Barrel length vs velocity 28" to 16.5" .308

[NikatKimber]

People have a hard time wrapping their head around the fact that a shorter barrel is more accurate when sight radius is not a factor.

Agreed, with a minor exception. They CAN BE more PRECISE. Accuracy denotes how close the group is to the intended target. So a longer barrel (if it generates more velocity - depends on load and cartridge) will be inherently more accurate, as it will have less drop and be less affected by wind. However, lack of accuracy can be accounted for (adjust sighting system) - lack of precision cannot.

Like most things gun related (or actually, pretty much anything at all) everything is a compromise. It's not as simple as "longer barrel = worse".

Here's another site that does a similar experiment:
http://www.ballisticsbytheinch.com/

 

[beastep]

I agree mostly.

 

[NikatKimber]

I agree mostly.

What do you disagree with?

 

[beastep]

I dont consider bullet drop a factor in accuracy.

 

[NikatKimber]

But it technically is. It's not a factor in precision, but it IS a factor in accuracy.

If you used a laser down the barrel of a rifle, that point would be "point of aim" for the barrel. The more accurate barrel is the one with less drop/windage.

 

[beastep]

Which is more accurate, a .308 that will shoot .5moa all the way to 1000yds but has a drop of 400" or a 300WM that shoots 2moa all the way out to 1000yds but only has 300" of drop?

 

[NikatKimber]

Which is more accurate, a .308 that will shoot .5moa all the way to 1000yds but has a drop of 400" or a 300WM that shoots 2moa all the way out to 1000yds but only has 300" of drop?

The .300 WM is more ACCURATE. The .308 Win is more PRECISE.

Lack of accuracy can be accounted for (adjust your scope), lack of precision cannot. The .5MOA gun will always be more precise than the 2MOA gun (ignoring any modifications to the gun).

Accuracy refers to the closeness of a measured value to a standard or known value.
Precision refers to the closeness of two or more measurements to each other.

https://www.ncsu.edu/labwrite/Experimental Design/accuracyprecision.htm

But you are correct in that given the choice, a shooter would be willing to give up velocity (inherent accuracy - more drop/windage) in trade for more precision (tighter groups).

My point originally is that shorter does not automatically mean tighter groups. It can; and especially for thinner barrel profiles usually will - but it is not a guarantee for better precision.

 

[beastep]

I agree with the shorter does not automatically mean tighter groups. We will just have to agree to disagree on the rest.

 

[Buzzgun]

This info is from Charlie Sisk of Sisk Rifles........he is a VERY well respected rifle builder.

For a long time I have wondered about how barrel length
affected velocity. I had always been told you need a certain
length barrel for certain calibers. I have read when folks
compared one gun to another with different lengths but I
always thought that was not an apples to apples comparision.
So I did a few test myself.
All these were Shilen barrels. I used the same brass through
out the whole test. All weighed to with 1 grain. Bullets
were tested on the Juenke machine. Powder charges were
weighed to .1 grain. The same rest, chronograph, Redding
press, primers all from the same lot, bullets for the same
box, same lathe, same crowning tool, same cutoff tool, and
each rifle done from start to finish on the same day.
Ambient temperature was the same because I shoot from inside
the shop. I held the rifle the same way on the rest every
time. I shot ten rounds first to break in the barrel. Then
cleaned with Sweets and fired one fouling shot. Then shot
five rounds and took the average. I used a midrange load
fron the Nosler book, not too hot but certainly not a
reduced load. Here is what I got.

22-250 Hodgdon 380 34 grains Federal GM210M Remington brass
55 grain Ballistic Tip
27 inches 3469 fps
26 3451
25 3425
24 3407
56 fps from highest to lowest

270 Winchester Hodgdon 4350 54 grains Federal GM210M
Winchester brass 130 grain Sierra
27 inches 3115 fps
26 3093
25 3071
24 3054
23 3035
22 3027
21 3001
114 fps from highest to lowest

300 Winchester mag Federal GM215M Winchester brass 74 grains
of Reloder 22 180 grain Partition
27 inches 3055 fps
26 3031
25 3024
24 3003
23 2984
22 2960
95 fps from highest to lowest

340 Weatherby Federal GM215M 250 grain Sierra
81 grains Reloder 22 Wby brass
27 inches 2837 fps
26 2817
25 2809
24 2791
23 2777
22 2755
21 2731
106 fps from highest to lowest

I think I will do a little more thinking before I recommend
a barrel length in the future. What do you folks think ?
Charlie


Here is the info about the 338 Win and the 257 Roberts.
338 Win mag
Winchester brass
Federal GM215M primers
Reloder 19....73 grains
250 grain Partitions
27 inches.....2806 fps
26 inches.....2787 fps
25 inches.....2761 fps
24 inches.....2743 fps
23 inches.....2716 fps
22 inches.....2697 fps
21 inches.....2676 fps
20 inches.....2656 fps
150 fps from 27 inches to 21 inches

257 Roberts
Federal GM210M primers
Remington brass
H-4350....45 grains
120 grain Partitions
27 inches.....2860 fps
26 inches.....2834 fps
26 inches.....2815 fps
25 inches.....2815 fps
24 inches.....2798 fps
23 inches.....2775 fps
22 inches.....2760 fps
21 inches.....2739 fps
20 inches.....2717 fps
143 fps from 27 inches to 20 inches
I want to test this on the next 450 Marlin I build and on a
222 Remington. If I get the same results with those, in my
mind the test is over. I think this will be enough data to
support the findings. Are there any folks out there who have
a degree in this sort of thing ? Maybe explain how many data
points would be needed to be able to say this would work
with the majority of calibers ? Someone with experience in
statistical(spell check) quality control ?
Charlie

A few weeks ago I done some testing with shortening barrels
with various calibers. I just finished this test with a 300
Ultra.
These loads were EXTREMELY HOT !!!!!!!!!
I will not post the grains here because on the third loading
the primer would fall out of the case . I never load this
hot , only this time for the test. I used Remington brass,
Federal GM215M primers, 220 grain round nose bullets. I used
the same procedures as the last test.
length.... H-4895 .....H-870
.....27 .....2740 .....3107 FPS
.....26 .....2709 .....3088
.....25 .....2685 .....3062
.....24 .....2663 .....3046
.....23 .....2636 .....3018
.....22 .....2612 .....2997
H-4895 lost 128 fps
H-870 lost 110 fps
Charlie

 

[beastep]

Very good info.