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Old 07-13-2020, 09:10 PM
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Chamber Throat Erosion.... Powder choices...



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Ok, Here's my question, in regard to throat erosion, is it better to use a slower burning powder versus a faster burning powder to achieve the same velocity. I know that my barrel on my target rifle is on the way out, I can see the alligator cracking in the area in front of the chamber and, whereas it used to shoot 1/2" groups at 200yds, it now shoots about 2" at 200yds. I have another barrel ordered, and will likely change my load, knock it down a couple hundred fps, down to the next node.
I've been using a slower burning powder to, I thought, hold off the throat erosion, by virtue of potentially lower temperatures in the initial phases and a slower build of pressure to reduce the "cutting torch"effect.
I wonder, now, whether a faster burning powder would achieve the pressure sooner and more in the chamber and less in the throat.
OR, is the difference going to be so negligible because I'm lowering the pressure and temp with a lower velocity load in the first place that I needn't worry about it??

DPSTX
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Old 07-14-2020, 01:02 AM
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What caliber? The BR shooters I know go through 3 barrels every summer. All you have to do is have that one cut back at the breech, and a reamer run back in to catch all new sharp rifling. No matter, if you get a new barrel, shoot what it shoots the best. You have to ask yourself, do you want the best accuracy, or a load to help the barrel last longer? I go for accuracy over everything else, every time.
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Old 07-14-2020, 10:21 AM
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Double base powders (with nitroglycerin) burn hotter. So use single base if you want maximum barrel life. Quick load has data on most powders that should help also.

The other best way to maXimize barrel life is to use the powder efficiently and shoot the minimum velocity that provides the desired results. Stay with powder/cartridge combinations that have good efficiency, using an excessively fast powder could give poor results all around and gain nothing on barrel life. If the desired result is low agg then it’s probably all of the N133 your PPC can handle. For the rest of us there is some happy medium. Too soft of a load and the cartridge won’t be full and may have poor ignition in the cold.

Does that help?

David

Last edited by dgeesaman; 07-14-2020 at 10:27 AM.
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Old 07-14-2020, 10:44 AM
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Slowest powder with the big slow bullets will help but it's less than you think. My other addiction to rimfires is barrel burning hotrods, while awesome you pay to play and barrels are like tires on a drag car.

I've burnt barrels out in 700 rounds with relatively light for caliber bullets and powders on the faster side of things, same cartridge can go 1000 with slower powder and heavy for caliber bullets. Bore jumps make a big difference, a 7 rum that smokes barrels in under 1k rounds with moderate loads can last 15-1800 As a 300 rum.

As far as bumping shoulders that was really popular with benchrest shooters especially those that own their own Machining as you could stretch another 500 rounds out of some of the moderate cartridges they used. With the cost of Labor going up, you see less and less of that. And with some of the hot rods we have nowadays from the factory the fire cracking is usually so severe you don't have enough of a tennon to bump it enough.

Honestly with modern actions being able to take prefit without a barrel nut it's the golden age for Barrel burners. Shooting hot rods 10 years ago when barrels took a year or more to come in was painful. I know a lot of places have 3-month turnarounds it's a good day to shoot over bore cartridges.
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Old 07-14-2020, 10:50 AM
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I know during an interview, that john krieger of kreiger barrels, stated that a heavier bullet in a rifle barrel, eats the chamber more than the lighter bullet, due to the heavier bullet needing more time to overcome iniertia.
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Old 07-14-2020, 12:02 PM
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Quote:
Originally Posted by Flintlock28 View Post
I know during an interview, that john krieger of kreiger barrels, stated that a heavier bullet in a rifle barrel, eats the chamber more than the lighter bullet, due to the heavier bullet needing more time to overcome iniertia.
That sounds plausible, my guess is that's true in more standard weight for caliber choices. Say a 190 308 vs a 150, wonder if it's true for the extreme heavy for caliber. Having smoked 223 wssm as well as 7 rums with both light for caliber 40 and 120g bullets and having also burnt them up with 80s and 175-180 class bulltlets respectively. The light for caliber definitely had the shorter life. Granted both had extreme velocities, 40 grainers in a wssm are in the low 4s starting load and take a barrel out fast....

When going from 120 b tips to 175 accubond lrs I went from retumbo to 869. The first Barrel didn't last nearly as long as this current one is lasting. Next barrels going to get used with ballistic tips cuz they're way more fun.... and barrels are cheap nowadays.
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Old 07-16-2020, 10:01 PM
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Thanks, gentlemen, for the answers. It's a 243, I shoot about 250 rounds a year in this barrel and it's 6 or 7 years old. 46.5gr of h4831sc. 95gr Berger VLD, barely seated in the case (about a .1"depth of the shank in the case, 2.910 oal.) velocity is 3133 out of a 27.5" barrel. Lapua brass. Quickload confirms all the data and the load was developed with its' help. If I can get the next node to shoot well a couple hundred fps less, then that's my plan. I may switch to H4350, but I'm not sure about that, after all, I still have 5 or 6 pounds of the 4831. I plan on having this barrel turned down and shortened on the breech end and put it on another rifle, cause I think once the chamber/leade is squared away, it'll still shoot fine. The chamber it currently has was cut with a really long leade, and even with the bullet seated out so far it still had quite a jump. It would shoot .5" groups at 200yds, though, with a scope on it... but it won't do it anymore. The next barrel won't have such a long leade, the long leade is the reason the bullets were seated out so far...
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Old 07-16-2020, 10:13 PM
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well the 243 is hard on the throat, most surmise because of the short neck. I've not shot a 243 enough to burn out a barrel, but my varmint hunting partner shoots a 243 ai enough to buy barrels in bulk.... He is a bit north of the pressure curve and usually starts thinking about a new tube at 1800. Keep in mind these are brutal firing strings so not what normal people do...

That barrel would provide ample opportunity for a setback.... probably a couple times if you keep an eye on it. Doubtful the difference in 4831 and 4350 would be enough to change barrel life.
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Old 07-17-2020, 07:35 AM
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Originally Posted by DPSTX View Post
Thanks, gentlemen, for the answers. It's a 243, I shoot about 250 rounds a year in this barrel and it's 6 or 7 years old.
I usually play around with .222 Remington and .223 loads, which are much milder and which are by reputation easier on a barrel, but unless that .243 load you stated is super-hot, or unless you are shooting those 250 rounds rapidly enough to heat up the barrel past bath-temperature, I'd be surprised if even a .243 barrel wouldn't last you at least 15 years of good shooting at that rate. Then again, it doesn't take much to surprise me.

You mentioned that your accuracy has dropped off. . . have you had a borescope down the barrel to see whether copper fouling is the problem?

In my own case, I am limited to 100-200 yards shooting so I have never needed a super-fast load. I look for the slowest accuracy node when I am doing load development. As long as the bullets are going into a tiny circle, I'm happy.
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Old 07-17-2020, 11:28 AM
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Thanks, gentlemen, for the answers. It's a 243, I shoot about 250 rounds a year in this barrel and it's 6 or 7 years old.
From what I've heard, that's a normal "accurate" barrel life. 243 is a barrel burner compared to 308. Not as bad as a 6-284 or 22-250, but I've heard 1200-1500 rounds is what others report for 243.

I'm a big 6BR / 6BRA fan. It does the same ballistically as 243 with 10gr less powder. It doesn't directly translate to longer barrel life, but it has to help and recoil is lower. I have a Sako AII in 243 that I bought without much inspection, and it turned out the barrel was pretty well cooked. I'm definitely going to rebarrel it with my 6BRA reamer.

David
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