Explanation...Please

[257Wthrby]

Ok, here goes....i loaded up some barnes TTSX 130's and some Berger 130's at 62 grains of IMR4350 and both with WLRM primers for my 270WSM

Barnes - COL 2.810 @ 3326
Berger - COL 2.740 @ 3244

Both shot groups of 5 that were all touching, my concern was the difference in speed, not much but 82 FT/Sec seemed odd for the same loads but different COL. The other thing that seemed odd was the Bergers shot 5" higher at 100 yards than the Barnes.
Im not really concerned with it other than not knowing why such a difference between the two, especially the Bergers hitting 5" higher.

 

[Deleted member 46119]

Used case capacity. As in % of case filled. The copper bullet reduces the case capacity.

Start resistance. As in the pressure has to build to a higher level before cork squirts out of the bottle.

 

[Deleted member 46119]

Bergers hitting high shows what influence Ballistic Coefficient and Sectional Density can have.

 

[Broz]

Could very easily be some false readings of the chronograph. Shooting Chrony??

Impact difference at 100 really only tells the bullets have different impact points due to their difference in shape and construction. I doubt you will see any measurable impact difference from BC at only 100 yards.

Sounds like you have a rifle that shoots well. Take them both out farther to see the possible benefits. If you go farther you can also detect an in accurate chronograph reading by the use of true world drops and a ballistic calculator or ballistic app.

Jeff

 

[FearNoWind]

I'd have to concur with Jeff. Is that 82 fps your average ES or something else? How are you measuring COAL? Berger and Barnes bullets are very different. Compare the technical data for the bullets you're using and see how they differ in sectional density and BC. Are these Berger VLDs or hunting bullets? Even among the Berger 130 grain .270 bullet family the sectional density and BC differ quite dramatically.

 

[gohring3006]

I agree with Jeff and fearnowind they both have different bearing surfaces which will affect pressure curves also.....

 

[257Wthrby]

Yes the 82 fps was an average, but i dont think there was more than a 10 fps difference between any of the 5 shot groups, fairly new to reloading so just taking in as much information as possible. I thought about the bearing surface / case capacity also, but didnt really know it could have that big of an impact.
Yes they are the Berger VLD Hunting bullets, i think i will try and take it out to 400 yards and see what i get, now i dont know which one i want to hunt with, they are both shooting great. I had a little more trouble finding the sweet spot with the barnes but i think im close.

 

[MagnumManiac]

The difference in POI is easy to explain; barrel time and bullet exit, as the barrel oscillates the bullets exit at different points in that oscillation.
I cannot see how SD or BC would have such a dramatic effect at 100yrds.

Cheers.
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