Please help me solve 6 Creedmoor Velocity drop. UPDATE

[DirtySteve]

More moisture. Your weighing water and powder. 300 fps doesn't make sense.

It can knock it down easily over 100 fps.. Then add in poor detonation from not a hot enough primer and it might get another 100 slower or at least a huge ES...

How does humidity affect powder?

You may have heard about a relationship between humidity and bullet velocity either in a book, on a reloading forum, or from a crusty benchrest shooter right after saying they get better ES/SD&#821…

chronoplotter.com

 

[SecondsCount]

Are you seeing any change in impact on the target?

 

[big5ifty]

Chronograph with Andiscan A2 (verified to be within 4 fps of a Labradar or Magneeto)

Have you tried a different chronograph ?

 

[drop_point]

A couple things here:

That is an EXTREMELY low charge weight. Are you sure your numbers aren't off?

BR-4 primers are typically also slow in 6mm Creedmoor.

Chronographs can crap out on you or give bad readings. Did your trajectory change?

 

[dellet]

Instead of trying things to get the velocity back, maybe eliminate something to Keep it from happening.

You said that new brass, restores velocity.
Did you check velocity on the first firing of the next set of brass?
Did you lose it again on the third?

Are you annealing before the first firing?
If not, maybe try that.

Check case capacity before and after each firing.

You might try not annealing.
Accuracy will likely suffer, SD/ES may open up, but if the huge velocity drop lessens, you have a good indicator. Plenty of people don’t anneal each firing or at all without losing 10% of their loads velocity.

I would suggest the cause being over annealing, not under. If it’s sealing at the shoulder, pressure is enough to expand the case. It’s just timing. If the neck is opening early, leaking pressure due to soft brass, the only way to fix that would be to crimp.

With overly soft brass, you would likely need pressure measurement while seating to pick it up. Might be able to feel it on an arbor press with a short handle.

Any time a chronograph throws strange numbers, change the batteries, and make sure lighting conditions are the same.

 

[drop_point]

If the AMP is over-annealing, I'd be quite disappointed.

 

[Doom]

Assuming you are not abusing your powder then it's unlikely that humidity is the issue. If new brass fixes the problem then brass is where the problem lies. What I would check is whether or not you are over annealing your necks and actually losing neck tension so that the bullet is releasing too early in the pressure curve. See if you can pull the bullet out or push it in by hand.

 

[Delfuego]

What kind of brass?

 

[Walt Krafft]

How far has your throat moved? What was your JAM dimension when the barrel was new? What is it now?

 

[KMart]

Well, it looks like Pudgy has left the building. Like so many new posters, they ask a bunch of questions and then take a hike. That is one reason that I am hesitant to help out a new poster. We see it too often.

So, for now, everybody is just talking amongst ourselves with no feedback from the guy that is having a problem.

 

[Barossa_222]

Just for comparison, my 6 creedmoor, Borden Alpine, 28" Brux 4 groove. I'm running 108eldms and 109 Berger lrht. Lapua srp brass, CCI 450 mag primers 4350 powder. Running 41.8grs behind both loads. The 108s are out at 3275 and the 109s are out at 3150. Same powder charge. No neck turning, but I had to flash hole deburr. Exceptionally accurate. ES and SD sub 10.

 

[Unknown Marksman]

Well, it looks like Pudgy has left the building. Like so many new posters, they ask a bunch of questions and then take a hike. That is one reason that I am hesitant to help out a new poster. We see it too often.

So, for now, everybody is just talking amongst ourselves with no feedback from the guy that is having a problem.

I apologize for dropping off the map, I didn’t mean to be rude. I’m a single dad of 3 young boys. I had an last minute out of area assignment come up and dropped the ball on this in my scramble to rearrange my schedule and meet deadlines.

To follow up.
As I continued to test even my new brass dropped velocity. The only thing left is the barrel. It started losing velocity after I cleaned it.

I used nylon brush (no brass) wipe on patch out, their accelerator and Montana copper remover.

