load development seating depth question

[Max_The_Phoenix]

Hi Guys
I am running to an issue that is very frustrating.
Rifle specs:
Defiance Ruckus Tactical
Barrel: 24” proof CF sendero light. 1:7.5
Chambered in 6.5 CM
Brass: peterson LR
primer: CCI 250
bullet: Hornady 147gr ELD-M
I followed Erik's method to find the jam, My JAM CBTO 2.188. I seat the bullet at 2.168 for powder charge test.
I load my rounds to the exact same CBTO, exact same headspace.
I found my optimal charge between 40.0 to 40.2 with the lowest SD/ES
I saw pressure signs at 40.4 gr with a small ejector mark.
loaded some rounds with 40.1gr H4350
3 rounds each for CBTO of 2.165 to 2.105
here is the question: looks like the further I go down with the seating depth I am increasing pressure due to decreasing case volume.
So if I found a good group. What should I do next? since I am getting ejector mark on cases.
Where do you go from there?
Any help will be appreciated.
Thanks

 

[ShtrRdy]

Are you able to measure velocity while shooting for groups without a Magnetospeed attached to the barrel?

What seating depth step size are you using?

Which cartridge is this?

 

[Max_The_Phoenix]

Are you able to measure velocity while shooting for groups without a Magnetospeed attached to the barrel?

What seating depth step size are you using?

Which cartridge is this?

6.5 cm
Yes I use Labradar

 

[ShtrRdy]

6.5 cm
Yes I use Labradar

Great! A couple more questions.

What velocity are you getting with 40.1 gr and CBTO of 2.168?

Do you feel the bolt lift getting a little harder?

Could you post a picture of the ejector mark you're seeing?

 

[Max_The_Phoenix]

Great! A couple more questions.

What velocity are you getting with 40.1 gr and CBTO of 2.168?

Do you feel the bolt lift getting a little harder?

Could you post a picture of the ejector mark you're seeing?

Around 2653fps @ 2.168 CBTO
The volt lift is not hard but it gets harder the further I increase the seating depth.
It is very faint mark but I will try to post it when I get home

 

[R_A_W]

I'll have to check, but I think 2.188" is slightly shorter than typical - but I could be wrong here.

Is this new brass? If so, what is the brass length (CB to shoulder datum)? Compare unfired/fired brass. Peterson brass has less volume than others, so you're likely to develop pressure sooner. Combine that with seating deeper in the case due to a shorter freebore & you would get pressure signs sooner.



If you use a standard LRP, do you get primer flattening or flow? What are the lowest & highest ES/SD you've seen? Do you know how old the Proof blank is?

Just to rule out the obvious 1) the brass is clean of lube, liquids, dust, etc., 2) the loaded rounds were not sitting in the sun 3) there are no irregularities on the bolt face

Could you post a picture of the ejector mark you're seeing?

x2

 

[CNC-Dude]

How does your base to ogive measurement compare to the OAL? I use Superformance in my 6.5 CM and am in the mid-2700 FPS range.

 

[DeathBeforeDismount]

First you need to back way off IF you are hitting acutal pressure. A few grains off pressure is not enough. When it gets super hot or is wet out, you will exceed that. Seen 2 of the best shooters in the world pull out of a match after day 1 becuase their ammo was unsafe due to rain. They loaded to close to pressure.

40.02 gr of h430 is not alot in a 6.5cm, especially with a 140-147 class bullet. I load around 40.8 with 153 and 156 and am well below pressure with similar length barrel. You could be reading the signs wrong.

Your first firing is usually going to see pressure quicker. Once the case fireforms its going to increase volume which will decrease pressure. My loads are always more accurate with more consistent sd/especially with Fireformed and trimmed /annealed/ fl bushing/mandrel brass.

CBTO are really easy to get wrong too. Take a bunch of measurements to make sure you aren't jamming to hard or not enough. .020 is hardly anything.

 

[KnowNothing256]

Agreed that if you saw pressure signs (ejector mark) at 40.4 gr, you shouldn't be running at 40.1 gr. Ejector mark is well over-pressure, and also (as you've just found), running very close to pressure means small changes can result in over-pressure.

Look for another good load 1-2 grains lower. I don't know Peterson brass capacities enough to know whether your load is light or not, but I was running over 2 gr more powder than you with the same bullet last year for a Hunter match. I was probably over pressure too honestly, but I was in Lapua brass which has less case capacity than Hornady. Sorry that this paragraph doesn't give you a ton of "aha" info; bottom line, if you're seeing ejector marks, back down at least a grain.

There can be gun-related issues that can cause ejector marks I think, but I'm less familiar with those.

 

[ShtrRdy]

Velocity wise, you should be able to go a little higher.

So, to answer your original question, back off on powder charge 0.1 to 0.2 grains as you decrease the length of the cartridge. Try to keep the velocity around what you were seeing with the original "good" load.

 

[Max_The_Phoenix]

I'll have to check, but I think 2.188" is slightly shorter than typical - but I could be wrong here.

Is this new brass? If so, what is the brass length (CB to shoulder datum)? Compare unfired/fired brass. Peterson brass has less volume than others, so you're likely to develop pressure sooner. Combine that with seating deeper in the case due to a shorter freebore & you would get pressure signs sooner.



If you use a standard LRP, do you get primer flattening or flow? What are the lowest & highest ES/SD you've seen? Do you know how old the Proof blank is?

