9mm: Worth Messing With Seating Depth For Accuracy?

[otisrush]

There are a few threads around on this topic....but I thought I'd ask and get current thoughts.

I decided to re-work-up and determine what my mainstream, go-to 9mm load is going to be. I did this because, while I thought I'd worked up an OK load previously, I was getting more and more frustrated with my results. Plus, I just recently decided to use the Lee FCD. Roll that all together and I thought "Let's go through the process again."

Last night I loaded up 10 rounds for each of 5 different loads. The bullet is the Zero Bullets 124g FMJ. HP-38. I loaded 3.9, 4.0, 4.1, 4.2 and 4.3 gr sets (of 10). I took them to the range today. I shot them while seated, with my wrists on a bag. (The gun is a Walther PPQ 5" barrel. I'm not shooting competitively. I just want a good, all-around load for cans, paper and steel plates.)

So.....those results point to the 4.0gr load. Great. However.......

Do folks *typically* (for their pistol loads) now play with seating depth a touch to see what happens? I know this is done for rifle. And I'm not (per comments above) looking to make match ammo. I'm just wondering if people typically play with seating depth, beyond making sure they plunk OK. Or do you find a depth that plunks, try different loads, pick the best, and then just start cranking out ammo?

Thx!

OR

 

[hdwhit]

Particularly with small cartridges, I start with the published OAL and if necessary I will try seating the bullet a little bit less (i.e. longer OAL) since it can sometimes help with feeding, but I will not go shorter than the published OAL.

 

[illinoisburt]

Particularly with small cartridges, I start with the published OAL and if necessary I will try seating the bullet a little bit less (i.e. longer OAL) since it can sometimes help with feeding, but I will not go shorter than the published OAL.

I agree. Changes of seating depth probably aren't going to measurably effect the accuracy for your stated use but it can have significant impact on feeding. A few thousandths can be really important especially with hollow points and flat meplat designs in an autoloader.

 

[Blue68f100]

With 9mm I have had good results with going shorter on the OAL. In my BHP it took a 3" group down to 1.5". I was forced to change the OAL so I could eject a live round without dropping the mag. With my other 9mm guns it made no difference. So the only way to know is try it and see what happens.

 

[ants]

General consensus for semiauto handgun: Seating depth is all about feeding. Not so much for accuracy.

But...

Once in a while we get surprised, when a small change in OAL
or different primer or different crimp actually helps a little!
It doesn't help often, it doesn't help a lot. But occasionally a little.
For your gun and your application, might not worth the time. You decide.

 

[wally]

With most bullets that I'm loading for autoloaders, my seating depth is set by what OAL fits my "tightest" magazine, usually Glock. I know others swear by the plunk test, its a necessary but not sufficient condition as they can plunk and shoot fine but still be a tad to long to reliably feed from the magazine when its fully loaded.

 

[LiveLife]

Do folks *typically* (for their pistol loads) now play with seating depth a touch to see what happens?

Depends on the powder type, charge used and bullet base length.

If you are using lower powder charges for lighter target loads, you can benefit from using shorter OAL/COL which produces deeper bullet seating depth which increases neck tension that produces better powder burn and more consistent chamber pressures. Yes, this is where greater neck tension/bullet seating depth/more consistent chamber pressures can overshadow barrel groove diameter/leade length/gas leakage variables and comparison range tests will determine which are the greater variables for the particular pistol/barrel and bullet used.

I often use lighter target loads and after I determined max/working OAL for full powder work up and identified powder charge that produced an accuracy node, I will incrementally decrease the OAL by .005" to see if accuracy improves. If it does, I will use shorter OAL.

Also with 115 gr FMJ/RN bullets with shorter bullet base, using really long OAL like 1.160"-1.169" reduces neck tension and seating deeper at 1.130"-1.135" will increase neck tension. This is where JHP/FN bullets produce greater accuracy over FMJ/RN bullets (longer bearing surface that engages rifling and greater rotational stability from center-of-mass shift towards bullet base) and perhaps why top bullseye match shooters prefer JHP over FMJ/RN bullets.

