MV "flyer", can anyone offer theory or advice?

[Napalmio]

Hi Folks,

 

I've been fine tuning a load for my Howa 308 for a while and have it pretty spot on now. I developed using OCW for starters in 0.2gr increments, then did the full range of seating depths in 0.2mm increments from saami spec to as far out the case as I was prepared to go (the option of touching the lands is not on with my chamber, i'd only have about 2mm of the bullet seated, but that's another topic for another day perhaps).

 

I realise that OCW and seating depth are no doubt inexorably linked, so varying the seating probably means my OCW data is less valid (although I would welcome any knowledge and advice anyone can give me in that area) but I sort of had to start somewhere and OCW seemed best.

 

I'm using Lapua brass, all from the same batch, SMK 2155 heads, TR140 powder and CCI benchrest primers. The barrel is the standard Howa 1500 sporter barrel so no great shakes, but I've found that this load groups fantastically once I've got about 20-30 rounds of coppering on board, then starts to tail off after another 40 or so rounds. In that sweet spot it's possible for me to group 3 shots (I know, 3 shots is meaningless etc....) into 0.4MOA at 300 yards, which is amazing for a cheap rifle and barrel. With a clean barrel the grouping is closer to 0.8 MOA or worse. I've attached a couple of pics of 200 yard and 300 yard shots from when I did the ballistic curve measurements just to show the level of accuracy is at least a bit repeatable.

 

HOWEVER..... Finally this weekend I got access to a chrony and this is where I need advice. The 5 shot string gave MVs of:

 

2384

2389

2387

2468

2385

 

Two things stand out in those results. 4 of them are fantastically consistent, way beyond my hopes. But, one of them is miles away. Bearing in mind that every round is wet media cleaned, neck sized using a Lee collet die, then loaded in the exact same way, every charge is measured on a balance and trickled to perfection and every bullet is seated and measured with verniers and rejected if it is more than 0.05mm away from spec, how can that random MV be explained?

 

Is it real? Or a glitch in the chrony? Or could a difference in neck tension do this? What other factors could explain such a difference?

 

Any help and advice you folks can give me will be most welcome!

 

Cheers,

Mick

 

[gbal]

Mick,

Probably impossible to diagnose.

What might help is if you recorded the POIs for these 5 chrono-ed shots-if the 4 that were an excellent 2386 +/_ 2 impacted clearly different from the rogue chrono shot at 2386 (ie some 82 slower ) then that would rather support that that cartridge was a bit underloaded(but not why-though seems more about powder than anything else)...you'd expect a good group from the 4 too,if the chrono is OK...

On the other hand,if that shot was also 'in the group',then probably the chrono had a blip on that shot (Or,much less likely -it was 82 fps slower,but no real effect....).

Without such a cross check on the maybe 'slow' load,I don't think we can give any diagnosis,especially as you report identical proceedures and clearly very sound reloads (other than maybe this one.....

 

gbal

[duey]

I would suggest tr ting to get your MV up to 2800, 2850 FPS as this is usually a sweet spot and although getting towards the top end of the loading for the 308 should still be comfortably below max pressure

 

Your MV variation could be down to many things, case weight more than others giving different pressure, neck tension, slight variance with the bullet itself, to name but a few but you may also find that the one round with the higer MV is still withinn the group and not the flyer

 

Happy hunting the probs it can get infuriating

 

Duey

[Vermincinerator]

Neck tension my friend, get rid of the lee collet die and invest in some kind of bushing die

 

Ian.

[Napalmio]

Thanks all for your input.

 

gbal, You're absolutely right, I missed the obvious step that would have been most likely to give me a clue! I'm going to repeat the exercise on a calm day to see if there is any variation in poi as you suggest. The wind was all over the shop on Monday so I didn't bother recording poi, but thinking about it i'm only looking for vertical dispersion so with hindsight it would have been perfectly viable and I deserve a slap on the bald patch.

