How much variance at chrono is normal

[fireman1776]

I finally picked up a chrono but was surprised to see how much variance I had in a ten round test. I’m wondering if my crimp needs adjusted. All rounds passed case gauge. 
 

127 conical brass monkey bullets over 3.6 TG. 1.150 oal. Shot out of a x5 legion. 

[Rnlinebacker]

7 minutes ago, fireman1776 said:

I finally picked up a chrono but was surprised to see how much variance I had in a ten round test. I’m wondering if my crimp needs adjusted. All rounds passed case gauge. 
 

127 conical brass monkey bullets over 3.6 TG. 1.150 oal. Shot out of a x5 legion. 

Range mix brass? What kind of primers? I'm assuming you have a good seating die

[fireman1776]

1 hour ago, Rnlinebacker said:

Range mix brass? What kind of primers? I'm assuming you have a good seating die

Ya mixed brass. Cci small pistol primers. All Dillon dies except for the crimp die which is Lee on a Dillon 750

Edited May 30, 2022 by fireman1776

[Tunachaser]

Inconsistent powder drop (or powder shacking out of brass as shell plate indexes). Variance in seating (not putting the same pressure on the handle.   Lots of others including chrono.  Crimping would be way down the list.

 

Do 20 or so measuring each powder drop, look for any spilled powder, adjust to make each as close as possible.

 

Measure COL on each round (different manufacturers have close tolerances.

 

Try to use the same pressure on each round.

 

Re-check with chrono.

 

How long have you been reloading?  What powder and bullets are you using.  AND must important is your ammo accurate.  Having a small SD is nice but accuracy and reliability is what is important.  Chrono factory loads and you might be surprised at the amount of variance.

Edited May 31, 2022 by Tunachaser

[AHI]

Mixed brass could be your problem as far as Chrono results. Now just look if you edit that 998 fps one. You actually have a fairly consistent load. That could be how you shot that one across the chronograph. When I work out a load  I use sengle head stamp brass. Just so to not chase non existent problem. Then when satisfied re Chrono with mixed. With mixed brass you can get 50 +/- fps  from high to low on average. On occasion more.

 

Edited May 31, 2022 by AHI

[Cowguy]

I’ll second AHI. When I got a chrono the spread was wild. If I sort brass the spread gets much closer, I blame the thickness of the different manufacturers.

[Rnlinebacker]

2 hours ago, fireman1776 said:

Ya mixed brass. Cci small pistol primers. All Dillon dies except for the crimp die which is Lee on a Dillon 750

That's normal for mixed brass. I use starline for my major match ammo and SD is less than 5. Rifle primers will help you a little for sure

Edited May 31, 2022 by Rnlinebacker

[Leezway]

47 minutes ago, Cowguy said:

I’ll second AHI. When I got a chrono the spread was wild. If I sort brass the spread gets much closer, I blame the thickness of the different manufacturers.

I’ll third AHI… that is/was my issues at the start….. now I sort brass just to eliminate that one variable…. Because boy are there some pretty big differences in manufacturers brass…

[iflyskyhigh]

I used mixed brass and get single digit to low teen SD’s with ES’s of 20-30 all day every day. In everything. From open guns to sun compacts. It’s not the brass.

 

Powder and primer selection CAN have an effect. But TG at the loading should be fine. I’m guessing it’s your technique, probably powder drop (TG should flow fine out Dillon). With a fast pistol powder like that small variations can make a big difference. But again, Dillon should hold +/- .1, which should not make that big a difference.

 

Like someone else said, you throw that 998 out and it’s pretty average for 11 shots. You probably spilled a little powder on that one and didn’t realize it. 
 

With cast you may be over or under belling? Inconsistent seating (especially with mixed 9MM brass, which is why I use mr bullet feeder power funnel, really helps with mixed 9MM brass)

 

Bottom line is large SD/ES is 99% consistency. I know it’s probably not much help, but something in process is inconsistent. Just change one thing at a time. Process of elimination. 
 

