What is the culprit?

[peterk123]

New brass. I resized them. I used a digital and beam scale for each powder charge. Same bullet (hornady 68 gr bthp). Even checked oal measuring off the ogive. Same primer (cci). I did not crimp the case mouth.

Brutal SD.

About my scales. Inexpensive digital scale. I think it is pretty good but probably a tenth or two grains off at times. The beam is a Lee. It's a bit of a pain to use but likely accurate. I have an RCBS 505 coming.

The good news is that the 68gr did fairly well, except for the ones that were way outside the average. Four shots went into the same hole, so at least I'm on the hunt. My gun (ar15 with 20 inch barrel and 1:8 twist) certainly prefers at least 68gr.



What could I be doing incorrectly in my process? Thx Pete

 

[67ray]

Am I not seeing the problem? You have a 1-1.5% delta on velocity. What were you expecting to achieve?

 

[peterk123]

Am I not seeing the problem? You have a 1-1.5% delta on velocity. What were you expecting to achieve?

Single digit SD.

 

[Mountain]

SD= ~ 20?
ES = ~71?

 

[Mountain]

What's the powder? Charge weight?

 

[Warm_Garand]

Bolt gun or semi-auto?

And sometimes deviation will settle down for me with 2X fired with minimal sizing bump--but powder and primer are definitely important variables as well.

 

[dhuze]

The culprit is probably your barrel, the gun, temperature variance, ambient and barrel. You aren't going to get identical shots each time.

 

[p..]

For a frame of reference, here is a page of chrono data from my 223 notes across a variety of loads with various powders, primers, and bullets with semi and bolt guns. I've gotten single digit standard deviation once.

 

[PatMcD]

Put away the chrono. The only thing that matters is the target.

 

[peterk123]

Thanks all. I'm not disappointed, just interested. If I take away the three "flyers" the groups would have been excellent. Trying to understand what makes a bullet go to the wrong place. The flyers were about an inch and a half or so off center.

Oh, and one more question. All of these went left three inches from how I had it previously sighted with factory ammo. So my "bullseye" was three inches left. I don't understand why that would happen.

Some more info may help.

The gun was well rested on sand bags. I know I'm not perfect but I don't think I pushed the bullet an inch and a half off the target. I had the magnification up to 18 so I would pick up any movement.

No wind.

It was cold out, 11 degrees.

First shot was obviously a cold barrel. It was a clean barrel as well. This one was high left and my biggest flyer.

First five shots were probably fired off within three minutes. The other five were in my pocket to keep them warm. I let the barrel rest for only a few minutes before shooting the next five.

Gun: S&W Companion ar15 volunteer with 20 inch barrel.

I know I know, just shoot. But I'm having a ball finally getting a chance to reload for rifle and learning how to get it right. What fun is reloading if you don't analyze your results to death?

 

[walter62]

I'd rather mag dump into a trash pile than analyze it

 

[Noreaster]

A clean barrel can cause a flyer, That is why you should take a fouling shot or 2.
A cold barrel can cause a flyer, Take the fouling shots above to get a little heat into it. Try to time your shot out and breaks between strings to keep the barrel at a nominal temp.

You will not see precision / competitive shooters using a factory smith and wesson barrel. Its not a dig on the gun, and its not a bad gun. It just has its limits.

On the flip side, how did you develop your load? If you have not done so, do a ladder. Perhaps you can find a combo that reduces flyers and gives a better group.

On my NM gun, that barrel liked sierras, and even favored the 77gr over the 69gr smks (at 100 yds, so stupid). I never chronod it, it was based all from groups.

 

[Warm_Garand]

All of these went left three inches from how I had it previously sighted with factory ammo. So my "bullseye" was three inches left. I don't understand why that would happen.

I'd say the short answer is barrel harmonics. Different powders with different burn characteristics producing different harmonics which causes the bullet to exit the barrel at a slightly different position during recoil.

 

[mac1911]

A clean barrel can cause a flyer, That is why you should take a fouling shot or 2.
A cold barrel can cause a flyer, Take the fouling shots above to get a little heat into it. Try to time your shot out and breaks between strings to keep the barrel at a nominal temp.

You will not see precision / competitive shooters using a factory smith and wesson barrel. Its not a dig on the gun, and its not a bad gun. It just has its limits.

On the flip side, how did you develop your load? If you have not done so, do a ladder. Perhaps you can find a combo that reduces flyers and gives a better group.

On my NM gun, that barrel liked sierras, and even favored the 77gr over the 69gr smks (at 100 yds, so stupid). I never chronod it, it was based all from groups.

Any time tou change ammo or anything in the load your zeros can be fubar. Want to see some POI shifts look at the pellet gun shooters and how much just a lot number can change there poi at just 10m

Anyhow : Crony is good to see if your in the ball park of data.

I will also recommend not shooting groups.
Print up some 10 dot targets maybe 1” dots on 1” graphed paper
Take 2 copies
One on the target frame and one on the bench.
Get a set order and pace of your shots.
I like to shoot 2 fouling shots into the back stop. Then every min or so pop off a test shot. One shot for each dot. Dont bother looking at the impact.
Record your crony reading on the bench target.
Now compare your velocities and impacts.
If you have very distinctive shifts in POI with the velocity changes
Example all velocities below X always go left and low and all velocities above y always go 90’ right . You might have to change something up.

If your not getting consistent shifts your chasing your tail.