High SDs and ESs

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bushpilotmexico

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Here is my question.....what controls SD and ES? I'm shooting a 30-47 that I just acquired and it's chambered for reformed .300 Savage brass.

The rifle came with 40 twice fired brass. The seller also send me 60 loaded rounds with the accuracy load worked out by the gunsmith who built the rifle.

While firing the loads thru my chrono although I was getting reasonable accuracy I noticed large variations in SD and ES. In some 5 shot groups there was as much as 150 fps difference.

Not completely trusting some one elses reloading I reloaded using the same powder and weight and the same bullet. The results were exactly the same.

Since the brass is WW I decided to sort all the brass by weight. To be honest there wasn't any more than 1.0 grain difference from the lightest to the heaviest and the majority were within .1 or .2 grains of each other.

Never the less I sorted by weight, reloaded them and saw the same large variations. SO if the brass is uniform, the powder weight is accurate, the bullet is custom, a BR primer and the seating depth is the same why am I getting spreads in velocity?
 
WHEWWWW!!!! :)


Anybody want to start this one?


Ok OK, I'll start......try switching brands of primers.


al
 
As always

My first advice is to sell that chronograph and never buy another. Refusing that, seat the bullet to firmly engage the lands. If the deviations remain, sell the chronograph.
 
What

size were the groups?If its shooting ok dont worry about it.
Jim
 
Was moly involved? When I was shooting moly (a long time ago) I noticed that I had a lot more velocity variation than with naked bullets.
 
bushpilotmexico said:
Here is my question.....what controls SD and ES? I'm shooting a 30-47 that I just acquired and it's chambered for reformed .300 Savage brass.

The rifle came with 40 twice fired brass. The seller also send me 60 loaded rounds with the accuracy load worked out by the gunsmith who built the rifle.

While firing the loads thru my chrono although I was getting reasonable accuracy I noticed large variations in SD and ES. In some 5 shot groups there was as much as 150 fps difference.

Not completely trusting some one elses reloading I reloaded using the same powder and weight and the same bullet. The results were exactly the same.

Since the brass is WW I decided to sort all the brass by weight. To be honest there wasn't any more than 1.0 grain difference from the lightest to the heaviest and the majority were within .1 or .2 grains of each other.

Never the less I sorted by weight, reloaded them and saw the same large variations. SO if the brass is uniform, the powder weight is accurate, the bullet is custom, a BR primer and the seating depth is the same why am I getting spreads in velocity?
Click to expand...

First, I agree with Alinwa. Second, I agree with Wilbur (especially on the "jam"). Third, what is "reasonable accuracy" ? I'm not sure I can say this here anymore - but it sounds like your load is short on charge weight - there is probably plenty of both velocity and precision left on the table . . . what bullet weight/powder/charge weight are you using? RG
 
Definitely look at: primers, consistency of primer seating, powder throwing/weighing technique, how closely you are controlling neck tension, how uniform the necks are, consistency of seating depth, uniformity of cases....

In a long pressure testing session a couple of days ago, we were able to cut the SD of pressure and velocity quite significantly by switching from one brand of bullets to another (same weight). That was a real puzzler, but over 50 rounds of each showed it to be a very reliable result.

German Salazar
 
I suspect the chronograph or the chrono setup. Maybe it is too close to the muzzle? Does the unit have a history of acceptable readings with other rifle loadings? How does it do with .22 RF across the screens.
 
30 47 cartridge

Don't know anything about the .30 47! Have had a time with the 204 ruger cartridge because not a lot of information. Have used over 1/2 a dozen or more different powders and everything else is the same. Have found a powder that now gives me 12-13 S D and better groups the rest is winchester brass,cci br primers and berger 40 grain bullets and shoot some what hot loads. I know that you have received better information. But I corrected my wide range fps. Good Luck craig
 
es and sd are tools that MAY be used to search for repeatable accuracy. just one more tool in your tool box. in the br game its alot of following the known path in loads, tho we are starting to see some "inovation" lately.

you have been given good advice, try primers, more powder,seating depth but let accuracy be the answer, not numbers(es/sd).

if the load you are using was developed for the rifle when new, you proabaly need a longer seating lenght,,,,throats wear, and maybe more powder..

mike in co
 
My 2 Cents

Alot of the variation can come from how you chronograph your loads.If you drop a case in the chamber close the bolt and fire it you tend to get lower velocity numbers.
If you put a cartridge into the gun close the bolt and wait for a condition a 125 fps variation is not unusual.
For just checking ES and SD don't worry about your accuracy and concentrate on getting everything done the same way.
Also a clean barrel will drop 100 fps or more so shoot a couple foulers first.
Lynn
 
I vote with the rest of the guys -- sell the chronograph. Mine drove me NUTS. Great shooting loads gave HUGE spreads in SD and velocity, like I was using 3 different bullet weights in the same string! Just couldn't be true. And remember SD needs a string of about 20-30 shots before it becomes meaningful.
Now I just shoot what shoots -- life is good again.
 
