Weird Velocity Readings

[Gus McCrae]

Went out to the range this morning to run some test loads out of my 280 Rem (Browning X-Bolt / 22'' barrel) and had some really weird readings thru my chrony.

Some quick info on the loads:

All 4-fired Winchester brass, full length sized and trimmed to 2.530''.

4 sets of 3 rounds loaded with 53.5 gr. of IMR-4350.

140 gr. Sierra Gameking (0.2 gr. over max according to Sierra's manual / 0.5 gr. under max per Lyman 49th edition.)

Set #1: 0.040'' off rifling / velocities: 2789, 2818, 2800 / 0.277'' group (one ragged hole)

Set #2: 0.035'' off rifling / velocities: 2694, 2804, 2982 / 0.384'' group (one ragged hole)

Set #3: 0.025'' off rifling / velocities: 3006, 2857, 2838 / 1.095'' group

Set #4: 0.020'' off rifling / velocities: 2826, 3114, 2592 / 6.988'' group (not a typo)

I had no pressure signs with any of the sets. Chronograph was set 12' from the muzzle and it was partly cloudy out (60 degrees).

I tested this same bullet & powder charge a couple days ago with pretty consistent chrony readings (2856, 2847, 2865 fps). Bullets were seated 0.030'' off of the rifling on this set.

I would love to get consistent 3000-3100 fps with this bullet, but I can't find a single load in 3 different manuals (Hodgdon, Sierra, or Lymans 49th) that will yield these kind of velocities without loading way over max.

I'm stumped. Does anyone have a thought as to why I'm getting these spikes in velocities?

 

[kraky]

What kind of scale do you use...if balance beam could it be sticking?
Is the battery newish in the chrono?
Either the chrono is screwing up or the powder charges are.

 

[Gus McCrae]

I'm using an electronic scale...each load is weighed. I check the electronic against a balance every so often, usually the first couple of loads per session. It always checks out fine.

The battery in the chrony is brand new.

 

[375fan]

First thing I'd suggest is set screens to chronograph out a little further to at least 15 if not 20 feet.
Second thought is 4350 is too slow burning for 22 inch barrel and your not getting consistent complete burning of powder charge resulting in wide variation of fps.

 

[Gus McCrae]

First thing I'd suggest is set screens to chronograph out a little further to at least 15 if not 20 feet.
Second thought is 4350 is too slow burning for 22 inch barrel and your not getting consistent complete burning of powder charge resulting in wide variation of fps.

What powder would you suggest?

 

[Lefty7mmstw]

My brother has been shooting 280's since he got out of diapers it seems and he's always at/over 3K fps with a 140 in a 22" pipe and usually nipping at 3050 fps.
He's using rl22 in a remmy with a 140 ct on top at present.
Top load for rl22 in the 2005 Alliant data for the 139 hornady is 59.5 rl22 at 3000 at 57.5 kpsi peak with a rem primer and remmy brass. I've seen him make some shots with that cal. that I likely wouldn't attempt and I'm a showoff behind a rifle.

ps. listen to 375fan on the chrono; you are likely either seeing the powder blast or getting double shadows from the sun angle if it's a low sun angle.

 

[Gus McCrae]

My brother has been shooting 280's since he got out of diapers it seems and he's always at/over 3K fps with a 140 in a 22" pipe and usually nipping at 3050 fps.
He's using rl22 in a remmy with a 140 ct on top at present.
Top load for rl22 in the 2005 Alliant data for the 139 hornady is 59.5 rl22 at 3000 at 57.5 kpsi peak with a rem primer and remmy brass. I've seen him make some shots with that cal. that I likely wouldn't attempt and I'm a showoff behind a rifle.

ps. listen to 375fan on the chrono; you are likely either seeing the powder blast or getting double shadows from the sun angle if it's a low sun angle.

It's funny you mentioned R-22. I'm getting 2950 fps with 56.8 gr. of R-22 behind a 140 gr. Barnes TSX with 0.75'' groups, so I loaded up some 140 gr. Sierra Gamekings & R-22...the velocities were horrible. I figured too slow of powder for a 22'' barrel with the Gamekings, so I switched to IMR-4350.

 

[Gus McCrae]

If anyone has QuickLoad and wouldn't mind running some numbers for me, I'd be interested to know what the max powder charge would be for this load I'm working on.

 

[lloydsmale]

first ill say that 4350 isnt to slow for 140s in a 280. Its about ideal. Secondly id have to ask what kind of chrony you own. Most cheap ones just are relibable or consistant. Third i agree that the farther away from muzzle blast that you can put your chon. the better. I dont usually recomend loading over book but if it were my gun id try bumping it up one grain and look close for pressure signs and see what that does. one last thing id try is a couple differnt primers. Some of your spreds if your chon. is reading right are to large. A diffent primer might help that. Even if your getting 1/2 inch 100 yard groups if your velocity spreads are large the load will most likely go to heck out at 300 yards.

 

[Gus McCrae]

first ill say that 4350 isnt to slow for 140s in a 280. Its about ideal. Secondly id have to ask what kind of chrony you own. Most cheap ones just are relibable or consistant.

It's a Shooting Chrony. It's not top of the line but I don't think it's junk either.

Third i agree that the farther away from muzzle blast that you can put your chon. the better. I dont usually recomend loading over book but if it were my gun id try bumping it up one grain and look close for pressure signs and see what that does. one last thing id try is a couple differnt primers. Some of your spreds if your chon. is reading right are to large. A diffent primer might help that. Even if your getting 1/2 inch 100 yard groups if your velocity spreads are large the load will most likely go to heck out at 300 yards.

Luckily I've got a couple of boxes of Fed. 210M's...I'll give those a shot after I push the chrony out a little ways. I'll change one variable at a time til I figure this out.

 

[lloydsmale]

I had two shooting chronys. Both were about junk. Some have good luck with them but i didnt. Mine were very sensitive to light and both read high and neither were consistant. First thing id do is find a buddy with a better chrono and try your loads just to verify your chrony is right before i wasted any more money on components. especially considering the accuracy youre getting.

 

[kraky]

Too close chrono can definately cause trouble...forgot about that idea.

 

[Gus McCrae]

Next trip out I'll set up closer to 15' and see if that makes a difference. I might even try to come up with a piece of opaque plastic to cover the gap between the skyscreens to minimize the effects of intermittent sunshine.

 

[Lefty7mmstw]

Next trip out I'll set up closer to 15' and see if that makes a difference. I might even try to come up with a piece of opaque plastic to cover the gap between the skyscreens to minimize the effects of intermittent sunshine.

give her a bit of overhang on the sun- in end too. Make it look like a cloudy day to the chrono....