In general, with most 115 gr FMJ/RN, like Walkalong, I prefer 1.130"-1.135" OAL (finished OAL variance my Pro 1000 produces on average) unless powder compression is an issue and will load longer up to 1.150"-1.160". With 124 gr FMJ/RN, I prefer 1.130"-1.145" OAL unless power compression is an issue and will load longer at 1.150"-1.160". BTW, Atlanta Arms which supplies match teams to include US Army Marksmanship Unit and Marine Service Pistol teams uses 1.130" OAL for their most accurate 115 gr FMJ MATCH AMU load that must produce smaller than 1.5" 10-shot groups at 50 yards (using match grade barrel fixture) - https://atlantaarms.com/products/9mm-115gr-fmj-match-amu.html

So I shouldn't feel bad for these 10 shot groups at 50 yards which were developed with Walkalong's suggestion of using lighter bullets for flatter trajectory/less bullet drop/vertical stringing? https://www.thehighroad.org/index.p...n-9mm-40s-w-45acp.799231/page-3#post-10245856

As to "plunk" test, for my newest Lone Wolf barrel with no leade, I need to use shorter than 1.120" OAL with RMR 115/124 gr FMJ or bullet will hit the start of rifling.

Perhaps shorter nose with longer bullet base/bearing surface (compare bullet lengths in the picture) for greater neck tension/accuracy were the reason why RMR decided to reshape their 124 gr JHP into 124 gr MPR?

I just recently decided to use the Lee FCD.

If you experience bullet setback, it won't matter how consistent your "finished OAL" is as your chamber pressure consistency will be determined by "chambered OAL" and resulting bullet seating depth which will affect muzzle velocity consistency (SD number) and groups size (accuracy).

FCD was made for .355" sized bullets. 115 gr Zero bullets I have are sized .356" and likely will get post sized with the FCD which may decrease neck tension fron post sizing/brass spring back - https://www.thehighroad.org/index.p...re-sized-the-same.818806/page-2#post-10567453

To check bullet setback (which can compress powder charge/increase chamber pressure), load some dummy rounds (no primer/no powder} and feed/chamber from the magazine without riding the slide. If you experience significant bullet setback of more than a few thousandths, I would load without the FCD.

I use Lee dies and usually experience less than .005" OAL variance with more consistent FMJ bullets like Montana Gold/RMR/Zero, etc. and get essentially no bullet setback with .355"-.356" sized jacketed bullets using .377"-.378" taper crimp from 1.110" to 1.160" OAL with Glock/KKM/Lone Wolf barrels.

 

[otisrush]

Thanks all. Great info.

Fortunately I've got a load identified that does well. And additionally fortunately it's on the lower end of the min/max range.

I may play with OAL a tiny bit and see what happens. But I think (hope) I'm in a no-lose situation as I've identified a load that works well.

Thanks a lot!

OR

 

[ants]

On the FCD in 9mm Luger...

Lots of 'wars' are fought regarding the FCD, I'm a non-combatant in those wars.
I don't care how hard you try, I won't let you drag me into a meaningless war over it.


But I will make an interesting point: Since the 9mm Luger cartridge is tapered,
the FCD is not a 'ring resizer' but rather a tapered full length carbide finishing die.
That means you can adjust the die body NOT to post-size your finished round,
regardless of bullet diameter and case wall thickness. Having adjusted the die body,
you can then adjust the crimping stem on top for an absolutely excellent taper crimp.
Adjusted properly, it is one of the best and most consistent 9mm Luger crimp dies available.
It will not post-size your cartridge, but it will crimp consistently on each cartridge.

 

[jmorris]

Do folks *typically* (for their pistol loads) now play with seating depth a touch to see what happens?

Generally just for function, not like you'll be seating out where a chambered round is close to or touching the lands, good chance it wouldn't fit in the magazine at that point.

