Throat erosion over time in a 47L

[reubenski]

I have 820rds of 6.5x47L on a very nice Bartlein barrel. It is my competition rifle and shoots great. About 200rds we're using 37'ish grs of RL17 pushing a 130 HYB at 2880. The rest have all been 36.7gr of Varget pushing the 130 HYB at 2830 - 2850.

At 500rds I got wise that my throat had eroded .035" and I needed to chase the lands. Well 320 rds later came pretty fast, about 5 weeks later and after shooting poor at a match and printing some piss poor groups I remeasured my seating depth with JLK's and Hybrids. Now my throat has eroded about .060" since new.

I am curious what other's are seeing if they kept record of details. .060 per 800rds seems like a lot. At this rate I will be at .180 by 2500rds. In fact I probably won't even make it that far before I exceed mag length or run out of neck.

 

[FeMan]

In my experience I think it is the barrel and not the round. I have had some barrel brands that have eroded quickly and others have not. I have over 1000 rounds on my 6.5x47l Krieger and haven't had to change seating depth yet. My Bartlein 284 throat moves like you describe above.

 

[Northridge]

Ive witnessed what you are experiencing from all major manufactures fast and slow erosion, to say it is normal throat erosion would be harsh. typical erosion beyond initial brake in is along the lines of .002ths to .003ths per 100 shots in most cartridges even larger ones but at times we get those fast movers and they typically are very good shooting barrels when you stay up on optimum seating depth. the really slow moving ones are the ones to be cautious about, even though your not measuring erosion, the front of lead to land face relationship is changing I promise you. bummer it is traveling so fast though.

Shawn Williams

 

[Alex Wheeler]

Ya, that is fast. Rl17 is hard on barrels as is fast shooting. Keep it clean of carbon, use jb and follow the lands. Its all you can do. My 28 Nosler moved .015" in 100 rounds. Dont think I will be practicing with it much LOL.

 

[Bart B.]

The more over bore powder charges are, the more throats erode down the barrel. Bore capacity; my formula is 1 grain of powder for each square millimeter of the bore cross sectional area. 6.5 squared X .7854 = 33 square millimeters; 33 grains of powder. Barrel life for match grade accuracy is about 3000 rounds for all cartridges whose powder charges are at bore capacity. It's based on best accuracy starting out at 1/4 MOA at 100 yards then opening up to 3/8 MOA. Double the charge and barrel life is 1/4th as much; 750 rounds. 37 grain charges will have about 2400 rounds of best barrel life at match grade level in your 6.5 barrel. My 264 Win Mag lasted 640 rounds after burning 72 grains of powder each shot going from sub MOA at 600 yards in a match to about 4 MOA over four shots. Its throat had eroded near 1/10th inch.

Hunting barrels have about twice the barrel lives; service rifles for combat, 3 to 4 times. Their accuracy standards are less stringent.

It works on the old math inverse square laws.

Most barrels start visibly degrading in accuracy after about .07 to .09 inch of throat erosion down the bore.

My data's based on what Sierra Bullets got in their various caliber match grade test barrels shooting their match bullets for accuracy quality control.

Fast shooting ain't hard on barrels. I've seen no difference in barrel life for 308 Win shooting half their shots 10 times a minute and half once a minute compared to those shooting once a minute.

 

[Pigdog]

bart b what about the weight of the bullet how do you factor that into your barrel wear formula etc. Ive seen it mentioned several times on here by various posters most notably a guy named kevin thomas who i believed worked for lapua and some of the other big bullet makers. He came to the conclusion that shooting heavy for calibre bullets (105-115 for a 6mm, 140's for a 6.5, 180's for a 7mm etc) that throat erosion was considerably increased by using these long bullets. In an old thread i believe it was mentioned up to 1/3 less barrel life shooting the heavy bullets. I believe the theory was these heavy bullets take a lot more to get going and leave more time for the heat to do damage. This is one of the reasons i chose 123 scenars over the 140's desipte the increase in bc for my 6.5x47l. Love to hear your thoughts on this

 

[Bart B.]

what about the weight of the bullet how do you factor that into your barrel wear formula etc.

I don't factor bullet weight in. My experience and that of others with heavier bullets in 24, 26, 28 and 30 caliber barrels used to base my formula on still tracks reality very well. Never heard from anyone it's a factor until now.

The only factor I didn't use that causes a 10% or more spread is the powder's heat index. Hotter powders increase erosion rate for a given bore capacity. Forum member mikecr used my bore capacity rule then factored in Quickload's powder heat indices. He used a little bigger barrel life round count for bore capacity so his formula yields a bit longer barrel life than mine does for the same conditions. Both are best used to show trends, not exact numbers. Just like Quickload. I'll post a table listing them.

Kevin and I have talked about this and he's agreed with my numbers. No mention of bullet length of heavier bullets came up. He learned about this when he worked at Sierra Bullets from their first ballistics test man, Martin Hull. I shot matches with Martin and learned lots from him.

