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View Full Version : 6.5x284-throat erosion per 100 rounds?



Kevin_Duckworth
01-07-2008, 04:11 AM
Yes I know everyone's mileage will vary, but could some kind person give me the benefit of their experience of the throat movement per 100 rounds with a 6.5x284. I'm guessing 3-5 thou?

Kevin

marion packett
01-07-2008, 11:23 AM
.003 has been my expereience.

Steve Shelp
01-08-2008, 01:11 AM
Kevin,
I shoot 6.5x55 Ackley a lot so the barrel erosion should be similar to a 6.5x284. I do shoot a little less powder so it is worth something in the "less barrel wear" department. But in practical terms it probably is not a measurable difference. Also note that erosion isn't linear. It normally starts out quick, then slows down as the throat burns out. These are real numbers from my records of my BR guns. 98% of the rds fired I used H4831 long and short using 140gr class bullets around the 2900-2950 fps mark with 50.X grs of powder.

(2) Lilja 9" twist LG barrels (5 shot strings)
----------------------------------------------------------------------
.020" for the first 500 rds
.011" for the next 300 rds
.003" for the next 450 rds

.039" average erosion of 2 barrels after retiring them around the 1400-1500 rd mark. All barrels were still shooting at this point, but I always went ahead and rebarreled to be ready for a full season with a fresh barrel. No train wrecks in the middle of the season that way.... as the story goes anyway.

So if I take 1450 (halway of 1400-1500 retired rds) and figure out the erosion per 100 rds equal .00268" for 5 shot strings.


(1) Lilja 8" twist 3 groove HG barrel (10 shot strings)
---------------------------------------------------
.009" after 249 rds
.027" after 674 rds
.034" after 900 rds


pulled this barrel off and haven't fired it since. It's still good. Using the 900rds for now this equates to .00378" erosion per 100rds for 10 shot HG strings.

So I would say that Marion's .003"/100rds of erosion is a pretty good number to go by.

Steve

dmoran65
01-08-2008, 07:33 AM
Steve --

Glad you put up your advancement (erosion) data. I took extra notice how your barrels wore faster at the get go, and then slow down as you go along. From a smaller caliber (6BR Improved) that I have kept track of advancement to my barrels, the first 300 to 500 rounds have been the hardest on the barrels also.

1.) - 6mm/.243 - Shilen - 28" HV / 8-twist / 4-grooves
--------------------------------------------------------------
- at 353 rounds = .009"
- at 534 rounds = .014" (.0026" per hundred average)
- at 922 rounds = .019"
- at 1319 rounds = .021"
- at 1844 rounds = .030" (.0016" per hundred average)
- at 2236 rounds = .037"
- at 2574 rounds = .043"
- at 2848 rounds = .049"
- at 3116 rounds = .056" (.0018" per hundred average)


2.) - 6mm/.243 - Shilen - 28" HV / 8-twist / 4-grooves
--------------------------------------------------------------
- at 352 rounds = .007" (.002" per hundred average)
- at 1226 rounds = .018"
- at 1860 rounds = .028" (.0015" per hundred average)


3.) 6mm/.243 - Bartlien - 31" / 7.75-twist / 4-grooves
--------------------------------------------------------------
- at 346 rounds = .006"
- at 1020 rounds = .015"


4.) 6mm/.243 - Brux - 31" / 7.8-twist / 4-grooves
--------------------------------------------------------------
- at 358 rounds = .005"


The 1st Shilen started out advancing quite fast, before settling in. It also copper fouled for the first 80 rounds of it's life. The last 500 rounds down it has seen a higher rate of advancement and accuracy is getting inconsistent.

The 2nd Shilen broke in good with minimal copper fouling after 15 to 25 rounds. This barrel seemed to lost accuracy at around 1500 rounds. It had a fairly short throat so I used a throating reamer an extended the throat .030" and cut a new crown on it at the 1860 round count. Not sure which was the fix, but it now shoots good again. It will be interesting how the erosion proceeds now. But haven't hardly shot it since doing the extra work to it.

Both the Brux and the Bartlien broke in exceptionally and I felt they broke in after just a few shots down each.

Thanks for putting your barrel advancement out here!!


Happy Shooting
Donovan Moran

Steve Shelp
01-08-2008, 05:49 PM
Donovan,
Your numbers look to be right in line with normal wear pattern. My numbers show me that all barrels regardles of caliber move quickly in the beginning then slow down.
I don't have the numbers in front of me right now, but my 338 barrel only wore a total of .026" or .027" for 1657 ?? rds. That is shooting 95gr of stick powder w/ a 300gr bullet. That larger bore makes a difference.

Keep'um small!

Steve

PPP MMM
01-08-2008, 06:18 PM
are interesting. Has anybody have a theory why this pattern occurs?

Shoot well
Peter

dmoran65
01-08-2008, 06:54 PM
Steve --

That is interesting on your .338.... but like you said, the larger bore makes a difference!!!
I posted my advancement data since you were good enough to share yours. No doubt there is different ways in which we each measure advancement, but my the numbers, the end results are similar!!!


PPP MMM --

I look at as a "work hardening" effect. And those sharp fresh reamer cuts give up faster then when they get rounded down.


