How to reduce SD & ES

[alton9]

Hi Fellows,
I got a Magnetospeed for Christmas, now I see my SD is 23 and my ES is 66 on what I used to think was a good load... Where do you start to try to lower these numbers? I'm already weighing every charge, flash hole deburring, primer pocket uniforming, etc. Do I change primers? Powder charge? Powder? Any help is greatly appreciated.
Alton9

 

[Steve Blair]

This thread is a good place to start. [br]
http://forum.accurateshooter.com/index.php?topic=3814361.0

 

[alton9]

First, are you absolutely sure the chronograph is reading correctly? An errant chronograph could make a load that previously gave great ES/SD values look like a bad load. If you have access to a different chronograph, I'd make sure your load gave similar numbers before concluding your load has suddenly gone bad. Alternatively, you could shoot a different load for which you also have solid velocity data and see whether it looks close to what you expect. If not, it's possible it may your new chronograph that is at fault.

Well, this is my first & only chronograph, so I don't have any previous numbers to compare to. I have no reason to doubt the numbers at this point, I just think they could and should be lower. Ignorance is bliss, unfortunately I'm no longer completely ignorant ;D Just would like some advice on what to change to make a difference in these numbers. Thanks alton9

 

[maxpower]

You didn't mention your cartridge or powder, but it could be that a powder change might help. Either a different speed or type of powder. Next thing to try would be different primers. You could either have a bad lot of primers, or the primers you are using don't suit the powder or firing pin.
It is possible to have a fairly wide velocity spread and still have a good short range load (see the 100yd BR shooters), but at long range, you will get a lot of vertical.

 

[Michael Courtney]

Hi Fellows,
I got a Magnetospeed for Christmas, now I see my SD is 23 and my ES is 66 on what I used to think was a good load... Where do you start to try to lower these numbers? I'm already weighing every charge, flash hole deburring, primer pocket uniforming, etc. Do I change primers? Powder charge? Powder? Any help is greatly appreciated.
Alton9

Need more details. Bullet, powder, primer, cartridge, # shots, etc. What is the load used for?

 

[alton9]

Ok,
The cartridge is .22-250, barrel is an 8 twist Brux, powder is h-4350 (37gr), bullet is 75 gr A-Max, brass is all same lot Win. on the first firing,primers are CCI lg rifle. All charges are weighed, brass is all prepped the same ( trimmed, flash holes deburred, pockets uniformed, F/L sized). This is a 1/2 moa load out to 300 yds, but at 600 it's more like a 1 moa load, and at 900 it's giving about 2 moa, dispersion at 600 & 900 is vertical. My SD & ES numbers are based on a 10 shot string. Load is used for long range coyotes & steel. I had always wondered if this load was as good as it could be, now with a chrony, I see room for improvement. Thanks, alton9

 

[Michael Courtney]

That load is on the warm side and also has a very high load density (depending on OAL). You might be crushing some of the powder cylinders when you load, or the compressed powder may be pushing the bullets back out over time so that there is variation in the OAL before you shoot.

The Hodgdon Extreme powders are supposedly resistant to temperature changes, but when when we really want tight velocity ES, we use a regular cadence (time between shots) and delay until right before the shot before pushing the bolt forward and down. Cooking the round in a hot chamber for more than a few seconds before the shot leads to more velocity variations and vertical spreading.

Hodgdon powders also have significant lot to lot variations. With a load that warm, a new lot of powder could be a stuck case or worse, unless you drop back down to a minimum load and work back up.

Assuming you're already being careful with the issues Donovan described, my next move would be to drop the load back down to 34 grains or so and shoot 5 shots at 0.5 grain intervals. Look at both the accuracy and the SD for each load. If you have a load that gives single digit extreme spreads and good accuracy you're done. If a load shows promise with accuracy and SD but isn't quite there, then I tweak the seating depth. Unless you need to go that hot to get accuracy, I'd recommend working with a milder load.

If you're going to keep shooting loads with such high load density, you can gain a bit of extra room by neck sizing the brass. Tumbling in stainless media also removes a bit of carbon and leaves a smidge more room. The usual drop tube techniques work also.

 

[alton9]

Michael,
Thanks for your thoughts. This load is really not that warm, it's below Hornady's book max, and about 200 fps slower than their book max. No pressure signs at all, even in warm weather. Load density is something less than 100%, there's no powder crushing going on and no bullets being pushed out from powder compression. I can hear/feel the powder in the loaded rounds move when gently shaken. Same lot of powder I've been using for the last couple of years.
I shoot pretty slowly, I don't let the barrel get hot. I learned long ago from an old benchrester about cooking rounds in hot chambers.
Hornady shows 37.2 gr of H-4350 at 3300 fps, I'm only getting 3100 fps. I'm afraid if I backed down to 34 gr. I'd be shooting at .223 velocities . If adjusting the powder charge will affect SD & ES, could I not work UP (carefully of course) from the current load and hopefully find the numbers I'm looking for?
I'm a little limited on seating depth, I hunt with this rifle, & don't want to jam, and risk sticking a bullet in the throat extracting an unfired round.
Thanks, alton9

 

[jonbearman]

Try xmr 8208,it may give you better results .

