Muzzle Velocity Comparison for Unequal Barrel Lengths

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MashieNiblick

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would optimally like to obtain an equation for correlation from the industry gurus here if at all possible

anecdotal experience or personal testing would be beneficial as well, however

listed below can be found some of my recent observations:


observations:
- .45 G.A.P. muzzle velocities seem to be on par with .45 A.C.P. + P muzzle velocities despite the shorter cartridge length

- www.fiocchiusa.com maximum muzzle velocity, barrel length, and bullet weight listings for .38 special + p and .357 magnum are as follows:
-- .38 special + P:
--- max muzzle velocity = 1100fps
--- barrel length = 3"
--- bullet weight = 110gr

--.357 magnum
--- max muzzle velocity = 1500fps
--- barrel length = 4"
--- bullet weight = 125gr


question:
- would it be safe to assume that the muzzle velocity of the .357 magnum round listed above would approach 1100fps for a 3" barreled pistol?
- if not, how close would it get?


there have got to be some real basic ballistics equations with variables of: bullet weight, muzzle length, muzzle velocity

i would assume that these equations would also have a powder weight term which would be multiplied by a coefficient of some sort

also i would assume that a barrel length coefficient would be needed and such coefficient would probably be exponential

i could solve for powder weight multiplied by the coefficient for both rounds, set the other sides of the equations = to each other, change the barrel length, and solve for muzzle velocity by myself if i knew the proper equation. . . .


if someone could point me in the right direction that would be great

any help would be appreciated

thank you in advance
- MN
 
No such formula exists, too many variables. It is not uncommon to see 2 different guns made by then same manufacturer, with equal barrel lenghts shoot ammo from the same box to quite different velocities.
 
I wouldn't expect you to loose more than about 150fps by using a 1" shorter barrel, but that's just a guess. I have no imperical proof of that. Youcan probably get that 150 fps back by handloading with a faster burning powder and/or jockeying around with several other aspects like overall length or powder load.
 
The only way to tell is to use the same gun, start with a long barrel and whack it off an inch at a time to see what the difference is.

Personally I don't care, just find the load that works in your gun, giving you the velocity you desire.
 
You could have three guns of the same caliber/chambering, and there would be no correlation between barrel length and velocity. I've never had a short-barreled gun shoot faster than one with a longer barrel, but I remember reading about a guy whose Commander showed higher velocities than any 5" gun he'd owned. I have .45s in 3.5", 4.25", 5" and 6" lengths, and even among five or six different barrels, there's a pretty progressive and predictable increase in velocity as the barrel gets longer.
 
There were some velocity data posted on the forum at M1911.org awhile ago, trying to correlate barrel length with muzzle velocity in .45 Auto. There was a spreadsheet posted with the results, and they did not show a correlation that was direct or consistent enough to possibly be reduced to a formula, or to use as a base for predicting what any ammo would do out of a different length barrel. lemme see if I can find the write-up ...

Found it. Here's the chart:
Muzzle_Velocities_01.jpg


And here's a link to the discussion: http://forum.m1911.org/showthread.php?t=90532&highlight=barrel+velocity
 
Great data- Thank you.

I reorganized the data, and although nothing definitive may be drawn from the information I believe some patterns may be seen.

Plot1:
ammochrt1.jpg


Plot2:
ammochrt2.jpg


Of note:
- 4 barrel lengths were used
- 3 firearm models were used
- 1 type was used in 2 barrel lengths (5” and 4.25” Para P-Model)
- Good data existed for 6 separate ammo types
- 4 ammo types were for bullets of 230-gr weight

Approach:
- First Plot:
- Data was grouped by ammo type and was plotted across all 4 barrel lengths
- For purposes of correlation and because of variable firearm models, linear trend lines were chosen and applied to the 4 bullets of 230-gr weight

- Second Plot:
- Data was grouped by ammo type and was plotted across 2 barrel lengths of the firearm model that was identical (5” and 4.25” Para P-Model)


- Synopsis:
- First Plot:
- For the differing model firearms of different barrel lengths, for the 230-gr bullet, and at the 3” to 5” barrel length range there was, on average:
- 41.44fps change in velocity per 1” of barrel length

