Soot on Shoulders

[Henryrifle]

I have a problem that I don't know how to solve. This is from several barrels & rifles all cut with the same reamer. This is what fired brass looks like:




Doesn't matter if it's virgin brass, turned or un turned. All have soot on the shoulders and I think that is causing some blow by that is negatively impacting down range performance.

As you look at the pics above you are going to thing that the case mouths are curled in. Maybe they are. That was an initial problem but I have been trimming them .020 short. A bullet does fit into a fired case mouth. Maybe that is the answer -- get a neck reamer and make sure the neck is a true cylinder rather than a cone.

I tried just about everything i can think of to stabalize ES and even when it is reasonable like in the 8 range the targets are all vertical. I've posted some targets below. I have dozens more that should all be 200-19X or 200-18x. I don't have a wind problem. I have a vertical problem.

If I were ordering this reamer today, I'd make many different choices like at the .200 line, the neck diameter and freebore as well but here it is:

And, lastly, here is what you get on paper:



Wide open to any suggestions you guys have.

Thank you,
Hank

 

[SG4247]

My brass looks the same and shoots the same way with a .315 neck and .203 FB. My SD at 600 on the shotmarker is roughly 16 fps.

My necks are turned to .014” and are cylindrical after firing, not sure why your are curled as shown.

Thats with 4831SC and 180 Hyb.

I’m gonna try N555.

 

[Henryrifle]

They're not really curled in much. That picture makes it look worse than it is. Changing powder isn't going to fix whatever this problem is.

Interested @SG4247 in your reamer spec.




Thank you,
Hank

 

[Intheshop]

Probably missed it but;

Does the soot happen with one particular bullet.... or across several different examples?

 

[JSH]

Was this the first time this brass was fired in this chamber? I have seen this on numerous wildcats, some radical changes, some subtle.

Anneal?

 

[AlNyhus]

Low pressure loads and/or slow powders will look like that....not enough pressure to seal the neck quickly and the gas gets past the lower neck and into the shoulder area before it finally seals.

The vertical shape of your groups on target also point to low pressure loads.

Good shootin' -Al

 

[Henryrifle]

Responses:

1. It's a 284 Shehane. There is only one projectile --so, I don't know if it does it with other bullets.
2. Not the first time fired. It does it on every firing. This brass is 5-times fired, annealed each time.
3. I agree that is is pressure related but using > 55 grains of H4831sc. MV > 2800.

I am not very confident there is a simple answer and understand this is not easy to diagnose especially w/o seeing the reamer, examining the chamber or seeing the brass.

This happens across 4 different rifles using premium actions and barrels, lapua brass at known 284/Shenane speeds.

Maybe the best answer is that it's just a bad reamer...

Open to any other suggestions.

Thank you all,
Hank

 

[AlNyhus]

Do other powders you've tried show the same thing?

 

[DaveTooley]

I have to wonder if the .2844" FB may be giving you a false reading on seating depth and you're jumping the bullet. Do you get land marks or a ring on the bullet? If possible I would come out on the seating depth and see if that increases pressure enough to flatten the groups some.

 

[Henryrifle]

Good morning, Dave. I am jumping the projectile about .022," touch - .022, but I've tried it Jam - .02 which should still be .004-.006 in the lands. I wasn't changing seating depth due to the soot, just looking for the right tune. I will try in the lands again just to see if that cleans anything up.

@AlNyhus - I can't be positive but will retest and see. Have H4350 and N555.

Thank you,
Hank

 

[AlNyhus]

I have to wonder if the .2844" FB may be giving you a false reading on seating depth and you're jumping the bullet. Do you get land marks or a ring on the bullet? If possible I would come out on the seating depth and see if that increases pressure enough to flatten the groups some.

