Question about barrel/charge slowing down

[EchoDeltaSierra]

I’m about ready to put up this hobby, move to India, take up absinthe and opium, and start writing morbid comedies. Please help.

Since installing my new Criterion nitride finish barrel in March, to the best of my knowledge and ability I've done everything "right" and am seeing a recent odd slowdown in my barrel. It's a 6.5CR 1:8 twist 21" barrel run exclusively with a Specwar 762 can. I have initial chamber measurements, measurements from the lands, and did both jump testing and OCW load development. I am a moderately experienced reloader and my reloading practice produces consistent ding-digit standard deviation. I load two lots of ammo, one is a 200 round lot of Nosler brass using BR-2 primers and the other is a 300 round lot of Lapua brass with BR-4 primers. I have just over 800 rounds through this barrel and it is plenty accurate and I've been regularly shooting this rifle and load at matches. Cleaning is every few hundred rounds or so using a Dewey bore guide and rod and only ever putting patches wet with Hoppe's No. 9 down the tube. I did clean once using Hoppe's No. 9 Bench Rest to take off a bit more copper.

When temperature were in the 40s, I did my final load validation and tuning. I landed on jumping my Hornady 140 ELDs .050" and pushing them with a 42.5gr charge of H4350. I was solid and 1000y validated my drop in my Kestrel and trued up velocity to 2795 fps in early April. I did a 600y range trip a few weeks ago and noticed I was shooting a bit low at 600y, so I got out the magnetospeed and check my load's speed and SD and dang it, I slowed down to 2750 fps (validated at 1000y). I figured that was okay, trued up my Kestrel and shot another match. Yesterday, I went to the range trip to revisit some hotter loads and shoot a few (finished off my 200 round lot), and FFS, my chronograph measured 2695 avg. fps. And in conditions that are 30 degrees warmer than when I measured the other loads.

Now I'm somewhat stumped. What could be happening that is causing my barrel/load to have lost 100 fps? I'm looking for some suggestions to try and just cannot find the issue or variability. It's still shooting plenty well. I'm still getting single SDs. I know my power scale, case measurements, etc. is all well enough accurate and within tolerances.

Thanks in advance for any thoughts or ideas of stuff to look at.

 

[918v]

Put new batteries in the MS.

Clean the barrel with a bronze brush. Run the brush in one direction only.

 

[ALShooter]

Ditch the hoppes and give boretech eliminator a whirl.

 

[abn31c]

Above is solid advice, but I'm curious as to throat erosion. How far off the lands are you now compared to load development?

 

[EchoDeltaSierra]

Put new batteries in the MS.

I hadn't thought about that and see how a lower voltage should impact the sensor. Battery swapped.

Also, I'll give her a good cleaning, though can say, the barrel comes clean by merely alternating 3-4 wet / dry patches.

 

[EchoDeltaSierra]

Above is solid advice, but I'm curious as to throat erosion. How far off the lands are you now compared to load development?

Just took a measurement and currently have about 030" of total erosion. This is my first real experience with a new custom barreled action and don't know what is typical nor what to expect.

Also, I do have a replacement already on order but am hoping for 3000-4000 rounds life out of this one.

 

[MarinePMI]

With that load, I think you'll be hard pressed to see 4000rds of life from that barrel. I run the same load (but with mostly RDF's) and accuracy began to fall off for me at around 2900, and by 3200, it was starting to throw flyers and exhibit other weird accuracy issues. It wasn't apparent at 600yds and in, but at 885yds, on a 4" spinner target, the flyers were pretty obvious. This was an AI barrel that Tooley made for the the AT's when they came out, so am fairly certain it was a Bartlein blank.

 

[supercorndogs]

You loaded the same charge in both different brands of brass? I am pretty sure Nosler has a more capacity than Lapua.

 

[Milo 2.5]

Are you loading from the same lot# of powder? Lot #'s can change things up.
This is also 2019, in the last 6 yrs alone some cleaning products have hit the market that are awesome. Either Hoppes you are using should just be dabbed around the room for aromatic therapy after you clean your rifle. If you have never brushed, of coarse your patches are clean after 3 jag trips. A carbon buildup close to the muzzle can create drag and drop your velocity, but bolt lift usually stiffens with that.
It may be your battery on the MS, let us know.
I call what you have going on a pressure dump, you have enough throat erosion, even though it is not a great amount, that the barrel is no longer generating the pressures you experienced earlier. You can either add some powder and try get it back, or go to a faster powder and I think just try duplicate the old speeds.
You could buy the exact same barrel at different intervals and end up with 2 different longevity scenarios. One barrel is just softer than the other.
I lost a 6mm comp match barrel at 1200 rds, the first dump was at 600 rds, brought it back with a faster powder, got 600 more, then done. .027" total erosion.

 

[EchoDeltaSierra]

You loaded the same charge in both different brands of brass? I am pretty sure Nosler has a more capacity than Lapua.

These were my set of Nosler brass for which I have extensive dated chronograph load workup data. Interestingly, there’s only about 15fps difference for the same load in Nosler and Lapua brass.

I’m a bit of an OCD data nerd, which tends to fuel my curiosities.

 

[abn31c]

FWIW,I just roasted a barrel in a matter of months with this
Lapua brass
Fed205m
130 hybrid
42 gr h4350 +or-
1600 rnds and im jumping 160 thou at max length.
Krieger to the rescue this week.

 

[Rynomar]

I had something similar happen recently as well. Average velocity on my 6.5x47L dropped 40fps after running 200 rounds through it over two days of shooting. I wasn't going crazy with mag dumps, but did have several magazines that I fired pretty quickly. I checked the distance to lands and had 0.041" throat erosion after 385 total rounds through the barrel. It is still shooting the Berger 140 grain hybrids really well, but I no longer have enough neck to chase the lands and am now at 0.045 jump with 0.244" of bearing surface in the neck. I was able to add another 0.5 grains of H4350 and get back to my original velocity though. I will just have to see how long it continues to shoot, but it looks like a new barrel is in my near future.

 

[abn31c]

Rynomar, was this a cut barrel or button?

 

[Rynomar]

Rynomar, was this a cut barrel or button?

This is a Bartlien with cut rifling.
6.5x47 Lapua
140 Berger Hybrids
Initial load -40.4 grains H4350
Initial velocity - 2,815fps
Initial COAL - 2.816 (-0.010)

Adjusted load - 40.9 grains H4350
Adjusted velocity - 2,820fps
Adjusted COAL - 2.830 (-0.0445)

I also meant to mention, I spoke to my gunsmith about it and he said that he doesn't personally worry about throat wear and chasing the lands. Recommended I stick with the Berger Hybrids, which are normally really good a jumping, increase powder, and shoot it until I am no longer happy with the accuracy.

 

[abn31c]

This is a Bartlien with cut rifling.
6.5x47 Lapua
140 Berger Hybrids
Initial load -40.4 grains H4350
Initial velocity - 2,815fps
Initial COAL - 2.816 (-0.010)

Adjusted load - 40.9 grains H4350
Adjusted velocity - 2,820fps
Adjusted COAL - 2.830 (-0.0445)

I also meant to mention, I spoke to my gunsmith about it and he said that he doesn't personally worry about throat wear and chasing the lands. Recommended I stick with the Berger Hybrids, which are normally really good a jumping, increase powder, and shoot it until I am no longer happy with the accuracy.

Ya, I'm done chasing as well. Also goin to a 28" tube for some easy speed.