Barrel Length

[Whitehorn]

Quick question:

How much performance do you lose with a shorter barrel? For example what is the performance difference between a 20" and 24" barrel assuming all things remain the same like type of rifle and caliber.

Thanks.

From my tests, about 25-30fps per inch. I would say anywhere from 100 to 150fps slower.

[gorse]

It depends on lots of factors. One general rule of thumb is the larger the powder charge....and the faster the velocity in the full-length barrel....the more loss there will be with a shorter barrel. As such, magnum rounds tend to lose much more velocity with shortened barrels than non-magnums. Having said that, I will concur with bigcountry on his numbers....at least for many non-magnum cartridges. For magnums, the loss is often more like 50-85 fps/ per inch.

[J Bolt 7mm]

(Ft/Sec.) Drop in Muzzle Velocity per 1"
2000-2500 10
2500-3000 20
3000-3500 30
3500-4000 40
These numbers are off of Remington's Rifle Balistic page.

[Vapodog]

ORIGINAL: SCHOOLBOY

(Ft/Sec.) Drop in Muzzle Velocity per 1"
2000-2500 10
2500-3000 20
3000-3500 30
3500-4000 40
These numbers are off of Remington's Rifle Balistic page.

This is good data and very believable.

Thanks for posting

[missed_another]

whitehorn... on the other end of the scale a barrel to long can also cause a loss of performanceon the fps scale. once the charge has been used up there now comes a drag effect inside of abarrel that isto long for the charge. for a .22 long rifle i know that the perfect barrel lenght is 19 inches. anything shorter can cause a lossof fps just as a longer barrel will cause a loss in speed. but the bullet will be more stable with the longer barrel. by keeping this in mind you cannot always say thatthere is always aloss of speed from a shorter barrel. every load is differant.

[Scott Gags]

Velocity losses vary by cartridge case volume and bore diameter. A small case with a large bore ie 35 Rem will not get perfomance improvements with additional barrel length beyond 20 Inches. The powder is going to burn quickley and the large bore will displace a lot of volume by the time bullet reaches the end of the barrel. That means the pressure levels in the barrel will be very low and the bullet will no longer be accelerating.

A 7MM ultra mag will have lots of powder to burn,and the bullet travelling down the barrel will displace less volume in an equal length barrel relative to the 35 cal barrel. This means very high barrel pressures at 20 inches and an accerating bullet.

The best quantification of this I have seen is a test using a 7mm-08 with a 24 inch barrel. The gun was fired repeatedly and an average velocity was measured. The barrel was cut to 20" and retested. The velocity only decreased by 60 FPS total or 15 FPS per Inch. I feel this is the best way to test because it eliminates variables between barrels which often timeshas more to do with the velocity improvements than the lenght. Many of the velocity increases from the high end custom barrels is due to reduced friction in the finely finished barrel not the additional 2 inches of barrel length. Most buyers will mistakenly attribute all of the velocity increase to the length instead of the finish.

[Tony Orlando and Dawn]

Missed Another has a good point. I've chronographed a lot of various guns. 22LR's actually lose velocity once they get past the 18" or 19" mark.

[Roskoe]

I cut a 6MM-284 barrel from 26" to 24" awhile back and recorded a 157 fps loss in velocity - same load and same chronograph. This is obviously a very over-bore caliber and likely represents a "worst case scenario".

[Whitehorn]

Thanks for all the feedback.. I was mainly curious with both the .270 and 7mm-08.