6.5x47L barrel erosion info

[XTERMINATOR]

Hi guys, I need some help, I have a 6.5x47L that lost 100fps from the last time I tested my drop. It was tested this winter from 200m to 800m, speed was constant at 2825fps, shot a few hundred rounds at 200m this spring and tested my drop twice this summer from 200m to 600m at 2725fps (same batch of bullet and powder) all atmospheric conditions have been taken in account

Round count is at 1300, 95% of them were in 140gr class (varget, H4350, N150) I have about .110" of throat erosion but rifle still shoot 1/3 moa and under. Could this speed lost come from the throat erosion? Should I set back the barrel or just up the load to gain back the speed I lost? Thank's

 

[jlow]

Did your neck tension stay consistent? Reduced neck tension can cause reduced MV.

 

[XTERMINATOR]

Same bushing and brass, nothing changed

 

[coldboreshot]

Depending on the number of reloads on that same brass, even if you still use the same bushing, the brass has gotten softer to the point of not maintaining the same tension. At this point, you may want to look into annealing the brass you have if you have access to it or, find someone who you can get a few pieces of new brass or purchase new brass and try again. I believe you will see the difference between the current brass and the new pre-annealed ones. Many shooters I know anneal their brass after only 3 or 4 reloads because of this very reason. Just my 2 cents.

 

[XTERMINATOR]

Brass is on it's 5th firering and been annealed after the third...

 

[coldboreshot]

Actually now that I double-take, yes, the .110" can have effect on reduction of speed. If you have ability to seat the bullets a little longer to the lands, run some samples and see if you gain any speed increase. Closing the distance of the bullet in the throat could give you a little more pressure which in turn will give you a little more peed.

 

[lee1982]

.001 erosion every 10 shots sounds like there is a problem. 100 fps loss after that few rounds also sounds odd. I wish I had an answer, and I hope someone that does can chime in.

 

[FeMan]

What powder are you shooting? It is posssible to get that much delta if using a temperature sensative powder and comparing hot and cold MV's.

 

[rpierce]

I know Jim See had that same issue with a 6.5x47 barrel in his tactical rig. He had way less than the number of rounds you had through it and his throat eroded as much as yours. Accuracy went to 3/4 moa also. It was a bad lot of steel. He has had a few issues with this manufacturer lately as his new 6.5x47 is only going 2600 fps with 40 gr of h4350, 26" barrel. Hes not the only guy I have heard that's had problems lately with this manufacturer. I don't want to blast a manufacturer on here so I will pm you who made his barrels so you know if its the same that made yours.

 

[XTERMINATOR]

FeMan, I have two pet load that gave me the exact same speed, 41.5gr of H4350 and 38gr of N150 (I shoot moly coated bullets). The 100fps speed lost was confirmed with both load so it's not a powder problem

rpierce, thank's for the info but I dont use a barrel from this manufacturer. I spoke with my gunsmith yesterday and he said that since the barrel stil give good accuracy, not to bother and just increase the load to gain back the speed, I will try it this week end

 

[X-Caveman]

Were these drop tests shot at the same range? Originally you mention 200M & 800M, then later 200M & 600M. The relative elevations of the 600M and 800M targets could throw off your calculations. It sounds like you didn't measure the velocity with a chronograph, but are inputting the come-ups into a ballistics program and playing with the velocity until it matches your trajectory. If so, are you 100% sure you have all of the info correct in the calculator? Has the software/ ballistics library been updated? Finally, is it the same scope? It just seems like a big velocity drop to be solely explained by throat erosion (or any other single factor). It could be a combination of things. I'd exhaust every option before adding powder. 41.5gr is already pretty hot for a 140gr pill.

Regardless, there's no way I'd touch that barrel if it's 1/3rd MOA. One of the beauties of the 6.5x47 is the long neck, so you can chase the lands. I have one with a similar amount of erosion with about 1,900 rounds thru it. I switched to a 140 hybrid, from a 130 VLD and it still shoots bug holes. I'll be sad when that barrel finally goes south.

Good luck and let us know what you find.

 

[XTERMINATOR]

Were these drop tests shot at the same range? Originally you mention 200M & 800M, then later 200M & 600M. The relative elevations of the 600M and 800M targets could throw off your calculations. It sounds like you didn't measure the velocity with a chronograph, but are inputting the come-ups into a ballistics program and playing with the velocity until it matches your trajectory. If so, are you 100% sure you have all of the info correct in the calculator? Has the software/ ballistics library been updated? Finally, is it the same scope? It just seems like a big velocity drop to be solely explained by throat erosion (or any other single factor). It could be a combination of things. I'd exhaust every option before adding powder. 41.5gr is already pretty hot for a 140gr pill.

Regardless, there's no way I'd touch that barrel if it's 1/3rd MOA. One of the beauties of the 6.5x47 is the long neck, so you can chase the lands. I have one with a similar amount of erosion with about 1,900 rounds thru it. I switched to a 140 hybrid, from a 130 VLD and it still shoots bug holes. I'll be sad when that barrel finally goes south.

Good luck and let us know what you find.

No not on the same range but both are at the same altitude and flat ground with no hills that could push the wind up or down

I have a chronograph but it has a 1% margin of error (+- 30fps) so I always prefer to confirm exact speed with my actual drop. When I do my drop test I always check my zero at 200m first, after that I check the drop by 200m increments (200-400-600...) and always check temperature and barometric pressure with my Kestrel. I have used this method for years and it has worked perflectly

At first I also tought that it was a problem with the ballistic program in my Iphone (Ballistic AE) but when I got home I comfirm the data with JBM on the net and got the exact same numbers. Just to give you an idea, this winter at -5c I needed 3.7 MILS to hit 600m now at 25c it takes 3.85 MILS

Did not change any piece of equipment, I have a NF NXS and it tracks perfectly. The problem realy comes from the barrel, most 6.5x47 shooter use the 123-130gr bullets, I have used the 140gr from the begining and I'm wondering if the longer bullet would erode the barrel faster, when you think about it, it's only logic that a bullet that is 20% longer would erode the throat 20% faster...

 

[mikecr]

when you think about it, it's only logic that a bullet that is 20% longer would erode the throat 20% faster...

WRONG
And frankly it sounds like you're merely fishing for validation of YOUR notions.

As mentioned, measure your actual velocities.

 

[dkhunt14]

If you moved the bullets out to chase the throat you gained capacity. I know a guy that throated a 300 WSM out around 30 thousandths and had to increase the powder charge 2 grains to get his velocity and accuracy back. Matt

 

[XTERMINATOR]

when you think about it, it's only logic that a bullet that is 20% longer would erode the throat 20% faster...

WRONG
And frankly it sounds like you're merely fishing for validation of YOUR notions.

As mentioned, measure your actual velocities.

Yes I am "fishing" for people with similar experience because all other reason that I can think of have been ruled out. If I have a couple of guys that have experience similar speed lost I'll stop my research and just add some powder, if not I'm open to suggestions that I might not think of.

Dont have acces to a magnetospeed, do you have a better way to mesure speed then actual drop? i won numeros tactical and steel match out to 1500m using this method, it has never let me down

Could you please explain why I'm wrong, to me more conctact equals more friction and more friction equals more erosion...

 

[sdnerf]

H-4350 may be your problem, it burns HOT and erodes throats prematurely. I-4831 is (~) same burn rate without the heat.