The 6.5 Creedmoor Forum

6.5 Creedmoor Technical Info => Reloading => Topic started by: dnellans on October 11, 2017, 08:27:31 PM

Title: longer coal and effect on case pressure?
Post by: dnellans on October 11, 2017, 08:27:31 PM
question that i’m hoping someone with quickload might be able to answer.

i’m currently running 43.8 grains of rl-16 with hornady 147’s seated at 2.81 coal (mag length). my lands are way out at 2.924 meaning i’ve got an enormous jump going on. now if i loaded same load to 2.91 say, maybe accuracy gets better/worse, TBD. but what is the expected effect of case pressure/velocity? is a 1/100th change enough to make a difference at all?

mostly just curious if someone with quickload has the time to run two scenarios changing only the COAL from 2.81 to 2.91

thanks
-d
Title: Re: longer coal and effect on case pressure?
Post by: rardoin on October 11, 2017, 09:42:32 PM
Just checked and I don't have the 147 in the bullet library in QL.
Title: Re: longer coal and effect on case pressure?
Post by: dnellans on October 12, 2017, 06:56:54 AM
Just checked and I don't have the 147 in the bullet library in QL.

appreciate you looking - i guess the question still stands for anything in the 140-143 class. the 147 is a bit longer but i’m just trying to understand if adjusting the COAL .01 will have significant effect or not.
Title: Re: longer coal and effect on case pressure?
Post by: rardoin on October 12, 2017, 07:11:07 AM
appreciate you looking - i guess the question still stands for anything in the 140-143 class. the 147 is a bit longer but i’m just trying to understand if adjusting the COAL .01 will have significant effect or not.

That I can do....gimme a minute :)
Title: Re: longer coal and effect on case pressure?
Post by: rardoin on October 12, 2017, 07:19:34 AM
Assuming Hornady cases with approx H2O cap. of 53.5gr./ 26" barrel/ ELD-X 143gr / Rl-16 at 43.8gr

COAL 2.81, 105% compressed load, 66,988 PSI, 2930 fps

          2.91, 102% compressed load, 62,931 PSI, 2895 fps
Title: Re: longer coal and effect on case pressure?
Post by: jvw2008 on October 12, 2017, 07:40:01 AM
QL does not know where your lands is located along a continuum of increasing COAL.  I t will continue to predict decreasing pressure. Once the ogive kisses the lands and especially when it gets jammed, the pressure will radically increase rather than decrease as the software predicts.
Title: Re: longer coal and effect on case pressure?
Post by: rardoin on October 12, 2017, 07:58:17 AM
Jerry brings up an important point to consider.  Even though you have a predicted 0.014" jump to the lands at 2.910" COAL.....don't count on it.  Your loads are at/near max for the shorter COAL and if your longer cartridges are actually very close or touching the lands the pressure spike could put pressures exceeding 70K which can cause damage.  If you try the longer seating depth I suggest backing off a half grain and firing a cartridge or two and check for pressure signs as you work up to 43.8gr.  You only need one or two loaded at each charge to check pressures.
Title: Re: longer coal and effect on case pressure?
Post by: dadajack on October 12, 2017, 07:59:14 AM
You should see pressures drop until you start engaging the lands at loaded length. The best thing to do is redo your load workup at 0.010" - 0.020" and fine tune from there. Anything less than 0.005" jump to the lands should not give a noticeable increase in peak pressure. As long as you give the ogive a running start at the lands, the engraving pressuse stays withing safe operating conditions, assuming you are using a safe powder charge.