Lynn

Those are good tips for new shooters.
Most experienced Benchrest Shooters will never let a round sit in a barrel much past 30 seconds while waiting on a condition, especially on a hot day. I will dump mine on the sighter.
Last Friday at New Braunfels, while practicing for the Bluebonnet, the Sun was just overhead at about 2:00pm in the afternoon. I had my cases sitting on the bench, (not paying attention), and when I picked the first one up, it was as hot as one that had sat in a hot chamber for a minute.
It's these little things that sometimes makes the big difference.........jackie
 
Being that this is a "point blank" subsection forum, I'm not surprised that the majority of the responses you got were to just forget about SD and ES. And it is true that for close range benchrest, SD and ES are not vital. It is whatever aggs the best that matters. If an SD of 50 fps gave "zero" inch groups, every guy here would shoot it and forget about the SD in a heartbeat and rightfully so. However, distance shooting makes SD and ES much more valuable information. Built in vertical dispersion usually accompanies high SD's at longer ranges. That being said, I believe what Mike in Colorado said that they can be used to find loading nodes and windows. I also believe that if you can find a load that has low SD's and also aggs well, it will be less temperamental or more forgiving than a load that aggs well but has a high sd. Of course, during the heat of the battle, if you feel you need to adjust something in the components, there is not time to chrono a load and fiddle around. So you just go with what your gut tells you will work.

Now for the interesting part. ES and SD are directly related to internal combustion and the whole sum of internal ballistics. They are an indicator of how efficiently the powder burns and how well the the four components and your barreled action are working together for the combustion. There are a myriad of factors and possibilities. The easiest way to change the SD or ES is to simply change the charge of powder. As little as .3 of a grain increase or decrease in weight might make the ES go from super high to super low. THis is in ammo that has even been made perfectly or as close as one can get it. Even if each kernel of powder has been counted out in each cartridge and they are identical in every possible way, if the combustion isn't right, the SD will be high. You can even take the ammo that you found to give low SD's in one rifle and fire it in another rifle and the SD can be and most likely will be totally different. This is part of the reason why factory ammo usually won't hack it for long distance accuracy shooting. The loads need to be tailored to each specific gun regardless of the amount of close range accuracy they can attain. If you do find factory ammo that gives gives good accuracy both short and long distance and it also yields small SD's, buy lots and lots of it! Chances are, when that lot of ammo changes, so will your results!
Now, ammo that has high SD and ES numbers can still be accurate at short range and by now you should be able to see why. If the occilations of the muzzle release the bullet in near the same point every time because of the short distance between the occilations despite the greatly varying speed, they can result in small groups at close range. But exterior ballistics show that loads with high variations in velocities can introduce vertical dispersion at longer range. There are, however, some barrels and loads that will coincidentally shoot well at distance with high SD's but such barrels are anomalies and can't be reproduced at will. They are part of that "hummer" barrel that "can do no wrong" theory that many Hall of Fame benchrest shooters have commented on. They were saying that these barrels do exist and that you can dang near feed it anything and it will shoot, and that they seem to be less affected by conditions (all in a short range context but it plays out for long range too).
So for the most part, SD's will help in load development, they will yeild smaller groups on average at longer distance if they are on the uniform side, and they show if your on the right track.

Hope this helps.
 
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Regarding bullets

GermanS1 said:
Definitely look at: primers, consistency of primer seating, powder throwing/weighing technique, how closely you are controlling neck tension, how uniform the necks are, consistency of seating depth, uniformity of cases....

In a long pressure testing session a couple of days ago, we were able to cut the SD of pressure and velocity quite significantly by switching from one brand of bullets to another (same weight). That was a real puzzler, but over 50 rounds of each showed it to be a very reliable result.

German Salazar
Click to expand...

I'll bet if you checked the bearing surface length of the two lots the ones that shoot the best have the most consistent bearing surface length.
 
Pete, I think you're right; I'll check them at some point. The "bad" ones were Lake City 173 grain match bullets (not exactly a super precision bullet) and since I was running a ton of shots to check some primers for SD I thought they'd be OK. I switched to Lapua 185's and SD and ES went right down - way down. I have a lot more faith in Lapua's QC than in Lake City's!

German Salazar
 
I appreciate all the info and advice. I will continue to experiment and keep everyone in the loop.
Once again thank you very much.
 
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