Rifle Barrel Life Using Low-Velocity Cast Bullets?

[beezaur]

Hi Guys,

Probably a silly question, but I am curious if anyone has any actual experience wearing out a rifle barrel shooting cast bullets.

To preemt a common misconception, yes, .22 lr barrels do wear out. In fact I have a shot-out .22 lr rifle barrel laying around somewhere from my rimfire days. I have no idea how many shots the barrel fired, but it was all subsonic target ammo, tens of thousands of rounds at least. There is a half-moon worn through the lands on one side from the slow action of gas cutting, not from cleaning. The smith who rebarreled it confirmed it with a bore scope.

Anyway, the rifle I am thinking of building is a .308 Win for long range and hunting. I also want to shoot cast bullets through it at about 1050 fps muzzle velocity.

Scott

[felix]

Barrels don't wear out as compared to being burnt. The accumulation of heat over time does the damage. Heat is amplified many times by pressure and where that pressure occurs in the barrel. Usually the hottest part of the barrel is in the leade section right ahead of the freebore (if any). (Throat = freebore + leade).
OK, that being the situation, full pressure loads are not to be used in your barrel, and this is irrevelent to powder speed. So, you will be looking for 30K cup max; and you should be able to use your QuickLoad to find what powder will push a 170 grainer 1100 fps. ... felix

[beezaur]

Thanks, felix.

by "wear out" I mean all factors, flame cutting during firing, abrasion during cleaning, all of it.

Quickload shows 6.2 grs Red Dot as producing 1050 fps from a 26" barrel with a Lyman 217-gr #311284. Peak pressure is 15,400 psi when the bullet has travelled around 0.5". By 1" travel the pressure is around 13,000 psi; 5" travel has a pressure of ~6000 psi. Muzzle pressure is 1000 psi. Loading density is around 28%, which is the reason for Red Dot.

It takes 8.8 grs 2400 to get the same velocity. Peak pressure is around 7500 psi. Muzzle pressure is still 1700 psi and the powder is only 97% burnt. Loading density is 21%.

Or so sayeth the computer.

These are the kinds of loads I am thinking of, heavy bullet and very light charges.

National match shooters report .308 Win barrel lives around 3000 rounds, but match shooters who shoot 3-shot strings often get 6000 rounds. Single shots can allegedly extend the life to 10,000 rounds. This is with full power, probably close to "maxed out" loads using powders that are fairly agressive, like Varget.

If it is even possible to get 10,000 rounds with high power ammo, I suspect you would get something like 10x that much with cast loads.

Another issue is, how "shot out" can a barrel be before it loses accuracy with cast bullets? In other words, can you have a barrel that is worn out from full power loads, will no longer group with them, and still shoot it accurately with cast bullets?

Scott

[felix]

Cast boolits, Scott, won't wear out a barrel. Jacketed bullets won't either. It's that damn heat generated by pressure. Now, the problem with using the powders you have shown is keeping them ignition friendly in that large 60 grain case, and burn correctly to produce the pressure over the longest haul possible. Try to find a powder that will produce 30K. Getting up to around 40K you will burn out a barrel (extend the throat very obviously, anyway) within 5K rounds. Remember, most things in life vary according to the natural logarithm curve which means here that 30K should extend your throat wear to 30K rounds or so. By then you'd be ready to change barrels anyway, and more specifically for a different bore size assuming no more guns in the house to satisfy the itch for something "heavy duty" fun and games. ... felix

[beezaur]

felix,

What do you mean by "30K?"

30 kJ/kg, the heat of explosion? Or 30k psi peak pressure? Temperature in Kelvins? Sorry, I don't follow. If you mean CUP, I am not sure how to correlate that to actual pressure, i.e., force per area, units like psi.

If Palma shooters can get 6000 rounds using *really* hot loads with 155-grainers, I find it hard to believe that any possible cast bullet load will do in a barrel at 5000 rounds. I'm open to it, just skeptical.

Have you tested this somehow?