 

Duey, I'm pretty confident I already have a "sweet spot", I loaded right up to max charge during the OCW process and where I am now was the clear winner, but you remind me of another question I need to ask regarding load data MVs compared to real world, which I'll put on a new topic. In a nutshell, the MV that I get (chrony or calculated from drop / distance) for a given charge is way lower than indicated in the load data for powder and bullet combo that I use.

 

Ian, I've done a ton of reading about the merits of one type of neck sizing vs others, and while I'll grant the Lee Collet die is pretty agricultural, I can't fault the results on target and am yet to read of tangibly worse results from anybody who has used one side by side with a Redding or equivalent. It's nice not needing to lubricate and the less I work the brass the better as far as I can see. That said, I'm always willing to read anything that can convince me I need to change... For now, if I was going to change anything it would be to slightly reduce the diameter of the mandrel, as I agree the Lee die is a bit "loose" off the shelf. I'll give it a try and see what happens! Would a difference in neck tension make such a difference in MV? Any detail you can offer or reading matter you can point me towards about MV vs neck tension would be most welcome.

 

Thanks again all of you for taking the time to reply and I'll look out for all your pointers as I go on.

[MTLEADFARMER]

Lee collet dies are fine, don't let anyone BS you. It's more than likely a bad read by the chronograph, 20 rounds is the what I like to run when I'm doing it. You didn't mention trimming cases, if you didn't do so.I also use a lee factory crimp die on everything I reload, I have never seen it degrade accuracy 99% of the time it improves.annealing also helps.

[duey]

I suggested trying to get your MV up to 2800fps ish to maximise the potential of the 155 bullet and the guy that designed the OCW system also advocates that his best results are always obtained nearer to the top end of the loading envelope

He's nearest recommendation to 155 with TR 140 is 155s with varget at a charge of around 47 to 47.5 gr

 

TR140, N140 and varget are all similar powders with similar loadings ( generalisation I know but close enough for this topic )

 

I've always got best results with 150ish bullets in 308 pushing them to the 2800 to 2900 region with a 10 thou jump but that's my finding in the rifles I've used

 

If your happy with your sweet spot you've found then that's great but I feel you may struggle when and if you start pushing beyond 300 yds

 

I'm not trying to be pissy and sorryif that's how it comes across its not meant just not one for writing essays

 

Happy days and tight groups

 

Duey

[brown dog]

As someone else has mentioned, I'd wonder if the slower case is lighter than the others (ie has greater internal volume, and therefore lower MV).

 

With that, I'd wonder whether the slower case has had more firings than the other cases...if so, it could have a work-hardened neck, which would give it reduced neck tension, and therefore reduced mv, when compared to other less work-hardened cases.

[Napalmio]

Duey, your input is most welcome. In fact it's lead me to learn more thanks to the follow up question you inspired me to post. Like I said, the 44.2gr charge weight was right near the top of the load data so a higher velocity didn't seem possible but with the input of the UKV community I'm realising that, at least in the case of Viht data, their max charge is very conservative in my chamber. Now I just need to learn how to safely read pressure signs then I will push the charge weight up when I develop my next load.

 

Brown dog, the "odd one out" is actually 80fps faster, rather than slower. The cases have all been fired 6 times, only ever neck sized and trimmed, but I have not yet annealed them. I'm wobbling between doing it myself (I've got tempilaq in anticipation) or just sending them to Spud because I'm scared I may cock it up From your advice maybe it is time for me to anneal and perhaps I will hone my mandrel a fraction just to increase neck tension. I've marked the case so I will weigh it and measure internal volume too, thanks for the tip.

 

MTLEADFARMER, do you have any knowledge of an optimum diameter for the mandrel in the 308 Collet Die? I'll search the web for info but if you know that will save me the research

[gbal]

Mick,try to remember to note velocity on the 'fast' marked case next time you fire it-if it's still a rogue on target,so be it-keep it as your fouler cartridge!

If you do increase powder ,remember pressure signs don't always appear-but a stiff bolt is pretty reliable as a diagnostic.Some of the others blur into agnostic -can't be sure ( small primer brass eg tends not to show symptoms so readily) and as ever,rifles vary.

g

[Murph]

Lee collet dies are fine, don't let anyone BS you. It's more than likely a bad read by the chronograph, 20 rounds is the what I like to run when I'm doing it. You didn't mention trimming cases, if you didn't do so.I also use a lee factory crimp die on everything I reload, I have never seen it degrade accuracy 99% of the time it improves.annealing also helps.