 

[Steve Blair]

Try xmr 8208,it may give you better results .

[br]
Jon, isn't 8208 XBR a little fast for 75 A-Max in .22-250? A full pressure load would barely reach 90% load density. [br]
It seems likely the OP's ES problem is that pressure is too low. I find lowest ES just under full pressure, in the area where velocities flatten for a few tenths of a grain. Shoot 3-shot groups at .5 grain increments until you locate the pressure bounds, drop back to the most promising groups and load around in .1 increments. Once you know the center of the node, adjust seating depth in .003" increments and 3-shot groups. I think you'l find what you are looking for. BTW, H4350 is an excellent choice at that bullet weight. I have a .22-250 that shoots very well with H4350 and Sierra 77 MK.

 

[Michael Courtney]

Michael,
Thanks for your thoughts. This load is really not that warm, it's below Hornady's book max, and about 200 fps slower than their book max. No pressure signs at all, even in warm weather. Load density is something less than 100%, there's no powder crushing going on and no bullets being pushed out from powder compression.

You're probably right about the load density, as other sources have not confirmed by original QuickLoad results on load density.

But I am hesitant to recommend you move increase the load above Hornady's book maximum. 37 grains is a bit above the maximum I've found in several other sources. Pressure in the 22-250 can also be very sensitive to seating depth. Having used a lot of chronographs over the years, I tend to be slow to take results from a hobby chronograph to tell me I'm safe increasing loads above book maximum.

A better idea would be to back down from 37 grains in 0.3 to 0.5 grain steps until your ES numbers drop. I assume you've checked the accuracy of your scale by weighing the bullets. If 75 grain AMAX weigh a grain or two high, then what you think is 37 grains might be less.

 

[Steve Blair]

Michael, regardless his chronograph, I use a Kurzzeit and my .22-250 loads, which I will not list, are notably above 37.0 with Sierra 77 MK. My load tuned ~.9 grains under maximum in my rifle. Having said that, the OP should obviously work up carefully, but it seems he has already done that. As you already noted, lot variations require caution and all loads, above or below some book value, should be determined cautiously. When I ran his numbers in QL, they were neither high pressure (~52k) nor high density (~96%). He is using Winchester brass, whose water capacity is well above QL's default value. [br]
I have never found low ES at low pressure, but I suppose anything is possible. My sense is the problem can be resolved by working up to full operating pressure.

 

[BigDMT]

The best way I found to reduce ES and SD is to just LIE about it. I do the same with the gas mileage in my trucks. Makes me feel much better ;D

 

[jcampbellsmith]

A couple of suggestions:

Get some Lapua brass - http://www.lapua.com/en/products/reloading/cases
Read up on the best powders for your bullet weight. The Nosler manual lists 8 or 9 different powders with N160 as the most accurate from their testing.
Anneal your brass regularly.

Regards

JCS

 

[MrMajestic]

The best way I found to reduce ES and SD is to just LIE about it. I do the same with the gas mileage in my trucks. Makes me feel much better ;D

And my fidelity! ;D
No, seriously, the posts about pressure are spot on!

 

[Michael Courtney]

I suspect a lot of theories in ballistics are subject to confirmation bias, in which the proponents tend to recall instances of data that confirm the theory and tend to forget cases that do not support the theory.

I just reviewed our data spreadsheets for a number of calibers and loads we've tested over the years. There are many, many cases where our data shows single digit velocity variations at relatively mild loads, and in some cases, distinctly light loads.

 

[alton9]

Thanks Guys,
I will carefully work up on charge weights. Michael, no disrespect, but I'd much rather increase velocity than reduce it, especially from the velocity I'm starting from. Thanks again to all, now I have an idea of what to do to make a positive change. For years, I could always find a "mid range" book load that would shoot better than factory stuff, but I didn't used to shoot over 100 yds. I'm still learning.........
Alton9

 

[savagedasher]

Two thing I would do. First I would drop the powder charge to 35 gr. And I would try different primers with the same charge. And don't over look Wolf or Tula. I get my best with them. Not many powders is better then H4350. Larry

 

[WyleWD]

alton9, in your original post you stated that you thought that the load you were checking was a "good load". I'm a little confused as to why you'd want to change it if you were satisfied with it BEFORE you looked at the ES and SD. And, just a thought, you might want to try that same load again on different days across the Magneto to see if there is any difference.

Otherwise if you follow everyone's advice on here so far you'll have a couple hundred bucks spent and maybe all you need to do is increase your powder a bit or change primers. JMHO. WD

 

[Michael Courtney]

Another thing to consider is the fact that single digit velocity variations are a 0.3% variation in the total velocity. Variations that small can be attributed to a lot of factors other than the powder charge, including barrel friction, engraving, bullet weight variations, case volume variations, primer, neck tension, etc.

One thing I have noticed is that many rifles have a bullet or two that they just love to shoot and will give consistency with just about any powder, primer, case, or load. If you are really committed to a given bullet, fiddling with other components can often bring satisfaction. But finding a bullet that a barrel really loves is often the better long term solution because this gives more margin for variation in factors over which the shooter has less control: temperature, air density, barrel conditions, etc.