I ended up calling Proof and they had me send the barrel in. They received it today. I will update with results.

On another note. I just spun on a new Proof 7 Rem barrel Wednesday . And last night and Today cleaned it with the same products. But this time used a brass brush per Proofs break in recommendation. Current round count on this barrel 76.

Borescoped and barrel is clean (did note a small chunk out of the rifling 8” up the barrel but no scratches lands look great no noticeable wear) but …… I’ve lost 100 fps and the more o shoot the more velo I’m losing!! I have used the exact same process on several rifles including 4 other Proof barrels without issue.

I shot most of my loads in this rifle with Adg , coal of 3.5500 (50 jump) 180 hybrid and 66 grain of H1000 with a velo of 2834. Zero pressure signs. (Previous barrel 69 grains @ 2980)

It’s only been these 2 new pre fit barrels I’m having issues with. Either I’m doing something wrong or the metal is different. Either way I’m nervous about cleaning any more of my proof barrels until I figure this out. I have 4 more I have yet to use.

I’ll contact Proof again Monday. Until then I’m going to see if I can foul the barrel at get some velocity back.

Once again I’d like to apologize to everyone to who took the time to try and help. Your kindness is appreciated. And I don’t mean to waste your. Time.

 

[Unknown Marksman]

Have you tried a different chronograph ?

I didn’t, but I ran some previous reloads out of couple other rifles and they were spot on.
Plus I loaded couple a grain over we’re I previous got pressure signs and still 300 fps slow with no pressure.

 

[Unknown Marksman]

How far has your throat moved? What was your JAM dimension when the barrel was new? What is it now?

I didn’t think to check that. Would have been a good idea. Lands looked great when I borescoped. No noticeable fire cracking or wear.
I sent the barrel to proof to check out.

What kind of brass?

Peterson SRP.

 

[Unknown Marksman]

Assuming you are not abusing your powder then it's unlikely that humidity is the issue. If new brass fixes the problem then brass is where the problem lies. What I would check is whether or not you are over annealing your necks and actually losing neck tension so that the bullet is releasing too early in the pressure curve. See if you can pull the bullet out or push it in by hand.

I ran every test I could think of. When I tried new brass again then velocity on it also dropped.

Every 10-15 rounds I’m losing more velocity. I believe it has something to do with the barrel. This showed up shortly after cleaning. Use coated cleaning rods, bore guide, patch out/wipeout and their accelerator and a little Montana extreme copper remover with nylon brush. I’ve used this method on many barrels with no issues.

I sent barrel to Proof to check it out.

On another note I just spun a 24” Proof pre fit 7 Rem and after cleaning with above process at 57 rounds, it has lost 100 fps and continues to loose velocity the more I shoot.

I’ve only shot 20 since cleaning, will shoot few more and see if I can get velocity back if I foul the barrel.

Bit nervous about cleaning anymore proof pre fits until I figure this out

 

[Unknown Marksman]

If the AMP is over-annealing, I'd be quite disappointed.

I have loaded over 2,000 rounds in the last 6 months for 6.5 PRC, 2-7 Rems , 7 saum with no issues. Don’t think it’s the AMP.
I also tried not annealing and new brass. Didn’t get velocity back. Pretty sure it’s working like it’s supposed to.

 

[Unknown Marksman]

Are you seeing any change in impact on the target?

Yes , POI has changed. Groups are reasonable given the circumstances ( I’m not focusing groups are .4ish to .7 ish) single digit SD and ES under 20

 

[Unknown Marksman]

Have you tried a different chronograph ?

I didn’t. I test other loads in other rifles. Velocity of previous loads hadn’t changed and drops are spot on.

 

[Beiruty]

Did you change the bullets?

 

[dthomas]

From what you're saying it sounds like something is going on with the barrels or your cleaning process. I would not stop cleaning. If you are using the same procedure you have been using without problems until these 2 barrels I would lean more towards a barrel problem. Hope you get it figured out.