R8 308 win short barrel, what speeds are you getting?

[Wildboarhunter]

So I have an R8 in 308 win with the short barrel, 52 cm long or 20,5 inches. I'm using 150 gr bullets, loaded with 45 gr of Lovex DO73,6 and getting about 860 m/s (2820 fps) of muzzle velocity. I'm courious, how much speed do you get with 150 gr bullets from a short rifle barrel like that with factory ammo and with reloads? Is 2820 fps like a little too much for a short barrel like mine? Primers don't seem to be flattened out of the ordinary.

[Corjack]

Does seem pretty zippy. Perhaps your crono is not accurate. Also may need to see what quickload predicts.

[Vaughan]

FWIW, using 150gr Norma FMJs, COAL of 2.750" and a bbl length of 20.5": Quickload suggests a mv with that load around 810m/s

In my experience QL usually over estimates mv a little, though gets surprisingly close.

[stokesrj]

I think I have told this story before but it makes some important points if you truly want to understand the real life variations of velocities between as nearly identical barrels as can be made by man.
In a class that I took at the NRA School of Gunsmithing in Trinidad Colorado we built ten National Match AR 15 A2 competition service rifles. All had Kreiger 1:8 twist barrels and Wylde Chambers. The barrels were new built consecutively by one of the very best barrel manufacturers, and all ten chambers were cut with the same chamber reamer. When the rifles were completed we took them to the NRA Whittington Center in Raton New Mexico and conducted a field a performance evaluation. All ten rifles shot 1/2 MOA or better using Federal Gold Medal Match 77 grain Sierra Match King loads. The average muzzle velocities varied by over 200 fps between the ten rifles. Everyone agreed this was a huge and unexpected variation. There was no measurable difference between the barrels even using the schools air gauge and no visible difference in bore finish, they were as smooth and consistent as it gets.

I don't think quick load or any calculator takes into consideration the realities of distribution of manufacturing tolerances and I would see 810 meters per second or 860 meters per second falling within the expected tolerances. This 50 meters per second equates to 164 feet per second less variation than observed in these nearly identical barrels.

This is why when we try to equate the speeds of a 20.5" barrel to a 23" barrel the results are often unexpected. My 20.5" 9.3X62 barrel actually produces higher velocities than two 23" barrels I've tested with some loads. The opposite is also true with other loads.

There were three tests done for the 300 Win. Mag, 308 Win. and .223 Rem. in which the barrels were cut in one inch increments. The results showed what I am talking about here in which at some point cutting the barrel one inch shorter had almost no affect, or, actually increased the average velocity. It also demonstrated that as we would expect the 300 Win Mag was more affected by shortening than the two lower capacity calibers.
The .300 Win Mag lost 39.6 FPS per inch of barrel removed.
http://rifleshooter.com/2013/12/300-win ... 0-win-mag/
The .308 lost 22.7 FPS per inch of barrel removed.
http://bulletin.accurateshooter.com/201 ... el-length/
The .223 lost 25.34 FPS per inch of barrel removed.
http://rifleshooter.com/2014/04/223-rem ... nds-rifle/

[Vaughan]

Indeed, which was why I noted "for what it is worth"......

[stokesrj]

Hey, I wasn't trying to diminish anything you had to say there, all very valid, just adding information.
Bob

[Vaughan]

My skin is not so thin

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[vodekz]

R - 8 308 win, I get 2900 FPS with 150 gr Partition and 23-inch standard or semi weight barrel. You lose about 25 fps per inch of barrel.
20.5-inch barrel I would believe you can get 2835 FPS with the same load and bullet. My load is 150 gr Nosler Partition with N140 VV, Lapua brass, Federal 210M primer.