Ladder testing 284 Win with 2213sc powder

[DaveMc]

Compensation is a reality but is brought about by large variations in projectile speed -- as was the case with older military ammo.

The old 303 is a very interesting case and many shooters claimed great compensation - it is easy to understand when studying the action design. Rear locking lugs , huge cutouts for magazine and ejector ports. Under firing the 303 would cause huge vertical migrations of low frequency. Tuning a full wood 303 to military rounds was a real artform and amazing reading.

I wonder how much longer range compensation may be possibly due to poor BC of the older Projectiles. Faster bullets slow quicker than slower ones (especially when not designed with low drag) so at longer ranges the velocities could start to even out. imagine at 700 yards say and the bullets are well compensated at this point - then they are also more consistent in velocity than when they left the barrel.

[macguru]

This is all very interesting.... I have a maths/physics degree but i have tried to arrive at empirical solutions to these issues because there are so many variables....

In plain English, you have a metal bar clamped at one end and free at the other that gets a jolt when the cartridge fires. The shock wave travels 10 times faster than the bullet so by the time the bullet gets to the muzzle the whole thing is oscillating in mixed wave motions that have absorbed the energy. It has waves transverse and longitudinal in the barrel that deflect the muzzle position at the time of exit of the bullet. The pattern of vibrations changes likes the octaves you get in music, but in each case there is a node at the action end and an antinode near the muzzle. As the vibrations change so does the group pattern printed on the target, under ideal conditions. It is physically impossible to remove the oscillations so what we are trying to do is minimise them , or ensure that the bullets lets go in the same sweet spot all the time........

I will try to go further with this mathematically but i think that ladder test is a great idea. The trick is to do it (tuning) experimentally with the minimum barrel wear ! Imagine my joy when my 6br shot bughole groups at 100m during break-in, using a friends load data !

[AlanF]

Another type of compensation is related to variation in bullet weight. A lighter than average bullet will generally have a higher velocity, but a lower sectional density, so will start faster but slow down faster and at some point have the same trajectory. This is why weighing bullets is seen by many as unnecessary.

This is an interesting discussion that you've brought about Tony. Thanks Dave and others for contributing. I consider I have a lot to learn about tuning - have tended to rely on taking several barrels to a Queens, and try them all in the leadup, then choose the "least worst" for the Queens.

One thing I believe about statistical analysis of load performance is that its more economical to ELIMINATE loads than to SELECT them. For example, it only takes two shots that are say 0.8 MOA apart to decide that you won't try that particular load again. This is what I like about ladders - you can quickly see powder charge "zones" that are not worth pursuing, then continue to eliminate other zones until you're left with something that hasn't put a foot wrong, so to speak. On the other hand, pouncing too soon on an area that looks promising can end in tears, because you may only find a problem after expending 20 shots or so, and then have to go back to square one.


Alan

[DaveMc]

This is all very interesting.... I have a maths/physics degree but i have tried to arrive at empirical solutions to these issues because there are so many variables....
!

What I am finding really interesting is the effect of different rifle designs. For those that don't have it I suggest grabbing a copy of "Rifle accuracy Facts" (Harold Vaughn). He goes into some fantastic strain gauge testing of hunting rifles and how barrel vertical impulses are caused by recoil lugs, asymmetry of action gas ports and screw holes etc. A very interesting read done by a "rocket scientist" or supervisor of the aeroballistic division of Sandia Laboratories..

Indeed vertical impulses can be greatly reduced by different rifle designs. Particularly in action symmetry, recoil lugs, heavy metalwork - light stocks, reverse taper barrels (or heavy barrel tuners) etc etc it goes on and on.

Alan - yes not only in external ballistics does the bullet weight compensation occur but also internal ballistics as well. A heavier bullet will build more pressure and hence "partly" compensate for what you think would be lower v. In fact it is a squared relationship and Vaughn covers this nicely (and succinctly) in his book as well - so it is a double whammy for bullet weight.

