OzFclass

Similar to the previous subject on variation.
I use a magnetospeed chrony for testing and cannot get ES under 15f/s. The chrony has given me various speeds at various loads which are acceptable, I've altered jump & jam to no end. with various loads the ES can go from 60-15 f/s. The question is, would neck turning improve this ES or do i accept 15f/s as good as it gets. Or could it be a barrel issue?
By the way, I'm using HBN coated projectiles.
Geoff

I would be happy with ES15'/s for 10 shots

Geoff- have you cleaned the barrel and tried non coated projectiles? A few people have turned away from HBN and either gone back to moly projies or naked projies as they found it made thier nice shooting rifles into shotguns.

More so, what do your targets look like? If you have good waterline/little to no vertical, then I would say leave it. I think some people are also jamming bullets to help reduce ES for long range.

I cant say i have much experience in this area but if you run a 15fps spread through a basic ballistics calc (15gr 3000fps .5BC) you only have a differnece of 3-4" at 1000y yards. I would be happy with that.

I'm one who went from HBN to moly. It seemed that they were giving erratic velocity spreads - good one minute & oh,dear the next. When I went back to moly, my 210 match rifle loads went under 10 fps (admittedly with PMC Russian primers) & the 6BR became a one holer.

In hindsight, I don't see much difference between HBN & naked bullets velocitywise for the same load, which leads me to believe that the coating process(es) I was using wasn't modifying the coefficient of friction like moly did. I'm guessing that I ran some loads on the ragged edge of disaster because i believed that they would act similarly to moly.

John/BradY
Vertical is the main problem & a stray wild shot. A pity i have coated them all. might have uncoat them somehow to do another trial. The way I'm going the B barrel will be worn out on testing. (only 300 rounds so far)
I hear what everyone is saying that 15f/s ES is ok but I'm getting a lot of vertical. Very careful loading, weighing/ batching projectiles etc that's why i thought maybe neck tension might be an issue to look at and cleanup the necks. (Projectiles are easy to push in)
Geoff

I will echo Barry's comments. I would also be extremely happy if my ES for 10 or 15 shots was 15. Not so happy if the best ES of all my 3 shot groups was 15 and worst was 60.

Please bear with me through the waffle.

Our velocity variations follow a "Gaussian" or normal distribution. In fact the normal distribution we see is affected by numerous factors which all have their own normal distribution (e.g. case capacity variations, bearing surface length variations, powder weighing, bullet weights, primer variations, neck tension variations, powder variations, barrel effects, gas sealing etc etc. etc etc etc (and more etc). These all overlay and combine to form the measurable effect of velocity spread and even the measurements (chronograph readings) have their own errors that follow a normal distribution.

NOW HERE IS THE CATCH: Reducing the error in one part alone will not necessarily have a corresponding magnitude of effect on the total velocity variation. Let me give you an example. Lets just say you were weighing powder on a cheap set of scales and your weights were varying significantly (e.g. sd 0.1 grains, es typically 0.4-0.6 grains)). Using a 6BR as an example this might exhibit itself as a velocity variation sd of around 10 fps by itself (es of 40-60 typically). Lets say your total measured sd is somewhere around 15. It is a mistake to think this is additive and that by removing the weighing variation you will see a corresponding drop of same magnification in velocity sd. By purchasing a set of top shelf laboratory balances to bring down the weighing error to sd 0.01 grains almost definitely will not see your velocity sd drop from 15 down to 6 fps unless you are doing everything else almost perfectly.

The big mistake made by a lot of "testing" is to tighten up on one factor (e.g. sort shells by case capacity or improve weighing of powder) test again and see no reduction in velocity spread and hence discard this factor saying it has no or negligible effect. This is even worse if just testing ES of small numbers of rounds.

What does all this talk of ES and SD mean in the real world.

If the rifle has great angular accuracy (e.g. can shoot quarter minute 100m groups) then an ES of 15 fps (over 10 + shots) should have an sd around 3-5 or below and will hold the x ring in vertical at 1000 yards for most of the time (the odd shot into the 6 ring).

As a rule of thumb you should use sd (not es) and an sd of around 10 fps over 10-20 shots will allow for 90% of shots to fall in the 6 ring. To hold the x ring you need to see sd down around 5! (and have good short range accuracy). Don't pick your best 3-5 shot string re ES - this will not give a true representation of what is going on.


ALSO Don't underestimate the effect of a barrel. I use the same load in lots of barrels. Some will consistently show SD of 3-5 in 10-15 shot groups. Same load in another barrel will show sd of 10-12!!!

I would like to enter a motion that everyone sends their barrels to dave for load development

ALSO if your velocity spread really is only 15 but you are still getting long range vertical - come back into 100m and test the accuracy. Some other problem (aside from loading) may be the cause. e.g. bedding, scope, barrel, technique etc, etc, etc.

Ok, I'm testing with 5 shot loads to find the speed I'm after and with every load jamming then jump, all the while looking at ES. Still getting vertical. Sd is quite good. so maybe a techinque thing as i have had a couple of good scores but mostly crap scores with vertical.
Geoff

Dave,

So your saying that ES really doesnt tell us much as SD, as long as you have an SD as low as possible, your ES and vertical should be good?

Man I think I need a Chrony..........

Some more rules of thumb.
You can't really calculate sd effectively with 5 shots (and certainly not 3) so ES is your only real indication BUT

If you do a "ladder" or string of 3 or 5 shot groups and measure the ES of each group -some by chance will be much smaller than others and it can mean very little. In other words ES of 3 or 5 shot groups are very prone to giving false positives. But should be treated as an indication of where to explore further. ie you can do load development like this but then needs verification e.g. 10+ shot groups (preferably with a chrony) of your given load - alternatively test at the range and see if it performs well in 10 or 15 shot matches - don't be surprised if it doesn't.

Shaun

They are all statistical values from one set of numbers. That set of numbers is critical. If you shoot 3 shots like dave said, you dont get a good representation of what you velocities are. Shoot a few 10/15 shot strings to get your initial data then work out your ES (max velocity minus min velocity) Then you can get an idea if your SD will be low. To calculate your SD you are getting your mean velocity from the data then working out the average amount shots vary from that mean velocity.

The velocities I told you for my rifle were indicative only, now way I would run ES and SD's seriously from 3 shots. It was more of an "I wonder" exercise.

As to whether it will show good waterline at 1000yds or not, well Im growing to like figures, but end of the day the target never lies. My 2213sc load sure shoots good vertical at 300m and at 600yds but what does it look like at 1000? Wont know until I prove it during club shoots.

Brad,

Well I look forward to seeing how it shoots. I may not be able to come this saturday due to commitments with the horses. Have to pick up our horse from the Vet

I do need to see how good my SMK load shoots though from my rifle over the chrony.

I don't know if any one has missed Geoffs bracketed post ( projectiles are easy to push in) well I see a problem there as seating depth and neck tension are an instant issue.
Geoff change your neck bush to a tighter one, 2-3 thou tighter or if you have non bushing dies borrow one to try.
Cheers
Paul