 

[herkyguy]

i played around with seating depth for my Sig MPX using 147 grain bullets and 800X - i did a lot of searching first though and came to the conclusion that with a faster-burning powder, it may not be the best idea to seat deeper as it could increase pressure with a fast powder. With 800X, i seated down about .05" with great feeding and cycling using 3.8 grains as a max load (still under published max load data of 4.0 grains).

 

[Dudedog]

In medium power 9mm loads I have generally found going shorter than what will plunk gives me a little better accuracy.
I never spent the time to do a really close 1 to one. (project for when I have more time)
(Made up numbers here)
Say for example if 1.10 gives me 1010fps and 1.08 gives me 1030fps and 1.08 shoots better, would the 1.10 load shoot better (or the same as 1.08 load )if I upped the powder charge to get 1030fps in the 1.10 load?
So is the one load better because of the OAL difference or because of the vel difference???

I would say it's worth trying a couple different OALs if is a load you will be shooting a lot.

 

[mdi]

Well, just my experience. For my rifle handloads, bullet seating (other than bullet manufacturer's suggestions) are the last thing on my list for chasing accuracy. For my handgun ammo, my revolvers have shown some difference in accuracy with changing seating depth, but inconsistent and barely noticeable results (and shooting mostly cast bullets with a need for roll crimping into a crimp groove) I gave up on the experiment. For my 9mm and 45 ACP. I have found no increase in accuracy with "optimum" seating depth/OAL and just load for consistency and function...

 

[Walkalong]

I load 9MM to an OAL that will function 100%. I have been able to make plenty of 9MM loads that way that can out shoot me, so I'm good with it.

 

[jmorris]

I have been able to make plenty of 9MM loads that way that can out shoot me, so I'm good with it.

That is the beauty of owning a pistol caliber carbine. Develop a load that can put 10 rounds into under 2.5 inches at 100 yards, then fail to do the same with an iron sighted pistol and know at least your ammunition didn't let you down.

...I've identified a load that works well.

Quantitative data might be worth having, what does "works well" mean in group size, with how many shots at what distance?

 

[ants]

In the original post, he said he shoots cans, and paper and steel plates.
"Works well" for him is probably minute-of-can at 15 yards.
He's not shooting competitively, if his ammo cycles every time
and hits the can or plate, that would work well for him.

For many hand loaders, that is the definition of success. Bravo!

 

[jmorris]

He's not shooting competitively, if his ammo cycles every time
and hits the can or plate, that would work well for him.

I agree and it wouldn't be worth messing with seating depth for accuracy unless you have nothing better to waste the time on.

 

[FROGO207]

I have tried changing the seating depth after finding a good load with several different pistols and it does not make a noticeable difference for my shooting. I do start with making dummy rounds that feed/cycle well at the beginning before I work up that load however.

 

[otisrush]

In the original post, he said he shoots cans, and paper and steel plates.
"Works well" for him is probably minute-of-can at 15 yards.
He's not shooting competitively, if his ammo cycles every time
and hits the can or plate, that would work well for him.

For many hand loaders, that is the definition of success. Bravo!

You pretty much nailed the summary! LOL

I don't have the specifics (which probably goes to the above summary) but I was probably shooting at 20 yds - and the best load of the 5 I brought produced probably a 2" group - with a couple of fliers. This was with me being seated and my wrists on a bag. So I can appreciate given that level of stability that might not be a "good" load.

The other targets (from the other loads I was testing) looked like I'd taken a shotgun to them. They were *all over*.....so much so I'm going to load up a couple of those loads (10 rnds each) and re-test them. It's too long to get into - but the last couple of loads I tested I was a bit rushed and I'm wondering if that contributed to me concluding they were no good. The overall situation at the range where I was was not optimum.

Thanks all!

