Gentlemen,

We were out shooting our .303's today, and did some comparison between my 21" barrel No.1 MkIII* and a co-worker's No.4 Mk.2, with a stock 25.25" barrel. The data is as follows...

Load #1 - Hornady 174 gr. RN Interlock, 44.0 gr. AA2520, CCI 250 primer, Fed. brass.

21" barrel - 2295 fps
25" barrel - 2502 fps

Load #2 - Woodleigh 215 gr. 43.0 gr. H414, CCI 250 Primer, Fed. Brass.

21" barrel - 1957 fps
25" barrel - 2203 fps

Load #3 - Hornady 174 gr. RN Interlock. 46.0 gr. H414, CCI 250 primer, Fed. Brass.

21" barrel - 2093 fps
25" barrel - 2374 fps

S&B 174 gr. FMJ

21" barrel - 2329 fps
25" barrel - 2434 fps
I am guessing this load uses a faster powder that the short barrel can use up easier.

What I can figure out, is that these loads, which are at or near maximum published, use slower burning powders, which my short barrel can not burn completely. The longer barreled model achieved velocities very near published values, with the 215 gr. exceeding book values by 80 fps. I think if I used a faster burning powder in the 21" model, I could achieve slightly higher velocity and achieve a more complete powder burn.

Any input or advice would be appreciated.

Joel Slate
Slate & Associates, LLC
www.slatesafaris.com

You're probably right about the powder speed having a lot to do with the difference in velocities between the two barrel lengths. I found WW 748 to give good velocities in a No. 5 Jungle Carbine. However, one slow powder load, a Sierra 200 grain .308" bullet with 47 grains of IMR 4350, gave us a muzzle velocity of 2150 feet per second from this 20" barrel. This load produced 1" groups @ 100 yards!! We also got 2500 with a 180 grain Sierra .311 bullet using 54 grains of WW 760, which is about as slow as IMR 4350. Federal 210 primers were used in both loads with WW cases. Cases lasted five reloads, rifle had minimum headspace. In this same rifle, FN ball ammo with 174 grain bullets averaged just 2200 feet per second.

Unfortunately in different rifles you are not only comparing barrel length but bores of each, and the differences in slop in the respective chambers.

In such a comparision some years back, I purchased a rifle in the same caliber as a primary hunting rifle. The purpose was to untilize the same ammunition and loads and reduce the ammount of ammo to carry to a hunt. The new rifle had a long barrel so we fired it as new then progressively cut off the barrel 1" at a time chronographing the loads after each cut. At the target length, the barrel was rechambered with the same reamer as the primary rifle cutting off a couple of threads of the breech end to "tighten" the chamber. Imagine the surprise when the velocity of the new barrel was about 100 fps slower! Careful measurement of the bore indicated a bore in the new barrel about .0004" larger, the only difference in dimensions. Since all other dimensions were the same it was believed that difference accounted for the velocity differential. It took one additional grain propellant in the new rifle to equal the same velocity. The experiment was a failure because of that small bore difference. You may have a similar difference in your comparisions of different bores, plus the likelihood of differences in chambers.

Gentlemen,

Thank you for taking the time to reply. I know this experiment wasn't exactly following the scientific method, but it was the best we could do with what we had on hand, and I feel it gives a good basis to judge the outcome.

It also was a whole lot of fun to do, which is probably the most important result of the experiment.

Joel Slate
Slate & Associates, LLC
www.slatesafaris.com

Gotta agree with Bob on this one. Apples and oranges.

Rifle Shooter did an article a couple of years ago using a single Swede Model 96. They shot it with the 29" bbl to establish a velocity baseline and then they proceeded to cut off an 1" at a time and recrown the muzzle. Took it all the way down to around 18-20" before they stopped. They demonstrated the standard 25-35 fps velocity loss/inch. If you are interested, let me know and I'll see if I can dig up the issue and report actual numbers.

Martindog

[This message has been edited by Martindog (edited 04-20-2002).]

Yep, I've seen several articles and tables on the subject of velocity loss in shorter barrels and 25-35 fps/inch is the rule. One could manipulate this a bit with certain powders, but this is the range I would figure when thinking of shortening a barrel.

For me all this means is the long barrel isn't the sacred cow many shooters believe.
Personally, I think the small loss in velocity is compensated for by having a rifle that is lighter, perhaps better balanced, and just generally handier and faster to manipulate...IMHO.

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A well placed bullet is worth 1,000 ft/lbs of energy.

It can vary from 20 fps per inch with smaller cases lower velocity to 50 fps per inch of barrel with the large capacity very high velocity magnums.