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Barrel life and loaded hot rounds

littlepod

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  • Oct 16, 2012
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    Last year I purchased some of this ammo - http://www.outbackammo.com.au/308-win-168gr-sierra-hpbt-matchking/ ADI Brass, 168gr SMK's. It's loaded hot apparently, like 2795 fps compared to the standard 2650 from FGMM. I got it during their big buy 1 get 1 free clearance, so I have a lot of it.

    I read here about people running hot rounds and it doing damage to their barrels, just put together a new Terminus Zeus w/ 308 Proof Competition 1:10T barrel and didn't want to wreck my barrel. New to all of this, but would like to keep my shit lasting. Is this going to dramatically cut my 308 barrel life like from the standard 6-8K rounds down to 3-4?
     
    Really it comes down to how much powder and what pressure the rounds are running at, both are actually unknown. We might guess that FGMM and other rounds might be loaded to 308/7.62 service pressures for auto loaders, and maybe the hotter rounds might be loaded to Maximum Average Pressure. What test barrel did they use? Are they "enhancing" the box velocity numbers to sell products? Have YOU tried chronoing a few rounds yourself to confirm they are hot?

    The more simple overall answer is, pressure is very important. Throat erosion is fire cracking of the steel, which is heat and pressure, moar pressure means more erosion. And it isn't some simple linear issue, going from 20,000 PSI to 40,000 PSI isn't double as harsh on the barrel steel, it is far worse than double. Some people may scoff at the difference between 55,000 PSI and 65,000 PSI, but in truth the differences add up pretty quickly. It ain't velocity killing these long range magnum or overbore cartridge barrels, its the big boi powder loads for bore size and pushing the thing to that 65,000 PSI general MAP ceiling. That performance you are getting ain't free.

    So, the last part of the question is the toughest. What is your threshold for acceptable accuracy? If we aren't talking about 4 MOA military acceptability, you set your own standard, so it is really up to you when the barrel is done. One man's limit is 3-4k rounds even if most of us would keep going till 8-9k rounds with a particular rifle for a particular purpose. Then remember, that each barrel will have its own nature and might wear quicker or slower.

    To cap off this over explanation for a public forum, if these Aussie rounds are as hot as you think, don't be surprised if it drops the premo accuracy life down to ~4,000 rounds. Every bit you keep pushing into that ultra high pressure, you keep accelerating that wear greatly. Then again, 308 enjoys a reasonable powder charge, even in hot loads, for the barrel size, meaning you might still get to eek out plenty of barrel life.

    Go shoot your barrel out and give us a detailed report!
     
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    Thanks @Duckford for the detailed answer. I haven't chrono'd this on my new custom action, but out of my Tikka T3X CTR it was shooting at 2700FPS out of a 20" barrel. FGMM was only shooting at 2580. I am guessing out of a 24" it'll be faster.

    I'm new to all of this, so I'm just learning. I'll probably just shoot this as is, but if I'm going to be shooting for many years I'll run less hot loads

    @Steel head this is my first custom gun, put a lot of money into it just want to take care of it where I can. It'll get a lot of use, but if just swapping ammo out can have a big influence then great. Only cost me 60c per round on these due to the July 4th buy 1 get 1 free sale. Can easily sell this and just load some new rounds. If it's just reducing life from 8000 to 5000 or so then that isn't so bad. If it was 8000 to like 2000, then I'd feel very wasteful.
     
    It’s not going from 8000 to 2000.
    Probably a combination of a bit more pressure and a efficient powder like we’re seeing available for reloading, you probably won’t even notice any extras wear.
    I personally feel your fretting over nothing.
     
    My .308 has a 24” Rock 5R barrel (1:10) & I shoot FGMM 175s though it. W/ a can I’m showing 2703 MV & it shoots really well w/ no complaints. I’d say shoot it & don’t look back. As they say, barrels are tires. I’d take @Duckford advice; shoot til your barrel til it’s toast & post a thread w/ results.
     
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    If you decide to change ammo let me know. I was thinking about buying a bunch of that stuff as bulk play ammo.
     
    If you decide to change ammo let me know. I was thinking about buying a bunch of that stuff as bulk play ammo.

    It actually shoots quite well. I sold off my FGMM because I was getting tighter groups with it. Behind the Chrono on my 20" I was getting single digit SD's ~ 8. Out of the fresh new proof Straight Jacket barrel - 2 to see where the scope was dialed, then 5 in the center. 1/2" group at 104 yards.

