300 PRC Velocity decreases every 100 rounds

[Mahziar]

Hi everyone
I am losing my mind
Setup;
Bartlein HV 1:9 28”
300 PRC AW2 Reamer
Defiance Ruckus
TT Special trigger
Mdc Acc
Bullet: Berger 220 LRHT
Lapua 4x fired brass FL sized (0.0015-0.002 bump)
Hodgdon Retumbo
Cci 250 primers

My first 2 ladders were done in 0.3 increments, after I found the area I want to play with, decided to run a expanded 5shots ladder test





the velocity is reducing every 100 rds with the same charge weight
Last range trip about 30-40fps
Barrel was cleaned the same way, this time I even uses 3 wet patches of CLR follwing by 3 patches of %91 alcohol and then boretech c4 and then boretech copper remover, and the. A few patches of jb, anyway the same way I clean everytime. The same lot of powder and primer. This time i used super trickler rather than Auto trickler v4
Why the heck i am getting lower velocity.
4x fired lapua brass, Below is the ladder test from last evening




The confusing part is that looks like the powder node stays close to where it was even with lower velocity, is that even a thing?
Like 77.1-77.4 @ 2789-2800
Then 77.1-77.3 @ 2774-2777
Then 77.5-77.7@ 2760-2749
Seating depth is increased to compensate the 20thou distance to the lands by 30thou from the first test to the last test

Right now my node with the lowest sd/es is 77.5-77.6 with just under 0.5 moa and 2756 fps
the barrel has 500 Rds count at the end of this test

 

[TaperPin]

Gas going around the bullet as the throat erodes will reduce velocity. You’ll have to hury and get that load dialed in or you’ll need a new barrel and have to start over.

 

[Straightshooter1]

Need more information, like:

Any changes in ambient temperatures you were shooting in?

Any changes in your powder moisture content?

Any changes in lots of bullets where there might be some change in bearing surface length?

Using the same lot of primers?

Using the same lot of powder or from a different bottle/jug?

 

[Mahziar]

Need more information, like:

Any changes in ambient temperatures you were shooting in?

Any changes in your powder moisture content?

Any changes in lots of bullets where there might be some change in bearing surface length?

Using the same lot of primers?

Using the same lot of powder or from a different bottle/jug?

Same lot of powder, primer, bullets
Powder from different jug since each 1lb is enough for ~80rds

Temp 85-70-65

 

[Straightshooter1]

Same lot of powder, primer, bullets
Powder from different jug since each 1lb is enough for ~rds

Temp 85-70-65

Certainly, the difference in temps would be a contributing factor to your issue as temperature get lower.

Also, moisture content of powder could be contributing as there can be significant difference that plays a part. Like a recent jug of powder I just bought (very fresh from the manufacturer) has a moisture content I measured at 58% and that compares to the couple of bottles I've been using that measures at 51%. That additional moisture content means less velocity that I've been getting. I'm just pointing this out, as it can be an additional factor to the temperature factor.

 

[wedgy]

What chrono ?

 

[Mahziar]

Certainly, the difference in temps would be a contributing factor to your issue as temperature get lower.

Also, moisture content of powder could be contributing as there can be significant difference that plays a part. Like a recent jug of powder I just bought (very fresh from the manufacturer) has a moisture content I measured at 58% and that compares to the couple of bottles I've been using that measures at 51%. That additional moisture content means less velocity that I've been getting. I'm just pointing this out, as it can be an additional factor to the temperature factor.

I am with you on this subject
How do you measure the moisture? How do you keep it consistent during loading season and storage?

 

[Mahziar]

What chrono ?

FX True Ballistics

 

[Straightshooter1]

I am with you on this subject
How do you measure the moisture? How do you keep it consistent during loading season and storage?

I use a Kestrel DROP D2 that I'll put into the container and seal it while I'm loading from a thrower containing powder from that container. That DROP D2 is connected to my Kestrel phone app and the time it take to charge up a batch of cartridges is enough time to get a good stable reading. Then I pour the leftover powder back into the container making sure the lid it tightly sealed, having removed the DROP.

