NSA Slugs without BC- POST YOUR BC

davidsng,

that's an excellent idea. I have yet to test my NSA slug samplers, but I'm fully committed to measuring and posting BC's. Just yesterday a neighbor said he'd take me to a 120 yard long shooting tunnel with two chronometers, right here at a the local Navy base. Hopefully those chronometers will work with tiny .22 pellets and slugs.... I'm super excited!!

Suggestion: Some BC calculators are less accurate than others. And all of them will calculate inaccurate BC's if we don't feed them right right atmospheric conditions under which the testing was done.

So, maybe we could report our BC's something like the following:



.22cal, 33grain NSA slugs.

Calculator ChairGun

Weather: 33.22 in Pressure | 68F | 55% Humidity

Average of 10 shots at muzzle (866fps) and at 75 yards. One chronograph only.

BC = 0.955



Happy shooting and testing.

Matthias

JSB Heavy Diabolos in .22 0.364-0.456 ???

Piledriver .22’s 0.096 same as .22WMR 30 grain but 1250fps slower.

NSA Almost anything .22 0.97/8-0.1

VK’s Almost anything .22 0.97/8-0.1

NSA & VK’s in .25 Slightly lower in same weight as .22’s like 33’s are 0.93-0.96

.30’s around 0.0456

.357’s around 0.0665

Reason I want (3) 257’s: A shorter barrel Raptor almost 28”. 1:14 TJ for 65 RBT NSA .193BC

Reason I want a 36” Texan in 1:14 same as above but 125-175 ftlbs

36” 1”OD chrome lined bull barrel 1:12-1:13 for 92-105 grain 257’s .212-??? Testing needs to be done. 95’s @ 950-1015 had 190-205fpe .212BC but I’m only at 700’ASL and 800-950 fps is fine. I’m waiting for that guy who was trying to match BC to caliber. Can anything do it? Maybe a single shot long .177 or .257?

Feel free to quote, edit, expound on what you’re seeing or reading. 

It is important to identify the rifle and barrel used in the tests!

Not sure how much difference air temperature plays in BC, but for the NSA 36.2 gr 0.25 slug I’m getting a significantly lower BC than the 0.1 reported. 

FX Impact MKII 700 mm w/ slug liner

Air temp 36 F

Altitude 1400 feet

Muzzle velocity 890 fps 

velocity at 65 yards 790 fps 

According to the Pyramyd air calculator, this works out to a BC of 0.069, compared to 0.1 reported.

(Not sure if it makes a difference, but barrel was very dirty but still shooting 1.5 inch groups at 100 yards.)

AirgunNH,

thanks for the data!

The JBMBallistics.com caculator allows to enter atmospheric data (with barometric pressure having the biggest effect...). The PyramydAir calculator does not consider atmospheric conditions....

I'm getting a BC of 0.081, with an assumed standard pressure at MSL of 29.92hg, and the G1 drag function (I hope I can attach the screen shot).

ChairGun (for which I would need my laptop) also calculates the GA drag function, a little more appropriate for airgun pellets.



Why the difference? 

(1) Every barrel is different.... (I hate this reason.) 



(2) Errors in the input data produce errors in the output.... E.g.:

—1 yard error in the actual range between the chronographs: —> 0.001 error

—If your barometric pressure (calculated for MSL) was actually not 29.92, but 28.92: —> 0.002 error

—9 fps total error in the averages of the two velocities (@ muzzle and @ target): —> 0.01 BC error, so instead of 0.080 you'll get 0.090

This velocity error is "easily achieved" (esp. with only one chrono, and using only a small amount of shots)...: Our guns often have an extreme spread of 10fps muzzle velocity, some a lot more. Now all you need is that, by coincidence, the first 5 shots are around 4fps higher than the average MV, and the next 5 shots 5fps lower. There you get a 9fps difference, and that offsets your BC by 0.01.

—Now, all these possible errors add up....



Thanks for sharing your data!

Not based any formula, but just on my initial FPS readings and my hold over MOA at a 236 yard target, my .30 caliber NSA 50 grain slugs are carrying a .055 BC according to the numbers on Strelock Pro. This number would likely change, and look better, testing the slug's BC over just 100 yards.

NSA .30 caliber 60 grain hollow point slug shooting 883 FPS with 175 yard zero gave a 20.76 MOA holdover at 236 yards, which in turn gave an overall distance BC of .080.

NSA 15.5 grn slugs

Edgun .177 Matador Std

muzzle velocity 926 fps (30 FtLb)

.071 BC