head stamps to use or not use. Mostly favor brass with a neck thickness of .011 and say use brass with neck thickness of .013 for your .223 loading. They say the list I saw was on another site and it has errors.

https://www.ar15.com/forums/armory/Making__300_blackout_cases_out_of_once_fired__223_ military_brass/42-443854/

[Baltimoreed]

Even the same headstamps will have different thickness as you’re cutting the brass shorter and the case thickness down inside of a piece of .223/556 brass is not a case parameter when it was extruded so the thicknesses can vary. A tubing mic is useful. I rechambered one of my builds to 300Hamr which should help with this as I only shortened the case a little plus it gives me a little more room for powder however at the expense of heavier projectiles. I don’t shoot subs.

[fixit]

Check out the 300 blackout website.... they have a sticky on the good, The bad, and the ugly!

[1006]

Are you taper crimping, no crimping, Lee Crimping?

Does your seating die have a crimp ring that is hitting the case mouth on some of the rounds?

If the 220’s are running fine, what is the difference between those and the others?

[popper]

Do they pass the "Plunk Test" in a cartridge gauge? Cartridge gauge will NOT show neck problem. They are for HS and COL. I suspect a loading/die setup problem. I convert 223 and have to neck turn but have had factory BO brass hang when using cast. Jacketed should not be a problem. Loaded OAL can be a problem, bullet jams the lands and extractor can't overcome. Anyway, the neck of BO is .335 and you need 1 min. for clearance. I check loaded neck dia (and COL) of all loaded rnds, .332 max neck dia. I made a tool to check OAL to ogive dim. Tired of pogo jams. You can't 'plunk test' an AR. I did an interesting test. Marked the shoulder of a FL sized case and chambered it. Note: shoulder from die and that in rifle DON'T match!

[Finster101]

He stated he is using factory .300 Blackout brass so the brass should not be an issue.

[Hannibal]

Once all the speculation settles I hope the OP will post his findings after he has taken measurements. Something somewhere is obviously out a spec a bit. Discovering what and correcting/compensating for it is what will ultimately solve the problem.

[Chainsaw.]

Once all the speculation settles I hope the OP will post his findings after he has taken measurements. Something somewhere is obviously out a spec a bit. Discovering what and correcting/compensating for it is what will ultimately solve the problem.

Whooo! Look at all those excellent responses! I love this board!
Correct Hannibal, just sticking with 300 factory brass so far to remove variables.
Haven’t gotten into the mic-ing yet, had to deal with fire wood tonight. I’ll get on it friday and post my findings.
I haven’t check the cartridges with a case gauge, cause, I didn’t have one. Have one in bound now.

Thanks again all. Be back in a few with some answers.

[imashooter2]

Are you using .308 jacketed and not .312?

[BattleRife]

It may be a crimp problem. Excessive crimp causes the neck to flare a bit.

Try chambering a new case, then seat a bullet as you would normally and try it again.

[Brassduck]

Just a stupid question, are the cases all the same length?

[Cottonpicker]

Small base sizing dies especially in the AR platform can eliminate chambering issues.

https://www.midwayusa.com/product/1011284542?pid=261325

[popper]

Case gauges allow you to set the shoulder (sizing die) and check for case OAL, nothing else. Check a fired case with your new case gauge, see where the head sits. Normally between the flat areas. If proud, use a feeler gauge to measure how much. Set your FL sizer die to get the same H.S. by sizing a couple cases. Then check the cases to see if they still chamber! If the empty case chambers good, check for case OAL with the gauge. Trim as needed (one time task). Your size die, gauge and chamber are ALL different! I don't care what the Sheridan people say. Crimp can bulge the neck too. None of my ARs need a small base die - the BO sizer is just a cheap Lee, works for 3 BOs. Then check loaded OAL. Set the seater die. I keep a dummy rnd to reset the seater whenever I change die or bullet type. AR don't have much camming power to help chambering the rnd, nor power to extract a bad one. Another area often missed is the tail of the bolt may have too much clearance in the carrier so gas leaks there and causes cycling problems. A can usually increases back pressure but ban also foul the shoulder area of the chamber - be sure to clean with a chamber brush often.

[frkelly74]

STICKY - Good/Bad brass list converting 5.56->300blk
Moderators:gds, bakerjw, renegade, bamachem


Here is the chart copied from its original posting This may be the list that Brass Magnet was referring to

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BallisticTools
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STICKY - Good/Bad brass list converting 5.56->300blk
Post by BallisticTools » Fri Apr 04, 2014 8:37 am

Originally compiled by tlee_20, updated with user reports. In general, the wall thickness around 1.360 inches from the base will determine success or failure. As a rule of thumb, if the wall thickness is greater than 0.014, there may be problems with the loaded diameter of the neck being too large to chamber easily.

