Barrel length
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Misssissippi Dave
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The difference is very slight. I doubt you would notice it very much, if at all. When you work up your load, you will probably find the most accurate load is going to be below the max level. I prefer accuracy over speed any day.
Barrel length difference of one inch will give you a slight velocity edge and a longer sighting radius. However, the length of the barrel means nothing in regard to pressure generated by the same loads. Use that data with confidence to work up (for accuracy), your loads. If they are safe in a four-inch, they are safe in a five-inch.
4" is just the SAAMI standard pressure/velocity test barrel length for this chambering. All commercial ammunition velocities are reported for SAAMI standard test barrel lengths except as noted, and for the few where there is more than one SAAMI standard test barrel length (some pistol rounds, particularly where rifles are made for them as well) then which test barrel length was used should be specified.
In your case you should see about 4½% to 6½% increased velocity over a 4" barrel, depending on bullet and powder used. That's small enough that gun-to-gun chamber tolerances can make as much difference in some instances, so there's no guarantee you'll actually realize the increase as compared to the test barrel velocity reported. It's just the difference you would see if you cut your own barrel down to 4" after testing at 5". As the others have said, there's no effect on peak pressure.
In your case you should see about 4½% to 6½% increased velocity over a 4" barrel, depending on bullet and powder used. That's small enough that gun-to-gun chamber tolerances can make as much difference in some instances, so there's no guarantee you'll actually realize the increase as compared to the test barrel velocity reported. It's just the difference you would see if you cut your own barrel down to 4" after testing at 5". As the others have said, there's no effect on peak pressure.
Whatever the change of velocity will depend on the burn rate for the powder you are using, which BTW, you haven't mentioned. With faster burners than W231 the difference will be pretty insignificant, but if you're using something from the medium-slow group like Silhouette, HS-6 or 3N37, you'll see a significant increase. I didn't mention Power Pistol because I don't use it because its got nasty muzzle flash. The powders I mentioned are spherical and will meter better anyway. 
guess again?
This statement is not entirely true; it is an assumption.
The asumption is that a longer barrel will automatically provide higher velocity.
Extensive chronograph testing proves this untrue. Normally (ha! I spit on that word!) a longer barrel shows an increase, but NOT always.
This statement is not entirely true; it is an assumption.
The asumption is that a longer barrel will automatically provide higher velocity.
Extensive chronograph testing proves this untrue. Normally (ha! I spit on that word!) a longer barrel shows an increase, but NOT always.
57K said:
The difference won't be nearly that big. QuickLOAD offered up 4½% velocity difference for a very fast powder and 6½% for a very slow powder in this instance. The reason is added barrel length won't stop increasing bullet velocity until the barrel is so long that the pressure drops to where it provides only enough force to overcome bore friction and no more. Even for the .22 Long Rifle, which uses very fast powder and has a huge expansion ratio, velocity won't stop increasing with barrel length until you get a barrel 16-20 inches long. Normal pistol barrels are nowhere near long enough for that to happen, even with fast powder loads.
Now if you were to tell me you saw no difference in velocity between a particular short barrel gun and some other, longer barrel gun in the same chambering, that's perfectly believable. As I mentioned before, chamber-to-chamber differences can easily account for bigger velocity differences than the percentages I gave. One time I was testing some match ammo in different club-ownded Garands, and had individual rounds in one rifle differ by 200 fps from individual rounds in another rifle. That was about 8% difference just due to headspace, throat, and bore conditions in the rifles. In handguns the percent difference can be even bigger because each thousandth of an inch of chamber dimension difference represent a bigger percent difference in expansion ratio in a short straight wall cases than it does in a bottleneck rifle case.
So, unfortunately, the only way you can say for sure that extra barrel length is not getting you anything in your particular gun is to start cutting the barrel down and measuring the velocity change that results. Comparison to another gun won't tell the tale.
Unclenick, that's not too surprising as far as velocity increase with barrel length increase, but when you examine load data, the medium/slow burners give the highest velocities to begin with. So the 6.5% increase from additional barrel length further separates even more from a faster burning powder where 4.5% is the velocity increase, even if proportionately considering the difference. Like say a medium slow burner giving 1200 FPS in the short barrel but 1278 FPS with a 6.5% increase. Compare that to a faster burning powder load at 1150 FPS from the short barrel where with the 4.5% increase for the longer barrel you get 1202 FPS. That's a 6.3% improvement by using the slower powder vs. the faster powder and I'd consider a 72 FPS improvement for something like a 115 gr. JHP in 9mm to be worthwhile.
57K,
It appears you're making an assumption that difference in terminal performance is the only measure of significance to the shooter. If, instead, it's trajectory calculations, the difference will have similar significance for both the fast and slow loads (not much, as it turns out for normal target ranges to 50 yards).
It appears you're making an assumption that difference in terminal performance is the only measure of significance to the shooter. If, instead, it's trajectory calculations, the difference will have similar significance for both the fast and slow loads (not much, as it turns out for normal target ranges to 50 yards).
First off, with the example I used with a 115 gr bullet in 9mm, who's gonna be loading above the 1150 FPS level that's more than typical with a 4" barrel using a fast burning powder? in a 5" barrel with your QuikLoad statement of a 4.5% increase that's 1204 FPS. Any number of medium/slow powders will give 1200 FPS and even higher at STANDARD 9mm pressure of 35,000 PSI/33,000 CUP from a 4" barrel, so with the 6.5% increase from your own statement, from a 5" barrel that velocity would increase to 1283 FPS which I actually understated at 6.3% because the actual difference would be 6.6%. That's simply basic math! As far as performance with a conventional cup and core 115 gr. JHP in 9mm, I'd much prefer 1283 FPS/420 FT/Lbs of KE to 1204 FPS/370 Ft/lb load. I don't need to rely on QuikLoad to tell me that!