- Second Plot:
- For the identical model firearms of different barrel lengths, for the 230-gr bullet, and at the 4.25 to 5.00” longer end of the barrel length range there was, on average:
- 81.00fps change in velocity per 1” of barrel length

- For the identical model firearms of different barrel lengths, for the 200-gr bullet, and at the 4.25 to 5.00” longer end of the barrel length range there was, on average:
- 97.333fps change in velocity per 1” of barrel length

- For the identical model firearms of different barrel lengths, for the 165-gr bullet, and at the 4.25 to 5.00” longer end of the barrel length range there was, on average:
- 142.67fps change in velocity per 1” of barrel length


- Therefore:

- Although only linear trend lines were utilized in the analysis, it may be safe for this leighman to assume that:

- Muzzle velocity increases exponentially in handguns with respect to an increase in barrel length

- Change in muzzle velocities due to bullet weight and with respect to barrel length will be considerably greater the lighter the bullet

- The exponential pattern of acceleration is thought to be due to pressure increase from burning powder occurring at a greater rate than that of barrel volume increase as bullet (read plug) travels through the barrel


My intuition figured as much yesterday, and I was able to quantitatively support it thanks to your data.

Too bad we don’t have access to a good formula, as that might prove pretty interesting. . . .

As said above by another poster, for a 110-gr or 125-gr bullet a 150fps per change from 3 to 4” barrel length when comparing .38 Special + P to .357 magnum seems a good approximation, and definitely in the correct order of magnitude.


Thanks again.
- MN
 
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only general trends can be used...

Mashie, you are over thinking it. One cannot make any valid correlation for changes in velocity, other than shorter barrels usually shoot slower than longer ones.

And that is not a hard and fast rule, because there are exceptions. As others have said, there are too many variables, and they apply differently to each individual gun and load.

I have personally seen a 4" shoot faster than a 6' (same caliber), and have seen 100fps difference between 3 different guns with the same barrel length, shooting the same ammo.

Now, these are uncommon, but not unheard of. Each gun and load combination is a mixture of individual variables, and may clock speeds above, or below a different gun/ammo combination.

Until you start looking at variations well above 100fps, its machts nichts where handguns are concerned. Because of the differences in individual guns.

Published velocities are to be taken as guidelines, and only really represent what they got with their gun and ammo. What you get with the same ammo and your gun can be quite different. Its usually pretty close, but it might not be. And thats just the way it is.
 
This is great!

Porting slows the velocities.

Revolvers are faster versus autos with identical barrel lengths.

Barrel/cylinder gap velocity has minimal variation.
 
Thanks, JW.

What would be very interesting for me to see (and to be able to gain a better understanding of the exponential patterns) would be a side-by-side similar plot of average muzzle velocities vs. barrel lengths for the following handguns:
- Ruger GP100, .357mag, 6.00" barrel
- Ruger GP100, .357mag, 4.20" barrel
- Ruger GP100, .357mag, 3.00" barrel
and
- Ruger SP101, .357mag, 2.25" barrel

10 shots a piece with the average muzzle velocity computed for each barrel length for each of the following 3 rounds:
- Hornady XTP, .357mag, 125-gr
- Hornady XTP, .357mag, 140-gr
- Hornady XTP, .357mag, 158-gr

These muzzle velocities could then be squared and multiplied by the appropriate bullet weights to obtain muzzle energy data points.

In a similar plot, these points too could then be plotted for each ammo type vs barrel length.

That would be a good control experiment and we would definitely, i believe, see some exponential relationships and behaviors- especially in the energy numbers.

I think we would find from an maximum energy delivery perspective, that the 125-gr round would outperform every other round by a long shot through the longest barrel, and that this however might not be the case for the shortest barrels. It would be interesting to see where the others would fall in in the mix.
 
