6x47lapua high pressure/speeds at low charges....please help

[Pwdrjnkie]

Hello all,

New member here with an issue I can't seem to figure out.

Surgeon 591 action
20" varmint 8 twist 6x47lapua barrel
W a .273 no turn neck
Cci450 mag primer
Lapua 6.5x47 brass sized w honed. forster f/I die (.268)...shoulder bumped .001
h4350,imr4451 & h4831
105 berger hybrid

I began doing normal barrel break in procedures cleaning fouling and copper while shooting average loads and getting expected velocities. As break in progressed, I began getting higher and higher pressures/speeds and continued to have to reduce my loads. I typically expect an increase in speed on new barrels, but not to this extent....

At the present, after 343 rounds, I now get the following results (speeds/pressure stabilized at 303 rds)...keep in mind the short 20" tube length.

H4350...35gr...2891 fps av
Imr 4451...34.9gr...2840
H4831...37.3 gr...2840

The rifle shoots under 5/8 min consistently, but the accuracy was in the 1-3s with higher load densities at higher charges....I just can't get even close to those charges without pressure signs...ejector marks/primer flattening usually starts .4-.8 grain past the charges I listed. I chase accuracy, not speed, but the high l.d. helps.

I've checked the possibility of carbon ring, copper buildup, etc.....completely clean.

Oh, and I'm .010 off the lands

If anyone has any ideas, I would appreciate them. I can usually figure things out, but not this one. Maybe that's just the way this barrel is? I just have this aching feeling im doing something wrong, but don't know what it is...

Thanks In advance.

 

[savagedasher]

Sound like the carbon ring has found you.
Larry

 

[JBT47]

Sound like the carbon ring has found you.
Larry

Agreed

 

[Pwdrjnkie]

I'll check a bit more into finding it/how to remove. Can't see anything in there w my bare eyes and never had this issue. Thanks alot for the quick replies! Call me old fashioned, but never been on a forum. Nice to have some help! Thanks guys!!!

 

[ShootDots]

I think the carbon ring issue could very well be the culprit. However, I would seriously consider bumping those shoulders back 2 thousandth MORE than what are currently bumping them. One thousandths is a VERY tiny amount. Give the brass some room to grow before the pressure builds. I bump all my shoulders back 3 thousandths and never have "abnormal" pressure issues..

 

[Pwdrjnkie]

I guess hindsight is always 20/20. Maybe my decision to stop using brushes on this barrel bit me. Ill go to town on the throat and see what comes out. Ive been loading for quite awhile, but this precision stuff is new to me in the past year or so. I just bumped them .001 so they chambered, but if .003 isn't too much growth/shrinkage over and over, will try it out. Brass prep takes so long, Ive probably been over hesitant for it to get ruined prematurely. Thanks.

 

[savagedasher]

I guess hindsight is always 20/20. Maybe my decision to stop using brushes on this barrel bit me. Ill go to town on the throat and see what comes out. Ive been loading for quite awhile, but this precision stuff is new to me in the past year or so. I just bumped them .001 so they chambered, but if .003 isn't too much growth/shrinkage over and over, will try it out. Brass prep takes so long, Ive probably been over hesitant for it to get ruined prematurely. Thanks.

Brush has been my friend and I haven't seen that problem . Larry

 

[JBT47]

I did the no brushing thing several years back. Carbon ring formed in all my barrels. I brush after I shoot every time now.

 

[22DASHER]

Don't be afraid of using JB or Iosso either!

 

[jlow]

Carbon ring is a likely culprit, but you have not mentioned anything about trimming. Your neck is going to grow as you shoot and if it is too long, you are going to get pressure problems even with a light load.

 

[Pwdrjnkie]

After necking down, the mouths were a little crooked. Being picky as i am, I squared them all off at 1.83 before firing. I measure each and every one during prep and havent had to actually trim any material in 4 loadings so far. Come to think of it, maybe that .020 between 1.83 and 1.85 is where that carbon is accruing? I'm brushing at the moment, but nothing is coming out.....time to try more aggressively...and nervously

 

[22DASHER]

You do not need to be nervous about it. You will not kill your barrel. Just don't start hooking it up to a cordless drill or using a brush religiously after every 15 rounds and you will be fine. You won't see the carbon being removed unless you have a borescope.

 

[Pwdrjnkie]

That's funny...not gonna lie and say that bright yellow dewalt bag hasn't been getting a look or two...

 

[ASbobcat]

Hello all,

New member here with an issue I can't seem to figure out.

Surgeon 591 action
20" varmint 8 twist 6x47lapua barrel
W a .273 no turn neck
Cci450 mag primer
Lapua 6.5x47 brass sized w honed. forster f/I die (.268)...shoulder bumped .001
h4350,imr4451 & h4831
105 berger hybrid

I began doing normal barrel break in procedures cleaning fouling and copper while shooting average loads and getting expected velocities. As break in progressed, I began getting higher and higher pressures/speeds and continued to have to reduce my loads. I typically expect an increase in speed on new barrels, but not to this extent....

At the present, after 343 rounds, I now get the following results (speeds/pressure stabilized at 303 rds)...keep in mind the short 20" tube length.

