Throat erosion over time in a 47L

[Larryh128]

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.

Readers 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.

That is exactly why I have always stated that the CNC "screw machine" all copper bullets are going to be more exact for size and weight in a lot. The big issue with them is and always will be, added cost per shot.

 

[avidflyer]

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 have seen lot to lot Bergers that are over 30k. Couldn't believe the difference in the latest lot....called Berger was told to rework load with new lot.....

 

[Down South]

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.

.015 in 100 rounds!.......

My FTR guns (.308s) tend to move about .001 every 100-150 rounds using Varget or H4895.

 

[Pigdog]

bart this is what kevin thomas wrote in an older thread not trying to stir the pot but what he says here and in other threads is not what you are saying. thoughts?

Davery25,

The answer here is yes, heavy bullets do wash out barrels faster than lighter ones, all else being equal. A complex equation going on here, but having shot out scores of barrels over the years, its been my observation that in any caliber, in any chambering, the use of heavy bullets is harder on barrels and gives shorter accuracy life than does a lighter bullet. In the example you're talking about here, a 55 vs a 45 grain bullet, I think the difference would be hard to discern. A comparison between the 50-55 against the 77 to 80 grain bullets is the sort of difference I'm referring to here.

Frank mentioned our conversation from a time back, but he's a bit off on what I said about friction. I think that has little (if anything) to do with this phenomenon. I suspect it has everything to do with dwell time, i.e., how long the bullet spends getting off the throat/leade upon firing. Basically, the longer, heavier bullets have more inertia, and it takes more to get them moving down the bore. This translates to a slightly longer time that all that hot gas is in the throat area, all the while doing its inevitable damage to the throat. Sectioning a shot out barrel, or even looking at one through a borsecope shows this quite plainly. The area ahead of the throat is very badly cracked and eroded, while from this point forward the barrel will look virtually untouched.

The flip side to this is that the heavier bullets offer better performance at distance, and hence are the logical choice for such applications. No such thing as a free lunch, and when you need the performance, you have to match the bullet/load to that application. Don't get attached to your barrel; they're strictly a replacement part, temporarily attached to your action. They're expendable, and the only way to not wear them out is to not use them.

Kevin Thomas
Lapua USA

thread http://forum.accurateshooter.com/th...ing-heavy-bullets-reduce-barrel-life.3755009/

 

[Pigdog]

Using the heat index table for powders varget=4050, H4350=3760. If you run the barrel life calculator at max 63kPSI for the 6.5x47l and putting in a general max load for varget of 37.7g and a max load of 42g H4350 for 123 scenars. This gives 1953 rounds of life with varget vs 2281 rounds with H4350. 328 rounds or roughly 15% better barrel life using H4350 than varget.

 

[Flouncer]

Using the heat index table for powders varget=4050, H4350=3760. If you run the barrel life calculator at max 63kPSI for the 6.5x47l and putting in a general max load for varget of 37.7g and a max load of 42g H4350 for 123 scenars. This gives 1953 rounds of life with varget vs 2281 rounds with H4350. 328 rounds or roughly 15% better barrel life using H4350 than varget.

Mr Dog, can you run the same calc using RL-17 ? As it was mentioned as a barrel eater, it would be interesting to see the comparsion to these similar (in burn rate and application) powders. - thanks !! RL-17 is my powder for the 8x57mm loads . . . .. . .

 

[Pigdog]

Sure mate if you are referring to the OP load of 37g of reloader 17 heat potential 3990 assuming this is a max load 63kpsi iam not familiar with reloader powders so not sure this is max but we will assume it is. This gives a barrel life prediction of 2184 rounds so in between varget and H4350

 

[FeMan]

I just measured my throat yesterday on my 6.5x47 comp rifle and it moved 6 thousandths in the first 1,100 rounds. I shoot 140 hybrids with H4350 at 2845. I shoot PRS so it was mostly 10 shot strings in under 2-minutes.

As far as life goes, my buddies last 6.5x47l barrel was retired at 4,500 rounds of the same kind of shooting and still shot well under 1/4 moa.

 

[reubenski]

I just measured my throat yesterday on my 6.5x47 comp rifle and it moved 6 thousandths in the first 1,100 rounds. I shoot 140 hybrids with H4350 at 2845. I shoot PRS so it was mostly 10 shot strings in under 2-minutes.

As far as life goes, my buddies last 6.5x47l barrel was retired at 4,500 rounds of the same kind of shooting and still shot well under 1/4 moa.

This is exactly what I am baffled about. I completely accept that a barrel is an expendable item. I was assuming that I would get 2000 - 2500rds out of it but at this rate of erosion I'm not even close. I have shot one F class match with the rifle and rest have been PRS matches. Barreled February 2017 and stopped shooting 130 Berger's well at 850rds in May. About 6 matches.

The 142 SMK's seat well in the case but haven't shot well. The 130 JLK's are only mediocre at best. I have shelved the rifle to get a new Dasher up and running and will likely have the barrel set back with a shorter freebore.

 

[reubenski]

I received a lot of good feedback by PM, thanks fellas. Going to run 'er till she blows and replace with a Krieger....