Edit: I'll also respectfully disagree with Robin, as much as I hate to, but I watch for pressure signs on high end loads every time I start shooting them, and consider one case with "signs" of pressure in 10 rounds one to many. Again, this is just my opinion, and Robin is a master handloader, so my disagreement with his low round count is purely that, my personal opinion not based on anything other than my opinion. Sorry to be negative @rardoin
Title: Re: longer coal and effect on case pressure?
Post by: rardoin on October 12, 2017, 08:25:36 AM
Edit: I'll also respectfully disagree with Robin, as much as I hate to, but I watch for pressure signs on high end loads every time I start shooting them, and consider one case with "signs" of pressure in 10 rounds one to many. Again, this is just my opinion, and Robin is a master handloader, so my disagreement with his low round count is purely that, my personal opinion not based on anything other than my opinion. Sorry to be negative @rardoin

I think we are on the same page DJ.  I suggested loading a single case at say, 43.4gr, 43.6, and 43.8gr to look for pressure signs before assuming the original 43.8gr load is safe.  I am in total agreement that 1/20 overpressure cases means I have a problem to solve and the load is not to be considered safe until I can diagnose the issue.

As far as Master Handloader???  Who me???  One of my fishing buddies did dub me a Master Baiter and I had no objection ;D
Title: Re: longer coal and effect on case pressure?
Post by: dnellans on October 12, 2017, 09:09:25 AM
thanks for all the replies guys. i actually have played with single loads loaded to touch the lands before and the difference between just off and touching is pretty amazing in terms of chrono’d velocity and (i assume) pressure spike.

that’s why i was curious about how much less pressure moving coal longer but not actually to the lands gets me since everything lists 2.81 as coal for max charges.

it looks like it’s not all that much different actually from 2.81 to 2.91 3000psi, less than i might have guessed. i’m pretty happy with my load/velocity at 2.81 but if i could generate same velocity with less pressure by loading longer and then bumping charge maybe .1 that’s interesting too. might load 10 up at longer length .002 off the lands but same charge and see if the group any better/worse than current load just to play around a bit before i invest in any accurate mags

Title: Re: longer coal and effect on case pressure?
Post by: dnellans on October 12, 2017, 09:11:52 AM
unless you’re really jamming them i don’t see a lot of guys advocating kissing the lands so i’ll probably stay a ways off them to avoid the pressure spike issues we’re talking about above
Title: Re: longer coal and effect on case pressure?
Post by: dadajack on October 12, 2017, 09:35:35 AM
As far as Master Handloader???  Who me???  One of my fishing buddies did dub me a Master Baiter and I had no objection ;D

I don't fish that much, but I have been married for 15 years now, so, the title fits me as well.
Title: Re: longer coal and effect on case pressure?
Post by: rardoin on October 12, 2017, 11:16:48 AM
I don't fish that much, but I have been married for 15 years now, so, the title fits me as well.

Sometimes a man's gotta take his love life into his own hands. ;)
Title: Re: longer coal and effect on case pressure?
Post by: rardoin on October 12, 2017, 11:25:21 AM
unless you’re really jamming them i don’t see a lot of guys advocating kissing the lands so i’ll probably stay a ways off them to avoid the pressure spike issues we’re talking about above