Scott

[PAT303]

Alot of people think that a barrel wears out by bullets going down them and causing the bore to wear oversize,but it is the blast from the powder at high speed,pressure,temperature through the throat area erroding the metal just like an oxy cutter works.It's been proven that quick firing doe's the damage more than anything else.A pro rabbit shooter once told me he shot out a Brno mod 2 barrel but it took him 250,000-300,000 22's to do it. Pat

[felix]

30K CUP (copper units of pressure) is an average pressure of sorts, certainly more so than any instaneous PSI measurement which is taken on an incremental basis. CUP is the best measurement for us because it indicates more of what the boolit/bullet sees. This is because of the "time" factor being automatically averaged by the inertia of the cupper cup, which includes starting to bend, and continuing to bend, out of shape. In addition, the boolit and barrel take an "average" time to react because of their inherent static inertia, which both must be overcome for any movement (boolit and barrel) to take place. In PSI terms, we typically add about 35 percent to the CUP to get PSI, or take 65 percent of the PSI value to get CUP. But, this is true only if we know that the testing PSI system has been operated as a DIRECT replacement for the CUP measurement. If not so stated, the PSI measurement is the PEAK pressure observed which will give a false reading for what WE want. However, the barrel steel folks might want to know about this peak. For example, all Marlin guns are now tested at 80K PSI to pass inspection. This value obviously is not a PSI representation of our desired maximum CUP value, but a "lab" value instead.

How many rounds it takes to blow out a throat depends on how deep the boolit/bullet is seated in the neck when the gun is first throated for the projectile of choice (game dependent). As soon as the projectile is seated outward more and more to compensate for throat enlogation, sooner or later the boolit cannot be held by the neck properly, or the projectile becomes too long for "auto" action from the magazine.

felix

[waksupi]

I have one old rifle, with the rifling washed out for about four inches. Still shoots cast great!

[felix]

Yeah, Ric, if you used your bore scope on that gun you should/might see black specs throughout those 4 inches. That would be lead filling up the holes for your accuracy enjoyment. Remember, the accelleration of the boolit is the material factor, and if that remains consistent, so will the barrel vibes, and thus your accuracy (potentially). ... felix

[jonk]

I remember hearing that some country (I think switzerland) rigged up some device to shoot standard bullets (jacketed, copper, cupronickle, steel, whatever, steel if it was switzerland) using compressed air and not burning powder, at the standard pressure for the service round. They found that even after 50,000 rounds, there was no wear whatsoever, ergo proving that all wear is attributable to the powder. I wish I could find the article, I lost it in a move a few years ago.

In any case, you will wear out the barrel faster with heavier powder charges, and slower with lighter ones. So while I have no answer per se, if you can get a few tens of thousands of rounds with your average highpower rifle with decent if not stellar accuracy by the end, I would suspect maybe 40, 50,000?

[9.3X62AL]

Interesting thread here.

My wish as a shooter and casting hobbyist has always been to be able to shoot enough to need to worry about barrel wear/heat-induced throat extension. :-)

I do have one rifle that has a "Weatherby" throat courtesy of extensive firing, my Rem 788 in 22-250. I bought the rifle knowing this was the case, and it was priced accordingly. My intent was to re-barrel it to 250 Savage all along, but the thing shoots so well with Sierra 60 grain HP's that I've balked at unscrewing the stock tube. The "problem" is that bullets need to be seated to 2.460" OAL to get within .030" of the rifling leade. Not a mistype, that is .110" over "book" max OAL. This makes the rifle a 2-shot platform--one can squeeze into the magazine under the bolt. The rifle will still do 3/4"-7/8" groups as is, so I am loath to take tools to it.

[carpetman]

I had thought about getting into reloading for several years. Then I got orders to Alaska and that sealed the deal. I bought a couple books to read during the trip and one was a Lyman reloading manual. Their cast bullet section of the 44th Edition mentioned a test where two identical 30-06's were shot,one using cast and one jacketed. The stated result was when the jacketed barrel was worn out the cast barrel had no measurable wear. This was one of the factors of my deciding to start casting as well as reloading.

[felix]

Very true, C-man. Lyman's books gave out cast loads that produced no heat in comparision. The only wear with low heat would be from powder/primer erosion which would not enter the equation as far as we are concerned. ... felix

[felix]

Yes, Scott, I have worn the throat in my BR gun, a 222 ackley, actually 22/40 because ackley never did "improve" a 222. The barrel started life with me, throated for the Remington BR 53 grainer seated very close to the bottom of the long 222 neck. By 1200 rounds full power the boolit was just in the case, and then I switched the gun to cast. Now, even a full caliber (Bator boolit) seats likewise. In other words, after 10,000 rounds the throat is now gone for any boolit that will shoot in a 14 twist. The gun will shoot 1/2 inches at a hunnert with pure luck on my part, but is still deadly at 120 or so on the rear end of a shotgun shell shooting off of a car top (fairly unsteady). ... felix