Effect of seating depth on groups?

[McHaggis]

I know that reducing the OAL will increase pressure etc but does this have any effect on accuracy?  

I know it does in long range rifle shooting but the ranges we normally shoot pistol I just can't see it'll have much effect if any.  But I need to try something....

Why you ask?  Shadow 2, 125gr coated lead conical with anything behind it, running around 125-133PF the accuracy at 8yds is nasty.  2" is typical.

Going to give up on these as they just don't shoot in this CZ.  OAL is 1.093"  

I've also tried 124gr Geco RN FMJ and they are much better but still average. 1" + at 8yrds with 4.1gr W231 1.15" OAL. 

I've also tried ADI ASP450 & AP50N behind these but these 2 generate worse groups.

I'm going to try a faster powder (APS350) and see how that goes but based on the faster powders I doubt it will be better but it works well behomg a LRN 145gr @ 127PF

All shooting is done over a sand bag rest.  Yes I'm fairly new to this CZ.  Been shooting it for about 16 months.

Any experience with changing seating depth and any noticed effect on group size?  Really looking for any ideas here at all.

 

[Sarge]

This is what’s so fun about load development. Changing OAL does indeed affect grouping. And in more ways than one. I found changing OAL and charge weights also moved group center of mass quite a bit. Meaning, one load grouped 2” and at one o’clock while another would group 4” at seven o’clock etc.

[Farmer]

Not a CZ but my 9mm XDM is a tad bit more accurate with the bullets .015 from the lands, but all the way to .050 or better it doesn’t make a whole lot of difference. My 45 though seems to prefer a bit more jump. Always have to remember that when you change depth your also changing psi and harmonics.  Not such a big deal with short barreled pistols but longer ones and rifles makes a big difference. I just have been working up some 147’s and have noticed they group to the right whereas 115, 124 and 135’s are all dead center with the 135’s being the best. 
Forgot to ask how are you supporting the gun or your hands on the sandbags? Have you tried off hand to see if it’s better or worse?

Edited September 30, 2021 by Farmer
Punc

[McHaggis]

@SargeSo what increments should I try?  Rifle I use 0.003"  Any suggestions in powder reduction when I reduce the OAL?  I was going to start bringing them down from 1.150" to 1.125" or even less to see what the resulting groups look like.

 

@FarmerI used a big Caldwell sand bag to help stabilize it.  Off hand is just as bad which is why I'm trying to sort this.  I thought it was my technique but I figured even I wasn't that bad of a shot.  Seems it wasn't all me after all.  

 

I also have a Magnetospeed hanging off the end of it during these load tests.

 

 

[stick]

Are you shooting mixed brass?  If you want to gauge the groups, all variables need to be the same.  All the same brass, sized the same, with the same OAL, powder within .01gr and crimp the same.  Different brass will change the pressure of the load due to wall thickness and size of the brass and the crimp of the bullet.

You also need to support the gun with sandbags to take out the human error. 

Edited September 30, 2021 by stick

[IHAVEGAS]

11 hours ago, McHaggis said:

Why you ask?  Shadow 2, 125gr coated lead conical with anything behind it, running around 125-133PF the accuracy at 8yds is nasty.  2" is typical.

 

That is worse than anything I have ever shot out of any CZ I think. Makes me wonder about the particular gun. 

I'd be inclined to install one of these https://cajungunworks.com/product/barrel-bushing-for-sp-01-10x/ , verify that the gun seemed right, pick up two or three boxes of factory loaded ammo of different weights, and reload based upon what the factory ammo taught me about the gun. 

[HOGRIDER]

21 hours ago, McHaggis said:

I know that reducing the OAL will increase pressure etc but does this have any effect on accuracy?  

I know it does in long range rifle shooting but the ranges we normally shoot pistol I just can't see it'll have much effect if any.  But I need to try something....

Why you ask?  Shadow 2, 125gr coated lead conical with anything behind it, running around 125-133PF the accuracy at 8yds is nasty.  2" is typical.

Going to give up on these as they just don't shoot in this CZ.  OAL is 1.093"  

I've also tried 124gr Geco RN FMJ and they are much better but still average. 1" + at 8yrds with 4.1gr W231 1.15" OAL. 

I've also tried ADI ASP450 & AP50N behind these but these 2 generate worse groups.

I'm going to try a faster powder (APS350) and see how that goes but based on the faster powders I doubt it will be better but it works well behomg a LRN 145gr @ 127PF

All shooting is done over a sand bag rest.  Yes I'm fairly new to this CZ.  Been shooting it for about 16 months.

Any experience with changing seating depth and any noticed effect on group size?  Really looking for any ideas here at all.

 

Hag:

I recently purchased my first CZ.......a Shadow2 Orange, and it was like learning all over how to reload for 9mm!  I'll have to say that right off the bat I tried some Federal Syntech 150g which produced very good accuracy; and I have also bench rested some 124g Syntech which also resulted in very good accuracy.  I developed an excellent 147g Zero JHP load for matches; and have recently been playing with 147g and 135g Blue Bullets coated lead.  Have also done a small test with Zero 125g JHP and JHP Conical.

