Barrel Wear with (mostly) Cast Bullets

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  • Last Post 17 February 2026
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Wilderness posted this 16 February 2026

There was a thread here on barrel life a couple of months ago. It became quite long so I'll start a new one to say my piece.

At the time, I tried a measurement on my 99 Savage .30-30, with a long-seated soft .312" bullet. I came up with .310" as the groove diameter at the start of rifling. When new, this barrel slugged .308", although that would have been just the tightest spot. I also still have my original Cerrosafe chamber cast. That barrel has now had over 7,000 shots through it, somewhere between 2,000 and 3,000 jacketed, and the rest full power cast bullet hunting loads.

The original thread got me thinking it was time to do another Cerrosafe cast. Groove diameter at start of rifling came up at .310", and that was still the measurement .800" ahead of the chamber. Originally there was a tight spot forward of the chamber when the barrel was new. Going on how it felt when being cleaned, this tight spot disappeared quite some time ago.

Rifling origin has moved forward .200", and the first part of the visible rifling is now quite shallow. Directly ahead of the chamber the dimension is now .312", which is probably why it shoots so well with my .312" bullets. All that wear seems to have produced quite a nice cast bullet throating arrangement, although discovering it was a shock.

To complete the picture I did a cast of my 1949 Marlin 336A .30-30, with four groove rifling. I don't think it had seen much use when I got it. I have been using it for Rifle LAS shooting, and have put 8,600 shots through it. The Ram loads have been high teen velocity with 170-185 gn cast bullets, powders 2208/Varget & 2206H/H4895. The others have been plain base 116 and 165 gn bullets subsonic with powders in the Red Dot to Unique range.

To all intents and purposes there is no visible wear in the Marlin. The rifling still starts straight off the end of the chamber. The groove diameter immediately ahead of the chamber as per the Cerrosafe is .310", back to .3095" an inch or so down the barrel. I do not have an original "slug" measurement or Cerrosafe cast for that barrel.

Two points emerge: The chamber casts have done a proper job of defining the wear situation; and full power cast bullet loads have been a lot more damaging than gentle ones - presuming the wear in the Savage is not all down to the jacketed bullets.

You are only as good as your library.

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Aaron posted this 16 February 2026

When I taught Process Management in the corporate venue, I always stressed "manage with data, not presumption." You have done precisely that with you excellent data logging. One can NOT doubt your conclusions based on data and mind boggling data logging over the years. My hat is off to your efforts and results.

I have to conclude as you have, that high pressure propellant particle impingement (abrasion) is the culprit here regardless of the projectile metal.  

I would modify your tag line to include: "You are only as good as your library and data."

Great write-up. 

With rifle in hand, I confidently go forth into the darkness.

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Wilderness posted this 17 February 2026

Thanks Aaron - I recall another saying "if you can't measure it you can't manage it".

You are only as good as your library.

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Ed Harris posted this 17 February 2026

My experience has been that pressure is more important than whether the bullet is cast or jacketed. Years ago I shot a Remington 788 in .308 with full charge loads using heat treated cast bullets and throat erosion was identical to jacketed bullets. Results were similar in a 788 in .30-30 loaded hot.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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Larry Gibson posted this 17 February 2026

"My experience has been that pressure is more important than whether the bullet is cast or jacketed."

My experience is the same as Ed's.  For example, the last few years I've done a lot of HV shooting with the 30x60 XCB cartridge in a new barrel.  I was using the NOE 30 XCB bullet loaded over mostly AA4350.  The measured velocities ran mostly 2900+ fps with measured psi's of 50,000+.  A meticulous count of rounds fired was kept.  That count is now 3,260 shots fired in that barrel.  Additionally, I have been tracking the rounds fired in my M70 Target 308W rifle.  It also has just over 3,000 rounds through it of which most have been with 175 gr MKs over 44.5 gr Varget.  The measured psi of that load runs 58,000 psi +/-.

The measured throat erosion of both is very close to the same.  Inspection with a bore scope also reveals similar erosion. 

Conversely, A 309 CBC rifle which has had several thousand 311291s over 4895 giving a measured psi of >28,000 shows little if any throat erosion.  Similarly, my 30-30 M-94s which see mild cast bullet loads mostly show negligeable throat erosion.

LMG

Concealment is not cover.........

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