6mm creedmoor powder charge and pressure questions.

[J.Kubiak]

Hi everyone! Just wanted to ask about FPS. I’ve made several powder tests and bullet seating tests and had pretty decent results. Turns out I’m getting decent standard deviation and extreme spread at 2 different powder measurements.

1.) 38.7-38.9 gr of h4350 is aprx 6 std dev and extreme spread of 14 with an avg FPS of 2970.

2.) 40.7 gr I had 3.8 std dev and ext spread of 9.0. With an avg FPS of 3086.

These were the best results I had testing from 38-41gr every .2 and both were really tight groups around 3/8 moa. I do see signs of over pressure, but I also have some signs on the lower powder charges as well under 39gr? Do any of you find that there are two sweet spots in your powder tests? If so is 40.7gr too much? 3086fps too fast for 6mm CM? Don’t know much about re loading or barrel life etc.
also another odd thing is I tested each powder gr amount with a bullet seating depth closer to the lands and one closer to factory Hornady I had that shot well. all of my powder tests performed better farther from the lands then they did closer, and significantly better actually. I read all over that closer is better (about .003-.005 off the lands or jam point some people call it). Thanks for any help!
pictures are of the 40.7 stats and group. The first of the 5 shots didn’t register for some reason.

 

[rustyinbend]

I recently learned a valuable lesson, the quite frankly, surprised me. Using an expander mandrel (like the 21st Century Kit) and opening up the neck before seating, can (and did for me) eliminate pressure signs at lower velocities. I had pressure signs at low charge weights, and a buddy suggested I open the neck beyond the standard size. In my 6.5-CM I went from .2630 (standard mandrel from L.E. Wilson) to .2645 (larger 21st Century) ... and my pressure signs disappeared and gave me lots of charge-weight headroom to get better velocities. Might want to give that a try. It worked for me. A side benefit was that it stopped the occasional "stuck bullet" in my Redding Competition Seating Die.

 

[Hickswr]

The following information would be useful:
Barrel length
Bullet
Brass

 

[J.Kubiak]

The following information would be useful:
Barrel length
Bullet
Brass

Sure sort about that.
26” 1:7.5 twist
115gr dtac rtb
Peterson

 

[J.Kubiak]

I recently learned a valuable lesson, the quite frankly, surprised me. Using an expander mandrel (like the 21st Century Kit) and opening up the neck before seating, can (and did for me) eliminate pressure signs at lower velocities. I had pressure signs at low charge weights, and a buddy suggested I open the neck beyond the standard size. In my 6.5-CM I went from .2630 (standard mandrel from L.E. Wilson) to .2645 (larger 21st Century) ... and my pressure signs disappeared and gave me lots of charge-weight headroom to get better velocities. Might want to give that a try. It worked for me. A side benefit was that it stopped the occasional "stuck bullet" in my Redding Competition Seating Die.

I have a 21st century mandrel at .2415 and my bullets are .2430 I’ll try using that next time after my Whidden Gunworks full length neck bushing die with expander ball.

 

[CK1.0]

What pressure signs are you seeing?

Yes, there can be 2 or more sweet spots; though, there's new thinking on this where plenty of us have come to the conclusion that: in reality there really are no sweet spots, the anomalies we see are most likely just coincidence and cannot be repeated with any regularity... so we just pick a speed and figure out how many grains that takes, done.

Is 3086fps too fast with DTAC's? Maybe/maybe not/Depends... I shoot DTAC's too, don't forget that at 115gr they're about as heavy as it gets for 6creed, and: heavier projectile + fast speeds = pressure (usually), so being that close to the edge where pressure can spike, you'll probably want to be mindful of the weather/temps (shoot that same load when it's 10 degrees hotter than when you last tested, and you could be in for an unwanted surprise). FWIW I run my DTAC's in 6creed nice and easy at ~2900fps @ ~75-80degF (hammers and no worries about potential pressure issues when it's hotter outside). Just depends on what you like: I prefer the heavier DTAC's going slower and use their advantage in BC to make up the difference vs running 105HT's and going faster up at ~3100fps.

Seating depth closer vs further to "the lands" or jam? The old/traditional thinking that being closer to jam (or no more than like .020" off) is another old trope that won't die. Yes, for some disciplines (like Benchrest) jamming the bullet is the norm, but for many of the other disciplines not wholly obsessed with punching paper at relatively close distances, that thinking has evolved too. Nowadays the complete opposite is gaining traction as it turns out many of the newer more modern bullet profiles love to jump (I'm jumping my DTAC's ~.100" to jam and it hammers).

Hope this helps little.

 

[J.Kubiak]

What pressure signs are you seeing?

Yes, there can be 2 or more sweet spots; though, there's new thinking on this where plenty of us have come to the conclusion that: in reality there really are no sweet spots, the anomalies we see are most likely just coincidence and cannot be repeated with any regularity... so we just pick a speed and figure out how many grains that takes, done.

Is 3086fps too fast with DTAC's? Maybe/maybe not/Depends... I shoot DTAC's too, don't forget that at 115gr they're about as heavy as it gets for 6creed, and: heavier projectile + fast speeds = pressure (usually), so being that close to the edge where pressure can spike, you'll probably want to be mindful of the weather/temps (shoot that same load when it's 10 degrees hotter than when you last tested, and you could be in for an unwanted surprise). FWIW I run my DTAC's in 6creed nice and easy at ~2900fps @ ~75-80degF (hammers and no worries about potential pressure issues when it's hotter outside). Just depends on what you like: I prefer the heavier DTAC's going slower and use their advantage in BC to make up the difference vs running 105HT's and going faster up at ~3100fps.

