147 gr. supersonic load issues?

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Gman87t
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147 gr. supersonic load issues?

Post by Gman87t »

Just finished a 300 Blackout AR build a few weeks ago, and have been trying to develop some loads for it. This is my first 300 Blackout, but I load ammo for several other calibers (mainly mil-surp bolt actions and semi-auto pistols). Below is info on the rifle and the hand loads.

16" SOTA Arms barrel carbine length gas .125" port
M16 bolt carrier
4.5 oz. buffer
standard buffer spring

147 gr. Winchester FMJBT
reformed Winchester 223 brass trimmed to 1.355"
unknown brass-colored primer (brass came primed)
Brass chambered fine and had about .002-5" headspace using the tape method.
2.155" OAL
H110 powder
15.6 gr. ~1905 fps
15.8 gr. ~1921 fps
16.0 gr. ~1939 fps
16.2 gr. ~1971 fps
All measured with chronograph.

My concern is the bright rings toward the base of the fired cartridges (see pictures). Don't know if this is an issue or not. I thought this was an indication of high pressure or excessive headspace, but I don't think either is the case here. Could it be something to do with a rough chamber or over gassed action? Ejection is fine at about 3:00-3:30. Funny thing is, the rings seem worse on the lighter loads. I haven't tried any factory loads yet due to scarcity. I would appreciate any thoughts on this.
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20X11
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Re: 147 gr. supersonic load issues?

Post by 20X11 »

Looks like a chamber issue...you might want to contact the barrel mfg. and show them those pictures.
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oldpapps
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Re: 147 gr. supersonic load issues?

Post by oldpapps »

First thing I would do is drag the web with a paper clip. If it is smooth, I would follow the advise of '20X11'.

Your are getting better velocity with your charges than I did.

Good luck.

Enjoy,

OSOK
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KingIX
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Re: 147 gr. supersonic load issues?

Post by KingIX »

Had the same issue.. but closer to the shoulder
turned out the chamber needed to be reammed with
a different reamer as my barrel was made with a reamer
That was colse to the end of its life


Get some factory loads even if its just a few.. and see if
it continues if yes.. the contact the manufacturer
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AxleSlider
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Re: 147 gr. supersonic load issues?

Post by AxleSlider »

because of the sharp "bands" it definitely looks like tooling marks and not change in color due to work hardening/over-pressure. Not saying you don't have both over-pressure and machine tool marks. but if there is no deformation in that area it is probably just the later. Take a jewelers screw-driver or small tool and run it along the inside of the case near the base and see if you can feel any case deformation ...
1slow01Z71
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Re: 147 gr. supersonic load issues?

Post by 1slow01Z71 »

Thats some good velocity for the charge. Im running half a grain more to get those same velocities.
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Gman87t
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Re: 147 gr. supersonic load issues?

Post by Gman87t »

I ran a sharpened paper clip on the inside of the cases, but couldn't tell that there were any issues there. I don't really have any first hand experience with what this should feel like, but I have a pretty good idea from what I've seen and read. Also, the cases felt the same as unfired ones (well, once fired reformed 223). If it is just tooling marks, is this something that needs to be addressed, or is it just cosmetic? Are there any downsides to just using it as is, and might this "polish" out over time?
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oldpapps
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Re: 147 gr. supersonic load issues?

Post by oldpapps »

I'm still leaning toward the chamber being rough, but.

Stick your probe (I have a large metal paper clip that one end is pulled out to give me the length I need and a hook is twisted on the tip) into the case, press toward the case wall and slowly pull out. If 'it' is smooth, it will feel like glass, if rough, it will drag and grate.

I do this to all of my bottle necked brass during my first inspection. Any grittiness, it's scrap.

As the brass was pre-primed, was it 'new' or recycled and how many times? As this isn't known, check the web. I load on the light side and have gotten 25 re-loadings after the conversion with Lake City brass and that brass was recycled from muli loaded 223s. The 300 is not hard on brass, thus my leaning toward the chamber. I hope it is the brass :|

Load with care,

OSOK

PS,
Welcome to the forum.
20X11
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Re: 147 gr. supersonic load issues?

Post by 20X11 »

Gman87t wrote:I ran a sharpened paper clip on the inside of the cases, but couldn't tell that there were any issues there. I don't really have any first hand experience with what this should feel like, but I have a pretty good idea from what I've seen and read. Also, the cases felt the same as unfired ones (well, once fired reformed 223). If it is just tooling marks, is this something that needs to be addressed, or is it just cosmetic? Are there any downsides to just using it as is, and might this "polish" out over time?
No...it will not "polish" out over time. It is more than a cosmetic issue. If it was mine, that barrel would be returned. Brass is too valuable to let a chamber tear it up like that.
Gman87t
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Re: 147 gr. supersonic load issues?

Post by Gman87t »

First, I would like to thank everyone for the replies.
Unfortunately, I believe, after further investigation, that it's my chamber. I'll have to contact the manufacturer and see what can be done. I don't know how their customer service is. I've had the barrel for almost two months. Hopefully they will resolve this. I'll try to post outcome.
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