Topic: Chrono Question

[adrewiske]

I need some "expert" advice from all the reloaders:
I switched over to the new IMR XBR 8208 for my 22-250. I use the RCBS electronic thrower/scale combo when making my rounds. I also finally broke down and bought a Alpha Chrony to configure ballistics tables. My question is, I went out and shot 10 rounds through the chrono and had ten diff. velocities from 3630 to 3730 fps. If the powder charge for each round is the same how come the diff. velocities? DO I take the ten and average the velocities for an overall or look at my thrower as a potential source of error?

[Jaggy13]

I don't reload for that kind of accuracy but I hear those guys talk about natting everything out. head stamp of brass, amount of times fired, weight of bullet...
They get nit picky about every detail.

[tgibson]

I don't reload for that kind of accuracy but I hear those guys talk about natting everything out. head stamp of brass, amount of times fired, weight of bullet...
They get nit picky about every detail.

Yea..what he said.  Wall thickness, head stamp, primer lot, weighing bullets...I just use the average of the 10 rounds.  Unless you are shooting F class you probably won't ever shoot as good as you load anyways.  Not trying to beat you up, just saying there are a lot of other variables out there that will have way more impact on your groups than 140 FPS.
Adios,
TG

[popsgunner]

yeah, what they said and......temp of gun after each round. What you should be looking for is a standard deviation of as little as possible, say 10-20 FPS. Thats consistent and accurate. IMHO
Pops

[adrewiske]

Good info, now that you mention that, my brass is mostly Winchester that is at least twice fired.

[ida83704]

My question is, I went out and shot 10 rounds through the chrono and had ten diff. velocities from 3630 to 3730 fps.

100fps spread is sorta a lot.  No idea what the cause is, but need to close the diff up some.

the 100fps diff with a 60gr Amax would be 16 inches at 925 yards.  925/950 would be the supersonic max

[RGinIdaho]

Sometimes it is just a matter of finding the pressure range that the powder best operates within.

May not be the best powder for that case capacity-bullet weight combo.

[adrewiske]

I get really good groups with the load, average roughly 1/2" for five shot group. Should I load up say 6 round groups with powder loads varying by a half grain and shoot them through the chrono?

[44magnut]

One thing you might try and that is use one piece of brass and use that for all your testing. This controls  all out side issues with brass.

[fastfire]

I use a scale that weighs to .01 or one hundredth of a grain and trickle each charge weather I'm loadind .223 or 50 BMG.
I think that does help consistancy of my group.
I think all the powder scales such as RCBS scales measure to .1 or one tenth of a grain.

Of all the things I have done relative to case preparation there are two that stand out as signiciant; 1) turning for consistent thickness; 2) annealing the case mouths. Both of these tend to assure that your bullet is held and released with consistent tension and I am convinced that this is one of the few things one can do that really helps.
I also use a primer pocket uniformer and debur the inside of the flash hole.


My scales, Denver Instrument MXX-123

http://www.denverinstrumentusa.com/balances/MAXX.php

[fj40mojo]

Of all the things I have done relative to case preparation there are two that stand out as signiciant; 1) turning for consistent thickness; 2) annealing the case mouths. Both of these tend to assure that your bullet is held and released with consistent tension and I am convinced that this is one of the few things one can do that really helps.
http://www.denverinstrumentusa.com/balances/MAXX.php

This! Spot on

[luvmy45]

Here's my 2 cents...

First, what distance are you loading for? If you it's less than oh, say 300 yards, you can probably pretty much use anything you want, at any SD and get good groups with an occasional flyer.

If you want to load out beyond that, and go for distance then you will want to tighten up your chrono load to less of a SD. However, it doesn't have to be perfectly the same... which is impossible. You just need to find the "window" that you gun likes and use it.

Goto the downloads section, and download the Incremental Load Development Method or as I've heard it called, the ladder method.

Once you find the window that your gun, bullet, powder, likes, you can load to that area and get good groups. You will still want to tighten up your tolorances in your reloading, like same cases, in the same reload cycle, and all the other stuff. Then use the chrono to set your data up for your range cards.

[adrewiske]

Thanks for the input, that "ladder" article is awesome. According to him though a scale that weighs to the tenth of a grain is alright, so I think I'm ok there. Maybe I should start over including brass that is all the same. I have too much of a "mixed bag" to get consistently accurate results.

[J Mack]

I need some "expert" advice from all the reloaders:
I switched over to the new IMR XBR 8208 for my 22-250. I use the RCBS electronic thrower/scale combo when making my rounds. I also finally broke down and bought a Alpha Chrony to configure ballistics tables. My question is, I went out and shot 10 rounds through the chrono and had ten diff. velocities from 3630 to 3730 fps. If the powder charge for each round is the same how come the diff. velocities? DO I take the ten and average the velocities for an overall or look at my thrower as a potential source of error?

Sorry I have no "expert" advice but I can share some of my beliefs.

This is the method I use to determine my best charge weight for a given bullet powder combo.  Dan Newberry OCW; http://optimalchargeweight.embarqspace.com/
Because I don’t want to weigh the charge weight of every round to the hundredth of a grain I look for what Dan calls a "pressure tolerant" load and throw all my loads on a progressive press. I look for a powder that has small grain size and a reputation for consistency for my go to powder and IMR 8208 XBR powder possess those qualities.
 
