Carbon on case shoulder 6 BRA

[LANDRO]

Shooting a 6 BRA, had great success fire forming with Lapua brass. Primed them, charged them with 29.5 of H4895, seated Berger 105 vld .020 into the lands and blasted away. ES almost into single digits and 1 hole groups common with 5 shots at 100 yd. This was the case for my rifle and my dad’s, I built them both with almost identical components.

After fire forming I cleaned the cases, annealed them with my AMP on code 153, sized them bumping the shoulder .001, opened the necks with .2400 mandrel, trimmed on Giraud, and found that .040 off the lands gave me a generous POI window with excellent accuracy, and 30.3-30.5 of H4895 all seemed to shoot well, leaning toward 30.4.

My problem is velocity. Accuracy is commonly in the 1’s-2’s with 5 shots, but ES on those 5 may be 20-30fps. SD from 10-15. I don’t find this acceptable. I noticed on my FF cases there is very little carbon, and it’s almost all on the neck. On my reloaded cases that have been processed, I’m getting a lot of carbon all the way down on the shoulder. I have a large suspicion this has something to do with my inconsistent velocities. Is the AMP code I’m using incorrect? I’ve burnt several cases and it keeps giving that code. I am wondering if the brass isn’t getting sufficient annealing? Any thoughts are appreciated. Picture is of FF cases on the left and processed cases on the right; you can see the difference in the carbon between the two.

 

[918v]

Why don’t you try a higher setting

 

[LANDRO]

That was my thought, but I’m not real familiar with how the AZTEC codes are generated. Think I saw where someone recommended 160 on 6 BRA… would that be a reasonable code to try? Don’t want to go torching a bunch of brass. Used to use tempilaq back in the day to verify temps but don’t have any laying around anymore. I guess technology in some ways makes us dumber.

 

[918v]

I would do one case at 157 and another at 160

 

[LANDRO]

Think I’ll give that a shot, thanks

 

[LANDRO]

I have 10 rounds loaded up for tomorrow… 2 at each of the following anneal codes: 153, 157, 160, 162, 165. Going to shoot them tomorrow and see if I can tell the point where they start sealing up at the neck. I can say I’ve already noticed a difference in sizing the cases; 153 has a lot of springback whereas the higher codes have much less. We’ll see what happens.

 

[just browsing]

AZTEC always uses 157 for me with standard Lapua BR, BRA, and Dasher.

 

[r.tenorio671]

...can't recall who/where, but....saw a post or vid where someone found differences in what code was generated during the testing of "clean" -vs- "dirty" cases.

 

[Haney]

Did you have it chambered for a no-turn neck ? If so ,maybe try .241" or .242" mandrel . Have you measured the neck OD of a loaded round and a fired round ?

 

[LANDRO]

The cases I’ve been generating codes with were clean cases, hadn’t tried dirty cases.

I have a no-turn chamber, neck od fired is .273, od loaded is .269.

 

[cooper_257]

carbon getting down the shoulder is usually from case necks that are to short.

 

[Haney]

The cases I’ve been generating codes with were clean cases, hadn’t tried dirty cases.

I have a no-turn chamber, neck od fired is .273, od loaded is .269.

OK, I was thinking that there was a chance the neck was not sealing .

 

[cooper_257]

your case length compared to how the neck is cut in your chamber. if your case length is to short it will allow exces gas and carbon around the neck. when using a suppressor it can cause so much carbon that after a few rounds you will start seeing pressure because the neck of the brass dosen't have enough room to expand and release the bullet

 

[cooper_257]

if you trim your brass to short or after fire forming it is on the short side for how your chamber was cut. it can also cause inconsistent velocity because the carbon build up around the neck is going to cause a tight neck and inconsistent bullet release.

 

[4O6shootist]

How far are you bumping shoulders back? Low psi powder charge? My 300wsm has a chamber neck 6.5k bigger than loaded rounds, no smoked shoulders but its pushed upper preasure.

 

[LANDRO]

I was able to fire the 10 rounds I loaded at different annealing settings; wind was blowing over 20 mph but that doesn’t really affect this testing. Accuracy is still good, still not sure what to think about the neck sealing up properly. Lowest amount of carbon seemed to be at anneal code 160. 153 and 157 still had carbon rings, and oddly enough 165 had the most carbon of them all. I figured it would seal the best. I’ll post some pics.

 

[LANDRO]

To answer the questions about neck length; I measured a factory Lapua BR case and it seems to be right at .315”, which is almost identical to what my trimmed cases are after FF. When I trimmed them after fire forming I took the shortest one and trimmed to that length, so only took .001” off most of them. Trim length once fire formed is 1.550”. The end of my chamber neck is 1.577”, so they could stand to be longer, but I wanted to acheive the chamfer to aid in bullet seating. I’ll probably let them grow for subsequent reloadings.

