Blackout chamber out of spec?

cr5 said:
First thing I did when I got home was test my handloads in the new 300BLK barrel for my ACR and they drop right in :D
I measured every dimension of the loaded cartridges and compared them to the factory loads I have and they were the same. Not sure what happened that day but I can't find any reason they wouldn't chamber in your rifle.
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Thinking about it I suddenly realized that barrel was chambered with a wildcat 30-221 reamer. The ACR bbl was chambered with a true 300 BLK reamer. I'm not sure the exact differences between those reamers but clearly there is some difference. I use mostly Fed 223 cases but as you noted there is some random stuff in my pile of cases and I had never seen a round hang up like that before.



gvanzeggelaar said:
Thanks for the help guys.

I'm going to do one or more of the following:

Size to 309
Neck turn cases
Buy some factory ammo/brass
As a last resort try to lap the neck area of the chamber a couple thou.
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Sizing your bullets a bit smaller is a good idea.

Before you neck turn hundreds of cases, measure the neck thickness ... that will tell you where the neck dimension will end up for the loaded round. Not all 223 cases are good for turning into 300 BLK due to varying case wall thickness.

The one thing I don't think I'd do is try to lap the neck. It is unlikely you will get it straight and concentric while leaving the shoulder and mouth nice and sharp. I think I'd just leave that alone.
 
gvanzeggelaar said:
To answer a few of the questions;

I am using a Hornady die set.
Winchester brass - Thinnest neck of the brass I have
Bullet is a NOE 311299

I built this rifle with the sole intention of shooting cast in it. I measured all the rounds before I even ordered the barrel to make sure this wasn't going to be an issue. Again, the min spec from saami is .335 at the neck, not .332,
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The die set shouldn't make any difference.

When you say that Winchester brass has the thinnest neck, are you measuring the 223 neck or the neck of the 300 after it is formed? Keeping in mind the 300 neck will be formed from the body of the 223 case.

I've tried some cast and had terrible trouble getting them to feed. However it does look like others are using this bullet in the Blackout.

Picture107-1.jpg
 
gvanzeggelaar said:
That looks like the very same bullet I am using. However I can't seat mine close to that long
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I searched for NOE 311299 and that is what it came up with. Notice how the front half of the bullet is actually under bore size so it can go up into the lands without touching them. The lands will only touch the stepped portion just ahead of the case mouth.
 
That is correct. The nose will ride the bore and the driving bands grab the rifling. It seems the NEA chamber has no throat. I can't have any of the stepped portion protruding from the case mouth
 
gvanzeggelaar said:
That is correct. The nose will ride the bore and the driving bands grab the rifling. It seems the NEA chamber has no throat. I can't have any of the stepped portion protruding from the case mouth
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Keep in mind your bullet is .003" oversize so it will engage the rifling sooner.

I just talked to Jeff about this and he tried dropping some factory ammo into one of their barrels and it went in and out fine. If SAAMI spec ammo will drop into the chamber without getting stuck then the chamber conforms to the SAAMI spec.

I have some .308 sized bullets not dissimilar to the ones you are using and I am able to seat them out even further than in the pic above.
 
Could the chamber still be slightly undersized assuming the factory ammo used is well under the max allowed. I have some cerosafe allow so I am going to do a chamber cast then we know for sure.
 
gvanzeggelaar said:
Could the chamber still be slightly undersized assuming the factory ammo used is well under the max allowed. I have some cerosafe allow so I am going to do a chamber cast then we know for sure.
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Unless the reamer is incorrect it is impossible for the chamber to be undersized. The only dimension the bbl manufacturer can control is the headspace and that has no bearing on the issue you are experiencing.
 
I would fire off a couple of jacketed bullets and then measure the neck of the fired case, add a thou and that should be the chamber measurement, or close enough to determine if your out of spec or your bullet is just to big as it stands right now.
If you really have your heart set on shooting .311 then neck turning might be your only option, however I have been shooting .309 plain base bullets out to 100 yards with decent accuracy and repeatability, it probably wouldn't hurt to try the .309 first, .310 if you have to and .311 if really absolutely necessary.......

just attacking it from a different angle........
 
Well i found the problem. The Hornady seating die isnt completely taking the flare out of the case mouth. Hardly noticeable but the flare is larger than the rest of the neck by about 4 thou. I took a chamber casting and the NEA chamber is to spec. the area around the neck measured pretty much dead on saami specs, if not a thou bigger. I will post pics of everything. Looks like a Lee factory crimp die is an order.
 
I use lee dies including the factory crimp and the rounds work great in my rifle.
$17 at WSS for the crimp die. Last time I was there they had at least 5 of them.
 
gvanzeggelaar said:
Well i found the problem. The Hornady seating die isnt completely taking the flare out of the case mouth. Hardly noticeable but the flare is larger than the rest of the neck by about 4 thou. I took a chamber casting and the NEA chamber is to spec. the area around the neck measured pretty much dead on saami specs, if not a thou bigger. I will post pics of everything. Looks like a Lee factory crimp die is an order.
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Where are you getting a case mouth flare from? Rifle sizing dies shouldn't impart any flare into the case mouth.
 
cr5 said:
I use lee dies including the factory crimp and the rounds work great in my rifle.
$17 at WSS for the crimp die. Last time I was there they had at least 5 of them.
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Had my 10" BLK out today and ended up with a few rounds that wouldn't go all the way into the chamber. These rounds were no crimped. I should try running them through the crimper and see if that solves the problem.
 
Cast 230gr with TL309-230-5R, you have to flare the case or it shaves the lead. Mine drop at .310 to .311.

Waiting for lee universal case expander and crimp die.
 
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I have issues with a neck diameter around .335-6 in both my 300 blk uppers. Usually when I have used some military brass as the parent case. FNM being the most guilty offender. IVI, LCity,rem and even Norc work well.

I just acquired a Lee factory crimp die as well and see if it helps out.

GC
 
With the crimp it looks like I will be able to use .311 bullets paired with any commercial brass. I will post results when I get the crimp die. I am curious how lead bullets are going to work with polygonal rifling.
 
gvanzeggelaar said:
Could the chamber still be slightly undersized assuming the factory ammo used is well under the max allowed. I have some cerosafe allow so I am going to do a chamber cast then we know for sure.
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It is possible that the reamer was slightly undersized. The reamer wears like any other tool does as it wears the chamber gets smaller. Due to the cutting geometry on a reamer they can wear out fast especially if run to fast or with incorrect lubrication.
 
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