I feel the same way.  I was working with a bullet and sticking with a 0.006" seat depth and it was working pretty darn good.  But, I would get unexpected vertical that dropped me out of the ten ring at least once per 20 shot string.  That dog would not hunt with the level of competition I am shooting with.  When I finally ignored the bullet makers recommended jump and experimented I found Nirvanna at 0.016" and + or - a thousandth was still in the money.  I feel that when the ogive is near touching, or touching and not jammed, any minor variation with ogive shape can cause my perceived distance from the lands to be inaccurate and pressures will vary a bit from shot to shot.  Further off the lands makes those small variations inconsequential.  
Title: Re: longer coal and effect on case pressure?
Post by: Danbonzo on October 12, 2017, 12:09:15 PM
Only time I jam is when I'm fireforming Dasher blue box brass. My match load for said same is .018 off the lands. Consistent laser with Berger 105 Hybrids.
Title: Re: longer coal and effect on case pressure?
Post by: dadajack on October 12, 2017, 12:22:17 PM
I jam all the time! On the way to work, on the way home, at the house, in the shower, at work... always jammin! I never stick it in the grooves though... never.
Title: Re: longer coal and effect on case pressure?
Post by: Zephhyr on October 12, 2017, 12:25:58 PM
Just thought I would throw some more data to consider.
IN MY RIFLE, with RL16 42.3gr, Hornady brass, S&B primers, and 147 ELDMs.
I hit the lands at a coal of ~2.909, max magazine is 2.880.
2.800 = 2682fps, SD 6.0, ES 19
2.830 = 2688fps, SD 4.1, ES 16
2.850 = 2696fps, SD 4.2, ES 13
2.860 = 2691fps, SD 5.9, ES 20
2.870 = 2708fps, SD 7.6, ES 31
2.890 = 2721fps, SD 7.2, ES 24 
The 2.860 proved to be the most consistently accurate coal. They were all 5 shot groups and I was rather surprised by the increase in velocity, as I was going on the assumption (you know what they say about that) that a longer oal would decrease the initial pressure spike (as long as you we not jammed into the lands of course) and thus the velocity.
Title: Re: longer coal and effect on case pressure?
Post by: dnellans on October 12, 2017, 01:45:29 PM
Just thought I would throw some more data to consider.
IN MY RIFLE, with RL16 42.3gr, Hornady brass, S&B primers, and 147 ELDMs.
I hit the lands at a coal of ~2.909, max magazine is 2.880.
2.800 = 2682fps, SD 6.0, ES 19
2.830 = 2688fps, SD 4.1, ES 16
2.850 = 2696fps, SD 4.2, ES 13
2.860 = 2691fps, SD 5.9, ES 20
2.870 = 2708fps, SD 7.6, ES 31
2.890 = 2721fps, SD 7.2, ES 24 
The 2.860 proved to be the most consistently accurate coal. They were all 5 shot groups and I was rather surprised by the increase in velocity, as I was going on the assumption (you know what they say about that) that a longer oal would decrease the initial pressure spike (as long as you we not jammed into the lands of course) and thus the velocity.

huh - now thats pretty interesting.  thanks for putting some data to it!  how long is your barrel?  did you shoot them in that order going longer?  could speed increase be attributed to change in barrel temp or having started with a clean barrel getting progressively more fouled?

at 43.8gr i'm running them quite a bit hotter than you are (2785-2805 depending on temp) mostly because i couldn't find anything i thought was really good in the 42.x range. next load down that shot well for me was down between 2600 and 2625 which is actually slower than factory loads.  maybe i wasn't looking hard enough in the 42.xgr range but since 43.8 seems to be working ok without issues even at 100F out, i'll stick with it for now.
Title: Re: longer coal and effect on case pressure?
Post by: Blinkster on October 12, 2017, 02:23:42 PM
Only time I jam is when I'm fireforming Dasher blue box brass. My match load for said same is .018 off the lands. Consistent laser with Berger 105 Hybrids.

My 6mm BR prefers that everything be jammed ~.010"...105's or 107's all like to be jammed.
Title: Re: longer coal and effect on case pressure?
Post by: Danbonzo on October 12, 2017, 02:48:09 PM
My 6mm BR prefers that everything be jammed ~.010"...105's or 107's all like to be jammed.
Yup I'd believe it, some of the best groups I've ever shot were from a .308 and I was about .003" off the lands.
Title: Re: longer coal and effect on case pressure?
Post by: dnellans on October 13, 2017, 01:49:22 PM
Was able to seat some bullets last night while watching the Cubs eek out a glorious victory!

Same cases/bullets/charges/primers everything, only difference was seating depth (2.81 versus 2.91).  I combined this with an experiment of using imperial dry lube (graphite) on the necks to see if that would help improve seating dept consistency and accuracy and it definitely did.

20 shots at each COAL,  1 minute rest in between shots,  even warmed the barrel up with 10 shots before starting.  Much to my surprise, and similar to Zephyr's results above the 2.91 COAL did not slow down, in fact it very clearly sped up.

20 shots at 2.81 - avg 2790.15, SD 9.81, ES 36
20 shots at 2.91 - avg 2801.75, SD 15.67, ES 46

The SD on the 2.91 went up and the graph is interesting to me. There is a pretty smooth trend of shots across the spread with the 2.81 seated loads.  the 2.91's have a clear bi-modal thing going on where about half are between 2780-2795 and then there is a big jump and they are 2810-2820. 

