Thoughts on govt profile barrels, re: accuracy

[khc3]

It seems to be a fairly common opinion that govt profile barrels are completely wrong, in that the greater mass of the barrel is located furthest away from the heat generated in the chamber during firing.

If skinny barrels are thought to be less accurate than heavy barrels, at least progressively, the greater number of rounds fired, am I correct in assuming this is because of thermal expansion of the barrel material, resulting in expansion/distortion of the bore?

If this in fact the case, could it be argued that, for barrels of equal mass, having more mass near the muzzle would minimize the effects of any thermal expansion nearest the point where the projectile leaves the barrel?

[Rascally]

Most "match" and "DMR" barrels are tapered from the chamber to the muzzle. I'm not sure what the opposite taper is supposed to accomplish, but I am sure that an SME will be along shortly to set us straight.

[17K]

It’s harmonics. The extra mass on the end helps to mitigate whip.

The government profile is all wrong, but they do shoot better than a lightweight, all things equal.

They’re also easier for the shooter to control. I spent quite a bit of time with BCM’s ELW barrels since 2015 and they’re a beach to shoot in some situations. A little extra weight on the end is almost always your friend when accuracy is the goal.

[sinister]

The thicker profile of the barrel from the gas block to muzzle was originally from the XM16A2. Bayonet training and static-line parachute landing falls were responsible for the barrel bending at the end of the handguards. It was felt that a thicker profile at the front sight block (since the bayonet is secured to the front of the A-frame) would prevent the barrel from permanently bending like a paper clip.

If you look at the HBAR, M4 SOCOM, and Daniel Strength-to-Weight (S2W) profiles you see where the barrels are thickest/ most rigid under the handguards, minimizing barrel "Whip."

[redpillregret]

It’s harmonics. The extra mass on the end helps to mitigate whip

Any data to back this claim up?

I’ve read articles that measured droop with longer strings of fire. They demonstrated government profiles dropped more and thus “whipped” more with heat due to increased mass toward the muzzle. I’ll look and see if I can find it again sometime.


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[sinister]

Try this one: http://www.thenewrifleman.com/why-ar...s-so-accurate/

[redpillregret]

Try this one: http://www.thenewrifleman.com/why-ar...s-so-accurate/

That shows SOCOM vs gov and talks about theory. Looking for data that measures whip of gov vs LW per 17K’s statement.

The article suggests the opposite; stating mass toward the chamber mitigates whip; thus increasing accuracy.

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[khc3]

I thought about the harmonics issue, but I'm thinking more about the phenomenon frequently described where lwt barrels have groups open up, compared to heavier barrels, faster when shot rapid fire. The reason usually given is that the barrel heats up faster than a barrel of greater mass.

[17K]

Any data to back this claim up?

I’ve read articles that measured droop with longer strings of fire. They demonstrated government profiles dropped more and thus “whipped” more with heat due to increased mass toward the muzzle. I’ll look and see if I can find it again sometime.


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My own testing. Look up MOLON. He did a test of LW/Gov/SOCOM barrels.

Rugers match or whatever Mini 14 had weight at the muzzle.

[redpillregret]

I believe we can all agree the mini is a whole different animal which does not translate to other rifles and that the design of the rifle necessitated unconventional measure to create precision.

Was yours and melon’s a scientific test with a statistically significant sample size to draw conclusions or was it anecdotal? I’ll do a search and see if I can find it.

I ask questions because this is literally the opposite result of years and years of data and testing on precision rifles. It suggests a tapered barrel properly stress-relived will typically be more precise and more heat-tolerant. Most heat is generated in the first few inches forward of the chamber, which suggests that mass is more beneficial there than at the muzzle.




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