Can anyone explain this

[lancetkenyon]

I am going to venture way out on a limb and say this is going to be a short range deer rifle. With a 16" 6.5CM running 140 NBTs, sounds like a stand rifle or pack rifle to me.

@ 400, there is only 2" difference in drops

At 500 yds (depending on environmental conditions), the difference in drops between 2553 and 2622fps is only 3.5". Or, 1.75" +/- POA if you zero for your average of 2587fps. What I would consider maximum acceptable and would limit my shots to here.

600+/- yards looks like about max to retain 1800fps impact velocity. But your variation in drops opens up to almost 6".

In other words, if this is a short range rifle, and keeping shots under 500, don't worry about it.

 

[Minero]

I am going to venture way out on a limb and say this is going to be a short range deer rifle. With a 16" 6.5CM running 140 NBTs, sounds like a stand rifle or pack rifle to me.

@ 400, there is only 2" difference in drops

At 500 yds (depending on environmental conditions), the difference in drops between 2553 and 2622fps is only 3.5". Or, 1.75" +/- POA if you zero for your average of 2587fps. What I would consider maximum acceptable and would limit my shots to here.

600+/- yards looks like about max to retain 1800fps impact velocity. But your variation in drops opens up to almost 6".

In other words, if this is a short range rifle, and keeping shots under 500, don't worry about it.

I hadn't looked at how it would affect short barrels, and by what you are saying, not that much, Personally don't like how rifles look with so short barrels, but that's just personal.

 

[cajun]

Get some 120 gr ballistic tips. They sell factory ammo. Really to little data but with that barrel your range is limited to where it won't matter much.

 

[NW Hunter]

Random thought….did you pull your rifle in tighter to your shoulder pocket on shot #2 without the muzzle brake? I've seen velocity increases when you do this.

 

[skipglo]

Or...although it's a very small sample...muzzle brake is changing the harmonics on that barrel in a positive way?

 

[fseaman.js]

Or...although it's a very small sample...muzzle brake is changing the harmonics on that barrel in a positive way?

this

 

[lancetkenyon]

Factory ammo? Or handloads?

If handloads:
Virgin brass? Or 1x fired (or more)?
What brand of brass?
Freshly annealed brass?
Neck tension?
How are you weighing charges?
What is your charge weight tolerance?
Powder? Charge?
Bullet variations?
Seating variations?
CBTO or COAL used?
Jam or Jump to Lands?

HOW DID IT SHOOT??

I haven't seen barrel harmonics make a difference in ES, but I have never considered that. I have seen harmonics effect POI.

 

[Turpentine21]

Get some 120 gr ballistic tips. They sell factory ammo. Really to little data but with that barrel your range is limited to where it won't matter much.

I went to the 123 eldm at 2775with my AR 6.5 CM with 20" barrel to extend my point blank range with thermal at night. I've been happy with the combination out to 450 yards. I use it mainly for up to 120 pound does or hogs of any size. It's a bit flatter than my Grendel with the same bullet