Velocity variation observation...

[bully_eye]

Now I know that there are numerous reason for velocity variation and what I'm about to relate is by no means conclusive or even very scientific but...today I was having a play with a mates' MagnetoSpeed chrony. I have NEVER used a chrony before. I had two batches of 308 ammunition. One which had been loaded about two months ago. One which I'd loaded last night. Using several times fired Lapua brass and Berger 175's the batch I loaded two months ago went from about 2660fps to 2695 fps. The 3 remaining rounds from the batch I loaded last night went from 2710-2715fps. Could the brass necks have loosened off enough (and unevenly enough) over two months to account for the lower velocity and pretty average es and sd or conversely did the rounds I loaded last night just have more consistent neck tension? I do wish I'd had more left of the batch I loaded last night to have made a bit more of a comparison but 5 fps es for 3 shots was certainly heading in a better direction. Oh and same batch of 2208, projectiles and primers.
Any thoughts or observations (apart from comments on my less than scientific sample group and haphazard experiment techniques ) ?


Michael

[DaveMc]

OK Michael I will resist pulling it apart too much but will make the point that with a 3 shot sample it is still very likely there is NO difference between these two groups. Just random chance can bring 3 shots together pretty commonly even with terrible sd.

In saying this however there seems a significant following of people that believe neck tension changes over time and you will get better velocity spreads from freshly loaded ammo. Some even load their ammo to a longer seating depth and then just push them in a bit further on the night before competition (takes some discipline to ensure it is done each and every time though)

I believe the theory is sound and it is possible for this to occur, not so much from "neck tension" but chemical reactions between brass and copper bullet that can "bond" projectile to case to differing degrees. Over time the two different metals effectively cause galvanic corrosion aided by neck lubricant.

Sounds feasible in theory but I have never seen results to prove this one way or another and think it would be highly variable from one loading process to another anyway (ie some would see it others would not).

Why don't you load 50 and put them back in the cupboard for a while and do the experiment again for us - would be very interesting with some solid data.

[bully_eye]

Again I apologise for my poor sample pool and maybe if I'd mixed the three new ones amongst the older ones....no I'd still need a much bigger sample pool. It's unlikely I'll ever intentionally load up 50 rounds to not shoot for a few months but it could happen. I usually load the night before or a least within a few days of my next shoot. I will chrony my next batch though just to see if the higher velocity MAY be linked to a firmer neck tension or at least freshly loaded rounds.
I fear that like people with bore scopes, exposure to other bits and pieces like a chrony is only going to add more questions and few answers.
Michael

[DaveMc]

Yes they do Michael and I certainly didn't mean to have a go - my data is also filled with literally thousands of 3, 5 and 10 shot tests as well. It is the nature of shooting that we can't burn out barrels etc for all the things we would like to test but with a forum group a lot of these things can be done by many. ie you test this one, I test another etc such that the load (for what of a better term) is shared and greater general group knowledge is gathered.

[BATattack]

its interesting reading. when I do load development I usualy try and do a ladder test at about 500 or a bit more depending on the conditions.

I shoot different loads round robin through a CED M2 and have a guy down the pits numbering every shot. at the same time I record the velocity of every numbered shot. when corresponding targets and fps are collated more often than not a high velocity shot (within reason) doesn't actually prove to print high on target or vise versa.

what does this mean?? to me it shows that the equipment we use has more accuracy error than the actual effect of the error at long range. ie whats the point of chasing low ES when the equipment you are trying to measure the results with are not accurate enough to provide real data.

I wonder what other people have found? have you been able to reliably show that a low or high fps shot does actually hit the target in the expected position?

[IanP]

Hey Adam, I think load development at 500 or greater (yards/metres) is a brave move. Lots of environmental disturbance over such a long distance. I know there is a pool of thought that adheres to doing long range load development but I have never been a fan of long range or using the "Audette ladder system" for load development.

I have always done load development at 100 metres and preferably at Para Rifle range which is fairly well sheltered in a tight and deep valley. Winds and thermal effect are minimal and shooting off the bench under cover in shade makes it a great facility to use chronographs etc.