 

I have to say that finding the OAL for MY BARREL then backing off .015" has proven to be an excellent starting point with regards to COAL!

 

The only powder I use is VV N320!  Also, I use same headstamp (Win) brass with Federal SP Match primers.  I truly think as stick mentioned above, when testing take out as many variables as possible!  My initial testing is from a cheap plastic Caldwell bench rest then finalized with a Ransom Rest.

 

Not being familiar with your current powders in use, I would look for something close to the burn rate of N320 or N330.  I honestly think the Shadow 2 series will be accurate with about any quality bullet if the other variables are correct.  I always test at 20yds and load for that 132-133PF range.

 

I would recommend to first find a correct OAL for the bullet you want to shoot then concentrate on testing for the results that get close to that preferred power factor!

 

HTHs!

 

 

[Trump]

Seating depth has a HUGE affect on group size. I found that out by simple experimentation. You wana go as long as possible at all times.

[HOGRIDER]

8 minutes ago, Trump said:

Seating depth has a HUGE affect on group size. I found that out by simple experimentation. You wana go as long as possible at all times.

Trump:

I have read this many times and can't really provide evidence to disprove it!  However, in this CZ S2 Orange, I was testing OAL for the Zero 147g JHP and found an average of 1.144" as my safe zone.  This was determined by reducing the max by -.015".  Many loading manuals use 1.142" as a standard for the Hornady 147g XTP JHP.

 

It was recommended to me several years ago to try a 1.125" COAL for the Zero 147g JHP with my standard N320 powder.  And I had used it successfully in 2011/1911 style pistols.

 

Decided to try it in the S2 Orange, and it produced the attached.

 

[Sarge]

18 minutes ago, Trump said:

Seating depth has a HUGE affect on group size.  You wana go as long as possible at all times.

It all depends on the gun. Blanket statements typically don't pan out when it comes to reloading either. My old G34 would take loads out to 1.155 in 9mm but 1.13 was by far the most accurate for the bullets, powder, etc in THAT gun.

[HOGRIDER]

2 minutes ago, Sarge said:

It all depends on the gun. Blanket statements typically don't pan out when it comes to reloading either. My old G34 would take loads out to 1.155 in 9mm but 1.13 was by far the most accurate for the bullets, powder, etc in THAT gun.

Excellent advise!

 

[Trump]

1 minute ago, Sarge said:

It all depends on the gun. Blanket statements typically don't pan out when it comes to reloading either. My old G34 would take loads out to 1.155 in 9mm but 1.13 was by far the most accurate for the bullets, powder, etc in THAT gun.

Not really a "blanket statement" but more of a general rule on OAL.

[Trump]

7 minutes ago, HOGRIDER said:

Trump:

I have read this many times and can't really provide evidence to disprove it!  However, in this CZ S2 Orange, I was testing OAL for the Zero 147g JHP and found an average of 1.144" as my safe zone.  This was determined by reducing the max by -.015".  Many loading manuals use 1.142" as a standard for the Hornady 147g XTP JHP.

 

It was recommended to me several years ago to try a 1.125" COAL for the Zero 147g JHP with my standard N320 powder.  And I had used it successfully in 2011/1911 style pistols.

 

Decided to try it in the S2 Orange, and it produced the attached.

 

I can tell you for a fact that as a general rule the longest possible OAL will make for more accurate group size and lower cartridge pressures, which in turn saves brass life,  and will also allow larger powder charge weights. A longer OAL will also contribute to cleaner chamber throats when using coated bullets in pistols in extended shooting sessions.

[McHaggis]

Yes I was shooting mixed brass this time.  The previous testing session was all done with the same head stamp (Geco) and I even weight sorted the cases.  This session too produced pretty crappy groups @ 10yrds.  All loads were thrown on the V3 autotrickler to 0.02grs.  A heavy sand bag was used.

 

The barrel to stock bushing fit is fairly tight.  Not as tight as cajun ones but there really isn't enough movement to cause these groups.  Especially left to right.

 

It does seem the heavier projectiles work better.  I was using 145gr LRN with 2.8gr APS350 and they seemed OK.  I changed because components are in short supply here too.  I usually go 0.015" back from just touching the lands.  I can not find any burn speed data which included the ADI powders that are common here.  I have the following I can play around with.  W231 (these next ones are all ADI) APS350, APS450, AP50N, AP70N. (from fastest to slowest).  W231 seems to fall somewhere between AP50N & AP70.

I'll check my results tonight to clarify.

The 125gr LCN I was trying needed to be 1.093" OAL to clear by 0.015".  The Geco FMJ RN have a longish taper and I can't get them out far enough and still have a decent amount in the case.  I'm talking somewhere around 1/8" and still not touching.  I loaded these to 1.150"  There was the odd group with these that seemed worth playing with.

 

Long as you can?  Closer than 0.015"  Just asking to clarify.

 

EDIT:   W231 is a bit slower than AP50N. With the 124gr Geco FMJ 4.0gr W231 averaged 1004fps where as AP50N averaged 1074 with the same weight.
APS450 averaged 982fps with only 3.6gr. I’m going to try more of this as these are too slow.  Groups at 3.6gr were 2.5” high by 1” wide.  Maybe they will tighten up with speed?  Don’t know if I don’t try but it doesn’t look promising. 