(the plot below I sorted the data, there was no trend of the faster shots being at the end of the strings, it would alternate from 2780->2815->2785 without any rhyme or reason)

So the theory that they should slow down due to less cartridge pressure appears to be busted, and clearly I shouldn't add any more powder,  cases looked identical between the two COALs, no more or less signs of pressure on either one, but this jumping of speed from 2780 up to 2820 isn't awesome.  I was shooting for chrono, not for groups so no idea yet if its more/less accurate but had no problem keeping either load on the 2MOA plates at 750 yards. 
Title: Re: longer coal and effect on case pressure?
Post by: Zephhyr on October 13, 2017, 04:03:54 PM
huh - now thats pretty interesting.  thanks for putting some data to it!  how long is your barrel?  did you shoot them in that order going longer?  could speed increase be attributed to change in barrel temp or having started with a clean barrel getting progressively more fouled?

at 43.8gr i'm running them quite a bit hotter than you are (2785-2805 depending on temp) mostly because i couldn't find anything i thought was really good in the 42.x range. next load down that shot well for me was down between 2600 and 2625 which is actually slower than factory loads.  maybe i wasn't looking hard enough in the 42.xgr range but since 43.8 seems to be working ok without issues even at 100F out, i'll stick with it for now.
My AR has a 24" Criterion barrel + suppressor.
The barrel / suppressor never got above comfortably warm. I would take a short break between 5 round groups just to keep the temperature in control.
I did fire them short -> long.
Title: Re: longer coal and effect on case pressure?
Post by: dnellans on October 13, 2017, 04:34:22 PM
My AR has a 24" Criterion barrel + suppressor.
The barrel / suppressor never got above comfortably warm. I would take a short break between 5 round groups just to keep the temperature in control.
I did fire them short -> long.

getting a bit off topic but can i ask what resolution +-.1gr or +-.02gr you're weighing your charges?  ES under 20 is pretty impressive
Title: Re: longer coal and effect on case pressure?
Post by: Zephhyr on October 13, 2017, 04:48:24 PM
getting a bit off topic but can i ask what resolution +-.1gr or +-.02gr you're weighing your charges?  ES under 20 is pretty impressive
Thanks, I've had pretty good luck getting consistent ES of 15-20 with RL16 and H4350.
I use an RCBS Chargemaster to throw the initial charge, .1 under,  then trickle it up on my bald eagle scale to within + - .02.
Title: Re: longer coal and effect on case pressure?
Post by: dnellans on October 13, 2017, 05:03:38 PM
i've gotta ask (per another thread i started) - what kind of SD/ES were you seeing if/when you were just using the RCBS with +-.1  before adding the bald eagle to within  +- .02?

I've been wondering lately if my current SD/ES are in fact limited by the chargemaster lite (+-.1) that i'm using.  brian litz's new book makes the claim you will never be able to reliably get an SD below 7-9ish if you're relying on .1gr precision from your scale.
Title: Re: longer coal and effect on case pressure?
Post by: Zephhyr on October 13, 2017, 05:23:56 PM
While I would see an occasional sub 10 SD using the Chargemaster alone,  it wasn't consistent enough for my ocd, with my current process is definitely more consistent and repeatable.
Title: Re: longer coal and effect on case pressure?
Post by: dnellans on October 13, 2017, 05:37:48 PM
While I would see an occasional sub 10 SD using the Chargemaster alone,  it wasn't consistent enough for my ocd, with my current process is definitely more consistent and repeatable.

thats super interesting for me to hear since I'm basically in the same boat. I can pretty reliably get SD's at 9-11 across 25 shot strings but never below,  maybe i will have to cough up for a gempro or something and start trickling up
Title: Re: longer coal and effect on case pressure?
Post by: MLN1963 on October 14, 2017, 01:55:53 PM
Maybe the increased speed with increased COAL is due to more complete combustion? If the primer can move around the powder a tad is it possible it is igniting more of it initially?