Weight variation in 223 AMAX Projectiles

[bobeager]

I have been working up a load for a new .223 7 twist F std job specifically chambered for the AMAX projectile. I started with 3 shot groups using 2206H. What had me scratching my head was that exactly the same load in prepared Lapua Match cases is that one group would be in "one hole" and another would produce vertical flyers.

So I purchased some basic electronic scales and weighed to projectiles! result was 4 distinct batches measuring 79.8, 79.9, 80.1 and 80.2 grains. The result was verified using balance beam scales.

Don't know if this will sort out the problem, will find out this weekend.

has anyone had a similar experience?

I also checked other projectiles in my stock -- Lapua Scenars spot on, Dyer HBC, Nosler 155 & 80's OK, AMAX 6mm 105's also OK.

[Woody_rod]

Thats really great Bob....

Now I have to weight all the stupid bullets as well. Thanks for nothing

[IanP]

The secret for getting great accuracy from the 80gr Amax is getting the chamber throat right (free-bore). Bullet weight will vary the velocity slightly (maybe 4fps) but a couple of tenths of a grain wont produce fliers.

If you want to calculate the velocity difference use this velocity predictor spreadsheet I put together and posted on safclass.com here: http://www.safclass.com/Spreadsheets/Bu ... dictor.xls

Its all been discussed before, look here: http://ozfclass.com/phpBB2/viewtopic.php?t=2343

Ian

[bobeager]

Ian, have used a PTG Uni Throater for additional freebore. was aware of previous thread and mention of Bad boxes".

Rod, could you weigh a small sample from your AMAX's, say 20 to 30, as I would like to know what other people find. my box was manufactured in Oct 2008.

I am using 30 thou jump, as suggestion from someone who really knows his stuff.

I am getting groups from .25 to .35. pretty OK but I am just trying to eliminate as many variables as possible.

[Lynn Otto]

Bob out of interest I grabbed our box of projectiles dated 10/2/08 and weighed a random sample of 50 with the following results:

4 @ 79.7 gr, 12 @ 79.8 gr, 15 @ 79.9 gr, 15 @ 80.0 gr, 1 @ 80.1 gr and 3 @ 80.2 gr.

Obviously they are happier to rip us off for a with of material rather than give us extra.

Of the 4 @ 79.7, 3 flickered into the 79.6 and likewise some of the 79.8 verged on the lowered figured. All up a variation of .5 of a grain.

We did not go ahead with the use of these projectiles, we preferred the Sierras.

Lynn

[bobeager]

I have 1100 of them, guess I will be using the scales.

[IanP]

It would be interesting to test for bullet imbalance. The slight weight difference of a couple of tenths is not a big issue but if it is causing an out of balance bullet then it is a different story. The scales we all use are at best plus and minus 0.01 grain accuracy.

A 7 twist barrel gives more spin than needed to stabalise the 80gr Amax (Sg = 1.6). If the bullet is slightly out of balance then more spin will give greater bullet dispersion down range. I use 8 twist and 7.7 twist for the 80gr Amax with both producing equal accuracy out to 800yds where my club's range ends. I use a 7 twist barrel only for the much longer 90gr Berger VLDs.

This is not much help to you if you only have a 7 twist barrel available but you could give some of your suspect bullets to a friend with an 8 twist barrel to test fire. If you change to 80gr Sierra MKs your 7 twist will now give a Sg = 2.06 to the shorter bullets and your chamber will be too long.

Litz recommends an Sg >= 1.4 (Sg = gyroscopic stability factor) as optimum but the least amount of twist needed to stabilse an out of balance bullet is better. With the 80gr Amax an 8 twist gives an Sg = 1.23 and for 7.7 twist Sg = 1.32. An Sg = 1.0 is the minimum required to stabalise a bullet (any bullet) so going to 1.4 gives a margin of safety but may not be necessary.

In discussion with Malcolm H recently he has noticed some dark stains on the jackets of the Amax bullets. While feeling smooth to the touch it could be lead deposits adhering to the jacket like solder does to copper. If this is correct then this may be causing out of balance on these stained bullets.

