Extreme velocity spread comment?

[rimfire]

Loading for a 7-30Waters 14" Contender barrel from Virgin Valley Custom Guns.

Have tried several loads looking for consistent velocities and am struggling to make a judgement.

1. With Win 748, CCI 350 mag primers and a 120 gr NBT I get 125-150 fps max variation from slowest to fastest shot [2150 to 2300 fps]

2. With Varget and a BR primer I am getting 100 fps slowest to fastest...but I got a number of rounds clustered a bit closer together and then a slower round.

Questions...What is considered a reasonable spread in terms of %?  Anyone here have the experience that a barrel might take a few rounds to settle down in velocity immediate after a cleaning?  Any suggestions for improving shot to shot variation.

Notes:  I am full length resizing, weighing every charge, seating a 120 grain NBT to within 0.020 of the rifling.

Thanks for your help.

[Jerry Lester]

Yes, it normally takes a couple or more fouling shots to settle a rifle in after a good cleaning.

As far as the ES question, if I'm loading for a rifle I strive for 30 fps or less with regular hunting loads. If I'm loading for "any" kind of long range shooting, I strive for 20 fps or less with single digits being my goal.

[Reed1911]

Try a different powder? AA2015 and 2460 have always done well as have H322 & H335. Also is the brass all from the same maker and same lot? There may be some internal changes that are combined with other factors to vary the spread so much. 100FPS ES is a very high number.

[Coyote Hunter]

Loading for a 7-30Waters 14" Contender barrel from Virgin Valley Custom Guns.

Have tried several loads looking for consistent velocities and am struggling to make a judgement.

1. With Win 748, CCI 350 mag primers and a 120 gr NBT I get 125-150 fps max variation from slowest to fastest shot [2150 to 2300 fps]

2. With Varget and a BR primer I am getting 100 fps slowest to fastest...but I got a number of rounds clustered a bit closer together and then a slower round.

Questions...What is considered a reasonable spread in terms of %?  Anyone here have the experience that a barrel might take a few rounds to settle down in velocity immediate after a cleaning?  Any suggestions for improving shot to shot variation.

Notes:  I am full length resizing, weighing every charge, seating a 120 grain NBT to within 0.020 of the rifling.

Thanks for your help.

rimfire –

You probably won’t be happy with my answer, but you asked.  I’m not sure I can make any suggestions to help you, but I’ll try.

First, the spread.  My .45-70 loads consistently provide 4- and 5-shot shot strings with 7fps Standard Deviation or better, and as low as 1.7fps.  Extreme Spreads are consistently at or under 8fps.  Not always, but mostly.  My .300 Win Mag often yields 4-shot strings with Standard Deviations under 7fps and Extreme Spreads around 15fps.My buddy shot a 4-shot string in his Marlin .30-30 and had a 4fps Extreme Spread.  So that’s what things look like when they are going well.  In general, I prefer a Standard Deviation under 10fps and an Extreme Spread under 20fps.  Doesn’t always work out, though.

If I was getting Extreme Spreads of 125-150fps I would stop and question everything – starting with the batteries in the chronograph, the chronograph itself, and the loads and the manner in which they were prepared.

A few thoughts come to mind.  First, after cleaning you should ALWAYS fire some fouling shots before shooting for the record.  Shooting a bullet down an oily or even a sparkly clean bore will yield different results than when the bore is fouled.  Second, you don’t mention how you are crimping, but inconsistent crimps could be part of the problem.  The solution is to trim all the cases to a uniform length.  That way you get consistent crimps whether using roll crimps or the Lee Factory Crimp Die.  Another thought that comes to mind is the condition of your brass – is it all one manufacturer, how much variation is there in weight, how many times has it been fired?  Using different vendor brass will exacerbate the problem, as will extreme differences in weight even if it has the same headstamp (vendor).  If the some of the brass has been work hardened by too many firings you may be getting inconsistent neck tension. – in which case its time to anneal or replace the brass.  Also, case necks that are too thick can cause problems.

A short while back I was getting some really strange results with the chrono.  In the past strange results were due to a low battery but this time it was due to a broken wire.

Don’t know it this will help, hope it does.

Good luck.

[rimfire]

I am absolutely going to try a different chronograph because it would seem that this makes little sense.  However, my 44 magnum loads had extreme spreads of 7-8 fps so who knows?

One other thing...last night I noticed that the firing pin strike on the primers leaves an indentaion where the edge of it is at center.  In other words the firing pin is well off center on the primer.  Could that cause problems like this?

[Steve P]

Try a Winchester primer and see your problem disappear.
My 748 load in my waters contender barrel has a sd of about 13.

Steve  

[Questor]

My question is this: if you didn't have a chronograph, would you be happy with your 100 yard accuracy?  If so, then the problem seems more academic than real. However, we're dirty fingernailed, hairy chested, manly handloading types and we cannot tolerate such an extreme spread. It is our identity to stamp out such anomalies. Since I do have a chronograph and I don't like the extreme spread you are getting, I'd try for a lower value, maybe 30fps difference.

The first thing I'd try is putting the chronograph farther from the gun. Having it too close has caused me some grief like what you're seeing (I use a PACT).

I'm not sure about your choice of primers, so I'd go back to a good manual like Speer or Hornady and use their exact recommendation.  If Speer says non-magnum primers, then I'd use non-magnum primers.

Another thing that might be awry is the bullet tension. I suppose it could make that much difference. Did you chamfer the case mouths?

Are there any obvious differences in the sizes of the flash holes? Is the brass from the same lot?  I'd concentrate on the consistency of the ammo components first, then go back to the range with the chronograph at least 20 feet away, then see what the results are.  

One thing that can affect a chronograph significantly is the angle of the sun, so if you're taking your measurements early in the morning or late in the afternoon, when the sun's angle is closer to the horizon, then you may want to try it at mid-day instead.

[rimfire]

Chrono was about 10 feet away so I guess I will move it fartehr just for kicks.  I have not seen any significant case differences but I will check closer.

Honestly I have not shot it for group size yet as I was hoping to find a consistent velocity load first, but I will try groups this weekend.

Thanks for your comments.

[Questor]

I know how frustrating this sort of thing can get. It gets to be a Quixotic quest for quality.

[james]

Check the length of your brass.  I solved a similar problem by trimming the brass to a uniform length.  Some of my bullets were probably hitting the lands and some were not which was giving a fluctuation in pressure & velocity.
james

[Steve P]

Check the length of your brass.  I solved a similar problem by trimming the brass to a uniform length.  Some of my bullets were probably hitting the lands and some were not which was giving a fluctuation in pressure & velocity.
james

Length of brass should have nothing to do with bullet depth and hitting the lands.  Length of brass can change pressure, velocity, sd.  Not by a whole lot though.    

Steve