Lowering velocity ES

[bullfrog]

I have a 6mmXC Model 70 Winchester built by GA Precision with a 27" Bartlein 5R barrel with a 7.5 twist. I am having trouble getting a load to shoot consistently under 1/2MOA 5 shot groups, and I have not been able to get a load with extreme velocity spreads of less than around 40 for ten shots. I have used H4350, H4831SC, and RL17 for powders and F210M, WLR, CCI 200, and Tula LR primers. The Berger 105 hybrids and 115 DTAC's have been the primary bullets worked with. I have also tried the Hornady 105 BTHP and Matrix 117 VLD. I am using Norma 6XC brass with Redding full length bushing sizing die and competition seater. I have tried jammed .015" to .130" off the lands with not a lot of difference. I have tried .268, .266, and .269 bushings (loaded round is .271). Nothing really stands out as being clearly better. I even bought a gempro scale to weigh out power charges to .02 grains.

43 grs. of H4831SC and 115 coated DTAC's seated .010" off the lands has been the best load so far. Average 5 shot group a little over 1/2" with ES of 40fps. This will not cut it at 1000 yards. The extreme spread alone will be around 8" of vertical. I had this rifle built as mainly a practice piece. If it is not shooting well I will not know if it is the rifle or me.

About the only thing I have not done is anneal my brass.

Any suggestions? Anybody got a powder/primer combination suitable for this size of cartridge that has shown very good consistency.

 

[royinidaho]

I have the same problem with a 270 Allen Magnum. Very frustrating.

On the second barrel and have/had the same problem.

I'm limited to US-869 powder. Bummer....

However, the last field test I conducted while trying a new bullet the ES was less than 10.

I was jubilant to say the least.

Nest step is to chrono shots while validating drops. I'll be a sad little boy (well old man) is the ES grows.:roll eyes:

The bullet is the 165 Matrix in 277 cal.

 

[Browninglover1]

Definitely anneal the cases and try again; I do mine every firing now and while I haven't validated the process on the chronograph it definitely improved my vertical at 1k.

Have you tried stuffing a little more powder in the case? Sometimes just a little bit more can get you to the next node and bring everything together.

 

[dkhunt14]

Annealing really helps. It seals the chamber and helps with bullet release. Sometimes more neck tension can really help. I like I the lands for more consistency. Try a different primer. Usually guns shoot more consistent at upper end. I have had Match guns that shot 20 ES and still would shoot 5 inch 10 shot groups at 1000. Could be the chronograph. Even my 35P doesn't record right all the time. Matt

 

[barefooter56]

bullfrog,
What is your "group shooting" routine? and what SD is your chronograph showing. Also what range are you testing at please?

 

[bullfrog]

Shooting 5 shot groups at 100 yards using sinclair heavy front rest and rear bag from a solid bench. I shoot 5 shots in a row without intentionally waiting for the gun to cool between shots. This rifle has a heavy barrel that is barely warm after 5 shots. I do let the gun cool completely between groups.

SD is around 10-16. The velocities are pretty much spread evenly thru the ES. In other words, I do not have 8-9 shots that are really consistent with 1-2 outliers that ruin the ES.

I even went so far as to weight sort the cases within .1 grain (something I never do). The weight sorted cases made no improvement at all. The Norma brass is already +/-.8 grains without sorting.

I have shot this rifle at 1000 yards just to see if the high ES would translate at long range. It did. All of my groups had about 10-12" vertical with about 4" horizontal.

 

[bill123]

Did u have GAP build the rifle?
How many rounds through barrel?
Do you have factory match ammo that shoots better?
Do you have other rifles that shoot better consistently?

 

[barefooter56]

Do you foul the barrel on a practice target until the rounds stop rising and begin to cluster before you group shoot or do Chronograph work? a 10 SD is not bad at all! Your vertical. Is it basically follow a straight line up or down on the target or does it run at an angle like from 11 to 4 o'clock or 2 to 7 o'clock?

 

[bullfrog]

The rifle is totally GAP built. About 300 rounds down the barrel so far. I have Tubb factory ammo with the 115 coated DTAC's that shoots about the same as my best load except the extreme spread is closer to 60 and the vertical is worse at 1000 yards. The vertical at 1000 is pretty much straight up and down. I do foul the barrel with the bullet I'm using before recording ES and groups. The first shot is especially slow when using the coated bullets.

I appreciate the questions. They are some of the same I might ask without knowing the shooter (like, are you shooting with a solid rest, is the barrel clean, etc.). This ain't my first rodeo. I have several rifles custom and factory that shoot better than this one with less work. My other GAP rifle is a 338 edge that shoots crazy good. Largest ES for it was 12. Nice round groups even at 1100 yards.

The groups this rifle is shooting at 100 yards is not my greatest concern. If I could shoot 3/4 MOA at 1000 yards I could live with that. My greater concern is the velocity extreme spread. I built this gun for practice with a more economical and lighter recoiling cartridge. In order for this rifle to fulfill my wants it needs to be more consistent. I do not want to wonder if the errant round was the fault of the rifle or me. I want to know it was me so I can hopefully improve upon this. I just don't have the confidence to say it is not the rifle.

 

[barefooter56]

Bullfrog,
Wow.... With a 10-14 SD.. have you had a friend who you trust as a good shooter take the load out to 600 and 1000? That way we could eliminate you. As a problem that is LOL!

 

[dkhunt14]

Most of the guys I know that shoot the 6 XC use H4350 and BR2 primers. Most of them shoot the Berger 105 VLDs or the 107Sierras and they are non coated. Now this is for 1000 yard benchrest and they strive for 10 shot groups in the 5 to 6 inch range or you wont be competitive. Most of the 6MM guys gave up on the DTAC bullets because they couldn't shoot small enough to win. They also anneal and that really helps with vertical at 1000 yards. Most guys also shoot them in the lands at 5 plus. Matt

 

[bill123]

The rifle is totally GAP built. About 300 rounds down the barrel so far. I have Tubb factory ammo with the 115 coated DTAC's that shoots about the same as my best load except the extreme spread is closer to 60 and the vertical is worse at 1000 yards. The vertical at 1000 is pretty much straight up and down. I do foul the barrel with the bullet I'm using before recording ES and groups. The first shot is especially slow when using the coated bullets.

I appreciate the questions. They are some of the same I might ask without knowing the shooter (like, are you shooting with a solid rest, is the barrel clean, etc.). This ain't my first rodeo. I have several rifles custom and factory that shoot better than this one with less work. My other GAP rifle is a 338 edge that shoots crazy good. Largest ES for it was 12. Nice round groups even at 1100 yards.

The groups this rifle is shooting at 100 yards is not my greatest concern. If I could shoot 3/4 MOA at 1000 yards I could live with that. My greater concern is the velocity extreme spread. I built this gun for practice with a more economical and lighter recoiling cartridge. In order for this rifle to fulfill my wants it needs to be more consistent. I do not want to wonder if the errant round was the fault of the rifle or me. I want to know it was me so I can hopefully improve upon this. I just don't have the confidence to say it is not the rifle.

Have you called George at GAP? He helped me out w/a somewhat related issue.
Didn't know where you were coming from so I thought I'd ask the basics since nobody else did. Hope u sort thi out.