Personally I have not had any problems shooting the Amax bullets in competitions and have won club comps and had highest scores using them. Having said that, I am conservative with the barrel twist rate I am using and maybe that has helped me shoot these bullets well.

Ian

[Lynn Otto]

I have 1100 of them, guess I will be using the scales.

We always buy full boxes of things so we have just short of 600 (by the amount we used for testing). They are not about to go stale so they can sit on the shelf, they'll be there if we ever decide we need them.

Lynn

[Lynn Otto]

Ian there are several other reasons that a projectile may be unstable and cause flyers. I can tell you that the weight was not the only place I found variations in what I looked at last night (yeah I was bored enough to sit and closely examine a box of projectiles ) Plus there is at least one thing that can happen in the jacketing process that will cause imbalance, that you will not be able to see.

Anyway I don't see us using these projectiles any time soon so no probs. Incidentally the Sierras are not perfect either so really like many things, it is personal choice and what works for you. But this is one box of projectiles I will be happy to leave on the shelf collecting dust.

Lynn

[Woody_rod]

Interesting stuff, now that we only use the AMAX in FS ourselves. We did use the SMK, but the price is BS, so we don't use them any more. With the dollar the way it is, the SMK (or any US made products) price should be coming down, not going up. Someone is having a go at us with the importing price I reckon.

The price is not the only thing we use to decide on projectiles of course, as the SMK has its problems as well. Our rifle is now set up for the AMAX, and simply wont shoot SMK's at all.

To make this discussion more complete, we should weigh some SMK's. I have a box that I use for our club rifle ammo, so can do this.

[Woody_rod]

Outcome of weighing some bullets this morning: (all in grains, and no particular total number, just a handfull)

SMK

79,80 = 1
79,85 = 3
79,90 = 16
80,00 = 6
80,05 = 1

AMAX

79,80 = 8
79,85 = 8
79,90 = 7
80,00 = 12
80,05 = 3
80,10 = 7
80,15 = 8
80,20 = 4

Would have preferred to have more SMK's, but only have that many left. The AMAX has a weird "either end" weight distribution with a lump in the middle.

We do get verticals now and then for no reason we can see....like just outside the V/6 top or bottom, but still outside the group.

[Lynn Otto]

Would have preferred to have more SMK's, but only have that many left.

Rod I have several thousand of them, what size sample would you like, I did 50 for the Amax's, would that do? Actually I'm so much bored as procrastinating on doing my university assignment.

But tomorrow, I need some sleep now.

[Woody_rod]

Lynn,

Not sure, but a good sample of different batches would be appropriate, say 50-100 at least from each box, chosen at random from the total. Like powder, where the smaller grains will eventually settle to the bottom, maybe bullets do the same. I would empty all bullets into a large baking tray, then spread across and choose them from one side to the other.

At this point, it is pretty clear that the AMAX has a much larger weight distribution than the SMK, which is a bit of a worry for us.

Mind you, we should also test if this actually does make a difference on the target, rather than suspecting it. We have seen a bit of elevation difference for reasons unknown to us with the AMAX at long range. A deliberate test of bullett weights in the upper end vs. the lower end weights would show this clearly IF it were a problem at long range.

I like to see evidence of things that can be measured or observed. Just having weight differences to me is not proof that the bullets will perform differently. Drives me to think we need to do some carefully prepared tests, the results of which can be measured. And, done in a way that can be repeated by others.

The rest of our reloading regime is pretty good (we think), and can produce accurate loads behind the bullet.

[bobeager]

Well after some empirical testing the result is that weight sorting had NO measurable effect at 100 yds off the bench and NO observable effect at 500, 600, 800 & 900 yds at weekend prize meeting. I fired un-batched at 900 yds and had a good waterline except for those flyers.

After discussing this with other .223 shooters present, it looks like my problem is that my loading is too much on the light side. I will increase my loads, test & report back.

Thanks to all who responded.

[bobeager]

Things looking much better--moly-coated to projectiles, increased powder load by .7 grains, 15 thou into the land and bingo--25 " group. many thanks to KHGS for advice.