Barrel wear/pitting v velocity?

[targetterror]

I've got 2 older milsurp rifles that are not giving me the velocities I would expect. One is a Garand, and the other is a sporterized 1917 (barrel still 26 inches), and both 30-06. I know that every rifle is different, but my velocity is several hundred fps slower than I would expect. The powder is new/opened within a year, and has given me expected velocities in my modern Savage bolt-guns.

Both of the older rifles definitely show some wear and tear. I don't know the various scales of barrel wear, but while the rifling is still present and fairly strong on both guns the metal is far shiny. There are no obvious pits or gouges, but it definitely looks rough. I'm wondering if in such barrels, this roughness affects how well the bullet seals to the bore, thus lowering pressure and velocity? Or possibly the flip side of that is that it creates more friction, thus keeping the velocity lower?

Both shoot decently other than the low velocity.



Components with all loads was Lake City Brass, CCI 200 primers, and IMR 4064.

My Garand data with a 168 grain SMK is (average velocity for 10 shot strings, giving the barrel time to cool in between):
43gr - 2185fps
45gr - 2285
46gr - 2359, 2385 (second string done on a different day)

My 1917 data with a 175grain SMK is (average velocity for 10 shot strings, giving the barrel time to cool in between):
47gr - 2473
48gr - 2558
49gr - 2597

Every load above is a good 200fps or more slower than pretty much every published load. I don't think my chronograph is off, b/c my Savage F/TR registers ~2800fps with a 175grain SMK (30 inch barrel, .308win).

Any ideas? What kinds of velocities are other people getting with IMR 4064 in 30-06? Neither the 46 gr load in the M1, nor the 49 gr load in the 1917 showed signs of pressure, though 49 grains is about published max.

 

[jimurphy]

Re: Barrel wear/pitting v velocity?

I think you're right, a worn, oversize bore will let gas slip past the bullet, leaving less to push the bullet, and a rough bore will cause excessive friction, slowing the bullet again.

 

[jbaldwin]

Re: Barrel wear/pitting v velocity?

Very well stated. Have a 243 taht is shot out at troat and chroney shows same load that it has always shot at 300fps slower as gases pass than it did just 4 years ago. Still will shoot just above an inch.

 

[Hummer]

Re: Barrel wear/pitting v velocity?

The rejection criteria for barrels when I was testing at APG was an average loss of 200 fps utilizing the same lot of test ammo I started with. We submitted weapons every 1000 to 1200 rounds for chronographing and recorded the average velocity. It it dropped 200 or more the weapon was considered to have failed.

Gov't barrels are purchased to very demanding specs. Buying a commercial barrel may or may not give you "factory velocity" as the only requirement for commercial barrels to meet is that you paid for it and it meets spec. Commercial barrels are about like the specs for a medium potato, in some parts of the country medium potatos are consider large in other parts.

30.06 was loaded with 4895 and ball propellant. In the 30.06 Match I have pulled down the weight is 46 gr. 4895 with 173 grain bullet.


On the 1917 under no circumstances should you let someone open it up for a magnum. Barrel in all probability is likely to fail shearing several fingers in the process.

 

[targetterror]

Re: Barrel wear/pitting v velocity?

Thanks for the info guys. Thats interesting to know that velocity is one of the determinating factors regarding barrel wear. It certainly makes sense, though I had always assumed that the major performance indicator would be loss of accuracy.

Sounds like my barrel is indeed shot out and I didn't even know it! Accuracy is still decent enough, but it is a little sad to get such low velocity from a 30-06. It just doesn't seem right that I can actually get better velocity from my K31 than from my 30-06.