The other 1% it can just be a combination the gun, bullet, and powder doesn’t like. For example I’m working on a 40SW load with 165s and HS6. I know for a fact my process is spot on. The charges are weighed to within +/- .05 of a grain. Still getting SDs in the high teens low 20s, ESs in the 40-50 range. Is what it is. 

Edited May 31, 2022 by iflyskyhigh

[ChuckS]

If that Lee die is a Factory Crimp die, swap in a standard crimp die and re-test....

[Jim Watson]

A PhD here got interested and concluded that "match grade" was a Coefficient of Variation (Standard Deviation as a percentage of the mean) of 1%, maybe 1.5%.  That would be 10-15 fps in this case.  But he was working with .38 wadcutters and was therefore trying for an SD of 7-11.  He got it, too, with swaged wadcutters, same brass, weighed powder. 

[ltdmstr]

40 minutes ago, Jim Watson said:

A PhD here got interested and concluded that "match grade" was a Coefficient of Variation (Standard Deviation as a percentage of the mean) of 1%, maybe 1.5%.  That would be 10-15 fps in this case.  But he was working with .38 wadcutters and was therefore trying for an SD of 7-11.  He got it, too, with swaged wadcutters, same brass, weighed powder. 

 

Used to be able do that with .45 on a Star reloading press using Fed brass, Fed primers, Bullseye, and H&G 68 200g LSWC.  Results on a 1050 and 550 are not even close.  As for OPs comments on crimp, that's likely not the issue unless it's excessive or inconsistent.  Should be .002 at most.  Problem is most likely inconsistency in brass, powder charge, bullet weight, or OAL.  Or some combination of those.

[fireman1776]

17 hours ago, ChuckS said:

If that Lee die is a Factory Crimp die, swap in a standard crimp die and re-test....

It is a fcd. Is there something wrong with the fcd? 

[fireman1776]

18 hours ago, iflyskyhigh said:

I used mixed brass and get single digit to low teen SD’s with ES’s of 20-30 all day every day. In everything. From open guns to sun compacts. It’s not the brass.

 

Powder and primer selection CAN have an effect. But TG at the loading should be fine. I’m guessing it’s your technique, probably powder drop (TG should flow fine out Dillon). With a fast pistol powder like that small variations can make a big difference. But again, Dillon should hold +/- .1, which should not make that big a difference.

 

Like someone else said, you throw that 998 out and it’s pretty average for 11 shots. You probably spilled a little powder on that one and didn’t realize it. 
 

With cast you may be over or under belling? Inconsistent seating (especially with mixed 9MM brass, which is why I use mr bullet feeder power funnel, really helps with mixed 9MM brass)

 

Bottom line is large SD/ES is 99% consistency. I know it’s probably not much help, but something in process is inconsistent. Just change one thing at a time. Process of elimination. 
 

The other 1% it can just be a combination the gun, bullet, and powder doesn’t like. For example I’m working on a 40SW load with 165s and HS6. I know for a fact my process is spot on. The charges are weighed to within +/- .05 of a grain. Still getting SDs in the high teens low 20s, ESs in the 40-50 range. Is what it is. 

I’ll try being more consistent on my pulls. I’m using the mbf powder funnel and will check about overbelling 

[Edwards30]

I'm shooting the same powder charge behind a 124gr coated bullet out of a legion as well.

My deviation is about 15-20fps using mixed brass.  I am using RCBS sizing & seating dies with a regular Dillon powder funnel followed by a Lee FCD.

Do you have any photos of how much your case is belled or what your crimp looks like?

[zzt]

2 hours ago, fireman1776 said:

It is a fcd. Is there something wrong with the fcd? 

 

No.  Keep using it for crimp only.   Since you are new at chrono, the most likely culprit is your chrono technique.  To get accurate results you MUST be using a good rest and firing at a target.  The bullet path MUST be parallel to the long axis and parallel to the measuring ports.  ANY deviation from that path with result in a longer flight time time between  the measurement ports, and a lower listed velocity.