Have to agree with all these points. I found I had less run off using lee collet dies compared to Forster bushing dies. I also use the lee factory crimp die with very good results. I haven't started annealing yet a s I am only loading 223 with lapua brass. As soon as I see any signs of my brass becoming past their best I just bin them.

[Guesty]

Duey, your input is most welcome. In fact it's lead me to learn more thanks to the follow up question you inspired me to post. Like I said, the 44.2gr charge weight was right near the top of the load data so a higher velocity didn't seem possible but with the input of the UKV community I'm realising that, at least in the case of Viht data, their max charge is very conservative in my chamber. Now I just need to learn how to safely read pressure signs then I will push the charge weight up when I develop my next load.

 

Brown dog, the "odd one out" is actually 80fps faster, rather than slower. The cases have all been fired 6 times, only ever neck sized and trimmed, but I have not yet annealed them. I'm wobbling between doing it myself (I've got tempilaq in anticipation) or just sending them to Spud because I'm scared I may cock it up From your advice maybe it is time for me to anneal and perhaps I will hone my mandrel a fraction just to increase neck tension. I've marked the case so I will weigh it and measure internal volume too, thanks for the tip.

 

MTLEADFARMER, do you have any knowledge of an optimum diameter for the mandrel in the 308 Collet Die? I'll search the web for info but if you know that will save me the research

I'd keep adding powder at say 0.5gn at a time and testing until I'd reached '308 performance' which is around 2800fps with a 155gn bullet. My Lapua 308 brass is worked by Redding body and Lee collet dies and is on the 12th load. I've not felt the need to anneal yet. I recently have had to anneal brass for fireforming to another calibre and it was surprisingly straightforward.

 

Undersized Lee mandrels are available, but maybe hard to find in the UK:

 

http://leeprecision.com/undersize-mandrels/

 

Perhaps you could hone yours down 2 thou to match the Lee offering? If you muck it up Hentry Krank have standard replacements.

[alcesgigas]

Already mentioned, but it's worth another go: if your chronograph was a sky-screen type chances are very good that the odd one out isn't. I've had three sky-screen type chronos and they all gave erroneous reads from time to time. Since acquiring my MagnetoSpeed V2 such happenstance is history.

 

Another way to eliminate flyers I and many others found is to treat bullets and bore with hexagonal boron nitride (hBN). I was skeptical a year ago when I started doing it with my LRKM in 338 Terminator using 300 grain OTMs. My objective was to retard barrel errosion and eliminate the fouling shot. I know hBN delivered the latter and the jury's still out on the former, but it looks good. This last suggestion may not be related in any way to your singular experience, but it may prevent similar for altogether different reasons.

 

Good Shooting

[Chanonry]

Well lots of things in reality.

 

The flaw here is that this is a sample size of 5. And you are trying to chase down an error on the basis that you believe there should be an obvious cause/effect and that is must be a factor within your control. That is an unrealistic assumption in my opinion.

 

It may have been neck tension - Collet dies do have their issues. I use bushing dies but I believe the best loadings I ever achieved were with a collet die. If there was a tension issue with one case we will never know now.

 

There may have been a dimensional issue with the bullet, bearing area, specific point you measured was high etc etc etc.

 

Scale may have had a blip on that load etc etc

 

Crony issue...

 

So far I have 5 potential sources of error without trying very hard and you are trying to diagnose a systemic fault (which may not exist) on 5 data points ? Does not work. Get a much larger sample size do a proper data analysis, see if there is a statistically valid error and then run some experiments to isolate the key variable.

 

Most of us can't be bothered with all that crap, just ignore the miscreant and load another round....

[kenbro]

Assuming it might be a neck tension issue, you can't be sure all necks will have the same tension if you haven't made sure all the necks are the same thickness.

Ken.