How Much Variance in Bullet Weight is Too Much?

[LHshooter]

Rightly or wrongly, when I reload I typically buy bullets, powder, and primers, work up some loads to verify power factor and then go to town and reload. I really never paid too much attention to how consistent the weight of the bullets are relative to the advertised weight.  For the past few years I have used 147 gn Hoosier Bullets and when I initially checked a random sample I found them to weigh an average of 146.8 gns with a standard deviation of 0.252. I thought that was pretty damn good.

 

Recently I bought some 124 gn bullets from Summit City and decided to check them. I took a random sample of 20 bullets and found the following:

Minimum = 122 gn

Maximum = 125.2 gn

Mean = 124.3

Std Dev = 0.634

 

While the mean looks pretty good to me, the std dev is 2.7x greater than the Hoosier Bullets I usually use. Is this good enough or should I go back to what I usually use. I decided to try the Summit City since they were a little less expensive and I read good things about them regarding accuracy and lack of smoke. I've never had an issue with the Hoosier Bullets as far as accuracy but sometimes they seem more smoky to me.

 

BTW - I used Blue Bullets in the past until I learned their weight variance is even worse than the Summit City results I just measured. Plus I had to pay sales tax.

[ColoradoNick]

it doesn't matter. 

[dtuns]

That amount would only matter if you were rifle bench rest shooter. Pistol no issues.

[Boomstick303]

25 minutes ago, ColoradoNick said:

it doesn't matter. 

 

As long as all of the bullets are above the indicated weight.  If you have rounds falling lower than advertised weight you could run into issues at Chrono.  Especially when loading to PF below 130.

 

I always check about a dozen rounds when I receive a lot of bullets to make sure none fall below.  

[Maximis228]

The cheaper the bullets... the larger variance you will run into. This isn't always true, but it sure does correlate. I've found blues to be the worst in weight variance, and it did not matter at all assuming you weren't going for 126 PF. 

 

 

[shred]

know your typical bullet weight so when you go to chrono and they are figuring off a 'light' one, you can have them pull the last one instead of shoot it should it come to that.

[LHshooter]

2 hours ago, Boomstick303 said:

 

As long as all of the bullets are above the indicated weight.  If you have rounds falling lower than advertised weight you could run into issues at Chrono.  Especially when loading to PF below 130.

 

I always check about a dozen rounds when I receive a lot of bullets to make sure none fall below.  

Exactly, that's what I was a little concerned about when I found 1 bullet 2 grains light. That's about 16 fps which could be an issue at chrono.  I typically try to load to PF of 130 to 132 for a little breathing room.

[shred]

I suspect that lighter bullets probably get a slightly higher velocity so it probably washes out at chrono time as long as the one they weighed is mid-range or better.

 

 

[Joe4d]

9 hours ago, dtuns said:

That amount would only matter if you were rifle bench rest shooter. Pistol no issues.

yeh until you dont make power factor,, thats a pretty large variance.. I shoot Bayou mostly for matches and have never noticed that much difference in random samples..They dont equal advertised, but when I weigh a few out of the box,,, then weigh 10/ weights are less than a grain... probably less than half a grain.

6 hours ago, shred said:

I suspect that lighter bullets probably get a slightly higher velocity so it probably washes out at chrono time as long as the one they weighed is mid-range or better.

 

 

yeh but they dont shoot the one that gets weighed..  shoot a heavy weigh a light ? hello no score.

[shred]

9 minutes ago, Joe4d said:

yeh but they dont shoot the one that gets weighed..  shoot a heavy weigh a light ? hello no score.

That's why you check what the first one weighed if you get down to round #8, so you can have them weigh the bullet instead of shooting it if the first weighed one was light.

 

[GrumpyOne]

Personally, I think if you are loading that close to PF floor, you shouldn't be surprised if you fail chrono. Temperature, altitude, humidity, they all play a part. Worrying about .5 grain difference in bullet weight should be the least of the worries.

 

For instance, a 123.5 gr bullet needs to go 1,012.5 fps to make power factor. A 122gr bullet needs to go 1025fps to make power factor. That 124gr bullet needs to go 1008.5 fps. The difference between a 124 and a 122 is 16.5 fps. And that is if all the conditions are exactly the same (same temp, humidity, altitude, etc) as when you chronoed the load initially and when you chrono at a match.

 

And, who among us, can tell the difference between a 132PF load and a 125.1PF load in during a match? 

