Velocity Issue with RL26, 300 WSM, ELD-x

[Lpart]

I am scratching my head on this one. I went to the range today to test groups and velocity with my 300 WSM. This is built on a long action and bullets are seated out to the long action mag limit. Testing 212 gr ELD-X vs 215 gr Berger.
All bullets coated with HBN. All loaded with 68.2 gr RL 26 and all bullets seated to same depth to the ogive (COAL 3.24 for ELD-X and 3.28 for Berger). New Brux barrel with only 24 shots down the tube.
For some reason the velocity for the ELD-X kept climbing with each shot until the 5th and final shot. I shot five rounds of each while alternating the bullets. ELD-x follwed by Berger followed by ELD-x etc. I waited a timed 2 1/2 minutes between shots. Temp was about 60.

Velocities were by shot in order.

ELD-X
2786
2803
2825
2852
2824

Berger
2777
2804
2795
2808
2804

Bergers grouped 4 into a 1/2 inch hole with a flyer to make it 3/4 inch.
ELD-X had 3 shots into a 1/2 inch hole and 2 flyers into another single hole
stretching the group to 3/4 inch.

How would you interpret this please? I have another heavier 300 WSM with a 2" longer barrel that shoots same load with Bergers uncoated into 1/2" at 2900 fps. Thinks of increased the load a bit to offset lower pressure with the coated bullets.

Based on previous with the 185 gr Berger I have some concerns with performance on larger game so I was hoping I could get the 212 gr ELD-X to perform as well for me.

 

[RockyMtnMT]

Looks like both bullets gained speed in the session. Hornady more than the Berger. Did you see any increase in pressure?

I have not yet had time to learn about the HBN coating but will be. Did you coat the barrel too?

Maybe one of the guys that have been working with HBN quite a bit will chime in. I think it has something to do with it though.

Not too long ago it was said that shooting two diff bullets in the same session can cause some fouling issues. So maybe that could be the problem.

Steve

 

[IdahoCTD]

I just shot the one I built this weekend with a 26" Brux barrel and got a little more velocity than you did with uncoated bullets. My loaded rounds are 3.199". I shot up to 71grs of R-26 with 215 Bergers before I got faint ejector marks at a MV of 3050fps and a .280" group. 70grs shot 2 in one hole and I pulled the 3rd at 2990fps.

I'd suggest stoking it up some. With coated bullets and a even longer throat you will probably be 71+grs before you get where it's happy. A Quickloads prediction was 71.5grs of R-26 with 215's at 3.2".

 

[Lpart]

Thank you. I couldn't find any load data and I guess I have been to conservative. I will stoke it up and see what happens.

 

[dok7mm]

I shoot several different 7mms with HBN and treat my barrel with a slurry mixture, prior to firing the coated bullets. My experience has been the opposite of yours. I shot 6 foulers today in a 7 mag, before fine tuning the seating depth. Running RL 26 @ 69.0 grs. and 162 eld-x. My foulers in order ran 3063, 3055, 3043, 3026, 3043 and 3057. I fired 3 shot groups from .010" jump to .060" jump. Average fps in order were 3054, 3060, 3053, 3054, 3068 and 3068. The best seating depth, in my rifle was .030 jump & SD of 2.3 and ED of 4.0 I am sure it won't be that low when I shoot 10, but it shot < than 1/4 moa @ 200 yds.

This probably won't help with your 300wsm, but my point is you have to treat your barrel and chrono your foulers until your speed stabilizes. I do this every time I clean. It also helps if you have non- HBN data from your rifle with the same load components. This will give you a much better idea of what's going on.

 

[dwm]

Is it a good idea to alternate shooting bullets of different manufacturers? We generally shoot all bullets of one type and then clean and foul the barrel over again with bullets of another type. Not sure how big of a difference this makes.

 

[eshorebwhntr]

If the HBN is acting as a lube, that would mean less resistance, so less pressure, less velocity. Maybe a product of more HBN on the barrel surface as you shot. I'm guessing here and just throwing out ideas. I don't have experience with HBN.

Another thing to remember is that Brux is a cut rifled barrel. Most cut rifled barrels take about 100 round minimum to settle in on velocity. Some more, some less. Usually velocity increases as they break in. Sometimes as much as 100fps.