6 Creedmoor accuracy help

[lennyo3034]

I have a 6 creedmoor that I am having accuracy issues with. When I first got the barrel, it was hammering 105 hybrids with .010" jump. 40.9 grains of H4350 pushing around 3100. .2-.3 MOA. 26" 8 twist. Rock Creek.

I now have 544 rounds on this barrel and its barely holding MOA. I have cleaned it. I have chased lands and tried different seating depths. I suppose I could change bullets but I have 1000 of the hybrids for this rifle. Throat erosion is around .020".

This is a very fast barrel. I took it to 1000 yesterday and needed 6.7 mils at 150 ft DA and 50 degrees. According to AB and custom curve on the hybrid, that puts my MV at 3160. Considering there is a LOT of empty space in the case at 40.9 grains of powder, that may be affecting SDs and accuracy.

I have a big match coming up in a week and a half, any recommendations that don't involve changing bullet or powder?

 

[Milo 2.5]

I do not think case capacity is what is getting you here. If you were to ask about throat erosion on here, you'd get 30 diff answers, I think for 544 rds down the barrel, .020" is substantial. Which "says to me" you shoot your rifle hot.
I would look for a pinch point, or constriction in the first 6" of your barrel being you have a velocity rise. Try loading and chronographing 5 rds with a half grain less powder and see where your velocity stands. The extra 60 fps you're at right now just may be enough it pushed your load over the edge, hence accuracy drop.

 

[lennyo3034]

Thanks. Unfortunately my magnetospeed is is broken so 3160 is just an estimate based on drops yesterday.

Luckily I just got a labradar in so I will test it today.

40.9 seems like a light load, but the velocities are saying otherwise. I did not think I was shooting a hot load based on the charge, but now I'm reconsidering based on what you're saying. I will try reducing to 40.4 grains. I had just assumed the extra 60 fps was just from the barrel breaking in.

 

[Milo 2.5]

Thanks. Unfortunately my magnetospeed is is broken so 3160 is just an estimate based on drops yesterday.

Luckily I just got a labradar in so I will test it today.

40.9 seems like a light load, but the velocities are saying otherwise. I did not think I was shooting a hot load based on the charge, but now I'm reconsidering based on what you're saying. I will try reducing to 40.4 grains. I had just assumed the extra 60 fps was just from the barrel breaking in.

Yes, without actual numbers, we do not know anything really, load both charges and shoot over LR. Get some solid data.
I have shot a couple Rock Creeks, mine sped up at normal 70-90 rd ct, 500 rds is an awful lot for a barrel to speed up.IMO

 

[Milo 2.5]

Thanks. Unfortunately my magnetospeed is is broken so 3160 is just an estimate based on drops yesterday.

Luckily I just got a labradar in so I will test it today.

40.9 seems like a light load, but the velocities are saying otherwise. I did not think I was shooting a hot load based on the charge, but now I'm reconsidering based on what you're saying. I will try reducing to 40.4 grains. I had just assumed the extra 60 fps was just from the barrel breaking in.

One more, you said you think your barrel is fast, think about this for a second, in order to be Fast, it has to generate pressure in your case at lower charges.
Another way for someone to consider their barrel fast would be if he can stuff abnormal amounts of powder in a case and end up with more speed w/o pressure.< Not your case.

 

[Doc68]

I rebarelled my rpr with a criterion barrel. I did my load development all over because I had the same issue. I'm currently loading 4350 at 40.2gr and am about 30 thousnadths off lands with 105gr eld-m. However my new barrel loves the 95gr TMKs from Sierra. I'm pushing them at about 3175 from a 26" barrel currently. Looking at .4-.6 MOA at 300yds. I noticed a lot more throat erosion with the criterion versus the stock rpr barrel. About 750rds on the criterion barrel currently with about the same amount of throat erosion as yourself OP.

 

[lennyo3034]

Snuck out to range and put 5 rounds through chrono. Average of 3161. I’m going to reduce load to try to hit 3100 again. Any suggestions on how much I should reduce by?

 

[Hollywood 6mm]

When I still ran Hybrids, I was running them at 2.82" COAL (which started them about .020 off, I believe) with 42.2gr of H4350, and they ran 3080-3125 depending on the lot of H4350. I found the Hybrids really didn't give a shit about jump, they were still sub-MOA with nearly .1" (that's not a typo...) of jump.

