400MODBB Barrel Speed Up Round Count

[Rocketmandb]

@Frank Green

Normally, I would have PM'd this question, but thought it might be something of interest to the greater community.

On barrel speed up round count, I usually count on the greater portion of the velocity gain being done by ~100 rounds, with it trailing off by 150 or so. On my new 400MODBB 300 PRC barrel (first of three I just put on rifles), I'm at 200 and the velocity appears to still be happily climbing.

Being a harder material, I'd expect it to take longer to speed up, but would like to get an idea of where I need to be. In your experience, how do the 400MODBB barrels compare to standard for velocity gain over round counts?

Barrel Info:
Chamber: 300 PRC
Barrel: 28" M24 contour, Bartlein 400MODBB
Load: 74.9gr RL26
Bullet: Berger 220

This is a graph of velocity over rounds 151 - 199 through my 300 PRC, and it doesn't look to be plateauing off.

As for performance, the thing prints nice groups:

First shots at 500 yards

Seating depth tests - love it when I get two good groups right next to each other (34 and 37 thousandths)

 

[R_A_W]

do you have the data for 0-150 rounds? Or just your initial velocity?

I will be running a 400modbb in 6.5prc in an NRL Hunter match w/ probably only 50-100rds on it, assuming Alamo completes it within their quoted timeframe

 

[Rocketmandb]

do you have the data for 0-150 rounds? Or just your initial velocity?

I will be running a 400modbb in 6.5prc in an NRL Hunter match w/ probably only 50-100rds on it, assuming Alamo completes it within their quoted timeframe

Not all of them, and there have also been varying loads across them.

 

[Hoyt7mm]

FWIW I've found that velocity continually trending upwards is a function of use RL powders (15.5, 15, 26). I've had barrels steadily increase speed with those powders even with regular cleaning. The same barrels didn't exhibit this (at all or much less) when using other powders such as h1000, h4350 or varget. Still use and really like the RL powders, just a quirk I've found over about a dozen barrels both mod400 and regular SS.

 

[db2000]

@Frank Green

Normally, I would have PM'd this question, but thought it might be something of interest to the greater community.

On barrel speed up round count, I usually count on the greater portion of the velocity gain being done by ~100 rounds, with it trailing off by 150 or so. On my new 400MODBB 300 PRC barrel (first of three I just put on rifles), I'm at 200 and the velocity appears to still be happily climbing.

Being a harder material, I'd expect it to take longer to speed up, but would like to get an idea of where I need to be. In your experience, how do the 400MODBB barrels compare to standard for velocity gain over round counts?

Barrel Info:
Chamber: 300 PRC
Barrel: 28" M24 contour, Bartlein 400MODBB
Load: 74.9gr RL26
Bullet: Berger 220

This is a graph of velocity over rounds 151 - 199 through my 300 PRC, and it doesn't look to be plateauing off.


View attachment 8366847

As for performance, the thing prints nice groups:

First shots at 500 yards

View attachment 8366845

Seating depth tests - love it when I get two good groups right next to each other (34 and 37 thousandths)
View attachment 8366867

75gr RL26
Please share your powder supplier

 

[kthomas]

At that sustained rate, you're .300 PRC will be making my .300NM feel inadequate in about another ~100 rounds

 

[Rocketmandb]

75gr RL26
Please share your powder supplier

Supplier? Who needs a supplier?

Old pic - I've added a couple 8lb jugs.

 

[Rocketmandb]

At that sustained rate, you're .300 PRC will be making my .300NM feel inadequate in about another ~100 rounds

I was pretty surprised to see the consistent upward slope.

 

[Bmghunter]

Supplier? Who needs a supplier?

Old pic - I've added a couple 8lb jugs.

View attachment 8367058

So that's the stash you told me of.

 

[Rocketmandb]

So that's the stash you told me of.

Part of it - yes

 

[Rocketmandb]

So that's the stash you told me of.

I love jugs...

 

[db2000]

Pow Porn!

 

[Frank Green]

How are you cleaning it and how often in between rounds?

 

[Rocketmandb]

How are you cleaning it and how often in between rounds?

At the beginning, I did a rough approximation of what you guys list on your website. Once I get past the first 50 rounds, I clean after every trip, which is usually 50 rounds.

As for how, right now it's all using Boretech Eliminator and patches. Currently no brushes, no brass, no abrasives.

 

[Frank Green]

At the beginning, I did a rough approximation of what you guys list on your website. Once I get past the first 50 rounds, I clean after every trip, which is usually 50 rounds.

As for how, right now it's all using Boretech Eliminator and patches. Currently no brushes, no brass, no abrasives.

I don't know how dirty RL26 is compared to other powders. I don't run it at all. So more cleaning might be needed to keep the powder fouling in check.

A lot of people think the copper fouling is the hardest to clean but that powder fouling/layer that gets laid down is actually the hardest to tackle. Once it gets away from you... it's very hard to get it back to a normal if you will.

Powder fouling can also cause accuracy issues besides the copper fouling as a fyi.