An Experience and a Question: Barrels and Ballistics

[alcesgigas]

Here's a big something that some of you surely know, but for those--like me--who hadn't experienced the following consistent paradigm:

In developing loads and sighting in my newly constructed Edge I couldn't help but notice how tight the objective lens cover was; it was nearly impossible to open and closing required a "hand heel hit." Probably harmless enough to the Premier 5-25x56 it protected, but fodder for some pessimism... I first removed the whole thing and sanded down the bottom; still too tight. So, when the sun reminded me how important a sunshade could be--by sending me home as I couldn't use the scope at all--I removed the offending cover.

Upon returning to the range later in the day my dime-sized groups (100 yards) disappeared--right off the target box--investigation showed I was now impacting 18" higher than previously. Which in turn explained how I was able to sight in at 100 yards in the first place. With 20MOA in the base and 20MOA in the rings there's no way a hundred yard zero is possible. We're talking a 30" Hart BR1000 barrel--over a inch where the scope pressured it--was it the scope or the barrel that most influenced the shift in POI? I cranked the turret all the way to bottom. Still too high. yesterday, without any further adjustment I was right on at 300 yards. Too easy.

With my chronograph on strike I have no way to learn my velocity, but my loads were 94 gr. of H1000/300 Berger OTM/Nosler brass at 3.810. Anyone care to offer their experience with a similar scenario?

 

[rscott5028]

If you're saying that your sunshade is contacting the barrel, I think it's commonly agreed that this is highly undesirable for the reasons you mention.

I did stick a NF benchrest scope with limited elevation adjustment on a 30 MOA rail and could not establish a 100 yd zero. So, I did my load development at 500 yds in favorable conditions. It was fine at 1k but, there was certainly nothing in a bind.

-- richard

 

[Mikecr]

You might wanna notice when a lens cover is digging into a barrel, & bending a scope..

 

[Bart B]

This situation's a good example when barrel's bounce off something as they're fired and shots go wild. No wonder folks want totally free floating barrels in stock fore ends with lotsa clearance around them so there's nothing for that barrel to bounce off of.

This sometimes happened decades ago when externally adjusted target and varmint scopes with 2 inch objective lens had their mounts on bases of the wrong height for the barrel and receiver used. Folks would bore sight and get a zero at 100 yards not noticing the front bell was 1/16th inch above the barrel, then moving the elevation up several MOA for long range that put the front bell hard on the barrel. Sometimes, such setups made the rifle shoot pickup size groups at 1000 yards a long ways from the target.