Bottom line is, if you are worried about making PF cause one of your bullets may be 2 grains light, maybe you should worry more about bumping your PF up instead, as you are already playing an odds game of missing PF at a match.

[fbzero]

At pistol differences, it doesn't matter much.  Wouldn't even enter my thought process unless I was a bullseye shooter.  For practical shooting, the only thing I'd suggest is to calculate your power factor with the lowest weight bullet you find and don't try to ride the minimum PF line so you don't run into any problems with illegal reloads in any sport.

[Racinready300ex]

I shoot Blues, which historically have always been a little heavy. So I math my PF based on advertised weight which will probably be low and don't worry at all about the bullet weight after that. 

 

If the gun doesn't group I'll try .356 bullets instead of the standard .355. Never needed to do more than that. 

[shred]

FWIW, humidity and altitude are irrelevant at chrono distances.  Maybe 1 fps difference from the bottom of Death Valley to to the top of Everest with a fat .45 bullet going through 10 feet of air. 

 

Temperature (of the ammo & gun) makes a significant difference (and temperature correlates with altitude).  Chrono hot and cold rounds to be sure.

 

 

[Joe4d]

5 hours ago, Racinready300ex said:

I shoot Blues, which historically have always been a little heavy. So I math my PF based on advertised weight which will probably be low and don't worry at all about the bullet weight after that. 

 

If the gun doesn't group I'll try .356 bullets instead of the standard .355. Never needed to do more than that. 

agreed, I think that Hi tek coating adds weight.. I am using bayou and missouri mostly and they all seem to be about 1 gr heavier than advertised,, but each box they are all almost the same..  IMO 2 grs apart ? points to bad QC.
Compared to the plain lead or the old black moly coating that was pretty spot on.

 

[Farmer]

I’ll throw another fly in the ointment. Brass. I was doing some ladder testing just to test increase of velocity per tenth of a grain of powder. I chose some Fed brass I had, bullets were within .2 and loads were hand weighed. In every group there was one round that was consistently 20-30 fps slower than the rest. This sparked another test, narrowing it down to 4 pieces of bass I found the one bad apple and marked it. It looked the same, same headstamp but it was one that had been glocked and ran through the push through sizer. Water volume testing showed that it had greater volume than all the others. I couldn’t visibly see any stretching internally but somewhere the case gained volume which lowered the vel. I may section it to try and get a closer look. 

[GrumpyOne]

1 hour ago, Farmer said:

I’ll throw another fly in the ointment. Brass. I was doing some ladder testing just to test increase of velocity per tenth of a grain of powder. I chose some Fed brass I had, bullets were within .2 and loads were hand weighed. In every group there was one round that was consistently 20-30 fps slower than the rest. This sparked another test, narrowing it down to 4 pieces of bass I found the one bad apple and marked it. It looked the same, same headstamp but it was one that had been glocked and ran through the push through sizer. Water volume testing showed that it had greater volume than all the others. I couldn’t visibly see any stretching internally but somewhere the case gained volume which lowered the vel. I may section it to try and get a closer look. 

Yet another reason NOT to chase the power factor floor. There are just too many variables when you are loading that close to minimum.

[zzt]

A 3.2gr Delta is enough that I wouldn't use those bullets if you gave them to me for free.

 

Case volume variation is something to consider.  It makes a difference if you are using mixed HS brass.  See attached.  I copied this from a thread here, but no longer remember who posted it.  

 

For 9mm major I use once-fired, fully processed brass with the same HS.  SDs range from 4 to 6.  For 9mm minor, I now use mixed range pickup.  I do have some problems.

9mm case capacities.pdf

[Farmer]

2 hours ago, zzt said:

A 3.2gr Delta is enough that I wouldn't use those bullets if you gave them to me for free.

 

Case volume variation is something to consider.  It makes a difference if you are using mixed HS brass.  See attached.  I copied this from a thread here, but no longer remember who posted it.  

 

For 9mm major I use once-fired, fully processed brass with the same HS.  SDs range from 4 to 6.  For 9mm minor, I now use mixed range pickup.  I do have some problems.

9mm case capacities.pdf 50.25 kB · 2 downloads

I tried powder (#9 because of its fineness and higher density) when trying to figure out my low numbers. It wasn’t until I checked it with water that it really showed up. 

[zombywoof]

My bullet pulled at chrono. I was confused at why my PF was 125.1, it should have been much higher until I got home and inspected the bullet. It was several grains shy of its weight. Chrono guy says relax you made it by a mile.