OR

 

[Toprudder]

Can't speak on effects of accuracy, but my determination of seated COL is this:

1) Must plunk. I generally go 0.015"-0.020" shorter than max plunk, just for safe measure.
2) Shorten the COL, if you have to , to fit the mag.
3) Shorten it some more, if you have to, to reliably feed.

If, after all of this, it is not accurate enough for me, I pick another bullet. There are many good 9mm bullets out there, I'm not going to chase COL trying to make a bad bullet shoot good. JMHO.

 

[SC_Dave]

I load 115 gr plated RN from RMR to a depth of 1.1 which is recommended in the Hornady book. I do periodically have a feed issue. I am considering lengthening the COL and I will see if the accuracy deteriorates, improves or stays the same and post back here. I personally think that it won't really change but IDK.

 

[Walkalong]

I load various 9MM RN bullets at 1.130 to 1.135 OAL with no feeding issues.

If you try that let us know if they shoot better, worse, or the same.

 

[Tuxedo007]

There are a few threads around on this topic....but I thought I'd ask and get current thoughts.

I decided to re-work-up and determine what my mainstream, go-to 9mm load is going to be. I did this because, while I thought I'd worked up an OK load previously, I was getting more and more frustrated with my results. Plus, I just recently decided to use the Lee FCD. Roll that all together and I thought "Let's go through the process again."

Last night I loaded up 10 rounds for each of 5 different loads. The bullet is the Zero Bullets 124g FMJ. HP-38. I loaded 3.9, 4.0, 4.1, 4.2 and 4.3 gr sets (of 10). I took them to the range today. I shot them while seated, with my wrists on a bag. (The gun is a Walther PPQ 5" barrel. I'm not shooting competitively. I just want a good, all-around load for cans, paper and steel plates.)

So.....those results point to the 4.0gr load. Great. However.......

Do folks *typically* (for their pistol loads) now play with seating depth a touch to see what happens? I know this is done for rifle. And I'm not (per comments above) looking to make match ammo. I'm just wondering if people typically play with seating depth, beyond making sure they plunk OK. Or do you find a depth that plunks, try different loads, pick the best, and then just start cranking out ammo?

Thx!

OR

Be careful with seating depth with the 9mm Luger. Your loads do not sound extreme or overly hot, but case volume on this cartridge is "limited" & it operates at a fairly high pressure. Make sure your cases have a tight grip on the bullets & also have a taper crimp to prevent deep seating of the bullet when the cartridge cycles from magazine to chamber. A few thousandths deeper seating can raise pressures significantly! I think over the years, I've inadvertently proof tested a few 9mm pistols...was lucky, no damage to me or the pistol. Am now much more focused when inspecting brass & the whole reloading process for this cartridge.

Good Shooting!

 

[Sunray]

With 9mm it doesn't make much difference considering there are no match grade bullets around.

 

[otisrush]

Be careful with seating depth with the 9mm Luger. Your loads do not sound extreme or overly hot, but case volume on this cartridge is "limited" & it operates at a fairly high pressure. Make sure your cases have a tight grip on the bullets & also have a taper crimp to prevent deep seating of the bullet when the cartridge cycles from magazine to chamber. A few thousandths deeper seating can raise pressures significantly! I think over the years, I've inadvertently proof tested a few 9mm pistols...was lucky, no damage to me or the pistol. Am now much more focused when inspecting brass & the whole reloading process for this cartridge.

Good Shooting!

Thanks. When I first set up the Lee crimp die I set it for "lite" crimp.

When working up a load I load up 10 rnds at each charge. For each charge (obviously - starting at the lightest load) I fire one round and inspect the case for pressure issues. Presuming none, I load the remaining 9 in the mag. At about round 5 I eject the unfired round and check COL - looking for any shortening. And I do the same right before I fire the last round. I want to see how COL does when the rounds are in the mag in a gun being fired repeatedly.

When on a lite crimp I was getting a reduction in COL of .005-.008" on that last round! That scared me enough to go back and set the FCD to "full crimp". Then that issue went away.