[ecomeat]

Personally I do 3 shot replicated ladders with about 1% load increase and 15 shot strings so this allows me to cover 2.0 grains or so in each with very good feedback with essentially 15 shot strings for velocity sd etc.
.

Dave,
So for me to take this (publicly of course !) to the next level, I should load 3 rounds of each "load".........increasing say 0.5 grains (thats your 1% approx of a 52gr - 55gr load)......and do 5 or 6 different loads (15 or 18 shots all together......plus 4 or 5 foulers to start , loaded at a mid-range load.
And then fired at the 5 or 6 individual targets, shooting all 3 shots of "Load 1", first....followed by all 3 shots of Load 2 at the second target, then all 3 shots of Load 3 at the third target etc etc ??
going back to my original target posted, I could start at load 4 or load 5 ? ie cutting out and not trying to replicate shots 1-3 or 1-4 in my original ladder test ??
Then starting again, going higher to have a look for the next node by working up towards 56.5 or 57 gr max (hopefully over 2900 fps).......probably with cleaning and 4 or 5 foulers after the first lot. So 45-50 shots total.

Bearing in mind that most posters agree that I should at least have a "look" for the next higher node with this ladder testing while I am at it, would I (or could I possibly) get basically the same final info, if instead of shooting at 5 or 6 targets jumping up 2.5 grains total (6 x 0.5gr increases)....if i did two separate ladder tests , of say 12 shots ea.....starting at 53.3 gr 2213sc (load 4 on my original test) and increasing in 0.3 gr increments for 12 separate loads, to a maximum of 56.5 gr 2213sc.....which should be just over 2900 fps. So shooting 12 individual loads on one ladder test target, then keep shooting and repeat the same 12 loads on a separate, second target ??
Wouldnt there be less chance of a novice like me manufacturing groups/results, if i shot two identical ladder tests, one after the other ? I guess what I am really saying here is shouldnt i try to prove that the first ladder test as posted wasnt just sheer arse ? Seriously, i just havent had the trigger time and experience that so many of you have had. Firing shot after shot after shot with exactly the same trigger pull, hand grip, shoulder contact, cheek weld if any, etc is probably something that a lot of you just dont even have to think about, but for me personally and probably many others that might be following this thread, its a bit harder.......... its not so much "self doubt" as it is being realistic enough to accept that i just might have got lucky the first time.
Human error just has to be factored in somewhere !
Or wouldnt it be the ultimate test for this exercise if i did 3 seperate ladder tests of 12 loads each.......which could also be measured and interpreted as a total of 12 x 3 shot replicated ladders, coz all of the data (distance above/below horizontal line through aiming mark, plus velocity) would be separately available for interpretation by whomever could be coerced into contributing !!!

[DaveMc]

Tony,
What I was really trying to say before turning sideways is it is quite OK to do it almost anyway you want to. Single shot Ladders, groups, replicated ladders can all work.

Personally I think you are going to be on the money close to where you finished last time (or in top 4 shots). I reckon start in the top few loads you did previously and work up. But wait for a good chrono - I would be surprised if at 54.5 to 55 grains if you aren't at 2800+ and the "sweetheart" area of most 284's. .

From where you are I think you have already roughed it in - shoot whatever you feel like, one single string ladder with small increments will probably best give you the "range" of the node in the smallest number of shots, replicated groups with bigger gaps will also work, as will 5 shot groups.

Finish it (confirm it) by shooting a 10-20 shot group in the middle of your "node."

Most of all enjoy it and don't let the detractors get you down!

[Brad Y]

Jeez I cant wait til you come back to WA again Dave. I hope you like beer and dont mind people picking your brain apart while consuming the beer.

[DaveMc]

I speak enough sh_t as it is Brad - give me a few beers and it really starts sprouting!

[Brad Y]

Ok then. Beer no. What about rum