Getting the best from our projectiles

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mitchellchandler_au
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Getting the best from our projectiles

#1 Postby mitchellchandler_au » Tue Oct 25, 2022 6:27 pm

Howdy all,
Was thinking the other day about what is the best or is there a best way to batch our projectiles. I was playing with batching by bearing surface into 0.002" lots and weight sorting into 0.2 grain lots. Is there any other way to batch projectiles I have missed? This being said I shoot fclass standard and will be playing in FTR soon. Is it worth the time and energy to do batching?
Firepower usally means an increased number of misses per minute. 50 misses are not firepower. One hit is firepower

Old Trev-39
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Re: Getting the best from our projectiles

#2 Postby Old Trev-39 » Tue Oct 25, 2022 7:55 pm

I have found variations in the base to the position where seater stem sits on the projectile. As this point governs or seating depth, any differences here, will deliver those differences to our jump setting. Maybe not as important in large jumps, but those working close to lands could have problems. I found this a good few years ago when checking base of case to ogive, and was getting a reasonable variation, which caused me to investigate further, and found the difference in the afore mentioned measurement.
Cheers,
Trevor.

AlanF
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Re: Getting the best from our projectiles

#3 Postby AlanF » Tue Oct 25, 2022 10:40 pm

Benefits of batching of projectiles in my experience vary depending on different brands and batches within brands, which may have a variety of uniformity problems. Lets say you've just bought 500 projectiles, hopefully all from the same manufacturing lot. You should then measure a sample of them (preferably not less than 30) in various ways. Base to ogive, OAL, inspect meplats for uniformity, and also weigh them. Then decide from that sample what problems are typical of that lot, and only do the batching that they need.

Base to ogive uniformity is a good indicator of manufacturing quality. But variances can be due to mixing the output from multiple machines, something Sierra has done in the past (and may still do). If there is variance in base to ogive I would batch into 0.003" intervals.

OAL is often overlooked but I've had batches that are very uniform in base to ogive, but up to 0.025" variance in OAL, which is bad for BC uniformity and hence bad for LR vertical. In this case either batch to 0.005" intervals or meplat trim to several batched lengths, and use the longest (highest BC) ones at long range.

Inspect meplats for uniformity of the diameter. If they clearly vary then meplat trimming may help, or alternately batch into 2 or 3 heaps based on diameter, and use the batch with smallest diameter for LR where BC uniformity is most critical.

Weight variation is generally not taken as seriously as dimensional variations, and I believe the reason is this. I remember seeing an analysis of this and it was calculated that a heavier bullet will have a slower muzzle velocity, all else being equal, but on the other hand it will usually have a higher BC because of the extra weight with the same cross-sectional area. So at LR, there will be a tendency for the two vertical effects to cancel each other out. If you do weigh bullets, I would just use it to cull out the extreme ones.

That's my 2 cents anyway. :D

AlanF
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Re: Getting the best from our projectiles

#4 Postby AlanF » Tue Oct 25, 2022 11:03 pm

Old Trev-39 wrote:I have found variations in the base to the position where seater stem sits on the projectile. As this point governs or seating depth, any differences here, will deliver those differences to our jump setting. Maybe not as important in large jumps, but those working close to lands could have problems. I found this a good few years ago when checking base of case to ogive, and was getting a reasonable variation, which caused me to investigate further, and found the difference in the afore mentioned measurement.
Cheers,
Trevor.

Thinking about that Trev, I'm not sure your deduction is correct. The seating process sets the distance between the seater stem contact point and the base of the case (not the base of the projectile). All that happens with projectile base to ogive variations is that the base of the bullet seats at various depths in the case, and the jam/jump setting should not be affected?

