6 Creedmoor pressure issues

[Kratos]

I wanted to get a sense of charge versus velocity for the Berger 109s and A-tip 110s in my 6 Creedmoor, just to see if the barrel has any life in it (probably around 800-1000 rounds fired). I loaded 80 rounds (40 with each bullet) as follows:

- COAL 2.850 (so both were jumping about 50-60 thousandths)
- brass: Hornady once fired
- all primers Federal 210

two rounds each, in 0.2 increments:
- N540 35.2-36
- N555 40.6-41.4
- RL16 40.6-41.4
- H4350 40.6-41.4

There is not a lot of data for these bullets out there, so this was intended to be pretty conservative. I was surprised to get ejector marks with the 109s at 35.8 grains of N540. I was more surprised when the primer blew right out of the first round with a 109 and N555 (I thought this might have been a fluke, so I fired the second round (at arm's length) and had a clearly flattened primer. Oddly, I don't remember noticing heavy bolt lift with either of these.

I continued and got ejector swipes on the lowest charges of each powered with the 109s. With the 110s, I was able to fire all the N540 and N555 rounds, but did see swipes on the middle charges of RL16 and H4350.

In terms of velocity, the 109/N555 loads that were very high pressure shot 3029 and 3037 fps. All N540 rounds were below 2950. RL16 and H4350 with the 109s were about 3050. And the A-tips were about 2900-3020. So not very high for this cartridge.

I am wondering if the neck in the chamber is tight? Fired case necks measured about .274-.275 OD.

Borescoping the chambering shows hideous fire cracking but I don't think there is a carbon ring (I believe there was but I think it's cleaned).

Thoughts?

 

[jepp2]

so this was intended to be pretty conservative

Not conservative at all based on my experience for the RL16 loads. Here is what I got.

 

[Kratos]

Not conservative at all based on my experience for the RL16 loads.

But I was starting at 0.7 grains below your max (and the book max) and still hitting pressure immediately. That seems odd.

 

[JimSC]

I initially tested 37.0 - 42.0 of H4350 using a 107 SMK seated .025 from lands with no pressure signs. My final load was 37.5 gns just touching the lands and 2800 FPS. This was with a 29 inch barrel.

 

[alby280]

Depends on what company's data you use,different max loads are there.Check nosler compared to sierra which is a major difference.

 

[jepp2]

But I was starting at 0.7 grains below your max (and the book max) and still hitting pressure immediately. That seems odd.

Different: powder lots, barrel, chamber, temperature, etc.

 

[Ranger188]

If your sure you don't have a carbon ring, you can check your neck clearance by
seeing if a bullet will drop freely into a fired cases neck.
Your loads in general are not hot. But you are showing a lot of signs
so something else has to be going on.
What barrel make are you using? You never said. Tikka's are very slow
Do you know your neck tension?
Sometimes just changing something like brass (company) will help.
The 6 Creed will toast barrels in 1000 rounds. Your barrel is probably on it's last shots.

 

[Kratos]

If your sure you don't have a carbon ring, you can check your neck clearance by
seeing if a bullet will drop freely into a fired cases neck.
Your loads in general are not hot. But you are showing a lot of signs
so something else has to be going on.
What barrel make are you using? You never said. Tikka's are very slow
Do you know your neck tension?
Sometimes just changing something like brass (company) will help.
The 6 Creed will toast barrels in 1000 rounds. Your barrel is probably on it's last shots.

Bullets don’t drop freely into the fired cases, not at all. I forgot to mention that, but that’s part of why I wondered about the neck clearance.

it’s a Bartlein that was chambered by Altus. I also should mention I had a blown primer with a factory round a while ago—I had suspected a carbon ring at that time and cleaned it very thoroughly, but still it goes toward a pattern.

I agree it may be on its last legs, just trying to see if it has a few more rounds left. I’m going to try turning some necks down 1-2 thousandths and see if that changes anything.

edit: neck tension should be about .002”

 

[Hohn]

How long is your free bore? It’s well known that some early reamers were so short that factory ammo was jamming and spiking pressure.
Definitely confirm reamer details.

 

[Ranger188]

both were jumping about 50-60 thousandths

 

[Kratos]

How long is your free bore? It’s well known that some early reamers were so short that factory ammo was jamming and spiking pressure.
Definitely confirm reamer details.

I don't know the absolute number. I did measure the distance to the lands with these bullets and they are jumping quite a ways, if that helps.

 

[shoot4fun]

I don't think the neck is too tight as most reamers are .274 neck and have a fairly generous freebore.
I shoot the 105 Hybrid with 42 grains RL16 and zero pressure signs. That load makes 3020 FPS with a barrel that has right at 1,000 rounds on it.
Every time I clean it (after every outing) I do a borescope inspection on carbon, copper and carbon rings.
I keep thinking it's done but it just keeps on shooting well.
Every barrel is different. Would you tell us your barrel's brand and twist?

