BS Busters Number 87: The Myth of the 18 Inch Barrel Velocity

[shane45]

personally I go with the shortest barrel I can while achieving the things I want. Why carry any more than you need to. The result is that only 1 of my AR's has a longer barrel. My precision rig in .260 rem has a 22". Everything else is a 16" barrel, both 5.56 and 7.62's.

[Chuck Haggard]

http://rifleshooter.com/2014/04/223-...friends-rifle/

http://www.ballisticsbytheinch.com/223rifle.html

[Molon]

http://rifleshooter.com/2014/04/223-...friends-rifle/

That's a perfect example of the junk-science I was referring to in my original post. They used a bottom-of-the-barrel chronograph and only one five-shot string for the 62 and 68 grain loads and only two 5-shot strings for the 55 grain loads.

[rifleshooter]

That's a perfect example of the junk-science I was referring to in my original post. They used a bottom-of-the-barrel chronograph and only one five-shot string for the 62 and 68 grain loads and only two 5-shot strings for the 55 grain loads.

Hi,

I'm the author of the "junk science" article.

Considering i've run 4 different Magnetospeeds (which cost around $400 http://www.brownells.com/shooting-ac...prod55606.aspx) and two different 35Ps, I wouldn't call them bottom of the barrel. In fact, if you look at objective research, you'll see that the Magnetto speed performs as well as any chrono out there. The spacing of the sky screens matters which is why the 35P has 2. It understanding a small amount of movement will change results. Magnetospeed solves this by have magnets fixed in place- they can't move. I regularly confirm the measured speeds with actual field data and they have been spot on. The little crappy ones are optimistic.

The 5 rounds per round per length limit is the result of time constraints. It tells as similar story as 10 and 20 shot group with less data. More rounds better, absolutely, but this was what we has time to do. Most of my graduate work dealt heavily with statistics, and yes, a larger sample size is always better, but you didn't control as much as you think you did in your experiment.

Back to your post.

Why didn't you use the same barrel and cut it? You could have controlled for headspace, bore diameter, chamber dimensions etc..
Did you slug both bores and measure the slug? All barrel makers will verify this changes within the same lot. Slug them both and let us know.
Did you measure the head space in both barrels? I doubt they are identical, refer to the combined gas law for why this would matter.
Did you make a chamber cast and verify the the same reamer cut both chambers? See above.
Did you measure both gas ports? See above.
Why did you only wait 30 seconds and fail to measure the barrels temperature? See above.

My view of the firearms industry is undoubtedly different than yours. The access to what goes on behind the scenes would call into question your assumptions of these barrels being the identical except for barrel length.

You did a nice job with what you had but I would hardly consider it definitive.

Trying to drag down what may be one of the most comprehensive barrel length pieces on 223 Remington available for free to shooters to make yourself feel better but is pretty lame dude. The other three articles on the subject were from accurate reloading, ballistics by the inch and Gemtech. http://www.dtic.mil/ndia/2010armamen...hilipDater.pdf

For what its worth, we've all spoken about our respective approaches and are happy to build on the data set.

I found your post because it was linked to mine. I read feedback and try to provide a better product for the next time around- that's how grown folks do it. I could have come and asked some hard questions you wouldn't have good answers for but that would have been immature.

Go google "223 Remington Barrel Length" and tell me who is the first hit. Actually read it and tell me how yours is better other than the sample size? You didn't control for temperature, bore dimensions, chamber, headspace.... (I did and had similar controls for temp as your arbitrary 30 seconds)

A better title for your post would have been "I bought 2 different barrels from the same manufacturer and shot them over my chronograph with two different types of ammo".

PM sent to you.

[rifleshooter]

Molon- I would also like you to post your complete data sets for further examination.

[rifleshooter]

The 35P was great in its day. Addressed a lot of short comings. That is why I bought one in 1994. Yep, 20 years ago. Same thing.


