Gunsmithing Factors in barrel life

[dbooksta]

I'm trying to get a sense of what the factors and trade-offs are for barrel life.

Suppose I have the following barrels all made in match-grade 6-groove cut-rifle stainless steel with similar profiles, and I only shoot the MatchKing load indicated through each one (these are all close to 60kPSI peak pressure):

<ul style="list-style-type: disc">[*]6.5 Creedmoor 1:8 24" 123gr @ 2900fps [*].308 1:12 24" 155gr @ 2900fps [*].300 Win Mag 1:10 24" 175gr @ 2900fps[*].338 Lapua Mag 1:9 26" 250gr @ 2900fps[/list]

And suppose I follow the same cleaning regimen with each one. Would the expected "life" of each barrel be the same? If not why not?

Now what if I start shooting faster loads through them -- say 110gr @ 3300fps through the .308? Does that have a significant adverse effect on barrel life?

What if I compare a 1:8 twist .308 to the 1:12, but shoot the same loads. Any adverse effect?

 

[buffybuster]

Re: Factors in barrel life

Read this.

http://www.accurateshooter.com/featured/overbore-cartridges-defined-by-formula/

It boils down to the volume of powder your burning to get through the case neck (bullet diameter). The more powder you burn through a smaller neck equals more blowtorch effect and reduced barrel life.

 

[bohem]

Re: Factors in barrel life

Operating pressure is a big factor too. Overbore is only part of the equation.

I run my 6.5 CM at 52ksi and get stellar accuracy. After 1300 rounds the throat has moved about 0.02"

I'm expecting the tube to run for about 4000rd overall (conservatively). Barrels are expendable items; at 4000rd of hand loads I will have thrown about $2200 down range. The cost to buy a new barrel is a small portion of the cost of shooting that many rounds.

If you're shooting factory ammo you're talking about a $5000 expenditure for 4000rd of fun.

 

[claudesapp]

Re: Factors in barrel life

Pretty interesting article at accurate shooter. I calculated 7mm-08 and it came in at 868, just before the Dasher

 

[dbooksta]

Re: Factors in barrel life

I don't understand the "Overbore" argument: Is this essentially saying that the propellant gasses are a dominant source of erosion, and a barrel can basically only take so much gas volume over its life? So, for example, if a .30" bore can take 4000 shots powered by 40gr then if you're instead putting 80gr behind each shot then expect half that barrel life?

I would have thought chamber pressure would be a more significant factor, but I guess the bore doesn't see chamber pressure, but rather the pressure and heat that makes it through the case neck, which is what Overbore gets at.

But is muzzle velocity not a significant factor? E.g., shooting 110gr bullets through the .30" bore (over similar powder/pressure loads) instead of 220gr doesn't make a big difference in barrel life?

 

[turbo54]

Re: Factors in barrel life

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dbooksta</div><div class="ubbcode-body">I don't understand the "Overbore" argument: Is this essentially saying that the propellant gasses are a dominant source of erosion, and a barrel can basically only take so much gas volume over its life? So, for example, if a .30" bore can take 4000 shots powered by 40gr then if you're instead putting 80gr behind each shot then expect half that barrel life?

I would have thought chamber pressure would be a more significant factor, but I guess the bore doesn't see chamber pressure, but rather the pressure and heat that makes it through the case neck, which is what Overbore gets at.

But is muzzle velocity not a significant factor? E.g., shooting 110gr bullets through the .30" bore (over similar powder/pressure loads) instead of 220gr doesn't make a big difference in barrel life? </div></div>

Yes, the key factor is how much hot high pressure gas your stuffing through what size hole.

No, doubling powder charge with the same bore size and bullet weight isn't going to cut barrel life in half. It will probably hurt barrel life much worse. I don't believe this to be a simple linear relationship. It is probably logarithmic or exponential.

Doubling velocity with the same bullet is going to take WAY more than double the powder, so barrel life is going to WAY less than half.

Chamber pressure is *relatively* constant across all high powered rifle chamberings - about 55ksi.

Muzzle velocity is a factor, but I think it is pretty much already "automatically" factored in by powder charge and bore diameter.

 

[Brutas]

Re: Factors in barrel life

Barrel wear is a combination of many things. Its like stacking tolerances, all of them play a factor. Pressure levels, capacity to bore ratio, powder type, bullet weight, bullet type, velocity, twist rate, chamber design and dimensions, seating depth, rate of fire, rounds between cleaning, amount of cleaning, cleaning chemicals, etc...

Add all of that on top of the steel used in each specific barrel and how it was made...

Guesses as to barrel life

.308 Win around 5000
6.5 Creedmoor 3000-4000
.300 Win Mag and 338 Lapua 1500 - 2000.

YMMV

 

[bohem]

Re: Factors in barrel life

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Chamber pressure is *relatively* constant across all high powered rifle chamberings - about 55ksi.</div></div>

For reasonable reloading and factory practices you're right. I bring this up to clarify my statement as a caution to guys who reload HOT:

My comment was in regards to guys who routinely run pressures up in little cases trying to get the capability of bigger cases for whatever reason.

I've seen a guy roast a 6.5x47 tube in 2200rd because he shot every round with a supremely hot load, the est. pressure on the load was 72ksi and he was getting the same kind of speed that a 260 does at 58ksi...

The brass was barely surviving 3 reloads, and only doing so because of the small primer pocket design.