Edited October 1, 2021 by McHaggis

[Sarge]

1 minute ago, Trump said:

Not really a "blanket statement" but more of a general rule on OAL.

Not even a general rule in handguns for action type shooting. 

[AHI]

This is how a old Bulls eye shooter (me) would approach this.  Find a quality bullet that you are planning to use.

Next pick a powder .   Find the max length you can load . Let's say 1.155 oal.  Now pick a starting powder charge.

Go in .2-.3 increments. Find the best powder charge. Then start pushing the bullet in.  We started at 1.155 then 1.150,

1.145,etc. Find the best oal.     Now Bulls Eye doesn't have power factor.  Does your load make PF? If not revisit powder

Change/ selection.

[McHaggis]

@AHI  So pull them back by 0.005” at a time and shoot for groups?

I shall try that with a few loads to see if I can get better results. 
I’m really beginning to thinking this CZ is a dud as I borrowed a Tangflo Stock ll extreme and shot way better with factory Geco 124RN factory loads.

My CZ shot ok with the same but not nearly as good.  Maybe I’ve just lucked out and ended up with a s#!tty barrel. 

[CocoBolo]

8 hours ago, McHaggis said:

@AHI  So pull them back by 0.005” at a time and shoot for groups?

I shall try that with a few loads to see if I can get better results. 
I’m really beginning to thinking this CZ is a dud as I borrowed a Tangflo Stock ll extreme and shot way better with factory Geco 124RN factory loads.

My CZ shot ok with the same but not nearly as good.  Maybe I’ve just lucked out and ended up with a s#!tty barrel. 

I've never bought a new CZ, they have all been used (5), but I did buy a couple of Tanfo's new.  Back to CZ, my Shadow 01, I never did get a set of sights that could be adjusted to POI to POA, close but no Cigar.  Close enough to shoot production.  Last year I decided to throw a DOT on it.   Due to "political" factors I had new loads to test.  My most accurate STI open gun is a tack driver, it connects all the holes at 25 yards with ease.  Next up the 12 yr old Shadow 01, with its new dot.  Ooh crap it is out shooting the STI.  All shots fired from a bench rest.   Then comes the real test, free style, same 25 yards, STI open nice group about 2" for 5 shots, next up the CZ, oops my FU is weak on this one, about 4".  Not the gun the Indian.  The steel test, like a steel challenge stage, on the timer.  Not believing it but I'm faster with the CZ, the timer don't lie. 

On rifle grouping is pure science and discovery just a couple tenths of a grain makes all the difference in the world.  In pistol the POI can move 4" at 25 yards just changing to a different powder (major power factor 9 mm), not so much with minor.   Test the gun and not the Indian, do some shooting on a bench rest.  Nothing wreaks havoc on pistol accuracy like a loose barrel bushing, then barrel lock up.  I had a gun that the slide was so loose on it, it rattled when you shook it, but it was still very accurate with good barrel lockup and a tight bushing.  When I shoot a strange gun I'm more accurate because I take more time on each shot, the psychology factor.  

[Farmer]

Have you closely inspected the barrel for defects? A friend of mine had a brand new Beretta Storm that wouldn’t shoot. I tried working up a load for him with no luck no matter what I did. After a good cleaning and inspection I could see that the chamber was off center. Just looking down the bore you could see where the lands were closer to one side of the chamber than the other. Once sent back and fixed it shot much much better and wasn’t picky about what ammo you used. If your not running your loads at max you can generally seat them deeper without much problem. On 9mm I would say you could go .030-.040 before having to reduce the charge by .1 or .2. A problem with seating out too far especially with light bullets is that it doesn’t leave much in the case and can give poor ignition.  Just some ideas for you. 

[McHaggis]

Barrel looks like the chamber is centred but there is the odd score mark and what looks like pitting around the mid point.  But with the teslong image viewed on my iPad everything is magnified and even the smallest of mark looks huge. 
This barrel has probably less than 2500 rounds down it so it’s still pretty new.
I’ve got a few rounds loaded with what seemed promising during testing and have them at 4 different OAL to see if there’s any noticeable difference.  Just need to find time to go test during the week when it quite at the range.  
I’ll report back once I’ve tried this lot.

Thanks for all the ideas and suggestions to date.  

[Darrell]

In all of my years of testing OAL makes a huge difference in accuracy depending on the bullet. For example PD 124JHP is loaded to 1.100 in PD's match ammo. In my reloads I started at 1.120 and worked my way down to 1.060 and found in my guns the best accuracy for me was achieved at 1.080 with that bullet. If you look at my spreadsheet there is all kinds of data you can look at concerning my testing of OAL. Now that I'm back home after the flood from IDA, I will be testing some of PD's 124 JHP V2's. I bought 4K and will start at 1.140 to start with on that bullet. Will let y'all know how it turns out. Haven't had access to my reloading equip. in 7 months. Looking forward to being back at the range testing again.