 

[LANDRO]

What mandrel are most people using for opening the necks after sizing (for those who use this approach)? I’m currently using a whidden die with .266 bushing then opening with .2400 mandrel. I have a full set and that’s my smallest one… I tried it because I was trying to get heavier neck tension for helping the neck seal. Even with that mandrel I don’t have near the neck tension I feel when seating in the new unfired cases. Just curious what everyone else is doing. Thanks

 

[Lawnboi]

Clean your chamber, with a carbon cleaner. Then shoot a few and see what happens.

On a few rifles I shoot suppressed if I don’t clean the chamber every so often I start getting shoulder sooting, the dirtier it gets the worse it looks on the cases.

Worth a shot

 

[Haney]

What mandrel are most people using for opening the necks after sizing (for those who use this approach)? I’m currently using a whidden die with .266 bushing then opening with .2400 mandrel. I have a full set and that’s my smallest one… I tried it because I was trying to get heavier neck tension for helping the neck seal. Even with that mandrel I don’t have near the neck tension I feel when seating in the new unfired cases. Just curious what everyone else is doing. Thanks

I use .241" most times . Are you opening the new brass with the same mandrel ?

 

[LANDRO]

Clean your chamber, with a carbon cleaner. Then shoot a few and see what happens.

On a few rifles I shoot suppressed if I don’t clean the chamber every so often I start getting shoulder sooting, the dirtier it gets the worse it looks on the cases.

Worth a shot

Thank you I will try that. I am shooting supressed as well

 

[LANDRO]

I use .241" most times . Are you opening the new brass with the same mandrel ?

On the new brass I’m not doing anything, just stuffing bullets and shooting. Travis at TS Customs did our barrels and he recommended that approach for the extra neck tension

 

[4O6shootist]

On the new brass I’m not doing anything, just stuffing bullets and shooting. Travis at TS Customs did our barrels and he recommended that approach for the extra neck tension

240 mandrel equates to 0035 neck tension with typical spring back. Most my 6mms have tuned in between 2 and 3 so you're not too far off.

 

[Haney]

On the new brass I’m not doing anything, just stuffing bullets and shooting. Travis at TS Customs did our barrels and he recommended that approach for the extra neck tension

I asked because I have measured many new Lapua brass with pin gauges and have found they vary so I uniform them with a mandrel before firing .

 

[LANDRO]

240 mandrel equates to 0035 neck tension with typical spring back. Most my 6mms have tuned in between 2 and 3 so you're not too far off.

Good to know thanks

 

[LANDRO]

I asked because I have measured many new Lapua brass with pin gauges and have found they vary so I uniform them with a mandrel before firing .

Yes sir I’ve found the same here, my first batch I used a mandrel on all of them but then tried without the mandrel and still had excellent accuracy for fire forming, even on cases with dented necks, etc. So I just started loading them and called it good

 

[LANDRO]

How far are you bumping shoulders back? Low psi powder charge? My 300wsm has a chamber neck 6.5k bigger than loaded rounds, no smoked shoulders but its pushed upper preasure.

Shoulder is getting bumped around .001

30.3-30.5 powder charge should be putting me toward the upper end of acceptable pressure. Primers are showing a little bit of flow at those charges

 

[918v]

What was the ambient temperature.

 

[LANDRO]

Today was right at 80deg

 

[LANDRO]

What was the ambient temperature.

Today was right at 80deg

 

[BuildingConceptsllc]

your case length compared to how the neck is cut in your chamber. if your case length is to short it will allow exces gas and carbon around the neck. when using a suppressor it can cause so much carbon that after a few rounds you will start seeing pressure because the neck of the brass dosen't have enough room to expand and release the bullet

How can you know that this isn't happening if you shoot suppressed all the time? I've wondered about this myself.

 

[just browsing]

Seems like there could be excessive clearance between case mouth and chamber end, or maybe even excessive freebore?

I’ve seen this occur in barrels toward the end of their life, where throat degradation effects the amount of carbon observed on the exterior case neck/shoulder and how far down the case it travels.

Sorta tough to show in the picture, but the cases on the left were fired around 1500 rounds, and the cases on the right were fired from the same chamber around 2800 rounds. There is decidedly more carbon on the cases to the right.

 

[Haney]

You could try just the opposite of what you are doing by using the largest mandrel that still allows you to seat a bullet without falling through the neck .This would get your brass closer to the wall to seal . You will know after just a few rounds .

 

[Cascade Hemi]

What is the chamber neck diameter and what is your loaded neck diameter? If you go up a half or whole grain of powder does it go away?

 

[Milo 2.5]

What is the chamber neck diameter and what is your loaded neck diameter?