Shooting on calibrated paper targets at 100m metres means I can see thru the scope exactly where my bullets are leaving holes and I can clearly see the difference in elevation for differing velocities. Its not just me that thinks load development is suited to 100m people like Robert Whitley to name just one, also favor this distance for the reasons I have given above.

I have consistently found in the short 4 years I have been F-Class shooting that the groups I shoot a 100m are a very accurate indication of whats possible and will be shot consistently at 1000 yards. The long range target shooter can have confidence in the loads developed at 100m.

Erik Cortina, USA F-Open team member has a long running thread over on accurateshooter.com titled long range load development at 100yards. Look here http://forum.accurateshooter.com/index. ... =3814361.0

Something different for you to consider trying Adam, when you next do some load development.

Ian

[Quick]

I do all my load testing at 300m. Its far enough that elevation starts to show up and close enough that enviromentals wont have too much of an indication. But I will also see how flat it shoots at 600yds and 1000yds. But I've found that a load that works well at 300m, shoots well at 1000yds aswell.

I havent shot at 100yds/m in ages and dont think its far enough to tell me much but I have read Erik Cortinas thread and I know some people have good results with 100yd loads too.

[DaveMc]

its interesting reading. when I do load development I usualy try and do a ladder test at about 500 or a bit more depending on the conditions.

I shoot different loads round robin through a CED M2 and have a guy down the pits numbering every shot. at the same time I record the velocity of every numbered shot. when corresponding targets and fps are collated more often than not a high velocity shot (within reason) doesn't actually prove to print high on target or vise versa.

what does this mean?? to me it shows that the equipment we use has more accuracy error than the actual effect of the error at long range. ie whats the point of chasing low ES when the equipment you are trying to measure the results with are not accurate enough to provide real data.

I wonder what other people have found? have you been able to reliably show that a low or high fps shot does actually hit the target in the expected position?

Absolutely. But as discussed in a previous topic you can get velocity compensation from some barrel vibrations at shorter ranges that help with vertical (as per Audette ladder) so 3-500 yard cvelocity vs height plots can get more confused. If you want to load develop at short ranges it must be accompanied by a bloody good chronograph for accuracy at long range (or at least have low velocity spread whether you measure it or not). I highly recommend a magnetospeed or PVM to do this properly. A group can shoot under quarter minute at 100 but if it has a 40 fps velocity spread it will cover greater than 6 ring elevation (in perfect conditions) and much worse when the range starts playing with it. I am very lucky to have access to a very calm 1000 yard range with almost no vertical wind effects (especially late in the afternoon). With a rifle that can shoot great elevation at 300-500 yards (or 100) the plotted elevation tracks almost exactly with velocity at 1000 yards in all our testing (and trust me there has been truckloads! and quite a few barrels/rifles).

but we are getting off topic a bit.

[johnk]

I understood that ladder testing was designed to achieve a spread of loads that gave the same coincidence of point of impact at a given distance, which proposition presupposes some beneficial relationship between velocity & impact point for a (limited) range of loads. The midpoint load of those with coinciding impact is usually selected as it offers the greatest fudge factor for imprecision in charge metering technique.

Like Ian, I've always (for somewhat more than a decade anyway) done my load testing at 100 yards over a chronograph, my expectation which is usually achieved being that the load exhibiting the smallest spreads (& SDs to a lesser degree) can be coaxed into exhibiting useful performance on paper over the full range of distances that it is to be used over. Coaxing usually involves tweaking seating depth or a barrel tuner, but occasionally will involve substitution of a component (a lot number of a primer or powder, for example).

John

[DaveMc]

Yes totally agree John. If you develop a load that is angularly accurate (short range etc) with low velocity spread it should be accurate right through. Same supposition can be made in reverse if done at 1000 (ie if it holds great vertical and has tight velocity spread then it will more than likely be a great 100m load too)). So many ways to skin this cat.

Compensation/audette ladder type loads can make up for poor velocity dispersion but generally only over a limited distance (e.g. 300-700) etc. An added bonus is they can be spectacularly accurate at these ranges if coupled with good velocity spreads.

