6.5 Creedmoor - Why am I not hitting pressure?

[MikeMcCasland]

Specs:
27" Bart with a SAAMI .199fb 6.5CM chamber
107 TMK ~ .030 off the lands, .250" of bullet in the neck.
Virgin Lapua SR brass
CCI 41 primer
Shooters World Precision powder (Lovex S062).

Figured one of you might be able to answer this, because I feel like I should be close to blowing primers, but I'm not...

I've been blowing out brass in a 6.5 Creedmoor with spare supplies I don't intend to shoot competitively; I'm doing this for positional shooting practice, and secondly because I genuinely enjoy working up loads (even if not for serious use).

This led me to try a combo of a 6.5 Sierra 107 TMK behind what should be an almost kernel for kernel replacement for Varget (Shooters World Precision). In all other applications I've tried it in, SWP hits pressure ever so slightly before Varget, and usually identical velocities.

This creedmoor is different though.

A year ago I loaded up some test rounds up to 40.8gr (which is the book max for Varget) with a 107 SMK, and every round was soot covered (i.e. not building enough pressure); meanwhile, I was getting relatively high velocities.

Today I revisited this effort, starting with 40.8, working up to 41.6.

Out of the gate, the 40.8gr charge is giving me 3150FPS, which is trucking. Varget at 40.8 (granted it's a 24" test barrel) is at 3090.

41.6 ends up giving me north of 3230 for an average, and the cases are still suit covered.

Bolt operates like butter.

I'm not against continuing to up the charge, but if I'm getting soot covered case at 3230, I would imagine I'd be up near 3400 before I actually hit pressure as is.

Any ideas as to why this combo is giving ultra high velocities, but exhibiting symptoms as though it's way under pressure?

The only thing I can figure is the soot covering is due to not having enough bullet in the neck to get a good initial burn.

40.8:


Cases:

 

[Kurz]

This chart is from an article about reloading the TMK over Varget:

https://rifleshooter.com/2018/02/6-5-creedmoor-load-development-sierra-107-tmk-and-varget/

I thought a comparison would maybe jog the thinking about the disparities you're noticing.

 

[MikeMcCasland]

Granted we're dealing with different powders here, but my thought is that his 2x fired Norma LRP brass has greater capacity than my virgin Lapua SRP brass; not sure how many rounds on his barrel either.

Regardless, I'm 100 FPS faster than he is at 40.8, and I'm using a powder that in every other application (.223, 6BRA, .308) I've tried it in, hits pressure before Varget, and usually gives you less speed.

My guess is that it's due to little bullet shank there was in the neck (~.250), but I don't know. I usually have more than a bullet diameter in there.

 

[RegionRat]

https://www.shootingsoftware.com/pressure.htm
https://oehler-research.com/system-85-ballistic-instrumentation/
https://www.omega.com/en-us/force-strain-measurement/c/strain-gauges


Mike, If you are going to spend a lot of time path finding new recipes or exploring the margins, play it safe.
Strain gages are not for everyone, but they do keep you out of hospitals.

 

[MikeMcCasland]

https://www.shootingsoftware.com/pressure.htm
https://oehler-research.com/system-85-ballistic-instrumentation/
https://www.omega.com/en-us/force-strain-measurement/c/strain-gauges


Mike, If you are going to spend a lot of time path finding new recipes or exploring the margins, play it safe.
Strain gages are not for everyone, but they do keep you out of hospitals.

I'm not looking to blaze any trails here.

This is me stopping and saying "something doesn't make sense".

You would think a SAAMI chamber, varget substitute, and light bullet would be pretty easy...but here we are.

 

[drop_point]

I have a 6.5 PRC barrel the same way. I was 3+ grains over max load and no pressure (and velocity wasn't crazy high either, but over book speeds). I lost my nerve and settled on a node I found near the top of what I was willing to try. I didn't measure jam, but understanding it is a pre-fit barrel, I began seating depth test at magazine length and worked shorter. I had best results at mag length.

 

[XTR]

Mike, how long is the freebore, and how far out are you seating the bullets?

The reason I ask is that a few yrs ago I had a 308 barrel that I had throated long for the 200h, when The 20 X came out I ordered a bunch without knowing the bullet dimensions. When I loaded the 20 X bullet into that chamber it would barely reach the lands, but it would I was loading those bullets in that barrel for years with about 50 to 80 thou engagement on the bearing surface, worked great, it was the load and barrel I shot at the FCWC.

At some point I was doing some pressure testing with my pressure trace. I tried using those bullets as a benchmark in a barrel throated for 215s, and I got what you are seeing. The only explanation I have is that there was not enough friction fit in the neck to hold the bullet and it jumped to the lands before the pressure expanded the neck and sealed it, and the necks were not expanded. You could not put a bullet in the fired case. Those cases looked like yours. I got smoke from the breach on about the 3rd one and realized what was happening.

