450Bushmaster.net

Ok here's the recipe
Bushmaster upper and lower, Hydraulic buffer and Ross Schuler Brake (Awesome guy).
42 Gr.Win 296
CCI 450
Hornady once fired1.690
FTX 200 OAL 2.203
Light Stab Crimp and Light Taper Crimp.
35 degrees

Here's what came off the burner.

Average Velocity And I say average because you have to average these numbers out.
2330FPS

Extreme Spread 181.6
Standard Deviation 82.86

.84 4 shot group at 100 yards best group yet with 450 that I bought in Dec..

Question
Why does the best group I get come from such extreme spreads and poor SD?

The next best group I got was
38 gr 296
CCI 400
35 degrees
The primer caused a delayed ignition.
Why good group with that load to?
What causes extreme spreads like this?

Hoot has run into this before...I'm sure he'll chime in here.

Who says that 82.86 is a bad SD? Is your .84 group a bad group? Or is your SD an indicator that you could have had an even better group?

First we need to understand more about SD.

Here's a great explanation done by Bramwell.. www.shootingsoftware.com/ftp/Perverse%2 ... f%20SD.pdf ..

Look this over, it may help allot or confuse you even more..

..t

just to add more confusion.


The standard deviation we obtain by sampling a distribution is itself not absolutely accurate. This is especially true if the number of samples is very low. This effect can be described by the confidence interval or CI. For example for N=2 the 95% CI of the SD is from 0.45*SD to 31.9*SD. In other words the standard deviation of the distribution in 95% of the cases can be up to a factor of 31 larger or up to a factor 2 smaller! For N=10 the interval is 0.69*SD to 1.83*SD, the actual SD can still be almost a factor 2 higher than the sampled SD. For N=100 this is down to 0.88*SD to 1.16*SD. So to be sure the sampled SD is close to the actual SD we need to sample a large number of points.

IMHO, SD is more of a concern with serious benchrest shooters, shooting at much greater distance, where Time Of Flight variations as a result of variations in velocity translate to vertical shot dispersion.

Believe me, is you were shooting the 450b at 500 yards, the velocity SD's we commonly see would have catastrophic impact upon our groups.

If you want to visualize this further, it's actually easy to do thanks to ballistic calculators. If we were shooting 250gr FTXs, that varied from 2200 to 2250, at a target sitting out at 500 yards, we would see vertical shot dispersion of 9 inches! with all other factors ignored. That same load at 100 yards only varies .2 inches. So, the range your particular caliber is normally used at has a bearing upon how important the velocity SD is to the group size. That's kind of an over-simplification, as many other factors come to bear.

To me, velocity SD is a useful tool for evaluating load or reload consistency and quality as a result of attention to detail. It doesn't reflect upon the rifle's or shooter's ability to deliver accurate shots. The impact that velocity SD has upon group size pales by comparison to most of our equipment and our own shooting shortcomings.

Hoot

Thanks WC.

Yep little confusing for simpleman like me. I did understand the concept. Not all the math.

Thanks Hoot
I see that at 100 yards it wont make much difference. It's just frustrating uniforming the primer pockets, deburring the flash hole and all the case prep to get a good group and the ES being what it was. If you never took the chrono to the range one would say awesome at that group. I feel that I am a 1 1/2" group shooter meaning if the gun will shoot a same hole group every time I will shoot 1" average maybe.
I will try loading the recipe again and see what the results are. I am using a Lee Turret press. I think I will buy a single stage press and try it. I don't like the slop in the turret press.
It just strikes me funny how one load with low ES may not be accurate in a particular weapon while a load with higher ES is accurate. One would think accuracy comes from doing the exact same thing repeatedly. Taking into account what the weapon prefers also.
Any ideas on my loading to get closer ES?
I did have good results with the
Barns 200 XPB
40 gr Lil Gun
2.200 OAL
Light Crimps
Velocity 2535
ES 15.42
SD 6.32

4 shot group
One Flyier dont know if it was me or the round but the other 3 were
.85 Group.

simpleman wrote:...snip...It's just frustrating uniforming the primer pockets, deburring the flash hole and all the case prep to get a good group...snip

I hear you. I treat every case I reload to "The Deluxe, Salon Treatment" like they were the most important I will ever shoot. While I may not see it all translate to great results, at least I have the satisfaction of knowing I minimized as many variables in the equation as I could. That's one of the satisfactions afforded to reloaders.