I am taking the liberty to post the reviews from Magnetospeed's website:

Reviews & Tests

Reviews:

http://www.realguns.com/articles/360.htm

http://www.realguns.com/articles/391.htm

http://snipershide.com/forum/ubbthre...3240356&page=1

http://68forums.com/forums/showthrea...nograph-Review

http://randywakeman.com/MagnetoSpeed...hronograph.htm

http://highcountryshooters.com/forum...at&Number=5556

http://forum.accurateshooter.com/ind...opic=3784927.0

http://www.youtube.com/watch?v=MgL9T...eature=related

http://www.youtube.com/watch?v=rwFnrFf6DrU



Magnetospeed custom prototype testing @ Southwest Research Institute
*Data provided by Southwest Research InstituteMagnetoSpeed LLC worked with Southwest Research Institute(SwRI) to quantify the ballistic accuracy of the MagnetoSpeed sensor package. SwRI uses a bench top range setup to do ballistic tests on ammunition and uses a double Oehler sky screen setup to accurately capture bullet velocity. In the table above, seven shots were taken all using the same ammunition (7.62x51mm M80) with the MagnetoSpeed sensor as well as the double skyscreen Oehler setup. Velocity 1 above is the velocity measured at the first set of skyscreens and Velocity 2 is read at the second set. When the muzzle velocity is back calculated based on the distance between skyscreen sets and the muzzle we obtain the "Calculated Muzzle" velocity in feet per second (fps). Comparing this to the Magnetospeed data we get percent differences of less than half a percent. This data series shows that the MagnetoSpeed is at least 99.6% accurate to the Oehler system used at SwRI for this test.

Magnetospeed Prototype: High-Speed Video Testing

.243 round just out-running muzzle blastThe SwRI data was good but we wanted to know with more certainty how the MagnetoSpeed sensor stacked up against actual bullet velocity. In order to do this we had to see the bullet and calculate the velocity based on actual measurements. It was time to implement high speed video into our testing scenario. The picture to the left shows a slide of the high speed video we took and the home page shows a slow motion animation of a .243 caliber bullet exiting the barrel and crossing the sensor deck. Based on visual calculations and several test shots we were able to document a 99.9% average accuracy level with the MagnetoSpeed sensor with respect to the video evidence.

Magnetospeed prototype tests by Legion Firearms LLC with AR-15

*Picture provided by Legion Firearms LLCJamie Wehmeyer at Legion Firearms agreed to do some testing for us on the MagnetoSpeed prototype. Using one of his custom AR-15 firearms he put over 100 rounds on the MagnetoSpeed sensor in about 5 minutes. He reported that velocity was right within the expected published range and all the shots had a max spread of 100 fps. When asked about the user interface he reported that it was "super easy to use". They shot mostly single shot and 3-round-bursts and had no problem picking up the velocity. Even though the MagnetoSpeed sensor was not really designed for rapid fire we had them do several series of continuous rapid fire. The sensor would record data up until about the 18th shot in the rapid fire series before giving an error. All in all a good test for the MagnetoSpeed and AR-15.


KMW- Long Range Solutions tests the MagnetoSpeed prototype
*Picture provided by KMW-Long Range Solutions.
Terry Cross at KMW-Long Range Solutions is an expert when it comes to building high precision rifles. We had him do some initial testing with the MagnetoSpeed Rifleman and one of his custom .308 rifles. He used Federal ammo and got a "100% read rate on every projectile". He said his next test will be to shoot the MagnetoSpeed sensor in tandem with a PACT chronograph using standard screens to see how the two compare. We are anxious to hear the results.

[TGS]

Internet Commandos and other self-anointed SMEs

As Tamara said about the irony....

and with the last few posts, that's gotta sting by now.

lulz.

[JodyH]

"What difference does it make?"
-Hillary Clinton-

[jetfire]

Well, now this thread is interesting!

[rifleshooter]

bump.