 

[Kratos]

I don't think the neck is too tight as most reamers are .274 neck and have a fairly generous freebore.
I shoot the 105 Hybrid with 42 grains RL16 and zero pressure signs. That load makes 3020 FPS with a barrel that has right at 1,000 rounds on it.
Every time I clean it (after every outing) I do a borescope inspection on carbon, copper and carbon rings.
I keep thinking it's done but it just keeps on shooting well.
Every barrel is different. Would you tell us your barrel's brand and twist?

It's a Bartlein 5R 1:7 left hand twist.

If most reamers have a .274 neck, then my fired cases should not be coming out at .274-.275, right?

Some bore photos. This is with a case seated fully:



Same spot but case withdrawn partially. Note there is a bit of carbon after the case, but none where the neck was:


Leade with firecracking:

 

[shoot4fun]

You have a carbon ring.
You also are dealing with a fast twist barrel. I have 6 Dasher that is 7 twist and it will show higher pressures with the same loads I normally shoot in my 7.5 or 8 twist barrels.
It is not an anomaly, as I see those same issues between my 6.5 and 7.7 twist 223 barrels.

 

[Kratos]

You have a carbon ring.
You also are dealing with a fast twist barrel. I have 6 Dasher that is 7 twist and it will show higher pressures with the same loads I normally shoot in my 7.5 or 8 twist barrels.
It is not an anomaly, as I see those same issues between my 6.5 and 7.7 twist 223 barrels.

Hmm. When I took the barrel off last time, I ended up soaking it overnight in CLR before scrubbing with a nylon brush. It looked a lot worse before that. Not sure how much better I can make it.

 

[shoot4fun]

Hmm. When I took the barrel off last time, I ended up soaking it overnight in CLR before scrubbing with a nylon brush. It looked a lot worse before that. Not sure how much better I can make it.

RL16 can build up fast. I let my barrel get pretty dark this last time before I really got after it with Holland's Witch's Brew and a bronze brush.
As for a carbon ring nothing works better than IOSSO cream.
Got mine shining like a new one and worried it wouldn't shoot well at the next match. It did. Shot one of my best ever matches.

 

[Bill K]

But I was starting at 0.7 grains below your max (and the book max) and still hitting pressure immediately. That seems odd.

You must remember every firearm and it's chamber is just different enough and that is why the loading books say start at the start load and work up. Yours apparently can not take the listed max loads, so work up and be safe and sane.

 

[Kratos]

You must remember every firearm and it's chamber is just different enough and that is why the loading books say start at the start load and work up. Yours apparently can not take the listed max loads, so work up and be safe and sane.

I realize there is variation, but I’ve never heard of this much variation as a normal thing. Nobody has a 6 Creedmoor that develops pressure at Dasher speeds and just says “oh well, different chamber.” I think there is something wrong.

 

[dnellans]

I've shot thousands of 109's and ~1k 110 in a 6 creed with RL-16 this year alone (PRS). 26 inch kreigers 7 twist.

40.7 gr RL-16
CCI 450
Lapua SRP brass
2.775 COAL (about 15 off)
Run at 3110fps
This load doesn't show pressure signs on the case and I haven't pushed it higher because 40.9 didn't shoot any better in my small firing pin gun and this gives me some leeway for dirt/rain/etc

in another gun with large firing pin

40.5gr RL-16
F210M
Alpha LRP brass
2.770
Runs at 3085 and the alpha brass shows a little bit of ejector shine but no hard bolt lift, I'm on 5th firing of brass but don't expect most of it to make it past 8th firing, starting to lose a few primer pockets each loading.
At 40.7 bolt lift starts being sticky and at 40.9 and above its trashing brass in a single shot.

I get lower speeds out of 4350 and/or hit pressure sooner at lower charge weights in the 6 creed across numerous barrels.

Granted neither of these are hornady brass which might have slightly more case capacity, but your experience on where you hit pressure with those two powders seems inline with my own.

 

[Kratos]

I've shot thousands of 109's and ~1k 110 in a 6 creed with RL-16 this year alone (PRS). 26 inch kreigers 7 twist.

40.7 gr RL-16
CCI 450
Lapua SRP brass
2.775 COAL (about 15 off)
Run at 3110fps
This load doesn't show pressure signs on the case and I haven't pushed it higher because 40.9 didn't shoot any better in my small firing pin gun and this gives me some leeway for dirt/rain/etc

in another gun with large firing pin

40.5gr RL-16
F210M
Alpha LRP brass
2.770
Runs at 3085 and the alpha brass shows a little bit of ejector shine but no hard bolt lift, I'm on 5th firing of brass but don't expect most of it to make it past 8th firing, starting to lose a few primer pockets each loading.
At 40.7 bolt lift starts being sticky and at 40.9 and above its trashing brass in a single shot.

I get lower speeds out of 4350 and/or hit pressure sooner at lower charge weights in the 6 creed across numerous barrels.

Granted neither of these are hornady brass which might have slightly more case capacity, but your experience on where you hit pressure with those two powders seems inline with my own.

That’s interesting data, thanks. Were you seeing similar speed from the 109 and 110 despite the much longer bearing surface on the 109s?