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Here are some actual chrono results with the same loads and different barrel lengths:

LRNFP= Lead Round Nose Flat Point

Marlin 18" ,158 gr LRNFP, 9.6gr Blue Dot, 1482.5 fps
Ruger BH 6.5" ,158 gr LRNFP, 9.6gr Blue Dot, 1272.5 fps
Ruger SP101 3" ,158 gr LRNFP, 9.6gr Blue Dot, 1171
S&W M60 3" ,158 gr LRNFP, 9.6gr Blue Dot, 1166
S&W M360 Ti 1.9" ,158 gr LRNFP, 9.6gr Blue Dot, 1019.5 fps

RJHP= Remington Jacketed Hollow Point

Marlin 18" ,158 gr RJHP, 9.6gr Blue Dot, 1405.5 fps
Ruger BH 6.5" ,158 gr RJHP, 9.6gr Blue Dot, 1225 fps
Ruger SP101 3" ,158 gr RJHP, 9.6gr Blue Dot, 1139.5 fps
S&W M60 3" ,158 gr RJHP, 9.6gr Blue Dot, 1129 fps
S&W M360 Ti 1.9" ,158 gr RJHP, 9.6gr Blue Dot, 945.5 fps

LFNGC = Beartooth Bullets Long Flat Nose Gas Check (yes 185gr not 158gr)

Marlin 18" ,185 gr LFNGC, 14.7gr Lil'Gun, 1713 fps
Ruger BH 6.5" ,185 gr LFNGC, 14.7gr Lil'Gun, 1388 fps
S&W M60 3" ,185 gr LFNGC, 14.7gr Lil'Gun, 1174.5 fps
Ruger SP101 3" ,185 gr LFNGC, 14.7gr Lil'Gun, 1160.5 fps
S&W M360 Ti 1.9" ,185 gr LFNGC, 14.7gr Lil'Gun, 1022.5

Each Group was shot on the same day at the same (or very close to the same) temps.

As mentioned above, actual velocities are very gun specific.

FWIW,

Paul
 
Post# 9

jwphillips2

Porting slows the velocities.
Click to expand...

How much?

I still think the bullet will still be accelerating past the ports until it completely leaves the barrel.

I was once told by an old range master the porting actually made them more accurate. He didn't have time to explain it was to busy in the store at that time.
 
MashieNiblick - Your plots and your analysis seem to have skipped over the fact that the data from M1911.ORG included an anomaly -- starting with the "standard" 5-inch barrel, there was a significant drop in velocity going to a 4-1/4" barrel, then essentially NO drop with the reduction to a 3-1/2" barrel, and then another significant drop going to a 3" barrel.

These data have been discussed on the M1911.ORG forum a couple or three times, and the author has stated that he hopes to repeat the test using two guns of each barrel length, fewer ammo types, and more rounds per sampling in the hope of obtaining better data. Given that the guy who collected and compiled the data isn't happy with the inconsistencies the data seem to suggest, IMHO it would be unwise to view them as indicative of anything more than what we already know -- shorter barrels usually generate lower velocity than longer barrels.
 
Speer did a test which was very interesting .Starting out with a number of 357 revolvers , all 4" barrels, they used one lot of ammo of 125 gr bullets. Velocities ranged from 1200 to 1600 fps !!!
Also understand that ammo companies can develop primers and powders that optimize velocities for a cartridge .You don't have the capability to do this so reloading will never match factory loads !
 
Not exactly...

Also understand that ammo companies can develop primers and powders that optimize velocities for a cartridge .You don't have the capability to do this so reloading will never match factory loads !
Click to expand...

Ammo companies optimize their ammo to work in ALL guns chambered for it. Handloading allows me to optimize my loads for the specific gun it is to be used in. There can be a significant difference.

While I cannot develope my own primers and powders, I can, and do use those sold by ammo companies, and suitable powders from powder makers.

Yes, sometimes ammo is loaded with powder that is not available to handloaders, but it is a rare occurence when there is no powder available to handloaders that will allow the same approximate performance.
 
unless you test you guess

No equation will provide a clue as to what will actually result from the gun and ammo in your hand.

Testing required.
Not guessing about that.
 
Correct.

The website link I provided demonstrates that quite clearly. The 6" Python velocity was lower than the velocity from a 4" 686 using the same load.
 
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