Consistent MV

[RobB]

Spent last Sunday afternoon at 1000yrds at Bisley having some quality recoil therapy but also testing a batch of 185 bergers in my FTR rifle.

I noticed a vertical variation on the target which of course can be a number of things, but the one I could easily check was MV. On went the chronograph (V3 Magnetospeed).

Looking at the muzzle velocity and found about a +- 15fps spread centre around 2830fps. So 30fps in total. POI also bore that out. All shots with MV above average were above the centre line, all below were below, including how far above and below so could discount barrel harmonics I believe.
On the target, and born out by the ballistics calculator, translated into +- 0.75 moa. That takes me from a v bull to a 4.

Question is, what should I expect to be able to get to as far as MV consistency?

All cases were ultrasonic cleaned (no more than twice used Lapua Palma small primer. RS 52 weighed to +- 0.06gr. Neck sized. BR 4 primers.

What I didn't do was weigh the Bergers. Will do that next time.

Anything else?


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[Triffid]

He only looked at large rifle primers, but Laurie Holland found they made quite a difference to the velocity spread:
http://bulletin.accurateshooter.com/201 ... -and-more/.

Then batching the brass by weight or volume to ensure consistent case pressure and neck-turning to ensure consistent neck tension.

Triffid

[20series]

Personally I wouldn't bother weighing out the Berger bullets you'll get board of how consistent they are...

it could be variance in your neck tensio

Alan

[StanDeasy]

Inputting your numbers into Berger's own ballistics calculator gives a predicted elevation spread of about +- 0.375 moa i.e. half of the actual result on the target. So the other half must be due to some other factor.

[WelshShooter]

What about the relative temperature while shooting? Some powders are not so consistent during colder weather, for example, Ramshot Tac doesn't seem to perform so well compared to the likes of Varget.

[RobB]

What about the relative temperature while shooting? Some powders are not so consistent during colder weather, for example, Ramshot Tac doesn't seem to perform so well compared to the likes of Varget.

it was only me on the target with no delay in shooting and therefore little temp change between shots. So I'm discounting temp change.


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[StanDeasy]

I have just noticed that you are using RS52 propellant. This was not designed to be used with heavy bullets in 308Win and could be responsible for your vertical stringing, due to random pressure spikes.

I would advise you to switch to a more suitable powder. If you have any doubts, speak to Nigel Cole-Hawkins the UK RS distributor.

[RobB]

Inputting your numbers into Berger's own ballistics calculator gives a predicted elevation spread of about +- 0.375 moa i.e. half of the actual result on the target. So the other half must be due to some other factor.

taking out the 2 or 3 outliers it was probably closer to +- 0.5 moa (human error, Sun coming out and harmonics in there somewhere). But even +- 0.375, would that be acceptable for F Class FTR? Bit of wind and your back into 4's. I'd prefer if the MV spread wasn't that large.

Sounds like I need to neck turn. Never done that yet.


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[RobB]

Thanks for the suggestions so far. Things to think about


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[StanDeasy]

You need to get your velocity spread down, ideally into single figures. I don't see neck turning helping that very much.