This ^^^ right here, figure out the neck dia of the chamber.
Another thing, if your cases were that carboned up, so is the shoulder in the chamber, until you clean that you will never have a fresh start.
The theory of the necks being too short, Dashers, with way less neck length seal off, not your issue.

 

[Milo 2.5]

your case length compared to how the neck is cut in your chamber. if your case length is to short it will allow exces gas and carbon around the neck. when using a suppressor it can cause so much carbon that after a few rounds you will start seeing pressure because the neck of the brass dosen't have enough room to expand and release the bullet

Not necessarily, hydro formed dasher cases can end up .025" shorter than FF cases, and it is all in the necks, we get this brass to seal off. Also, short neck to chamber length neck does not always equate to a carbon ring, incomplete burns and initial powder choices are far bigger culprits.

 

[Cascade Hemi]

The theory of the necks being too short, Dashers, with way less neck length seal off, not your issue.

Yeah. OP could probably cut half the neck length off and still have the brass seal with proper pressure and neck clearance.

 

[CK1.0]

I have a no-turn chamber, neck od fired is .273, od loaded is .269.

For 6mm/.243”, a loaded neck OD of .269” and a fired neck OD of only .273” is really skinny… I’d investigate that some more..?

I’m using necked-up Lapua 22-250 for 6CM (so the necks are ~.001” thinner than usual 6CM cases) and my loaded neck OD is still .272”. (This is after seeing an AMP on Aztec every firing and a .268” bushing before a .241” mandrel.)

 

[Milo 2.5]

For 6mm/.243”, a loaded neck OD of .269” and a fired neck OD of only .273” is really skinny… I’d investigate that some more..?

I thought most Dasher reamers were .272" in the neck, same case here. If Peterson brass is used, neck dia is stepped up to .274". Plus, if his necks were overly tight, no doubt it would be sealing off and he would be into pressure. He also stated he was up to 30.4 gr of H4895, sounds like a stiff charge.

 

[CK1.0]

I thought most Dasher reamers were .272" in the neck, same case here. If Peterson brass is used, neck dia is stepped up to .274". Plus, if his necks were overly tight, no doubt it would be sealing off and he would be into pressure. He also stated he was up to 30.4 gr of H4895, sounds like a stiff charge.

Yeah, the numbers just looked odd to me: I mean, if a 6mm/.243” bullet’s OD is supposed to be ~.243”, then a loaded neck OD of .269” means a .013” case neck wall thickness (.269 - .243 = .026, .026/2 = .013).

Which I guess sounds fine… just skinnier than I’m used to seeing (maybe it’s different with Dasher/BR/BRA, but I’m more used to seeing a .271” - .273” loaded neck OD), so I was thinking maybe his necks are loose in the chamber, not tight. IDK.

 

[4O6shootist]

Yeah, the numbers just looked odd to me: I mean, if a 6mm/.243” bullet’s OD is supposed to be ~.243”, then a loaded neck OD of .269” means a .013” case neck wall thickness (.269 - .243 = .026, .026/2 = .013).

Which I guess sounds fine… just skinnier than I’m used to seeing (maybe it’s different with Dasher/BR/BRA, but I’m more used to seeing a .271” - .273” loaded neck OD), so I was thinking maybe his necks are loose in the chamber, not tight. IDK.

Lapua laoded necks are 268-2685, alpha bra and 6gt are 269, I think that diameter with a 272-274 chamber are pretty standard no-turn. My new 6bra is being cut with a 140fb 274 nk reamer, all my alpha brass measures 2685-269 loaded. So I'll have 5k clearance, which is usually what a strive for in a field gun.

 

[Archer0826]

Th

OK, I was thinking that there was a chance the neck was not sealing .

This

 

[Pav67]

If it’s a .274 chamber and .268-.2685 loaded round not uncommon.I just pulled a dasher barrel with 2100 rounds that had soot on shoulders the whole time.Wasn’t an issue.Clean the chamber when you clean the rifle.I was using lapua brass with a .274 chamber

 

[kthomas]

I don't have the AZTEC, but my AMP code is way different.

I'm using AMP code 73 for mine.

 

[spife7980]

I don't have the AZTEC, but my AMP code is way different.

I'm using AMP code 73 for mine.

The preaztec code system is way different from the aztec system

 

[kthomas]

The preaztec code system is way different from the aztec system

Ah gotcha, thanks.

 

[LANDRO]

Thanks everyone for the input. I’ve been out of town a few days but back home now and I think I’m going to clean my chamber and then re-test at anneal code 160. Going to get 20 or 30 loaded up and see what they look like when I know everything is clean from the start.

 

[Mxracer532]

The cases I’ve been generating codes with were clean cases, hadn’t tried dirty cases.

I have a no-turn chamber, neck od fired is .273, od loaded is .269.

Mine is .272 fired. But I am using alpha brass. Not sure of chamber. It was chambered by Preece precision.