http://www.rimfirecentral.com/forums/showthread.php?t=98330

 

Wouldn't it be more fun just to go shoot some and see for yourself?

 

.22lr BC/actual velocity/drop etc.-SHOOT IT.

Unless you have some pretty sophisticated equipment, calculating a Ballistic Coefficient can't be done. BC's from reliable sources are plenty good enough.

Factory specs out of a test barrel for the T-Bolts say 1255 fps at the muzzle. I have a chronograph and out of a 20 inch barrel I get 1180 +-15FPS and out of a 24 inch barrel I get 1215+-10FPS. Both are bolt action rifles.

Don't really matter though cause IMO and IME the best way is to shoot the weapon with the ammo. Ballistics calculators will get you close enough for goverment work but shooten will tell.

When I do that kind of stuff, I zero the rifle dead on at 25 yards, 10 round groups, and then I put up a fairly large target at 100 with a good clear aiming point and shoot the best I can another 10 round group without changing the sight. I take and figure out the center of the groups, assuming I am shooting well and then go back to my ballistics calculator and back into the muzzle FPS. I then record that FPS and use it for further reference. That way you don't need a chrono.

Generally, and generally is the operative word, what the chrono says and what actually happens is like within 1/2" at 100 yards but even if the chrono is dead on when I do the fps bassackwards the actual drop can be in that range anyway. Again, most of the time, the chrono is like dead on but the drop is a tad different which then leads to the question of the BC posted. You can mess with the calculators etc. to finger that out also.

Again IMO and IME you just gotta shoot if, if you can, to see. Especially if you are gonna shoot farther than 100.

noremf(George)

 

100 yard drop

At what range are we talking being zeroed at ? I'm zeroed at 50 yards and at 100 yards my high velocity ammo ( 1250-1300 f.p.s.) hits 4" low. My scope is mounted fairly low, 1 3/8ths inch from center of scope to center of bore. If you have a much taller mounted scope, like high rings or see thru rings, the arc of the bullet in flight will be even more pronounced. If you could get the rifle barrel perfectly level and measure the drop from where it comes out the muzzle to 100 yards, it would probably be much more( 8-10 Inches ?) So lots of variables here, but for a 50 yard zero, 4 " sounds good. The thunderbolt is a bulk, econo round, right ? So if it's a little slower, 5.5: drop for it. I have some Win Super-X Hyper, a 40 gr. H.P. at an advertised 1435 F.P.S.. I'll have to see what the drop is on those at 100, and maybe try some Yellow Jackets and Velocitors as well.

 

Hmm, okay, but are the figures from the software program at least useful for getting on paper? For example, if I set up a large box at 150 yards to shoot and the program tells me I need to adjust up by 38 clicks, then couldn't I just set it up 38 clicks, shoot and see where it lands on the box, and then zero from there?

What I want to do at that point is then see how many clicks past 38 it took to get zero'd, and then write that down so I then know, "Okay, so 150 yards is this many clicks up from my 50 yard zero."

That's all I basically wanna use it for. Doing the old fashion way is fine, but uhh... Walking back and forth 150 yards multiple times is going to get old real fast, so I just wanted to use the programs figure to at least "get on paper" quickly.

 

Some good info here. Shooting is always best, and yields the most fun, and accurate info.

But, according to my calculations, with Thuderbolts having a 40gr solid and a BC of .139, under ideal conditions, the drop would be 4.7MOA or roughly 4.8". This calculation takes in a lot of assuming ideal wind, an altitude of 3400ft above sea level etc.

 

I would say using a ballistics calculator would provide the best accuracy in conjunction with a chrono to measure the velocity. Although it may be close enough for "government work" your gun may not shoot it at the published velocity so you should measure it. Or, just shoot at some targets.

The ballistics calculators I use have worked accurately for me. With a single chrono it is easy enough to take an average of speed readings at two different distances from which you can figure the BC. I did this, plugged the info into my ballistics program and created scope tapes. Both of my guns are spot on at all practical shooting distances out to 100 yards. I have not shot beyond 100 yards using the info but I have no reason to doubt it wouldn't be accurate.

You can play with the figures in the program and see that, unless there is something wrong with your gun, it should be close enough to get you on paper with the listed velocity. Dropping the velocity from 1255 to 1100fps is only about 2 inches of extra drop at 100 yards and 6" at 150 yards.

 

The rem sub sonics I use in my Savage mk II BTV need 31 clicks of "up" to move from 50 yards to 100... so not quite 8 inches

 

Sounds like it's pretty close then, especially since my zero right now is actually at 43 yards.

I went shooting today but I forgot my measuring wheel so I couldn't get any real shots lined up at 100 yards. However, I did find out that with my current zero, I'm still shooting minute-of-milkjug at my estimated 100 yard line. So it looks like that drop is still below 5" :bthumb:

 

About 3-4 inches

with good ammunition. Meaning like good brand high velocity ammo. No offense but I do not use Thunderbolts because they are so dirty and seem to have a lot of FTF relatively. But, this is my field experience rule-of-thumb without getting into math figures, etc. Just figure if you are going to shoot 22LR at 100 yards a drop of 3-4 inches in your slug.

 

With good match (subsonic) ammo, a zero at 50 yards gave me a drop of about 6 inches at 100 yards, plus or minus whatever the group variance has.

 

The external ballistics will probably change with every different lot # u get.