Seating depth closer vs further to "the lands" or jam? The old/traditional thinking that being closer to jam (or no more than like .020" off) is another old trope that won't die. Yes, for some disciplines (like Benchrest) jamming the bullet is the norm, but for many of the other disciplines not wholly obsessed with punching paper at relatively close distances, that thinking has evolved too. Nowadays the complete opposite is gaining traction as it turns out many of the newer more modern bullet profiles love to jump (I'm jumping my DTAC's ~.100" to jam and it hammers).

Hope this helps little.

so this is very interesting! always learn so much from you guys. I shot this ammo on Thursday at Angeles and it was 95 deg out and a little humid. there is a chance that I will shoot it at temps around 100-105 at some high desert matches but mostly shoot at CA tac and Pala, or Burbank which is 70-90 deg most of the time. Do Hugh temps create MORE overpressure or reduce the pressure? looks like I'll go back to the testing and stay at or under 3000 fps and hope I get as good of STD DEV and EXT SPRD as I did with the 40.7. thanks a lot!

 

[Rocketmandb]

so this is very interesting! always learn so much from you guys. I shot this ammo on Thursday at Angeles and it was 95 deg out and a little humid. there is a chance that I will shoot it at temps around 100-105 at some high desert matches but mostly shoot at CA tac and Pala, or Burbank which is 70-90 deg most of the time. Do Hugh temps create MORE overpressure or reduce the pressure? looks like I'll go back to the testing and stay at or under 3000 fps and hope I get as good of STD DEV and EXT SPRD as I did with the 40.7. thanks a lot!

First, I'd say that ~3100 with 115 DTACs is pushing it - you are likely at the high end of a reasonable pressure.

Second, heat will push pressure up (and thus, muzzle velocity). You'll get a load all perfect down there in Burbank, then you'll head across the hills to go shoot in the desert somewhere and you'll pick up a bunch of pressure and velocity.

I had a very similar velocity node (almost exact, as a matter of fact) at 3080 fps with 105s when I had my 6 CM. I couldn't match it when I tried the 115s due to pressure. Sold the 6 CM a while back when I got my 6 BRA, still have the box of 115 gathering dust on my shelf - they don't work in the BRA either.

EDIT: To clarify - the 115s didn't work at a high enough velocity to warrant using over the 105s.

 

[CK1.0]

Higher temps mean more fps, and that usually means higher pressure, just something to be aware of...

Now, will that mean that you'll run into problems ? IDK. You are using H4350 (which is probably one of, if not, the most temperature stable powder out there), so you might be ok... just depends on how close to the edge of seeing pressure signs you are? Hard to guess where that line is until you're right up on it, or have stepped over it...

I'll say this: it's not coincidence that many guys all end up running about the same speeds when using similar components. Some barrels are faster than others for sure, but the difference is never that crazy... so if every one else's load sees pressure around a certain speed range when using the same recipe of components you're using, once you're in that neighborhood, you should be paying attention and on the look out, because if the number you're seeing is too good to be true, maybe it is. As rifle shooters, we all tend to feel faster is almost always better (except when it's not), because of flatter trajectory and all that blah blah blah, but there's no rule that says you have to go as fast as you can...

JMHO here, but another thing to consider, especially with 6creed is: how you decide to run it also affects how it "feels" and how fast you'll cook it.

On the top end with 6creed (with a 115gr bullet, for a 105 add ~100fps), roughly-speaking, going ~3050fps vs 2950fps only really saves one click at 1000yrds, but due to the added pressure, flattening your trajectory for that click might cost ~500rds in barrel life. Then there's the "feel" thing: for the last couple years the trend, especially with the pros, has been to go to a smaller 6mm variant for more barrel life and less recoil, because it turns out most feel all that extra speed isn't really as necessary as those other things. But, after the last year, with the more exotic brass (6GT/Dasher/BR/etc) drying up and being next to impossible to track down, seems like there's a lot more guys running a 6creed again, except now, "detuned" a bit for a little less recoil and a little more barrel life, kind of like a big Dasher or something.

Point is, ballistically, the round shoots straighter than you or any of us need it to, so no need to live with more recoil than you have to, or waste components trying to find the speed limit if one doesn't feel like it.

Before you put too much faith in low SD's read this: https://precisionrifleblog.com/2015/04/18/how-much-does-sd-matter/

 

[CK1.0]

still have the box of 115 gathering dust on my shelf

I'll buy them if you'd like to get rid of them!?

 

[J.Kubiak]

First, I'd say that ~3100 with 115 DTACs is pushing it - you are likely at the high end of a reasonable pressure.

Second, heat will push pressure up (and thus, muzzle velocity). You'll get a load all perfect down there in Burbank, then you'll head across the hills to go shoot in the desert somewhere and you'll pick up a bunch of pressure and velocity.

I had a very similar velocity node (almost exact, as a matter of fact) at 3080 fps with 105s when I had my 6 CM. I couldn't match it when I tried the 115s due to pressure. Sold the 6 CM a while back when I got my 6 BRA, still have the box of 115 gathering dust on my shelf - they don't work in the BRA either.

EDIT: To clarify - the 115s didn't work at a high enough velocity to warrant using over the 105s.

Very interesting! I’ll def find a lower pressure/FPS. Side note: Want to sell the 115s?