To keep the powder moisture stable, I'll use Boveda packets for the moisture content I want. I have packets in with my various powders that sit around and don't get much use, just to be sure the moisture stays where I want it to be. These packets work two ways, in that they'll eithers add or subtract moisture to get to where the stated packet says it's designed for.

 

[moondog]

Never experienced that. I've been using the AW2 reamer for 2 barrels now although I'm going to try a shorter freebore next. I've pulled barrels around 1200 rounds that were still shooting good. 215 Bergers +.006. H1000 @ 2970. In fact, the current barrel with 600 rounds looks good enough to warrant a set back with the new Reamer.
Could just be your Chrony.

 

[LCazador]

What was your head measurement when brass was new? You load looks pretty and it looks like it flat lined from 78.3 to 79.2 in the second test. You may be over expanding the case on each load therefore making more powder capacity. Only way to know is what is case head diameter now and what was it when new?

 

[Mahziar]

I use a Kestrel DROP D2 that I'll put into the container and seal it while I'm loading from a thrower containing powder from that container. That DROP D2 is connected to my Kestrel phone app and the time it take to charge up a batch of cartridges is enough time to get a good stable reading. Then I pour the leftover powder back into the container making sure the lid it tightly sealed, having removed the DROP.

To keep the powder moisture stable, I'll use Boveda packets for the moisture content I want. I have packets in with my various powders that sit around and don't get much use, just to be sure the moisture stays where I want it to be. These packets work two ways, in that they'll eithers add or subtract moisture to get to where the stated packet says it's designed for.

Just ordered the Boveda and Kestrel
Thanks

 

[Mahziar]

Never experienced that. I've been using the AW2 reamer for 2 barrels now although I'm going to try a shorter freebore next. I've pulled barrels around 1200 rounds that were still shooting good. 215 Bergers +.006. H1000 @ 2970. In fact, the current barrel with 600 rounds looks good enough to warrant a set back with the new Reamer.
Could just be your Chrony.

This chronograph always gave me accurate numbers and never miss a shot
I also need to mention looks like my gunsmith chambered my barrel with maximum headspace not the minimum

 

[rijndael]

Missing a shot and giving an accurate readout from each shot are two different things. My shooting buddy's magneto speed doesn't miss either, but lately it's missing 200 fps from the readings.

Headspace is irrelevant here.

 

[Mahziar]

What was your head measurement when brass was new? You load looks pretty and it looks like it flat lined from 78.3 to 79.2 in the second test. You may be over expanding the case on each load therefore making more powder capacity. Only way to know is what is case head diameter now and what was it when new?

I don’t have the new measurement
But I know the fired is 0.5325-0.533 and the sized is 0.530

 

[Mahziar]

One of my questions:
The confusing part is that looks like the powder node stays close to where it was even with lower velocity, is that even a thing?
Like 77.1-77.4 @ 2789-2800
Then 77.1-77.3 @ 2774-2777
Then 77.5-77.7@ 2760-2749

 

[moondog]

If you know your original dope, its pretty easy to ck to see if your come ups have changed. After I find a good load at 1k, I get a baseline velocity. Get a solid zero then true it up at distance. Keep notes and see if the changes are matching your lost velocity. Sounds wierd.

 

[David Christian]

I did not see any round count on the barrel in this thread, did I? Taking a random stab here:

Are you over cleaning and opening the bore? Ask me how I know.

Have you tried to shoot your test, take the rifle home, don’t clean it and then go back the next day with the barrel seasoned to repeat the test? I have used this process to dial in my cleaning process such that I am cleaning the barrel, yet not removing the seasoning needed to produce consistent results on target.

I can think of a whole host of issues related to changing barrel conditions which could cause the tailspin. Getting the barrel to a steady and consistent state is the key for me.

Good luck!

 

[Mahziar]

I did not see any round count in this thread, did I? Taking a random stab here:

Are you over cleaning and opening the bore? Ask me how I know.

I don’t khow if I am over cleaning but I think I am going to stop using jb bore paste.
500 Rds as of today
What’s your experience in this regard?

 

[David Christian]

I don’t khow if I am over cleaning but I think I am going to stop using jb bore paste.
500 Rds as of today
What’s your experience in this regard?

Over cleaning opened my bore. This lead to reduced speeds and less accuracy.