I'd start checking screws all over - action, scope base, rings, etc. to make sure something isn't loose, and possibly try some factory Hornady ammo (assuming you're not throated too short) and see if you can eliminate the accuracy issue.

 

[lennyo3034]

with 42.2gr of H4350, and they ran 3080-3125

That is in line with what load data I’ve read and a friend’s barrel.

3160 with only 40.9 is awfully fast. I didn’t realize I was hotrodding it until I got the new chrono.

 

[Hollywood 6mm]

That is in line with what load data I’ve read and a friend’s barrel.

3160 with only 40.9 is awfully fast. I didn’t realize I was hotrodding it until I got the new chrono.

What's your COAL at with the 105?

 

[lennyo3034]

2.830”

I’m going to load some with .5 grain less powder and try again tomorrow.

 

[Hollywood 6mm]

2.830”

I’m going to load some with .5 grain less powder and try again tomorrow.

How far does that currently put you off the lands?

 

[lennyo3034]

I’m shooting for .005” jump. Although my most recent batch of 105 hybrids has considerable variation in the meplat.

 

[Hollywood 6mm]

I’m shooting for .005” jump. Although my most recent batch of 105 hybrids has considerable variation in the meplat.

Honestly, at least in my experience, there's zero reason to chase lands with the Hybrid - they really don't care about jump. Like I said in an earlier reply, I've had them shooting sub-MOA with something in the ballpark of .1" of jump in a well-worn (1700+ rounds) barrel without any issues.

 

[lennyo3034]

That’s what I’ve heard as well. I was chasing to try to get my Accuracy back, but that was before realizing I had picked up so much velocity and am now probably out of my node.

 

[Ranger188]

Your load does seem fast. Could be one of a couple of things
You said you cleaned the barrel, did you check for carbon ring?
I know you have to chase lands, is their any chance your jamming the bullet?
Either one of these will cause pressure and increase in fps.
With a 105-107 g bullet and H4350, I had to be 42 or higher in powder to get 3100+ fps
What kind of brass are you using?

 

[Aggie]

The Hodgdon data is a bit hotter than yours and they are getting a velocity of 3,071 with 42.4 grains.

You do have a fast barrel.

I looked up an article in Handloader Magazine. They were using a Ruger Predator with a 22 inch barrel and a Zeiss Conquest Scope 4-16X44mm.

The used a 105 gr. Berger VLD Hunting with 41.5 gr. H4350. Overall loaded length was 2.800". They were getting 3,011 FPS. This load grouped at .53" at 100 yards.

 

[lennyo3034]

I cleaned the barrel about 100 rounds ago. I did clean the throat with boretech carbon cleaner and got rid of the ring that was starting to develop. Went to range and shot these today. Still a little fast so I may try 39.8 and 40.0. Accuracy is better but still no where near where the barrel started.

 

[lennyo3034]

I settled on 40.52 which gets me 3140 and a little over 1/2 MOA. SD of 4.

Unfortunately that’s knocking on the door of one club series I shoot (3150) and well over the speed limit of another (3100). When I tried dropping to 40 grains to get closer to 3100, accuracy and SD was terrible.

 

[lennyo3034]

Your load does seem fast. Could be one of a couple of things
You said you cleaned the barrel, did you check for carbon ring?
I know you have to chase lands, is their any chance your jamming the bullet?
Either one of these will cause pressure and increase in fps.
With a 105-107 g bullet and H4350, I had to be 42 or higher in powder to get 3100+ fps
What kind of brass are you using?

Lapua SRP brass with CCI450.

 

[Aggie]

The next step may be to look over case and cartridge runout with something like a Forster Co-Ax Case and Cartridger Inspector. Hopefully a friend will loan you one. You can check:

Neck wall thickness
Case and cartridge runout

That way you remove some of the variables.

Read about what it is measuring and see if that is one of the issues.

Case Inspector - Forster Products

Co-Ax® Case and Cartridge Inspector Improve your shooting accuracy by fine-tuning the uniformity of your cases and cartridges. Measures “accuracy-critical” dimensions: Neck wall thickness Case and cartridge runout (concentricity) Uniquely supports case/cartridge to check both bullet and case...

www.forsterproducts.com

 

[RampedRaptor]

H4831 sc