bbl. length vs. velocity test results

[Caspian 32]

I finally cleaned my desk at work and found my scribbling from a test i dd awhile ago.

 

I was asked if shortening a barrel would lessen the effect of a shotgun. At the same time i was hearing people talk about "losing velocity" when chopping a 12 ga. bbl. I thought to myself, maybe some velocity was lost, but not enough to make a difference. Well, it's kinda hard to argue without facts to back you up (although some on here haven't picked up on that yet).

 

So here goes. I had a cheapo 31 inch barreled break open single shot 12 gauge for the test. I cut the barrel in 6" increments from 31" - 7". I used the following ammo: Aguila mini slugs, Winchester 3" 1 oz. slugs, and Remington 2 3/4" 1 oz slugs.

 

.......Aguila........Winchester...........Remington

31"..1022...........1725....................1557

25"..1137...........1685....................1498

19"..828.............1542....................1411

13"..1139...........1433....................1324

7"..1024.............1134....................1131

 

some observations: The Aguila numbers are all over the place. ideally i would have used 3 shots for each measurement, however i was limited in the amount of ammo i had from the same lot. QA?QC issues with power charge is the only way i can explain it.

 

The other 2 3/4 & 3" shells lose velocity, but not an appriciatable amount.

 

The neatest thing is that the 7" barrel only gives the slug 4" to gain the 1131 fps since the barrel length is measured from the breech and 3" of that is shell.

 

There may be some lessened velocities due to a gas operated system, but i think it's evident that there's not enough loss to matter to the receiver of a 1 oz. slug.

 

Caspian

[Bvamp 604]

thats interesting in the aguila column....looks like the mini shells have so little powder in them that they dont care how long or short the barrel is. I would have thought a mini shell would have a shorter wad than it apparantly does to allow for more powder.

 

the other thing that catches my eye is that the 3" and 2 3/4" velocities arent really that far apart, until they are fired out of a long goose barrel. 100 feet per second out of the common 19" barrel length? thats all you get out of the 1/4" of extra powder? seems like a waste of money to me now, buying 3" slugs. I guess the 3" buckshot is still good to have, because you get those extra 3 pellets in there.

 

 

how was the flash on the 7" tests? It had to be pretty big, because it looks like 1/3 of the powder was outside the barrel before igniting from those #'s.

[Caspian 32]

i dunno about the flash. I was concentrating on NOT hitting the chronograph with 1 oz. off lead while shooting a shotgun with no sights. I wasn't blinded, so it must not have been that much. the slug loads may have a flash inhibitor similar to high end handgun ammo.

 

caspian

[Bvamp 604]

good point.

[dinzag 31]

Nice work! Thanks!

[G O B 3,516]

Good job! The decrease in velocity is more linear than I had thought. Also the mini shells are even less sensitive to barrel length.

 

G O B

[acetomatoco 0]

Thanks for the info Caspian

Here is a Saiga site with alot of information you guys might want to keep in your favorites if you do not already have it. It explains the Saiga as well as give a velocity chart to compare the 580mm barrel and the 430mm barrel. Even though their velocity is in meters per second,their numbers converted to Feet per second come out lower for some reason.

http://club.guns.ru/eng/saiga12.htm

It also has a chart comparing accuracy with 2 different chokes.

 

Happy Reading

Ace

[Caspian 32]

33g = 1.16 oz.

53g = 1.86 ounces...OUCH!

 

Their velocities are lower b/c they're using heavier loads. Not to mention they're using different ammo.

 

I would expect a gas operated system to be slightly slower, but by the time you figure in standard deviation, it's neglegable if you could really calculate the difference. you'd need some factory premium loads to really tell.

 

Caspian

[kmoore 3]

It cracks me up that a 7 " bbl makes a 3 " magnum perform only 10% better than the Aquila

 

 

thats interesting in the aguila column....looks like the mini shells have so little powder in them that they dont care how long or short the barrel is. I would have thought a mini shell would have a shorter wad than it apparantly does to allow for more powder.

 

the other thing that catches my eye is that the 3" and 2 3/4" velocities arent really that far apart, until they are fired out of a long goose barrel. 100 feet per second out of the common 19" barrel length? thats all you get out of the 1/4" of extra powder? seems like a waste of money to me now, buying 3" slugs. I guess the 3" buckshot is still good to have, because you get those extra 3 pellets in there.

 

 

how was the flash on the 7" tests? It had to be pretty big, because it looks like 1/3 of the powder was outside the barrel before igniting from those #'s.

 

Numbers are funny things.

 

Think about the differences between the shells this way. difference is 131 fps, which is a 9% increase over the 2 3/4 shell. Going to 3 inches is an increase in length of .... 9%.

 

For me, question would be more along the line of .. what would be a meaningful difference in MV? Personally, these differences are big! but they come with 6 inches of bbl change, so if you are just reducing a few inches then I could live with it.

 

Interesting stuff, thanks for sharing.

[CGuns 3]

580 mm barrel is 22.8 inches, or the 22 inch barrel in U.S. Markets

 

430 mm barrel is 16.9 inches and is not availabe on U.S. Saiga 12 imports.

 

Basically, they are saying that when the barrel was dropped from 22 inches to 16.9~17.0 inches, 26% of the length was decreased, but this only reduced velocity by 6.75% and energy by 6.25%.

Very insignificant. This applies to 2.75 shells. Figures are above for 3.0 magnum shells, under 73mm.

 

All things being equal, let us evaluate this further.

Rounding up:

23 inch barrel to 17 inch barrel in test is a difference of 6 inches.

Velocity loss is about 7% rounding up

Energy Loss is about 6% rounding down

 

With a 18.75-19.0 inch barrel, I am guessing velocity loss would be:

4.6ish

and energy loss would be 4.0-4.1ish

 

I haven't measured my barrel exactly yet, but I trust the measurement of the 22 inch barrel being nearly 23 inches in length. I made my calculations using that as the length...(~22.8-23.0inches)

 

Regards, CGuns