Mastering velocity ES 284W

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RDavies
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Re: Mastering velocity ES 284W

#16 Postby RDavies » Tue Oct 17, 2017 8:12 pm

Some of the earlier 183 Sierras were undersized and might have gone well in the tight freebore you have, but the later lots are closer to normal size, while the Bergers are very slightly oversized. It is likely that a gunsmith can run a standard spec reamer in your chamber without having to touch the threads or anything else so it should be an easy fix.
I agree the 9" twist is not enough for 183s at 284 velocities, especially if weather is cool so the 180 Bergers would be the go. If you decide on 180 VLDs, just jam them .010" and tune powder loads around the 2830 area and experiment with .3gns either side of that speed, you should be close then or at least notice a trend.
As for bad ES once the barrel is fouled. Some barrels get better ES once they get more shots though them, while some get better ES when they are relatively clean. Each barrel is different, you will have to check yours once you get the chamber recut.

Audax
Posts: 16
Joined: Wed Sep 27, 2017 8:48 am

Re: Mastering velocity ES 284W

#17 Postby Audax » Wed Oct 18, 2017 4:19 am

Hi Rod,
Yes the SMK"s are right on the edge of stability so I do keep the rounds in a 12v sandwich warmer approx 35C. temp. when the ambient temperatures are cooler.

Problem was as I explained trying to maintain 2857fps limits with the ES wandering around the 2840fps region there is the risk of exceeding the max. Solution is to cure the ES or consider Bergers as you all have suggested. 180gr Bergers also have a bigger window of opportunity being lighter the limit is 2882fps.......looks like all roads lead to the Berger door.

I will open the freebore clearance at least 0.0005" try that and post the results here if you are interested....?

Norm
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Location: Gippsland, Victoria

Re: Mastering velocity ES 284W

#18 Postby Norm » Wed Oct 18, 2017 9:58 am

Audax,

Keeping your rounds in a sandwich warmer may not help with bullet stability. Although it may slightly help maintain your muzzle velocity by about 10fps or so.

I have found that keeping rounds warm does help greatly with ES in large capacity rounds. ADI powders are quite temperature stable but do perform better when shot at a warm temperature. I think this is why shooters from the warmer states have such good results and us poor Victorians struggle with our loads during frosty months.

Audax
Posts: 16
Joined: Wed Sep 27, 2017 8:48 am

Re: Mastering velocity ES 284W

#19 Postby Audax » Wed Oct 18, 2017 12:28 pm

Yes Norm I have heard they can get a bit erratic at lower temperatures, and it appears there can be as much as 20fps with 284W over the range of summer and winter temperatures we get. I only keep them warm to mitigate the ES not to help the stability....hopefully keeping them warm and up to speed will enable that.

Try heating them in a portable unit. They cool off rapidly once out of the heater, but after a few shots the chamber temperature should keep them warmer than the ambient temperature. The rounds can get very hot so I place a wheat bag in the bottom which acts like a heat sink and also moderates the temperature to ~40C max.

Those shooters from the warmer states also have to contend with flies, but that is still better than flyers I guess........

Gyro
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Location: New Zealand

Re: Mastering velocity ES 284W

#20 Postby Gyro » Wed Oct 18, 2017 3:03 pm

My own experience has me totally convinced you need to keep a very close record of the ambient temp when you develop a load. If you develop a load that happens to be at the lower end of a node on a warm day, then that load shot on a cold day will likely NOT WORK. Same with a load developed on a cold day at the higher end of a node will likely give u issues if shot on a warmer day.

Guys manipulate these factors by putting the ammo in your pocket for the early morning cooler temp ranges, or place the ammo in the sunshine, or actually letting the warm chamber do some heating by closing the bolt early on the next round ........ lots of tricks to help the cause !

A "temp stable" powder does NOT mean you don't need to worry about the temps.

Audax
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Re: Mastering velocity ES 284W

#21 Postby Audax » Fri Oct 20, 2017 12:50 pm

Further experimentation today revealed some interesting data. The freebore was enlarged to 0.2844" (half a thou larger than the bore for testing the SMK projectiles [ID 0.2839"]) meaning by default the Lapua Scenar-L now has zero clearance. Interestingly the results for both projectiles with zero clearance yielded similar results.

It still remains a mystery why the ES/SD reduces as the freebore is enlarged......do I now enlarge it to the dimensions Matt is alluding too......?

Freebore result and calcs.xlsx
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pjifl
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Location: Innisfail, Far North QLD.

Re: Mastering velocity ES 284W

#22 Postby pjifl » Fri Oct 20, 2017 2:22 pm

I have given a lot of thought to the relative importance of neck clearance and adequate freebore diameter in really long range shooting compared to obsessive turned necks and snug fits in short range benchrest shooting.

Short range shooting can tolerate far more variation in velocity and more of a limiting factor is the presentation of the projectile absolutely aligned to the bore.

A small amount of loading runout always presses the projectile sideways against the freebore. More with a smaller freebore diameter. You can check this by felt pen inking the projectile and watching rub marks.

Very small variations in runout - and there will always be some - probably influences the release of the projectile and varies V somewhat.

But the long projectiles used in long range shooting mean that small runout of the projectile will result in much smaller angular presentation error of the projectile to the lands compared to the short projectiles used in BR shooting where precision presentation of the projectile is more important than velocity consistency.

Thus blindly copying short range BR practice is not ideal for LR shooting.