Neck thickness data:

Factory Blackout brass

Gemtech (factory 300 BLK) - 0.011"
PNW Arms - 0.011"
RP - 0.010"

Converted brass

Good:
ADI - 0.012"
Aguila - 0.012"
A USA - 0.012"
FC - 0.013/0.014" [Note 1]
GFL - 0.012" (Fiocchi) Some GFL may have different thickness
HB - 0.013"
Hornady (223 headstamp) - 0.011"
Hornady (nickel 223) - 0.012"
IK03 - 0.012" [Note 4]
IMI - 0.012" [Note 4] Listed on both lists, but seems like more often good than bad.
IVI - 0.013"
IVI ('85) - 0.012" (runs great)
LC - 0.011"
LC (converted blank) - 0.012"
M193 - 0.011/0.012"
Norinco 223 - 0.010"
NOSLER - 0.012”
PERFECTA 223 rem. - 0.012"
PMC - modern "bronze" and "X-tac" are good, older PMC with small letters may have problems
PS - 0.011/0.012"
PSD - 0.011"
RA - 0.013"
RA ('69) - 0.012"
RP .223 - 0.011"
SSA - 0.012"
TAA - 0.013-0.014" [Note 4]
Tula - 0.0115"
TW 67 - 0.012”
TZZ - 0.012"
WCC - 0.010/0.011" (Some less common WCC headstamps run thicker, but the majority are good to go)
Winchester - 0.011"
WIN NT - 0.011"
WMA - 0.011" (Winchester Military, equivalent to WCC)


Thick neck wall, bad without neck turning:

AB 556 - .015" to .016"
ATI - 0.015" [Note 3]
CBC - 0.014/0.015"
CJ6 - 0.015"
CJ 8 - .014"
DNL - 0.016"
FNM - 0.016" [Note 3]
FRONTIER - 0.015"
GECO - 0.015/0.016"
Hot Shot - 0.014" [Note 3]
HRTRS ( Herters?) - 0.017"
ICC - Reported as bad
IK03 - 0.015" [Note 4]
IMI - 0.015" [Note 4]
IVI - 0.015"
KFA .223 REM - 0.015"-0.019"
L2A2 - Reported as bad
MAST - Reported Bad
MKE13 - Anecdotally reported as troublesome
MPA - 0.015"
Norma - 0.015"
NPA - [Note 3]
PMC (old headstamp) - 0.015"
PMP - 0.015"
PPU - 0.014/0.015" [Note 3]
RAM 223 - .014"
RORG - 0.015"
RWS - 0.014-0.015"
S&B - 0.015/0.017"
SADU - 0.014/0.015”
TAA - 0.013-0.014" [Note 4]
T - 0.015
SADU 5.56 - 0.014-0.015"
Wolf Brass .223 - 0.014"

General notes:

There's no consistent difference between "5.56" and "223" when it comes to brass.

Many manufacturers may use different sources for casings at different times. This means that even within the same headstamp, it is possible that a particular batch was from a different source and may be different. Treat this list as a rule of thumb, and double check before processing a large quantity.


Note 1:
"FC" brass includes several types of brass that don't seem to come from the same factory. Most of them are good to go, but the "thin web" FC that turned up a few years back tends to have thicker walls and will cause neck thickness problems. Some FC that runs thicker is the newer stuff. Has beautiful annealing marks on it. Has FC @ 12:00, numbers @ 3:00 and/or 9:00 (May have both, could just have one), and the year @ 6:00


Note 2:
NPA is very low quality brass, with a super small flash hole, and is likely to cause broken or stuck decapping pins, or other problems.

Note 3:
The brass marked with this note may require extra sizing force, and machine flex may cause them to headspace too large if the machine is not set up specifically to do this "harder sizing" brass. This is due to thicker brass, alloy variations, or variations in factory anneal. This isn't always universal within a headstamp, for example, some older PPU had the problem and others did not.

Note 4:
This brass is included in both the good and the bad list based on differing user reports. It is important to keep in mind that sometimes a single headstamp can be made at multiple factories on multiple differing manufacturing processes. Other times a manufacturer that has their own brass factory might bring in brass from another manufacturer during times of high demand or to fulfill a large contract.
Last edited by BallisticTools on Tue Nov 23, 2021 9:59 pm, edited 26 times in total.
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AnotherMadHatter
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Re: Good/Bad brass quick reference list - sticky please?
Post by AnotherMadHatter » Fri Apr 04, 2014 1:13 pm

[Chainsaw.]

Okay. I got the Mic out and here were my finding.

The ammo I’ve loaded that runs great, the neck is ~.3320

The ammo that jams, the necks are measuring at ~.3350. A couple at .3360. Thats at least a thou over bore of the neck. This is confirmed by the marks I’m finding on the necks.

Now, the question is why… All of the projectiles are .3085s, no .312s mixed in.

At to add one more thing into the equation, and this is important. The batch that runs are 220s, the batch that jams are 165s, same brass, same dies, same crimp…..what am I screwing up…��

Lee crimp die BTW.

[Omega]

Okay. I got the Mic out and here were my finding.