Happy Shooting
Donovan Moran

tim in tx
01-09-2008, 01:41 AM
i shoot 6.5-284 shehane with h4831 in a lawton presently and so far i am looking at 275rds .013,500 rds .015,1000rds .021 from the original fresh cut depth. hope this helps sir tim in tx

PPP MMM
01-09-2008, 02:58 PM
Steve --

That is interesting on your .338.... but like you said, the larger bore makes a difference!!!
I posted my advancement data since you were good enough to share yours. No doubt there is different ways in which we each measure advancement, but my the numbers, the end results are similar!!!


PPP MMM --

I look at as a "work hardening" effect. And those sharp fresh reamer cuts give up faster then when they get rounded down.


Happy Shooting
Donovan Moran

,,,,,,,,,,,,but someone may find it interesting. When I was serving in the army as an armourer I had the opportunity to mill several discarded machinegun barrels. according to the books these barrels had somewhere between 3500 and 5000 rounds of rapid fire through them. Now the interesting part.... The cartridge was 7.62mm x 54R loaded to 3350Atm. which coresponds close to 48 000 psi. The case has .350" long neck. The provided specifications were 150gr/ 2880. a very mild load. The erosion of the the area that once was the throat was totally burned out to the length of the cartridge main body ( some 40mm +) and at the widest spot which happen to be about about between 6-9mm from the end of the neck was more than 10mm in diameter. The widest area had big deep cracks resembling a dry mud on the bottom a lake. The grooves were gone for some 55mm from the neck down, which means some 2.2"+ of a freebore. The barrels were replaced only because the machinegun would stop cycling most likely to the drop of pressure. The shape of the burned area was resembling the shape of a candle flame. Steel was not stainless and the cadency was 650/minute and believe me everybody who would get the hands on the gun would try to burst the bastard. In the dusk the barrels would glow. I personally would be incline to believe that it is more the heat(3000+Celsius) and the sandblasting effect of the gunpewder that would cause the most damage as in this case the bullet would jump some 2-2.5" without touching anything. The flame heat and the speed of the unburned gunpowder squeezing around the bullet would. Just my 2c.

Shoot well
Peter

Big Al
01-09-2008, 04:11 PM
Things are sure different in today's action Army. In the bad old days when I was under the direct command of General Washington :D . All the machine gun barrels in the M-60 and the M-134 had stellite liners. I have seen barrels with untold thousands of rounds from the M-134 with perhaps a million or more rounds never show any throat erosion. The cyclic rate of fire for the six barrels was the two rates of fire @ 2,400 and 6,000 per minute. Divided by 6 to get the shots per barrel. Yes they had six seconds burst limits. An average day with a full combat load you would do 6 to 8 loads of 9,500 loads per cycle. You do the math.

The M-60 barrels were the same, not one indication of throat erosion. The M-60 barrels would start having head space problems due to ware in the locking lug recess do to bolt camming, and would be scrapped when you had a case head separation. The cyclic rate of fire for the M-60 was then 600 rounds per minute. The M-60 I maintained were free style guns used by the crews of Charlie model gunships. Ore burst times would be the length of time for a rocket run or a mini-gun run @ from 120 to 140 knots an hour in a combat dive. A combat load of ammo was a re-pact can of mini-gun ammo (which was 1,500 rounds) with the repack, would bring the load up to 2,200 rounds per can. Always had one spare repack can on board to share between the gunner and crew chief (insurance can). Again you do the math.

I still have in my tool box the throat erosion gage that I used in my two tours of duty in Vietnam for the 7.62 NATO and the gage for the 5.56 NATO.

With the 7.62 I never found a barrel from combat or from the aerial gunner school in Ga. that showed any erosion.

I did find a great many rifles (M-16's) with throat erosion and scrapped a lot of the barrels. That was at the ordnance center in Hawaii. the principle cause for the loss due to erosion in the chrome lined barrels was found to be other than what you would expect. It was, in most cases do in large part to Mom and Pop America sending cleaning kits to their kids that contained aluminum cleaning rods.

It was always fun to watch the shipments come in to us at Schofield Barracks. They came in 40 foot open trailers with slat sides. They pulled them out of the cargo hold of ships using huge electromagnets. When they came into the yard that's how they would take them off with a crane and magnet and drop them in heaps.

Yes, thinking back on it, it was the "Bad Old Days". :eek:

PPP MMM
01-10-2008, 02:03 PM
I enjoyed your interesting experience and you answered my question which I always had. How long the sixes must last? The throat weare in your case is amazing.It's from one extreme to the other. It looks like the US army put far more thought to the material used in their machine guns than our army did.

Shoot well
Peter

Big Al
01-10-2008, 02:31 PM
Back in the "Bad Old Days" We the guys in the armours shack got to wondering how accurat the M-60 barrels with the liners really were? We took a brand new arsenal barrel and after a lot of machining got it fitted up to a 98 Mauser action and shot ball issue ammo. Shocker to all of us, the darn thing was past decent, it shot vary well. No it would not have turned the Br for score boy's heads. Considering the equipment we had to do the work and the rest of the materials on hand (this was 1970's), It was a surprise!

PPP MMM
01-11-2008, 12:55 PM
I have no idea what this barrel is from but it's from a US publication so one could assume it comes from a US made machinegun. Someone smart with a military experience should be able to identifie it, I hope so anyway. The claim here is that the barrel done 3000 rounds. This is something what our barrels looked like too. Another 2000 rounds through this one and it will look like those I was describing earlier.

Shoot well
Peter