Never saw a difference with 150 - 155 grain ones in 308 Win to 168 - 200 grain ones in same chambered barrels. Comparing 200's from 30 caliber magnums to 155's in 308's, my barrels for both tracked within 10% of calculated life with my formula. It's a rule of thumb, not exact science.

 

[BoydAllen]

Back in the day, a friend who was right in the thick of high power competition told me that they had found that in their magnum prone rifles that some powders were a lot more erosive than others. This would probably have been with a .300 WM and heavy bullets. I asked him which powders caused faster wear and he told me that they were the slow Reloader powders. I forget which one(s). Evidently the better ones were the Hodgdon single base stick powders in the appropriate speed. When you shoot a lot of rounds per year differences in powders' barrel wear characteristics can be a significant issue.

 

[Bart B.]

Here's my powder heat index table:

 

[AckleymanII]

I have noticed that R#17 eats barrels, throat growth in length, dia, and fire cracking in the barrel...6 xc

Hawkeye and Lyman bore scopes to see with, over size reamer pilots to measure throat growth in Dia. on a Grizzley rod.

The extra speed with R#17 comes with a price. I use #17 as a special purpose hunting round powder only, no high volume use for this powder.

 

[Bart B.]

Military throat erosion gauges tapered from about .309" to .299" over their 1.200" long gauging section's middle part. Taper is .010" per inch, .001" per tenth inch of gauge length.

https://www.google.com/search?q=m1+throat+erosion+gauge+picture&client=safari&hl=en-us&prmd=isvn&tbm=isch&tbo=u&source=univ&fir=OAAjV65oRXDxTM%3A%2CSYmFuCBfs0leJM%2C_%3BMeeaP9jqcAcCNM%3A%2Ce8i7SzXQVc2hnM%2C_%3B3MX5s53rYqrbNM%3A%2C7jfer3cJBzJBoM%2C_%3BILFaXRQcQtAtIM%3A%2C9dAMkt_FeghdjM%2C_%3B4Cq3ZlRBKEcqSM%3A%2Cca8BcsIf0T5i_M%2C_%3BOpNkAQKYRAAZCM%3A%2CsAmh6j6TV-h5mM%2C_%3BqvP-6Zf89Sk3zM%3A%2C18jel1g4c7Aj1M%2C_%3BQixSukT_wreX3M%3A%2CQWQsVpkuEyLmPM%2C_%3BuDtJoSaYMlTkVM%3A%2CQWQsVpkuEyLmPM%2C_%3BfYEYCXZ3BmAUnM%3A%2Ci9RrXQzUk_x-oM%2C_%3BgkDOBeOnVp34fM%3A%2CgqBM0dxeJB43MM%2C_%3BWNPTHKPSg0WqWM%3A%2CmwmVsE4B6y-qlM%2C_&usg=__Xv2-6c7S9P3RyqWEFFi8-Gn92Zs=&sa=X&ved=0ahUKEwjwg4LgzM_UAhUG2IMKHWDzAk4Q7AkIOA&biw=1024&bih=671#imgrc=WNPTHKPSg0WqWM:

Put in the chamber whose bore diameter is .3000" diameter at the end of the throat and "0" on the gauge scale aligns with the receiver reference (back of receiver ring on 30-06 M1's, front of left receiver lug on M14's and 7.62 Garands). Scale is marked every .100" numbered '0' to 'REJECT' in odd number increments one inch away. Armorers often used these standards for erosion limits fo replacing barrels bases on these gauge readings:

* 3 To 4 in match grade barrels for top scoring team members, replace the barrel or relegate the rifle to a new shooter not on the team. If in standard service rifles, give it back and keep shooting it. This is at 3000 to 4000 rounds.

* 5 to 6 in match grade barrels for competitive shooters not on the main team, relegate it to regular service then rebarrel. If in standard service rifles, give it back and keep shooting it. This is at 6000 to 7000 rounds

8 to 9, keep shooting it. Happens around 8000 to 9000 rounds.

'REJECT' (same as '10'), rebarrel then use the old one for a tent stake. Barrel has about 10,000 or more rounds through it.

 

[Catgunguy]

Thank you Bart B. for the chart. Very informative.

 

[Pigdog]

Thanks for your thoughts Bart

 

[Drop Port]

I have 820rds of 6.5x47L on a very nice Bartlein barrel. It is my competition rifle and shoots great. About 200rds we're using 37'ish grs of RL17 pushing a 130 HYB at 2880. The rest have all been 36.7gr of Varget pushing the 130 HYB at 2830 - 2850.

At 500rds I got wise that my throat had eroded .035" and I needed to chase the lands. Well 320 rds later came pretty fast, about 5 weeks later and after shooting poor at a match and printing some piss poor groups I remeasured my seating depth with JLK's and Hybrids. Now my throat has eroded about .060" since new.

I am curious what other's are seeing if they kept record of details. .060 per 800rds seems like a lot. At this rate I will be at .180 by 2500rds. In fact I probably won't even make it that far before I exceed mag length or run out of neck.