Just to rule out the obvious 1) the brass is clean of lube, liquids, dust, etc., 2) the loaded rounds were not sitting in the sun 3) there are no irregularities on the bolt face


x2

Brass length: 1.4845 after resizing
Col: 2.108
Measured the case volume after sizing at 50.0 grs

- I have around 500 rounds down the barrel
- lowest sd/es with CCI BR2 was 5.43/13.51
-never got primer catering or flow with magnum ir Lr primers


No the brass wasn’t under the sun
Here is the picture

 

[Max_The_Phoenix]

How does your base to ogive measurement compare to the OAL? I use Superformance in my 6.5 CM and am in the mid-2700 FPS range.

C.B.T.O= 2.168 (0.020 off the jam)
C.O.A.L= 2.902

 

[Max_The_Phoenix]

First you need to back way off IF you are hitting acutal pressure. A few grains off pressure is not enough. When it gets super hot or is wet out, you will exceed that. Seen 2 of the best shooters in the world pull out of a match after day 1 becuase their ammo was unsafe due to rain. They loaded to close to pressure.

40.02 gr of h430 is not alot in a 6.5cm, especially with a 140-147 class bullet. I load around 40.8 with 153 and 156 and am well below pressure with similar length barrel. You could be reading the signs wrong.

Your first firing is usually going to see pressure quicker. Once the case fireforms its going to increase volume which will decrease pressure. My loads are always more accurate with more consistent sd/especially with Fireformed and trimmed /annealed/ fl bushing/mandrel brass.

CBTO are really easy to get wrong too. Take a bunch of measurements to make sure you aren't jamming to hard or not enough. .020 is hardly anything.

I do agree with you
Back in march when temps were around 55-75 here in bay area I was getting ejector mark with br2 primer at 41.2gr @ 2703fps
I do seat my bullets with arbor press and check all of them for testing and all are the same length
For powder charge test I seat them .020 off the jam

 

[Max_The_Phoenix]

Velocity wise, you should be able to go a little higher.

So, to answer your original question, back off on powder charge 0.1 to 0.2 grains as you decrease the length of the cartridge. Try to keep the velocity around what you were seeing with the original "good" load.

So you mean if I find a good seating depth, just back off .1 or .2 to see if the pressure goes away?

 

[BLKWLFK9]

Was your barrel cut with your action on sight or was it a prefit? No matter wtf Defiance says about the rukus, it is not consistent enough for prefits. Im wondering if its your chambering because 40.8 is not a high charge weight for a 6.5cm at all. You shouldnt be near pressure with that weight. This is assuming you are using H4350.

 

[R_A_W]

Brass length: 1.4845 after resizing
Col: 2.108
Measured the case volume after sizing at 50.0 grs

- I have around 500 rounds down the barrel
- lowest sd/es with CCI BR2 was 5.43/13.51
-never got primer catering or flow with magnum ir Lr primers

50.0gr is definitely on the low side for 6.5cm

1.4845" headspace is extremely short, like under SAAMI minimum - double check your measurement. Are you using a Hornady LNL comparator with the 0.400" datum piece

I'm guessing this is a prefit. I'd stop shooting it & get some Go/No Go guages

 

[Max_The_Phoenix]

Was your barrel cut with your action on sight or was it a prefit? No matter wtf Defiance says about the rukus, it is not consistent enough for prefits. Im wondering if its your chambering because 40.8 is not a high charge weight for a 6.5cm at all. You shouldnt be near pressure with that weight. This is assuming you are using H4350.

It was cut with my action on sight,
I tought about it for a while cause I have a weird issue after sent back the gun to the smith for polishing the chamber
I have to size down from 1.4905 to 1.4845 in order to close the bolt freely with ejector and firing pin removed,
Before that brass would grow to 1.4865 and I would have to size only 2 thou
I don’t know I am to the point to send the barrel to rechamber with another smith using my own reamer

50.0gr is definitely on the low side for 6.5cm

1.4845" headspace is extremely short, like over 50 thou too short from SAAMI minimum - double check your measurement

Using short action custom headspace gauge
I don’t remember but I think it shows 20 or 30 thou smaller than hornady gage

 

[R_A_W]

I can't comment on how the SAC comparator measures, other than SAC and Hornady both list Datum C for 6.5cm (0.375" datum).

Using a Hornady LNL 0.375" (datum C), my fired brass is 1.559"

That being said, SAAMI uses a 0.400" datum (PDF page 51/375), at which my fired brass measures ... hold on, just lost my allen wrench haha 1.535"

I think Manson guages are also based on a 0.400" datum & I assume that a 0.400" datum is standard for 6.5 Creedmoor. It's very weird that Hornady & SAC both recommend a 0.375" datum, but that's probably why SAC's comparator measures 25 thou longer than it should. If that is correct, then your brass would actually measure 1.459" at the 0.400" datum. That would be way out of spec - SAAMI minimum is 1.4864"

 

[ShtrRdy]

So you mean if I find a good seating depth, just back off .1 or .2 to see if the pressure goes away?

Actually, I was thinking if you made note of the velocity when you found the powder charge it liked, ( before seating depth test ), and then when doing seating depth testing try to keep the velocity about the same.

The picture of the primer looks fine. There is a slight swipe on the case head that I wouldn't worry about yet based on bolt handle lift feels okay and bullet velocity is on the low side.