This is nothing more than a theory but I have never seen anything better.

Peter Smith.

pjifl
Posts: 557
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Re: Mastering velocity ES 284W

#23 Postby pjifl » Fri Oct 20, 2017 2:23 pm

I have given a lot of thought to the relative importance of neck clearance and adequate freebore diameter in really long range shooting compared to obsessive turned necks and snug fits in short range benchrest shooting.

Short range shooting can tolerate far more variation in velocity and more of a limiting factor is the presentation of the projectile absolutely aligned to the bore.

A small amount of loading runout always presses the projectile sideways against the freebore. More with a smaller freebore diameter. You can check this by felt pen inking the projectile and watching rub marks.

Very small variations in runout - and there will always be some - probably influences the release of the projectile and varies V somewhat.

But the long projectiles used in long range shooting mean that small runout of the projectile will result in much smaller angular presentation error of the projectile to the lands compared to the short projectiles used in BR shooting where precision presentation of the projectile is more important than velocity consistency.

Thus blindly copying short range BR practice is not ideal for LR shooting.

This is nothing more than a theory but I have never seen anything better.

Peter Smith.

Audax
Posts: 16
Joined: Wed Sep 27, 2017 8:48 am

Re: Mastering velocity ES 284W

#24 Postby Audax » Fri Oct 20, 2017 4:36 pm

Yes so true Peter....BR powder loads invariably are "thrown" and so is the brass if a shot deviates from the group.

Not so with the purists....we need BR accuracy with LOW ES, and I do wonder why greater clearances both in the neck and freebore affect the ES so dramatically. And are we making a trade-off in accuracy to lower ES/SD.......maybe.....?

Gyro
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Location: New Zealand

Re: Mastering velocity ES 284W

#25 Postby Gyro » Fri Oct 20, 2017 4:49 pm

Good question. Maybe best to develop a load with a jammed bullet to help with some of the alignment that's being lost here ?

pjifl
Posts: 557
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Location: Innisfail, Far North QLD.

Re: Mastering velocity ES 284W

#26 Postby pjifl » Sat Oct 21, 2017 1:29 am

Maybe I did not explain my theory very well.

I believe with extremely tight or zero tolerances on neck clearance and freebore diameter, jamming the projectile actually works against you with respect to best Vsd.

If there is even a minute amount of cartridge runout, the jam will jack the projectile and case neck sideways. This will result in heavy bearing of both projectile and case neck on one side so extra friction of the projectile as it leaves the case neck.

Moderate but not excessive tolerances will go a long way to negating this effect.

It fits in with what Matt has suggested - a slightly enlarged freebore diameter and not rediculously small neck clearance.

It is also worth noting that it is the ANGULAR misalignment as the projectile hits the lands that causes its axis of rotation to be slightly different from its geometric axis. And with longer range longer projectiles this ANGULAR misalignment will be reduced compared with short BR type projectiles. So the Angular misalignment problem is less severe in long range shooting in any case.

Peter Smith.

Gyro
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Re: Mastering velocity ES 284W

#27 Postby Gyro » Sat Oct 21, 2017 4:31 am

I hear u Peter. As u say it's just theory and is surely a very difficult thing to nail down ?

Perhaps it's a "provisional" theory ?

Extra chamber clearance around the case and bullet can perhaps be proven to improve JUST the ES ?

I would wonder if the extra friction from a bullet touching on one side of the freebore section would be in the same order as the extra friction from varied neck tensions. Variations in neck tension - and by implication annealing - is I notice these days being increasingly believed to have negligible effect on ES.

Audax
Posts: 16
Joined: Wed Sep 27, 2017 8:48 am

Re: Mastering velocity ES 284W

#28 Postby Audax » Sat Oct 21, 2017 7:50 am

Yes Peter unfortunately we do have these theories that are difficult to implement. You did explain enough for me to understand exactly where you are coming from.

It is precisely that alignment theory that was behind the design for my reamers and re-sizers. I have four and three work exceedingly well, except for the 284....which has the ES problem. The other three 6.5 x 284, 6mm Dasher, and 7mm SAUM have ES of max 3fps and 100yd grouping capability of ~0.25". The 284 will do that too, but strangely increasing the freebore clearance from zero to 0.0005" the ES has halved from ~40fps to 21fps.....blows all my theories out the window......!

That theory is the cartridge when chambered will be supported by the base and the projectile, virtually self-aligning with 0.001" clearance at the body/shoulder junction. Runout on the case neck and bullet tip is zero in 98% of loaded rounds. Consistent zero neck runout is very important, and can only be achieved by special attention to the neck walls which are quite variable from the factory. The trick is to run up a mandrel on the lathe at the nominal bullet diameter, and press the case onto it, machining the neck to 0.0005" - 0.001" under the chamber size, then fire-form it. The outside is now as true as can be, then with all mounted in the lathe, use an adjustable reamer to true the inside to the axis of the body. Repeat the "mandrel" exercise, but this time machine for your finished clearance requirements ....voila runout solved......! Some care is required to ensure the headspace is consistent not to compromise the self-aligning virtues, but is easily achieved with good annealing practises.....

I know there are many that advocate "no-turn" necks, but I cannot understand how that works given the intrinsic misalignment present....! There will be also many who say "works for me", and that is what I need to understand so I can spend less time in the workshop, and more time playing tiddly-winks......!!!


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