The ammo I’ve loaded that runs great, the neck is ~.3320

The ammo that jams, the necks are measuring at ~.3350. A couple at .3360. Thats at least a thou over bore of the neck. This is confirmed by the marks I’m finding on the necks.

Now, the question is why… All of the projectiles are .3085s, no .312s mixed in.

At to add one more thing into the equation, and this is important. The batch that runs are 220s, the batch that jams are 165s, same brass, same dies, same crimp…..what am I screwing up…��

Lee crimp die BTW.Post up some pics of the necks, I suspect your crimp may be too light or non existent. If it was crimping correctly they would all be much closer than that. With a heavier bullet, it is longer, so your crimp die may not be set correct for the shorter 165s.

[1006]

Are you taper crimping, no crimping, Lee Crimping?

Does your seating die have a crimp ring that is hitting the case mouth on some of the rounds?

If the 220’s are running fine, what is the difference between those and the others?

Check and make sure your seating die was not bumping the case mouth with a built in crimp ring

This has happened to me, every now and then a slightly longer piece of brass gets in the batch, and the seating die is set too low for it.

[popper]

Neck thickness, from your measurements is .013" min. .335 is spec for neck, yours may be tighter - my McGowan barrel is and I must neck turn converted brass. The FCD can bulge cases a tad, not as bad as taper crimp. I got a NOE bullet sizer inset to check neck dia but you could ream a fender washer to do the same. If it don't fit it don't go in my gun.

[frkelly74]

I posted that list of brass neck thickness measurements. When I was first trying to form up 300 BO my nicest looking brass was marked PMP and it did not form a nice sharp shoulder , and none of them would chamber when I made dummy rounds with 308 147gr FMJ bullets. So I started thinking about reaming necks but someone on here suggested trying different brass, I.E. Lake City and others and don't you know the lake city , RP, and PMC worked well without any neck reaming. That list calls off the thickness of the metal in the sides of the brass and there are two lists. one good , thinner, and one bad , thicker. If your wall thickness is .012 then that will add .024" to the bullet diameter and these seem to work just about right in my rifle. A wall thickness of .015 adds .030" and this is too big. This may or may not be relevant if you are using brass that worked well once but not as a reloaded round, but I found it useful. The .308 + .024 makes .332" which is .003" under specifications cited above... and works. The .030 + .308 makes .338" which is .003 over spec as cited above and will not feed in my rifle.

Norma, CBC, and PPU brass like the PMP brass did not work well either.

[Chainsaw.]

I posted that list of brass neck thickness measurements. When I was first trying to form up 300 BO my nicest looking brass was marked PSD and it did not form a nice sharp shoulder , and none of them would chamber when I made dummy rounds with 308 147gr FMJ bullets. So I started thinking about reaming necks but someone on here suggested trying different brass, I.E. Lake City and others and don't you know the lake city , RP, and PMC worked well without any neck reaming. That list calls off the thickness of the metal in the sides of the brass and there are two lists. one good , thinner, and one bad , thicker. If your wall thickness is .012 then that will add .024" to the bullet diameter and these seem to work just about right in my rifle. A wall thickness of .015 adds .030" and this is too big. This may or may not be relevant if you are using brass that worked well once but not as a reloaded round, but I found it useful. The .308 + .024 makes .332" which is .003" under specifications cited above... and works. The .030 + .308 makes .338" which is .003 over spec as cited above and will not feed in my rifle.

Norma, CBC, and PPU brass like the PSD brass did not work well either.



Converted brass from 223? Or 300 factory brass?

I am ONLY using 300 factory brass.

[Chainsaw.]

Ok. I FINALLY got my case gauge.

I went through a bunch of my rounds. 1 out of maybe 10 doesn’t fit….completely random.

[almar]

Some beat me to it. My problem was the brass sizing and annealing. I first thought it was the neck like you.

[Chainsaw.]

Sizing as in not setting the die correctly?

[popper]

1 out of maybe 10 doesn’t fit….completely random. In what way? Bad HS, neck too big, shoulder in wrong place? Wilson or Sheridan? My understanding is the Sheridan is cut to min. SAAMI specs.

[Hannibal]

To make certain that the neck diameter is indeed where the problem lies in the rounds that won't chamber take a fresh blue of black magic marker and cover the entire case with a nice, even coat of ink. Let it dry well and then check it in your case gauge. Probably should do 2 or 3 to be certain it's the same problem every time. Then let us know what you see. That will determine what needs to be addressed/corrected.

[Chainsaw.]

Well one thing I have figured out with the case gauge is that I dont have one issue, but two. The most prominent issue is in my brass being all range pick ups. Many of the cases (20%?) have some sort of rim scoring. Some have a hard extractor mark that is pulling the lip of the rim out leaving it to get hung up, a few have a much smaller protrusion off the rim, but enough to hang up. Fixing/elimination of those cases is resulting in only a few of the cases being problematic. Those remaining ones are neck size issue, for the time being Ill just eliminate those cases entirely.