Hoot

Simpleman, your ES looks wonderful to me.

Granted I am new to the .450BM, but certainly not to ARs or precision. I have run numerous tests comparing bolt guns to ARs with the same loads, prepared differently. From tumble, FL size and load on a progressive, to de-prime, sort, weigh, uniform flash holes, ream primer pockets, Giraud trim. I've done this for .223, .260 and .308.

The SD on a gas gun will almost always be 1.5 times that of a bolt gun with the highest quaility ammo. The SDs between minimumally processed and benchrest procssed brass in an AR platform...negligible to maybe a 10% betterment. The best SD I ever got on the .260 (AR-10 WAY tuned) was with minimally processed brass. Same load in the bolt gun (same barrel length, cut with the same reamers) had about an equal SD. On a gas gun, I am happy with SDs in the single digits and ES below 25. For bolt gun presicion, I want much better.

Basically, so long as you load the actual rounds consistently, the brass being processed to the best standards vs. minimally in a gas gun become neglible.

Hoot wrote:IMHO, SD is more of a concern with serious benchrest shooters, shooting at much greater distance, where Time Of Flight variations as a result of variations in velocity translate to vertical shot dispersion.

Believe me, is you were shooting the 450b at 500 yards, the velocity SD's we commonly see would have catastrophic impact upon our groups.

If you want to visualize this further, it's actually easy to do thanks to ballistic calculators. If we were shooting 250gr FTXs, that varied from 2200 to 2250, at a target sitting out at 500 yards, we would see vertical shot dispersion of 9 inches! with all other factors ignored. That same load at 100 yards only varies .2 inches. So, the range your particular caliber is normally used at has a bearing upon how important the velocity SD is to the group size. That's kind of an over-simplification, as many other factors come to bear.

To me, velocity SD is a useful tool for evaluating load or reload consistency and quality as a result of attention to detail. It doesn't reflect upon the rifle's or shooter's ability to deliver accurate shots. The impact that velocity SD has upon group size pales by comparison to most of our equipment and our own shooting shortcomings.

Hoot

Just to extrapolate on Hoots explanation and put in a little perspective here. A 9" group at 500yds is 1.8MOA!! That's well inside National Match Standards and well within Minute of Grizzle and will easily kill any deer type Grazing Animal at that range, or so I say it will. In that vain, I say there are things going on with our Bullet/Cartridge combination, that transcends Any/All conventional, modern day thinking. So much so, that when we get to the 400/500yd line, our Taylor Knock-out, really-really shines, and I hope you guys will prove this, in next years' Contest!!.

In other words, we keep looking for bench-rest standards and we don't have a bench-rest Competition System, even though most here have seen bench-rest groups. Head-Up guys, an even bad day at the range, still means, Meat-on-the-Table, under the worst of conditions. Everything considered, with all of the Bullet, Cartridge, and weapon combination variables, the phrase "Bang-Flop", has never had such appropriate meaning, .."in the history of ever" (to quote our Tex-Sleep-Dawg)..

..t

Like Hoot and Wildcatter said. We spend days and nights fussing with all the variables because we have a little bit of perfectionist in us as reloaders and shooters. Then, whatever our results have been at the range, we take Thumper where it belongs (out in the woods) and when we point it at a deserving critter the intended game just falls over dead. I think pretty soon I'll have my hogs so well trained that when I carry Thumper into the swamps they are just going to start falling over dead before I even get it loaded!