Tim L
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Re: Getting the best from our projectiles

#5 Postby Tim L » Wed Oct 26, 2022 8:44 am

AlanF wrote:
Old Trev-39 wrote:I have found variations in the base to the position where seater stem sits on the projectile. As this point governs or seating depth, any differences here, will deliver those differences to our jump setting. Maybe not as important in large jumps, but those working close to lands could have problems. I found this a good few years ago when checking base of case to ogive, and was getting a reasonable variation, which caused me to investigate further, and found the difference in the afore mentioned measurement.
Cheers,
Trevor.

Thinking about that Trev, I'm not sure your deduction is correct. The seating process sets the distance between the seater stem contact point and the base of the case (not the base of the projectile). All that happens with projectile base to ogive variations is that the base of the bullet seats at various depths in the case, and the jam/jump setting should not be affected?

I think the point Trev is making is that there can be variations between the ogive and the place where the seating stem makes contact. i.e. when we seat we are "trying" to ensure the ogive is a set distance from the head of the case but any variation in the profile of the front taper of the bullet will lead to a variation in that length.
Pretty sure everyone has experienced the odd loaded round that just comes out different!
Unfortunately a variation in the bullet shape isn't the only cause.
Stiff seating will cause the shoulder to compress when the bullet is inserted, it will then spring back giving a longer round.
Recently I'm also finding more "unround" bullets. They wobble in the comparator, turn them 45 and they wobble on that new access. Essentially they are oval at the ogive. I have some pretty good measuring gear but can't measure this, but it's easy enough to feel.

AlanF
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Re: Getting the best from our projectiles

#6 Postby AlanF » Wed Oct 26, 2022 9:31 am

Yes Tim. Seating stems usually contact the ogive closer to the tip than comparitor nose-pieces, so if the ogive varies in shape it'll give rise to Trev's findings. And where neck tension is on the high side and variable it'll result in varying jump/jam amount. When a loaded projectile shows a prominent mark left by the seating stem, it usually indicates high neck tension and shallower seating.

If you want to check for ogive shape variation, one crude way is to use several different calibres of comparitor e.g. for a 30 cal projectile check base to ogive with 7mm, 6.5mm and 6mm as well.

Old Trev-39
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Re: Getting the best from our projectiles

#7 Postby Old Trev-39 » Wed Oct 26, 2022 7:55 pm

Hi All,
Tim has recognised the point I was making. The different positions of the stem on the proectile gives us different jump measurements. I have found up to .005" in this. As I said probably not of great concern for big jumps as I use, but would make a difference to those using small jumps or supposidely"JUST KISSING LANDS". This difference would give you asmall jam and small jump variation in your loads which would not bear well. I have never shot closer than .020" and have a 6.5 wildcat that shoots V.L.D's well at .060". Discussing this wit Peter Smith one day he said he found jumps up to .125" did not really affect accuracy.
Cheers,
Trevor.

Snipe
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Re: Getting the best from our projectiles

#8 Postby Snipe » Sat Nov 26, 2022 2:11 pm

When my .223 lost that new barrel accuracy with over 6,000 rounds, I tried chasing the lands and stuff but nothing helped until I fluked it with a much longer jump.
It's not like new but often shoots a clover with the other 2 flying a bit to make it closer to 1 MOA at 100yds rather than the preferred 1/2 MOA.

It didn't work with my other factory 6.5CM varmint barrel though.
I did get it to shoot a cold bore flyer and 4 touching the other week with a mild load 130gr load with 130gr TMK Sierras rather than 140gr ELDm I had been shooting.

Due the projy shortage, I tried a 9-shot load development and a few tweaks either side on the next few shoots.
I was happy as I thought the rifle was just a plate shooter rather than a group shooter.
It is still not as consistent but I enjoy plate shooting more than groups so will shoot it till it's shot out.

ShaneG
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Location: Cairns

Re: Getting the best from our projectiles

#9 Postby ShaneG » Sat Nov 26, 2022 7:18 pm

I have tried most all of the batching measurements and have found ………
My only batch i do now is overall length
If the pills are weight consistent then OA length is determining BC
I have also been down the meplat and point route
Even there you need to sort by OA length first and think only useful for ELR?


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