When do 139gr Lapua Scenars go transonic?

[trental]

Well I went and shot my first thousand yard match today (3x1000) with my 6.5 Creedmoor. I was using my typical 139 grain Lapua Scenar and it seemed like they were going transonic at 1000 yards. These are leaving my barrel at 2750 fps, and they should still be going 1450 fps at 1000 yards. Despite that they have that velocity I was still getting keyholing in the paper. I must be right on the edge of stabilization because only about one fourth of the bullets keyhole and I was still able to hold the 10 and 9 rings mostly. I had some fliers and even had two bullets miss the 48"x48" target board completely. I thought something was wrong with my gun until my spotter got back to the line and told me that my bullets were making oblong holes in the paper.

I have an eight twist barrel and I'm running well above subsonic at the target so I'm kind of surprised that I'm seeing keyholing with this load. I think if I want to keep using this bullet I'm going to have to speed it up a little bit. Who else is running the 139 grain Lapua and have you shot it at 1000 yards? I'm only at 41 grains of H4350 so I think I can bring that up to 42 maybe 42 1/2 grains to get up to 4850fps and see if I can keep this bullet stabilized all the way to the target. I may have to limit my 41gr load to 800yds. It's a freaking hammer at 600yd.

Needless to say I didn't win today with a 517-8x. You get 2 bullets that don't hit the target and you might as well pack up and go home.

 

[Steve Blair]

Your velocity and twist are fine. There must be another cause. How many rounds down the barrel? Have you borescoped it recently? Check the crown and first few inches of the muzzle. The Scenars are a little small in diameter but should not cause this.

 

[trental]

About 500-600 rounds down the barrel, basically still new. This gun shoots in the .2s to .3s at 100yd, and shoots very well at 600yd as well depending on my wind skills that day. My last 3x600 match was a 577-18x and my best 20-shot string with it is a 197-10x. Nothing world class but not bad either.

I have lots of other options on bullet choices but I think I am just right on the EDGE of stability at the target. My spotter said that 75% round holes and 25% oblong with one or two of those being extremely oblong. What's crazy is that they were still hitting within the 8 and 9 ring. I'm guessing that they are juuuuuust starting to buckle at 1k.

 

[Steve Blair]

No, an 8" twist is more than enough for that bullet. Many folks run an 8.5" twist. Check for copper fouling at the muzzle.

 

[trental]

I'll check it out. I only had 66 rounds through it since it's last cleaning. I don't have a borescope but I'll see what it looks like with a bright bore light.

 

[trental]

Ok, just checked the barrel for copper. Looked down the muzzle with a very bright light and saw no evidence of copper fouling at all. Just carbon but not overly dirty either. Moved the light to the chamber end and again looked down the muzzle. Looks surprisingly free of copper fouling. Round count now is 146 since last full cleaning. I was getting keyholing from the beginning of today (66 shot round count).

My "come up" from my 100yd zero was 29.5 MOA and according to my muzzle velocity and ballistic calculator that is dead on. So I have to be right in that 1450fps range at the target. The two shots that missed the target, one went high and the other went just at the edge of the board at 3 o'clock.

 

[Nomad47]

Carbon ring?

 

[ohearchai]

Trental, was sort of rifle are you shooting, barrel lenght, etc, when you chronongraphed your load originally what Chrony were you using. Also have you changed powder lots recently. Leave the rifle as is and shoot it at a reduced distance and see what they results are.

 

[Erik Cortina]

I shoot 139's at 1,000 with no issues out of a 1:8" twist barrel. I push mine at 2,900 fps. out of a 6.5x47 Lapua.

 

[dooley]

I use 139gr scenars in a 260, never had any problems at 1000yds, but then I run them at 2850 fps, at 600yds a friend (is'nt it always the way) using my rifle put 5 rounds in a fraction over 1 inch using the scenars, according to quicktarget unlimited even running yours at 2750 fps they should be still be travelling at 1379 fps, which should be more than enough unless you were shooting into a heavy headwind, I am using a 1-8.5 twist barrel,
try again with a little more speed, there cannot be anything else wrong with your rifle if it shoots in the 2's and 3's at 100 yds.
dooley (UK)

 

[trental]

Trental, was sort of rifle are you shooting, barrel lenght, etc, when you chronongraphed your load originally what Chrony were you using. Also have you changed powder lots recently. Leave the rifle as is and shoot it at a reduced distance and see what they results are.

Good call. I might be able to get out Tues and shoot it at 300.

This is a factory Savage LRP with a 1:8 twist barrel at 26". Still using the same 8lb jug of H4350 that I worked up loads with. Shot over a Chrony Beta Master.