Muzzle velocity estimate without Chronograph

13219 Views 22 Replies 9 Participants Last post by BKeith, Oct 4, 2010

SLCscottie

Discussion Starter · Aug 12, 2010

I don't have access to a chronograph at this time and I don't want to spend the money. And I just need a rough rule of thumb or experience with this matter.

So what should I expect the muzzle velocity difference to be when using a
Rock River AR15 with a 16 inch barrel 1 in 9” rate twist instead of a
Remington 700 26”, 1 in 12” twist (Hornady Data used from their reloading book)?
My guess is a loss of 150 fps.

I reloaded the 223 Rem using Hornady Data:
55 gr #2266 SP w/c
B.C. 0.235 C.O.L.: 2.200”
Varget 25.5 gr
Velocity per book 3100 FPS

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SLCscottie

Discussion Starter · #2 · Aug 12, 2010

approximately 40 fps per 2 inches

approximately 40 fps per 2 inches
I agree that a Chrono is the best way to go.

I've been doing some searching after posting this question.

I estimate roughly 40 fps every two inches after reading the article posted at this sight.

http://www.loadammo.com/Topics/October05.htm

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SLCscottie

Discussion Starter · #5 · Aug 18, 2010

Interesting. I estimated 2900 fps.

broom_jm said:
Quickload suggests that load, with a 16" barrel, will come in right at 2900fps and with a 26" barrel, velocity would be around 3240fps. A gain of roughly 350fps, or 35fps per inch of increased barrel length. That's a lot, but then again, the .223 Rem really needs more than a 16" barrel to burn all of the powder it can hold.

Incidentally, QL shows that as being a 110% compressed charge. A slightly faster powder, like H322 or IMR4198, might be in order. Both show the same velocity and higher ballistic efficiency, without being compressed so much. Particularly if you do most of your shooting with the 16" barrel, the Varget load is not ideal.

Interesting. I estimated 2900 fps: http://www.thehighroad.org/showthread.php?t=538300

200 fps muzzle velocity loss
so instead of 3100 fps for a 26 inch barrel I may be getting 2900 fps for a 16 inch barrel.

(10 inch difference / 2 inches) time 40 FPS = 200 fps change.

Quickload is very impressive. Thanks for running the numbers.

Before reading your response I went out and bought BL-C(2). A quicker burn rate makes sense in the shorter barrel.

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SLCscottie

Discussion Starter · #7 · Aug 18, 2010

Excellent Information Nick

Seriously.
It took me almost two hours to get through your post. I had to pause and read almost all of Dan's web sight and did some more reading on the reviews of the Chrono you mentioned before getting to the end of your post. Also the review on Quickload.

Funny how one good question leads to several leads on fascinating information.

I will have to adjust my load development method from just the ladder method.

Reloader 10X I may try later. I will have to work with the BL-C(2). I do have to admit the Varget is accurate.

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SLCscottie

Discussion Starter · #8 · Aug 27, 2010

Here are the recent results of BL-C2 and Nikon M223 scope

broom_jm said:
I was going to suggest that powder, as well. The quicker powder will be a little more efficient, not be as compressed, and possibly result in less muzzle flash.

I took my M223 Nikon scope and my 16" AR to the range Wednesday with the new load.

BLC2 27.0 gr Hornady Book has 27.4 at 3200 fps
Bullet 55 gr #2267 BT-FMJ w/c

Estimated 2900 fps for my 16" barrel AR15.

Zeroed at 100 yds
Went to 300 yard range next.

Used the BDC Bullet Drop Compensation reticle on the M223 Nikon scope and found quite a big spread of about 15 holes. Looks like about 2.5 inches on average below target. I shot quite a few to see the rough average with a visual.

Then I took the info from Handloads.com using 2900 fps and used the turret knobs to move the elevation up 12 inches. Minus 12.09 per Handloads info.

I hit almost bullseye off by about an inch. Next target total miss then next one about an inch and a half off.

Yea I know maybe luck on the first one using the turret for elevation adjustment. Maybe pure skill

Here is the interesting part:
When I plugged in the 3140 fps that Nikon recommends for bullet velocity with a 55 gr bullet into the Handloaders.com program it moved the 300 yrd drop from -12 to -9.45 that is the 2.5 inch difference rough average that I needed.

Accuracy observation using the M223 scope:
I do better with crosshairs using the turret for elevation.
I'm all over with my group using the circle reticle for the Bullet Drop Compensation. I have heard of this before on debates over BDC.

Data I plugged into the Handloads.com Ballistic Calculator:

Elevation 4500 ft.
Temp. 92 f
Sight Height 2.5
BC .243
55 gr

Velocities: 2900 fps and 3140 for comparison.

Do I like this New Nikon Scope? YES

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SLCscottie

Discussion Starter · #14 · Sep 4, 2010

Thanks Broom

broom_jm said:
The shooting world is full of ironies, and the circle reticle arrangement on the BDC-type scopes is one of them. At ranges close enough to sight in for maximum PBR, the silly circles aren't needed. At longer ranges where you might benefit from them, they are simply too imprecise, as an aiming point, to result in good groups; you need fine wire lines to put on your target and the circles simply subtend too large an area, at those longer yardages. Using a ballistic calculator and predictable turret adjustments is the only way to go if you want to maintain good accuracy beyond whatever PBR you have chosen.

Good work looking at all the "science" and then getting out there on the range to make sure it all adds up. Isn't it great when your effort pays off?

Thanks. Plus it is a lot of fun. The original question generates more fascinating information that I have heard and not heard before.

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