Short barrel magnum velocity?

[carbonrod]

I am considering a 20inch barrel for portability, but am wondering about the decrease in velocity. I have heard several rules of thumb, but have not yet seen any published measured data on the muzzle velocity of a 20 inch barrel and a magnum cal. For a caliber, I am considering 300win mag, or short mag.

 

[buzzgun]

I copied and saved this from another board I read......the info is from well known gunsmith Charlie Sisk. I am interested in this discussion because I want to build a 22" barreled 7 wsm.

[ QUOTE ]
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

[/ QUOTE ]

 

[Wild_Bill]

Hi i have a Rem Model7 Magnum in 7mm SAUM and i believe their is a reason they increased the Magnum barrels to 22" i would not go under it with the magnums get a 22" barrel and you will not loose to much to a 24" barrel but at 20" you will increase the muzzle blast a lot and also loose more velocity.

Cheers Bill
Australia

 

[Black Diamond 408]

Check out the threads on the long range pistol area, they are using 18 to 20" bbls on their rigs. Almost all calibers are being used, 338 Lapua with a 20" bbl is still producing hefty velocitys.

Dave

 

[SqueakyHunter]

Wow. Buzzgun (and Charlie Sisk) - excellent work.

I see it's been several years since this info was updated. Perhaps I can jumpstart the thread again.

I was especially intrigued by Charlie Sisk's info related to the .338 WinMag and the .340 WbyMag. I love medium bores - .323 to .375 – and I suppose the .338 caliber offers the best of all possible worlds as a medium bore.
I have long reviewed the reloading manuals (Nosler, Hornady, Lyman) and wanted to setup a test to find the optimal powder/barrel/bullet pairings for the .338 caliber. That is, instead of just assuming a .338 WinMag has a 24inch barrel, and then experimenting with the loads in the book to find one you like – I want to find the "optimization" points for each bullet-weight/powder combination. Where "optimum" means; the most velocity, least muzzle flash, for each given barrel length – let's call that "the most efficient load."

A chart that shows:

• For a .338 cal., 225 grain Nosler Partition, from a 26 inch barrel – here is the best cartridge/powder/bullet combination
• For a 24 inch barrel – use this combination
• For a 22 inch barrel – use this combination
• For a 20 inch barrel – use this combination

Then I can use that reference chart to help me pick my cartridge and rifle configuration relative to any given game & hunting condition.


I love carbine style rifles. I own and shoot a pair of Remington Model 600 Mohawks my father gave me back in the 1970s…and I'll take them to my grave. I also owned and hunted with a 26 inch barrel .300WbyMag in those heady college days when I thought I knew more about guns than my father. I later sold the long skinny Weatherby, and have not owned a long barreled rifle since.

I would love to see Charlie put together a Big-Bore chart as well. I owned a custom .416 RemMag for several years with a 22 inch barrel. Factory ammo in that rifle reliably clocked 2400 to 2410 FPS. That short .416 has clobbered Lion, Buffalo, Elephant, Leopard, Eland, Kudu, Sable, Waterbuck, Zebra, Wildebeest, and Impala. It is great – though I ultimately gave it to a buddy who hunts Africa far more often than I.

As I contemplate a return to the Dark Continent, I would love to have a new Buffalo/Elephant thumper with a 22 or even 20 inch barrel. The challenge is what cartridge - bullet-weight - powder combination would be optimal in a short, fast handling dangerous game carbine? Is the .416Rem the way to go again? Or maybe a .458 Ackley, or a .460 Short A-Square?

Maybe I'll go find Charlie and we'll figure it out together.

 

[Long Time Long Ranger]

Squeakyhunter, I love the 338's and have worked with them since the 70's. When I had my range I tested 338's in barrel lengths from 24-34 inches. The larger calibers gain very little in velocity as the barrel length increases. With the 338's you can gain more per inch with the big 338-378 wby and similar size cases using extremely slow powders like H-870. But still not very much. Cases smaller like the lapua and ultramag cases gain very little per inch of barrel. Back in the 90's when I was testing variations of the Lapua and the 338-300 RUM I always averaged less than 100 fps from 26-31 inch barrels. That is when I realized a shorter stiffer barrel was better for me in these cartridges than a long one for hunting purposes. If you have a horse or a four wheeler to get your gun there then go long and heavy. If you have to walk like I do then go short. Both kill just as well. As I get older I realize carrying all that extra weight for a few fps just isn't worth it. What are a couple more clicks at long range anyway.

 

[Forester]

Promising...

I just finished a 7mm Remington Mag lightweight rifle with a 22" Benchmark barrel. I came really close to making it a 24" but wanted to stick to a pretty tight weight budget for this one.

No final numbers yet but it appears that there will be plenty of velocity available despite the short barrel.