I find it hit or miss, my 47L Bart has the same round count and not a fraction of what you are seeing. Your load is even lethargic compared to what I'm running. I might have lucked out or you might have bad luck, either way in my experience each barrel often varies. Back around 2009-2010 when Crucible steel file chapter 11 and barrel steel went sideways I had a great barrel that when belly up in 300 rounds.

 

[BoydAllen]

Bart,
Thanks for the chart. Interesting info. I will save it.
Boyd

 

[reubenski]

Thanks for the input fellas. My smith measured four bullets in my chamber and a test chamber he cut in a barrel end today and agreed with my measurements. I reckon it is one of those deals; it is what it is...

We also borescoped it and it has mild fire cracking. One of the problems is that the reamer is one of those freebore that balance 130's and 140's. At this point I think I am just going to switch to JLK's or 142 SMK's.

 

[Drop Port]

Another thing to take into consideration when checking erosion is use the same bullet. I have seen lot to lot dimension vary more than I would have ever thought was considered acceptable by the manufacturer. I take a measurement to the lands when the chamber is cut an use the same bullet to periodically check, it remains in the die box.

 

[savagedasher]

Another thing to take into consideration when checking erosion is use the same bullet. I have seen lot to lot dimension vary more than I would have ever thought was considered acceptable by the manufacturer. I take a measurement to the lands when the chamber is cut an use the same bullet to periodically check, it remains in the die box.

I like t have a dummy chamber cut when I get a new barrel . Larry

 

[reubenski]

I have measure an average of 10 JLK's, 10 Scenars, and 10 Hybrids all from the same lot and box. The Hybrids had a .006" ES from BTO and the JLK's had a .003" ES. The Scenars fell in between the two. When I switched lots on the Bergers the new lot measured .003" (on average) longer than the old lot.


I have read this before about people keeping a bullet to measure. This sounds a little ridiculous to me. People often come up with 3 to 5 thou difference when measuring their throat pending how hard they push the bullet into the lands when measuring. And a lot of those folks claim only .002 growth in 2400rds. Search the forums here. The reports are all over the place; 0 consistency in reporting. If I had .015 to .030 variation in bullets from lot to lot I wouldn't be shooting them, regardless of whether I kept a bullet to measure or not.


I have measured nothing with the bullets I have used that would account for a 30 to 50 thou variation. As I said, my smith measured my chamber, comparing his test chamber using 4 of the same bullets from boxs of 142 SMK's, 130 OTMs, 140 Berger BTLR, and 140 Hybrids. All confirm 50 thou of growth over a fresh cut chamber using the same reamer, within 2 to 3 thou of the each other.

 

[Bart B.]

Ferris Pindell, one of the "P" letters in the 22 PPC and 6mm PPC cartridges, was a tool and die maker at Sierra Bullets. He was one of the best but the bullet pointing dies he made with the mills he ground to shape them have tolerances. They get transferred to the pointing die. A few thousandths extreme spread is normal within a lot. More from lot to lot. That die is the last one used of several on a sheet of copper for jackets coining, cupping, drawing with a few different dies, trimming, boat tailing, coring a precision lead slug and it finally gets used to form the ogive pointing the bullet. Then the lanolin based lube is cleaned off as they're tumbled in wood chips that makes them shiny bright, inspected for flaws and dimension specs to be put in green boxes, if the pass inspection.

Several thousand bullets can be made with each set of dies and cores. Replace on die or batch of cores and a new lot number is assigned. During production runs, ten bullets are grabbed as they fall out of the pointing die then loaded in readied cases to shoot in a rail gun. Results recorded. Then another ten are acquired and shot. Many 10-shot groups of their natch bullets all have to be under an inch in their 200 yard indoor range. And some lots are fractionally better than others

They know each lot of bullets won't have identical ogive shapes and dimensions. Neither does those of any brand. Buy an entire lot of bullets to last the life of your barrel if you must. You might get a discount. Buy several lots, test 'em all then use the best. Save the other lots for your next barrel a few hundred or thousand rounds later.

Sierra used to set aside their best lots of 30 caliber match bullets then sell them at rifle matches. They tested in the twos, at worst, in their hundred yard range with many groups in the ones and zeros. Proof they all stabilized very well by then. They were ugly and greasy as lanolin was still on them and they weren't tumbled shiny and inspected for flaws. But loaded and shot as they were. A few in each plain brown cardboard box of 1000 (hand written type labeled them) would have a flaw such as a dent or jacket fold. 996 good ones in a box was the norm. These "standards" (used for quality control of test barrels) produced the best scores and were used setting most records for years 1960 through the 1980's until Sierra stopped that stuff after moving to Missouri. They tested about 5/8ths to 2/3ds better group sizes through 1000 yards than the shiny ones sold in green boxes at retail that still met their 100 yard 1/4th inch test group average spec.

Reamers used to chamber barrels have tolerances exactly like those "chambering" bullet making bullet forming dies. All lots of jacket copper are not equal. All bullet makers know that. It was not until the late 1980's that some was good enough to consistently make 28 caliber long, heavy bullets that shot as precise as 30 caliber ones. Early 1990's for 26 then 24 caliber ones. Later, 22 caliber ones finally came about.