Rimfire BC Information

[Skylerbone]

I'll begin with my situation; I purchased a Leupold CDS scope for use with a .22lr rifle and I'll need to provide info for Leupold to make my dial. I would prefer to specify the particulars rather than sending them a generic "I shoot Brand X". I have the manufacturer's info for a few rounds and I own a chronograph which should pin down the true velocity.

To my question, i have conflicting reports on BC for rimfire, specifically CCI's figures compared to the more generalized chart which I normally consult (below).




The numbers are considerably off in fact, with CCI posting much lower BCs for their bullets. The above chart was created by extensive evaluation at Aberdeen where results showed so little variation between typical .22 round nose bullets (LRN) including HP and copper washed, as to suggest they may all be classified together based only on weight and velocity.

Would you advise sticking to CCI's info (.120 BC for SV) or .145 BC based on the 40gr LRN at 1070 fps as the chart suggests? My thinking is that if anything changes quality-wise with CCI, something like .155 BC would keep me squarely in the red box where I would prefer with most ammo in the 1,000-1,100 fps range. Thoughts?

 

[Rule3]

Not that someone here can not help you, but if you want more info than you can possibly digest go to RimFire Central.

Not only will you get information overload you will also get how to spend 10 times what your rifle cost on replacing every part part.!

YMMV, but CCI standard velocity 40 gr LRN is the preferred non high end ammo. It works well in a SW M 41.

Of course there will be a 100 different answers on ammo

 

[Skylerbone]

I'm an RFC member as well, and while my question isn't reloading specific, I figure the guys who pay attention to BC will congregate here.

The rifle is a CZ 452 Trainer in stock form excepting a home trigger adjustment, with Talley rings and a VX-2 4-12 X 40 AO. Setting this up for my 10 year old daughter to target practice with and I wanted a simple system (CDS) to aid in swapping distances from near to far and back again.

My go-to ammo has been Aguila SE Subsonic in LRN and LRNHP (HP for small game hunting) but the new production non-Eley Primed has been disappointing with .3" groups at 25yds, more than double the previous size. My log indicates CCI SV was a virtual tie on accuracy (.487" at 50 yds overall average) with cost being the deciding factor at the time.

Long term I expect my daughter to graduate to more expensive ammo which led to my thoughts on selecting a more "generic" middling BC to keep the CDS system relevant. It may well be splitting hairs with .22lr and not make a bit of distance on paper, but I'm hazarding the question while understanding full well that I have yet to wring out the full accuracy potential from the rifle (mainly because it's a sporter meant for shootin critters).

 

[Blue68f100]

Your daughter is old enough to learn what the drops will be a set distances. As you know 25 yrds and 55 yrds end up being the same. Most people have problem when it's close than 25 yrds compensating.

I would hold off on the CDS for now till she moves up to the better ammo. Then actually measure the drop and supply that ammo velocity. With real drop numbers the CDS will be correct.

 

[Sunray]

Ballistic coefficients have nothing whatever to do with scopes. Very little to do with accuracy either. Ballistic coefficient is a measure of how a bullet overcomes air resistance in flight. Really isn't something you need to worry about with a .22.
You have to try a box of as many brands as you can to find the ammo your rifle shoots best(and cycles the action of a semi) regardless of the BC. Once you've found that ammo, just sight in according to the ballistics chart for that brand and bullet weight.

 

[Skylerbone]

Blue, I may dig into my stash and try some Lapua, RWS, and Eley to see how they group and if one stands out, base the dial off of that and the chronograph. Then she can learn and chart her own elevation, saving the dial for later.

Sunray, I've found what shoots well with the rifle at modest prices and I understand BC. Leupold CDS (Custom Dial System) scopes offer a prepaid elevation turret with the standard graduations and custom engraving of yardages based on supplied information (one parameter being BC).

I realize it may result in as little as a single click's difference at any given yardage but I'd prefer the most logical starting point and the money has already been spent. I'd have opted for the non-CDS version but it was out of stock and only $10 less. The scope won't likely see field use as she has other rifles for that purpose unless she prefers to dial out parallax on the fly to simply ignoring it with a rimfire specific scope's 50-60 yds. factory parallax setting. Good enough for minute of squirrel head but again, this one was set up for range duty.

 

[Dudedog]

Ballistic coefficients have nothing whatever to do with scopes

Sigh....read the OP again.

It does if you are have a BDC scope or custom BDC dials made for a scope.

BDC scope drops are calibrated for bullets with a certain BC at a certain MV which is why the OP was interested in the BC of .22 bullets.

Sure it's not a .30 RN vs a Berger VLD but he wants to try to get the comp adjustment ring as close a possible.

If it was me for fun I would make up a spread sheet and replicate the formula to caculate drop at various ranges and then plug in a reasonable range of 22 LR BCs to see just how much difference it makes.
But to me it makes perfect sense try to get the comp ring as close as possible.