Like other have said my biggest gains have come from brass prep but I only concentrate in the areas that net me the biggest gains. The three areas that I focus on are shoulder height - neck size and thickness and neck hardness or temper.
For shoulder height I only bump the shoulders .001” to .002”, don’t assume that your die was built correctly and setting it up as per the manufactures recommendations wont cause you issues. Bumping your shoulders more than a couple of thou will cause big issues with your headspace resulting in some hard to read accuracy issues.
 For neck size and thickness I have started using bushing dies and turning my necks for consistency, just enough to knock off the high spots. I’ve seen factory dies that have severely under sized the neck for the given caliber and brass that created some hair pulling tail chasing days so check this area very closely. I size my necks -.001” to -.002” under loaded round size.
For the neck hardness or temper you will notice that as your brass gets worked more the effort to seat bullet increases even if everything else stays the same. For low ES and SD numbers you will have to have consistent neck tension. You can help you self with this buy keeping you brass separated by head stamp and firings. I’m in the process of building an annealing machine to temper my cases to address this very issue.

I’ve loaded a fair amount of ammo with the mindset above that shoots well under ½ moa and I know that I could squeeze more accuracy out of my loads with some weight sorting   and weighing the powder of every case to the lowest amount of my ability then loading on my single stage press but I have not seen a significant differences in group sizes over just throwing them in my progressive press and driving on, at least not enough to justify the extra effort.



Standard deviation for dummies... Hope this might help.   
Link: http://www.techbookreport.com/tutorials/stddev-30-secs.html

[luvmy45]

According to him though a scale that weighs to the tenth of a grain is alright, so I think I'm ok there. Maybe I should start over including brass that is all the same. I have too much of a "mixed bag" to get consistently accurate results.

Yup, if your in the window with the ladder method you can be off by a tenth of a grain either way and still get great groups.

Having matched brass is a good idea... I used mixed brass for letting the kids shoot, or when I just want to toss rounds down range, for precision shooting, all of my brass for that load is in the same firing sequence.

[adrewiske]

Man, once the reloading bug gets you, you're screwed! Is there an alternative to reliably using a tactical scope past 500yds without spending days at the reloading bench developing loads that shoot velocities with an acceptable SD? I don't mean that to sound like I"m trying to take the easy way out, but I really don't know if I have the time or money to do all of the above listed methods.

[RGinIdaho]

From what you note, in your case, accuracy is not the issue. The barrel obviously likes that bullet in that velocity range. A wide range at that.

Play with the current powder charge to see if the extreme spread begins to decrease with .5gr changes. If it does not, move on to another powder. A tenth of a grain charge variance is not a lot to worry with as noted above and may not show anything over the chrono in a give day.

[luvmy45]

Is there an alternative to reliably using a tactical scope past 500yds without spending days at the reloading bench developing loads that shoot velocities with an acceptable SD?

The goal is not to shoot velocities with an acceptable SD, the goal is to shoot small groups and distance.

If you do the ladder method or the OCW method, you will end up with a load that will shoot good groups at any given distance.

The by product of that will be the velocity that that load likes in your rifle with that bullet weight. As you build in more consistency with your reloading techniques, same brass, better measuring, playing with powders, seating depth, your SD will shrink as well.

Don't put the cart before the horse, and chase the rabbit down the hole...
  But it is a fun hole to chase it down.

[ida83704]

Maybe I should start over including brass that is all the same. I have too much of a "mixed bag" to get consistently accurate results.

This is probably most of your issue.
Perhaps, go get a bag of new Winchester brass, keep it segregated from the rest and see what happens

[adrewiske]

I think you're all right, I was trying to put the cart before the horse. I'm think I'm going to start over with new brass (Nosler Custom which is expensive as heck) and use the ladder method going in both directions from the load I already have and see what happens.

[fj40mojo]

I think you're all right, I was trying to put the cart before the horse. I'm think I'm going to start over with new brass (Nosler Custom which is expensive as heck) and use the ladder method going in both directions from the load I already have and see what happens.

Have you considered Lapua? IMHO it's better brass. I've heard complaints about Nosler being soft and puking out primers prematurely.

[luvmy45]

Can't say I've used Nosler, I just started with Lapua for reloading and haven't looked back, and have some federal gold match factory that I've shot and have some of it I reload.

Basiclly my lower class brass, however you want to put it, is for targets less than 300 yards, where the variation isn't detrimental to hitting a target. Or letting my kids shoot, or letting people shoot my gun suppressed. You know, for the those times when you really don't need the accuracy. 

My good stuff is for longer range and for tack driving at 100 when I need it. (Or I think I needed it, the gun will still outshoot me  )

[adrewiske]

Thanks for the heads up on the Nosler brass before I went out and wasted my money. I think if that's the case, I'll go with Lapua for the 22-250, Norma for the Wby. and go from there.

[fastfire]

Do you trickle your powder charges?
If not you may find your 10 shot average will get smaller if you do.

[adrewiske]

Fastfire- what do you mean and why is that? I just use the change master and periodically check the throes weights in a manual scale.