 

I'd master your technique before I went searching for other hob goblins.  You may find everything else is fine.

[cperazza]

In my experience SD that wide in range will have to do with no enough crimp (0.002") or variations in powder throw (something loose in your set up). 

 

Like the fellas have stated... Do a batch sort same brand of brass, separate the bullets by weight and length, measure each powder throw. A video of the press would also help point out possible issues. 

 

BTW, might have missed it, what chono are you using? 

 

Good luck, let us know how the next range trip goes. 

[zzt]

He is using a Lee FCD for crimping.  If set up properly, you can expect the crimps to be perfect.

[ChuckS]

14 hours ago, zzt said:

 

No.  Keep using it for crimp only.   ---snip---

The crimp portion is fine. When I was chasing down SD in .40 like the OP, I had read that the sizing ring can cause variation in neck tension since the bullet swages down and the case rebounds to a degree. To illustrate his point about the bad part of post-seating re-sizing, the guy suggested a worst-case demo of taking the decapping pin out of your sizing die and sizing a loaded round. The bullet will be loose, maybe even fall out. So, I knocked out the sizing ring with a punch and magically, the SD dropped by ~ 50% with nothing else changed. Crap range brass gave ~10-12 SD with no extra love. 

[fireman1776]

21 hours ago, Edwards30 said:

I'm shooting the same powder charge behind a 124gr coated bullet out of a legion as well.

My deviation is about 15-20fps using mixed brass.  I am using RCBS sizing & seating dies with a regular Dillon powder funnel followed by a Lee FCD.

Do you have any photos of how much your case is belled or what your crimp looks like?

I’ll get some photos. 

[fireman1776]

18 hours ago, cperazza said:

In my experience SD that wide in range will have to do with no enough crimp (0.002") or variations in powder throw (something loose in your set up). 

 

Like the fellas have stated... Do a batch sort same brand of brass, separate the bullets by weight and length, measure each powder throw. A video of the press would also help point out possible issues. 

 

BTW, might have missed it, what chono are you using? 

 

Good luck, let us know how the next range trip goes. 

Prochrono dlx

[fireman1776]

19 hours ago, zzt said:

 

No.  Keep using it for crimp only.   Since you are new at chrono, the most likely culprit is your chrono technique.  To get accurate results you MUST be using a good rest and firing at a target.  The bullet path MUST be parallel to the long axis and parallel to the measuring ports.  ANY deviation from that path with result in a longer flight time time between  the measurement ports, and a lower listed velocity.

 

I'd master your technique before I went searching for other hob goblins.  You may find everything else is fine.

What else would I use it for other than crimp? I’m not sure I’m following? 
 

This most recent time I chronoed I was freestyle without a rest just shooting into a berm. So you may be on to something! 

[fireman1776]

4 hours ago, ChuckS said:

The crimp portion is fine. When I was chasing down SD in .40 like the OP, I had read that the sizing ring can cause variation in neck tension since the bullet swages down and the case rebounds to a degree. To illustrate his point about the bad part of post-seating re-sizing, the guy suggested a worst-case demo of taking the decapping pin out of your sizing die and sizing a loaded round. The bullet will be loose, maybe even fall out. So, I knocked out the sizing ring with a punch and magically, the SD dropped by ~ 50% with nothing else changed. Crap range brass gave ~10-12 SD with no extra love. 

What crimp die do you recommend? I have the Lee fcd and Dillon 

[ChuckS]

I use the Dillon that came with the die set. It has been fine as I do not change my current load much. I use a micrometer seater to adjust things but the "crimp" (de-belling actually  ) has been constant. If you have a Dillon, try it and see what happens at the chrono!

[jwhittin]

Everything mentioned can affect the standard deviation of your ammo but to what end?  What really matters is accuracy AND being able to pass a PF check.   The latter is what the STD is used for.  Here is a post that explains how.