Measure your necks and see if they are expanded, is that barrel chambered for 140s?

crank up your neck tension a thou or two

 

[MikeMcCasland]

Mike, how long is the freebore, and how far out are you seating the bullets?

The reason I ask is that a few yrs ago I had a 308 barrel that I had throated long for the 200h, when The 20 X came out I ordered a bunch without knowing the bullet dimensions. When I loaded the 20 X bullet into that chamber it would barely reach the lands, but it would I was loading those bullets in that barrel for years with about 50 to 80 thou engagement on the bearing surface, worked great, it was the load and barrel I shot at the FCWC.

At some point I was doing some pressure testing with my pressure trace. I tried using those bullets as a benchmark in a barrel throated for 215s, and I got what you are seeing. The only explanation I have is that there was not enough friction fit in the neck to hold the bullet and it jumped to the lands before the pressure expanded the neck and sealed it, and the necks were not expanded. You could not put a bullet in the fired case. Those cases looked like yours. I got smoke from the breach on about the 3rd one and realized what was happening.

Measure your necks and see if they are expanded, is that barrel chambered for 140s?

crank up your neck tension a thou or two

I think you nailed it. I just went and grabbed some of the fired cases, and a bullet can't be inserted into a fired case neck.

Brass from the 107 loads is .290 fired, and brass from 140 Hybrids is .295 fired.

What's strange though is the brass is virgin Lapua brass. I didn't do anything fancy with it either; ran it through a .263 sinclair expander and seated the bullets. SAAMI 6.5CM .199fb reamer used to cut the barrel.

It makes me wonder what/how it sealed in the chamber, because it was obviously building pressure to deliver that kind of velocity. The SDs weren't terrible either, so it was getting good ignition.

I may set the charge back down to ~40.5 and seat the bullet way off the lands.

On a related note, is this the hack for TR? We can finally run our 20Xs at 3000fps without pressure?

 

[Earnhardt]

Quickloads says your load should be at 3249 fps with a 2.75 COAL (I guessed at the COAL), pressure says 64,583 psi

SAAMI max is 63,091

So, Quickloads says you are pretty much exactly where you are supposed to be with your load combo

 

[DirtySteve]

Just a wild guess but the soot could be because the gas is looking for some place to go and is being forced by the case mouth into the chamber. A different sign of over pressure!???? IDK..

 

[243winxb]

Reasons for soot. Long jump/freebore. Low neck tension, powder to slow, to little bullet shank in case neck, magnum primer needed.

Use the search at top of page. Enter "soot"

 

[darkangel_r2]

shooters world precision with a 123 at 2.75 tops out at 41.4 in their load data. A lighter bullet with a tiny bearing surface like the 107 seated at the same depth will need a bit more to see pressure. I'd keep going up until you see classic pressure signs or you find something that shoots really well.

If you don't want to add more powder try increasing neck tension a little to see if that cleans up your brass a little.

 

[Bc'z]

View attachment 1282291
shooters world precision with a 123 at 2.75 tops out at 41.4 in their load data. A lighter bullet with a tiny bearing surface like the 107 seated at the same depth will need a bit more to see pressure. I'd keep going up until you see classic pressure signs or you find something that shoots really well.

If you don't want to add more powder try increasing neck tension a little to see if that cleans up your brass a little.

I shared a picture with @MikeMcCasland a while back.
Using SWP load data I started with a charge of 40gr pushing a 123gr scenar, neck tension was high .005 using a .286 bushing with Peterson brass 1x fired. Same tension I run with the 123 scenar and IMR4166.
1st shot blew primer out of the pocket, bolt lift was STIFF.
Needless to say I pulled down the rest of the charges.
Before increasing charge weight I'm thinking an increase in neck tension will help achieve enough pressure to stop the soot.

 

[darkangel_r2]

I shared a picture with @MikeMcCasland a while back.
Using SWP load data I started with a charge of 40gr pushing a 123gr scenar, neck tension was high .005 using a .286 bushing with Peterson brass 1x fired. Same tension I run with the 123 scenar and IMR4166.
1st shot blew primer out of the pocket, bolt lift was STIFF.
Needless to say I pulled down the rest of the charges.
Before increasing charge weight I'm thinking an increase in neck tension will help achieve enough pressure to stop the soot.

Yeah peterson brass is heavy stuff. For 6.5 creed 170 grain case vs 165 for lapua or 147 for hornady. I usually work up from min for lapua brass which I would suggest even more strongly for peterson.

Their load data used hornady cases which could certainly explain the difference.

I agree that if he is achieving the performance he wants in terms of accuracy and velocity that he should probably just grip the bullet a little tighter to see if it cleans the fired brass up if that's his only concern.