Barrel speed up with low velocity chamberings

[Odysseus1911]

Do you find that with low velocity chamberings, barrels take longer to speed up?

I have a 8", 1:8 twist, 5R Bartlein chambered in 300 blackout that shoots slow despite having around 200 rounds through it.

 

[supercorndogs]

Most of my cut rifled barrels never sped up. There are many reasons a similar charge weight may make different velocities. Different chambers, components, different twist rates, different bore diameters, the list goes on. I wouldn't exactly expect an 8" blackout to be a speed demon. 2% or 3% of 1500FPS is half 2 or 3% of 3000FPS, it might be easy to loose in the noise.

 

[Odysseus1911]

That's interesting. The way people talk, you'd think barrel speed up was universal.

At any rate, I'm only getting an average 2003 fps from my load:
Speer TNT 125,
19.3 grains H110,
CCI BR-4,
New Starline brass,
COAL 2.100"

Even extrapolating for the 8" barrel I was conservatively expecting 2000 fps at 18.8-19.0 grains.

 

[larryh128]

Personally I don't think you are off by much. If you want more speed Lil Gun powder at 19 grs or slightly more should improve your speed.

 

[bfoosh006]

Fully agree with the above post.

 

[r.tenorio671]

...in my experience LilGun gives me more consistent fps than H110/W296 & similar speeds. My locale has avg year round temps of 83F+ so H110/W296 get kinda tricky when I'm close to the borderline charge weight for my barrels. The 125 TNT is my preferred projectile as well.

 

[r.tenorio671]

That's interesting. The way people talk, you'd think barrel speed up was universal.

At any rate, I'm only getting an average 2003 fps from my load:
Speer TNT 125,
19.3 grains H110,
CCI BR-4,
New Starline brass,
COAL 2.100"

Even extrapolating for the 8" barrel I was conservatively expecting 2000 fps at 18.8-19.0 grains.

.....that's a pretty good FPS for an 8" barrel. The charge weight is in the upper limit so I'd monitor your brass life. Between my 16" 5R and 10.1 button rifled barrels, there isn't really an appreciable difference in FPS for a fully functional and accurate load that I can use interchangeably between the 2 with the 125 TNT. What I found was that as I went higher in charge weights, before I got to the "max", I would see a downturn in speed and an increase in SD.

....If you seek more speed, try the Nosler 110 Varmagedon, Hornady 110 Vmax, both of which I've safely reached 2400+ w/LilGun but had high SD's up to 55+. The Berger 115 TGT FB can get to 2200 easily w/LilGun. YMMV

 

[Odysseus1911]

I'm definitely sticking with the TNT. I can live with 2000 fps, was just expecting a touch more is all.

I noticed that downturn in speed, too. 19.1 grains gave an avg. 1965 fps. 19.2 averaged 1985.

At 19.3, I'm getting very slight brass flow into the ejector hole, but no swipe or extractor marks. Primers look good. I may back down to 19.2 grains or even 19.1 grains as the velocity was still pretty close and I could get a little more life from the brass.