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    My .308 has a 24” Rock 5R barrel (1:10) & I shoot FGMM 175s though it. W/ a can I’m showing 2703 MV & it shoots really well w/ no complaints. I’d say shoot it & don’t look back. As they say, barrels are tires. I’d take @Duckford advice; shoot til your barrel til it’s toast & post a thread w/ results.

    As true as barrel changing being part of high power rifle shooting is, I'll be devil's advocate in a way. Barrel life can be very important in some ways to some people, in example:

    - people on budgets of time and money who can't shoot much. Some folks can't justify the time and/or money to do more than 500 rounds of accurate high power rifle per yer, let's say. Johnny Shootsum has a mortgage and a wife who wants him to spend more time with her, kids got new braces what ever other expenses come up. If he can crawl out to the range and do his half a thousand per year with the time and money he has, a 8,000 round barre life will last him a long time. By the time he wears through his first barrel, the mortgage is paid, the kids have gone off to school, and now he has the cash and time to burn through a second much faster.

    In this vein, for hunters and others who only shoot, say, 100-200 rounds per year, an 8,000 round rifle barrel is a lifetime barrel. A super overbore super magnum high pressure barrel burner can sometimes be the kind of barrel that even some part time, less serious shooters might find the round count and time to burn through. In some cases, a 308 with service ammunition might be a multi generational barrel for some hunting families, whereas some of the worst cartridges might be going goofball by the time the original owner goes.

    - people on a budget in general, especially cheapos like me. I can push to keep cheap, but decent, handload 308 service pressure match rounds to 50 cents a piece. Thick wall NATO brass and lower powder charges of more moderate loads may not always yield the best long range velocity/trajectory, but they save a lot of money, and they give the barrel as much life as possible. $4,000 and I'll try my damndest to get 8,000 rounds downrange, and just reaching the point of replacing an expensive barrel; someone buying hot factory rounds for overbore cartridges might be replacing a barrel in the same amount of cash, but at half or less of the rounds down range.

    For me, 16,000 rounds could mean two barrel changes and a fresh new one, and closer to $8,000 in components. For some of the worst overbore, 16,000 rounds might mean four barrel changes, all cost money, and what kind of cost in ammunition? For the cheapo shooter, a man might get many more rounds down range for the same exact budget. This shouldn't determine what you shoot, but it ain't exactly nothing, either.

    - for a far flung hypothetical fun argument, "The Big One", wither it be Mad Max, WW 3, Bugaloo, ect. If you expect your rifle for militia duty, the essence of the 2nd Amendment, where might you be in an emergency? If you have a 3-4k round barrel burner, and you shoot a lot, could you theoretically end up with your DMR or sniper rifle sitting with an almost burned out barrel when the Chinese paratroopers land the next town over? 4k rounds on a high use rifle with a very long barrel life means you still have a lot of life left, while short barrel lives means the highly active shooter is always running a barrel close to that rebarelling. A rather ridiculous argument, but I'd figure I'd just throw it out there for the hell of it.

    Serious, high round count shooters who put the money and effort in don't mind "changing the tires". The more serious, the more they treat them like how racers treat tires, run them hard and swap them out. For those without the means or the passion, those hard road tires have some appeal.
     
    Once you start shooting enough you'll realize barrels are a consumable. Get the load you want, and just focus on taking care of the barrel if it's a hot round. People say copper is tough, but the real culprit of hurting a barrel is excessive carbon build up.
     
    My concern would be acceptable accuracy. find what shoots well and use it. If its a barrel burner, that will hurt, but afterall, hitting the target is the issue. Everything else is really secondary. We purchase rifles to shoot. If they wear out, we wore them out.

    That said, I have a tendency to shoot light to medium loads, If They do the Job. If I can’t find a load that will work, stout or light or somewhere in the middle, I’ll find a rifle that I can get to work, get the job done for which I purchased it to do. Heck, were not married to them, they’re tools

    So, to answer the question. Nice rifles are nice. But if the loads you purchased are working, doing the job in the rifle you purchased them for, use em. As a previous poster said, barrels are like tires. They are going to wear.
     
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    rate of fire is also important, and heat can build up quickly and add to the equation for wear rate. maybe this isn't as much of a factor on a bolt gun.