H4350...35gr...2891 fps av
Imr 4451...34.9gr...2840
H4831...37.3 gr...2840

The rifle shoots under 5/8 min consistently, but the accuracy was in the 1-3s with higher load densities at higher charges....I just can't get even close to those charges without pressure signs...ejector marks/primer flattening usually starts .4-.8 grain past the charges I listed. I chase accuracy, not speed, but the high l.d. helps.

I've checked the possibility of carbon ring, copper buildup, etc.....completely clean.

Oh, and I'm .010 off the lands

If anyone has any ideas, I would appreciate them. I can usually figure things out, but not this one. Maybe that's just the way this barrel is? I just have this aching feeling im doing something wrong, but don't know what it is...

Thanks In advance.

Try BoreTech C4 Carbon Remover applied with a patch around a .22cal brush into the neck area. Let it soak for 15min and check with another wet patch. IF you have a carbon ring, this will show it.

Do you tumble your brass and not follow with annealing? Have you noticed a gradual increase in bullet seating pressure? The necks can get very hard after a few cycles of tumbling/resizing, and I found pressure issues in mine if I did not anneal (AFTER tumbling) every 4 cycles or so.

Since I discovered this issue after blowing primers and extractors, I no longer tumble brass. Just buff the outside with #0000 steel wool and brush the inside of the necks. No more pressure issues.

 

[KMart]

I have to agree with the carbon ring. Another thing is, you say that the chamber neck is .273". What is the case neck diameter when the bullet is seated?
Also, what is the highest velocity you have measured without getting pressure. At the powder charges you have listed, you shouldn't be getting pressure.
The Berger manual shows velocities close to what you have but with 3-5 grains more powder. They also use a 24" barrel and the Berger manual seems to be quite conservative.

I saw someone with this problem in a 6 br. He had inadvertently deprimed his cases with a large decapping pin (.080). Does your decapping pin measure .062 or smaller.

 

[jlow]

After necking down, the mouths were a little crooked. Being picky as i am, I squared them all off at 1.83 before firing. I measure each and every one during prep and havent had to actually trim any material in 4 loadings so far. Come to think of it, maybe that .020 between 1.83 and 1.85 is where that carbon is accruing? I'm brushing at the moment, but nothing is coming out.....time to try more aggressively...and nervously

OK, looks like you got your cases by necking down from a 6.5 case - I missed that.

Did you check neck thickness after? My understanding is necking down usually produced cases with excessively thick necks that usually needs to be turned. Depending on chamber dimensions, that may be a problem that increase your sensitivity to a carbon ring.

 

[dixiecricket]

have you checked the calibration of your reloading scale?

 

[Milo 2.0]

I have to agree with the carbon ring. Another thing is, you say that the chamber neck is .273". What is the case neck diameter when the bullet is seated?

I'd look here also.

 

[Pwdrjnkie]

Wow, all great info! Did repeated cycles of brushing, soak and patching out and got very small traces of carbon out, followed by one patch that contained a tint of blue. Maybe the shooters choice will tell me something as well. I will try that and go get some bore tech today.

Yes, I anneal each loading which may be a bit too much, but bullet seating pressure seems more uniform, so I do it. Case neck dia averages .270-.2705 measure with a mic, there may be better ways to more accurately measure dia close to the shoulder where I would expect thickening, I'm just not sure what the tool would be....I've never neck turned... yet). Highest velocity without pressure was around 2870 range w imr 4451....and around 2925 w h4350.....then cratering, ej marks, etc to follow. The scale gets calibrated each use and double checked with another scale. And, decap pin is small....same one I used when shooting the previous 6.5x47 barrel without issue.

Will continue to investigate today. May be a few small problems compounding in very small tolerances and equaling one big problem.

Thank u all for the great info guys!...will post results...when found

 

[jlow]

Wow, all great info! Did repeated cycles of brushing, soak and patching out and got very small traces of carbon out, followed by one patch that contained a tint of blue. Maybe the shooters choice will tell me something as well. I will try that and go get some bore tech today.

Yes, I anneal each loading which may be a bit too much, but bullet seating pressure seems more uniform, so I do it. Case neck dia averages .270-.2705 measure with a mic, there may be better ways to more accurately measure dia close to the shoulder where I would expect thickening, I'm just not sure what the tool would be....I've never neck turned... yet). Highest velocity without pressure was around 2870 range w imr 4451....and around 2925 w h4350.....then cratering, ej marks, etc to follow. The scale gets calibrated each use and double checked with another scale. And, decap pin is small....same one I used when shooting the previous 6.5x47 barrel without issue.

Will continue to investigate today. May be a few small problems compounding in very small tolerances and equaling one big problem.

Thank u all for the great info guys!...will post results...when found

If you only have a pair of calipers, the easiest way to measure average neck thickness is to measure the diameter (where the neck would hold) of the bullet first, seat the bullet, measure neck diameter and then subtract out the bullet diameter and divide by 2. You should do this at a number of locations. It's not going to be super accurate since it is a caliper but it should give you thickness to the thousand.