Sd...big numbers

davide montini

davide montini

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Eh fellow reloaders can you give some inside here
Did some load developer and the group was sweet ..but the sd numbers were like 50.5 out to lunch
Fn fnar ...7.62x51 or 308
20” barrel
210 m primers
Benchmark powder
Ivi brass already fired from the gun
175 tmk’s
Ave velocity 2540fps
....what gives ...I don’t see what I’m doing wrong.....?
Using magneto speed ...and will retest once Labradar comes in ?
I’m guessing the brass??
Powder measured twice...Lyman Gen 6 and Dillon dt 300 electronic scale
All other grouping shots had way lower sd’s
 
Internal ballistics

What is a sized neck outside diameter

What is a loaded neck outside diameter

What is a fired neck outside diameter

dispose of the magneto speed.
 
It helps to understand statistics. Standard deviation is a highly variable statistical measurement that varies along with the number of repetitions that are being measured. SD will be much smaller in a group of 20 than it will be with a group of 3. In fact SD is almost meaningless until you get to groups of 10 or so.
 
Hi David, I'm glad I seen this early, as you are going to literally be bombarded with suggestions here. Take my advice, if you are measuring consistent powder charges and have consistent OAL do not go down the rabbit hole trying to lower your SD. I have wasted so much time and money playing with trimming, and neck tension, and weight sorting stuff, it's all pretty much a waste of time if you don't need sub 10fps SD. Considering you are shooting an FNAR I'm pretty confident you aren't shooting any F-class matches or benchrest (the only 2 disciplines I would waste time doing 99% of the brass prep and sorting stuff people do.) and thereby don't need sub 10fps SD's.
So here it is man, start changing components, I would suggest the powder first. There is nothing wrong with IVI brass, I use IVI brass myself and doing no brass prep except cleaning and resizing I get an SD of 12 FPS over 20 shots fired. There are a ton of people out there claiming rediculous SD's after firing 3 or 5 shots, which is statistically meaningless. Your bullets and primers are good quality, and you should be able to get a good SD just changing to a different powder. For that weight of bullet try Varget/IMR4895/H4895. I know they are super hard to get right now, but I tried benchmark with heavier slugs in my .308 and it was no good, I got early pressure signs and slow muzzle velocity.
Like I said, I've been down this road before, I tried all kinds of stuff trying to get my chosen components to work, but for me it was my bullet choice, the gun just didn't like my hornadys. I was getting like 18fps SD's and pulling my hair out. Then I changed to 155gr lapua scenars and boom, doing everything else the same SD's went down to 12. Oh and that's not even weighing every charge, I load on a dillon xl 650 progressive press like an animal, mainly because I have a life and spending 14 hours in the reloading room to get 20 bullets loaded doesn't appeal to me.
Good luck man, don't stress, the solution is easier than you think. this is exactly what I do:
1. Clean brass in tumbler
2. lube brass
3. resize, prime, charge, and seat in the dillon
4. tumble loaded rounds to get lube off
5. go shoot
 
davide montini said:
Eh fellow reloaders can you give some inside here
Did some load developer and the group was sweet ..but the sd numbers were like 50.5 out to lunch
Fn fnar ...7.62x51 or 308
20” barrel
210 m primers
Benchmark powder
Ivi brass already fired from the gun
175 tmk’s
Ave velocity 2540fps
....what gives ...I don’t see what I’m doing wrong.....?
Using magneto speed ...and will retest once Labradar comes in ?
I’m guessing the brass??
Powder measured twice...Lyman Gen 6 and Dillon dt 300 electronic scale
All other grouping shots had way lower sd’s
Click to expand...

What was the powder and charge weight?
 
Powder change was 39.0...benchmark...1 full grain above my starting charge ...like what the hell ?
I find very odd ...
use at own disposal...not liable for any problems if you use this load data
Got it off the Hodgdon website
 
Hitzy said:
Not sure you will ever get good ES or SD with any piston semi.
Click to expand...

Depending on the rifle, I would agree with this.

In the case of the OP's rifle, I would expect SD to be acceptably close.

I've had the opportunity to shoot a couple of those lovely rifes and both of them were much more consitently accurate than I expected.

Velocities had to be pretty consistent to shoot slightly under 1 moa out to 300 yards.

OP, that rifle was made as a mass produced sniper rifle, to be issued with appropriate ammunition, by designated shooters.

Both of the rifles I shot were being loaded with handloads on Federal Gold Medal Match brass, using CCI BR2 primers, 45.0 grains of W748 under 178grn Hndy Amax bullets, seated out as far as the magazine would allow.

Velocities averaged at 2530 fps +-15fps.

I would suspect your cartridge case capacities are inconsistent for a starter. IVI is excellent quality brass and capable of many reloads, when properly taken care of but weights are often quite different. I had some with primer flash holes that were to small for the standard decapping pin.

It's possible you have a rifle with issues beyond your control but when it comes to SD spreads, that's usually a quality control issue of the ammunition being fed.
 
Last edited:
4064, TAC, and BL-C(2) all worked great through various semis I own(ed). I'm sure it has been mentioned but low SD is hardly a requirement for accurate ammunition.
 
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