[Quick]

So how many do their testing over a Chrony? Ive always just worked up a load that shows little to no elevation at 300m (.75" or under vertical) and run with that. I do have Chrony but I have a great mistrust of it.

[IanP]

So how many do their testing over a Chrony? Ive always just worked up a load that shows little to no elevation at 300m (.75" or under vertical) and run with that. I do have Chrony but I have a great mistrust of it.

A chrono is a big help in load development and really an essential. How else will you accurately know your ES and SD or muzzle velocity. As others have said before the Magnetospeed V2 is as good as it gets and the new V2 with its adjustable and longer bayonet is the one to buy for f-class. The much bigger muzzle blast cut away eliminates the elevation difference that the original version caused. The old version as you rotated the bayonet around the barrel the group would be slightly shifted to the opposite direction the sensor platform was facing. Muzzle blast "pushing" on the sensor platform caused most of the shift to the group with the original V1 Magnetospeed. Very minor problem but the the V2 doesn't suffer from it in my testing with heavy barrels.

My ideal load testing conditions would be to shoot in a tunnel 100 metres long and totally wind and mirage free. I would then know what I see on the target is what is possible under perfect conditions. I just need to win x-lotto to enable purchase of a property and construction of a tunnel.

Second choice would be to move to Qld and get conditions that are much better that I experience down here in SA. Dave, any properties for sale near you

Ian

[Quick]

Ian,

I see you point. The other way I have worked out my MV is by zeroing at 300yds/m and then based on drop to 1000yds (with correct enviromentals) I can get a pretty accurate MV. I did this for my 308 Berger load and it works perfectly out to 1000yds. I need to rezero my 6mm as my previous zero was done with my copperhead load and my current load is with SMKs.

However I dont know my ES or SD of my load at all beyond what I see on target at long range. Im usually trying to get my load to 1/2 to 3/4 X Ring at all rangs in elevation.

[Brad Y]

After using a magnetospeed the other week I quickly realised the value of an accurate chrony. The shooting chrony I currently have is not worth the box it comes in at telling me anything reliable. But shooting over the magnetospeed showed a velocity around 2875fps with a good ES for the few shots I put over it. Without the magnetospeed on the rifle it shot 3 shots all level waterline at 300m. I took that load straight to 600yds and shot a 60.8 in a front fishtail wind. More importantly it gave me an inkling on extra powder to try and get into the 2930fps node, which has since shown even more promise in terms of vertical. Im yet to chrony it with the magnetospeed- will do this weekend hopefully.

I dont think SD tells you much and quite alot of well respected shooters in the USA will agree- its just another statistic. If you have a good ES then your SD is going to be good anyway. What we all want is single digit ES.

I have also worked up loads the long way which is measuring vertical at long range and testing it through all the shorts and longs over a period of a few weeks. It works fine, but puts more rounds through the barrel than using a chrony probably would. Im going the chrony route now as soon as the tax man comes I will get myself an MS2.

The main problem I see at 100m testing is our guns are capable of making one hole groups at that range. If your measuring lots of one hole groups its easy to say well they all "work" when really one may shine at long range and others show vertical. I feel 300m just gives a group a bit more opportunity to show you something. Now with ET's you can set the monitor to give you X and Y dimensions of each shot on target. Write them down, plug them into a spreadsheet and you will soon have an idea of what shoots best vertical. Chrony that load for a few 10 shot strings to get an idea of ES and if its around or under 10 then the only other tuning you can do is seating depth.

This thread and also the other one on tuning a 284 where Dave shared (again ) more info on how he does his testing really shows how switched on some people are at load development.

Ian your idea of a tunnel would be awesome, even a heap of sea containers stacked all in a line with each end cut out and one of these
www.bullseyecamera.com at the end on the target.

[johnk]

There's a lot of discussion, particularly among rimfire benchresters about the interesting eddies that occur in confined spaces & the tendency of loads to shoot away from close hard surfaces. Apparently, the tunnel isn't all that ideal after all.