Dave, I saw that on the print and wondered about that. That snug of free bore diameter can cause a lot of gas not only with accuracy but as you pointed out...a correct seating depth. We see this at times in the 30BR's. -Al

 

[AlNyhus]

Hank, to Dave's point....before doing anything else, strip the bolt and seat a bullet long enough to be well 'in' the rifling....like .015-.020. Polish the bullet with some 0000 steel wool, close the bolt and see what the marks look like. Post a pic of the bullet.

Dave's question: "Do you get land marks or a ring on the bullet?" may be a nugget of gold. -Al

 

[Alex Wheeler]

The soot in itself is not hurting you. When I run a lot of neck tension with non annealed brass I will see that sometimes. Usually my BRA has some soot on the shoulders, shot the smallest I have ever shot like that. I have to wonder about all of this soot reading on the neck, at least for the stuff I do I have never seen it mean a thing. If you necked that brass up from 6.5 then its going to have a lot of memory and I would anneal it one time. The curling in of the case mouth is because the necks work hard more at the mouth. The harder brass wants to spring back more. I would agree that the fb diameter is too tight.

 

[Henryrifle]

No land marks or ring on the projectile.

Let me make sure I understand what y'all are suggesting:

Y'all are saying that perhaps I have misidentified the start of the freebore as the start of the lands and I think I am loading .022 off the lands but, instead I am really .022 off the beginning of the frebore.

Is that the suggestion?

Thank you,
Hank

 

[AlNyhus]

No land marks or ring on the projectile.

Let me make sure I understand what y'all are suggesting:

Y'all are saying that perhaps I have misidentified the start of the freebore as the start of the lands and I think I am loading .022 off the lands but, instead I am really .022 off the beginning of the frebore.

Is that the suggestion?

Thank you,
Hank

It's very possible. -Al

 

[gunsandgunsmithing]

The groups and the soot indicate low pressure. Don't overthink this unless you've ruled it out. If you don't have pressure signs, bump the charge up on that thing or try a faster powder.

Wind can induce vertical, specificaly head and tail winds. As can lighting or mirage. Tune can induce vertical. Gun handling, a nose heavy gun and a front bag that's too hard, can induce vertical. I'd KISS it before looking for less likely issues. Once you rule out the more obvious stuff, then look at the other possible causes.

 

[DaveTooley]

No land marks or ring on the projectile.

Let me make sure I understand what y'all are suggesting:

Y'all are saying that perhaps I have misidentified the start of the freebore as the start of the lands and I think I am loading .022 off the lands but, instead I am really .022 off the beginning of the frebore.

Is that the suggestion?

Thank you,
Hank

Not the start of the freebore but the end. I had a 243 AI reamer that rolled an edge up at the end of the FB when new and you could not get land marks. That can happen very quickly as tight FB reamers wear at the junction of the FB and the leade. Then you develop a choke point.

 

[ShtrRdy]

I have an experience to share and it might not be related to the OP's issue. I had some soot on the shoulders and on some of the case body for 6mm Creedmoor Lapua brass. The brass had been loaded and fired 3 times. I was using 105 and 115 grain bullets and launching them at mid to high 2900 fps velocity. (not a mild load)

I decided to anneal some of the cases and try again and that has taken care of the soot past the neck problem.

 

[gunsandgunsmithing]

I have an experience to share and it might not be related to the OP's issue. I had some soot on the shoulders and on some of the case body for 6mm Creedmoor Lapua brass. The brass had been loaded and fired 3 times. I was using 105 and 115 grain bullets and launching them at mid to high 2900 fps velocity. (not a mild load)

I decided to anneal some of the cases and try again and that has taken care of the soot past the neck problem.

I agree but the op did say it happened on virgin brass as well as fired, fwiw.

 

[243winxb]

I have been trimming them .020 short.

This may have reduced bullet hold? Change neck tension? Dont want the bullets moving out of the brass to soon.

Measure the length of the chamber. https://bulletin.accurateshooter.co...-chamber-length-with-home-made-modified-case/

Is a magnum primer being used?