Seating depth and accuracy?

[Zaydok Allen]

Does seating at different depths have any relevant impact on accuracy with pistol cartridges? I'm just thinking in regards to the riffling engagement.

I've experienced a bit of inaccuracy with 45 Colt ammo being shot through my 460 mag. However right now I'm just loading 45 acp practice ammo. A question about seating depth in a different thread made me wonder if it has any real impact on accuracy in semi automatic rounds at distances of 30 yards or less.

I would think any affect would be compounded if shooting longer distances.

Thoughts?

 

[Axis II]

I noticed just a little bit with my 9mm and 38spl reloads but i test them offhand and not on a rest because well i don't shoot handgun from a rest. I played with it a little in the 9mm for armature matches and i was able to get things a little tighter.

 

[mdi]

My favorite cartridge is the 44 Magnum and I started reloading it in '88. At one time I experimented with seating depth and firing various OALs from my 5, 44 Magnums, but did not see any marked improvement in accuracy (3 revolvers, one Contender and one Puma). Perhaps if I had given the Contender more time and worked with different bullets and different seating depths, I could have seen better accuracy, but, from my experiments, I don't think my groups would have shrunk appreciably (most on my Contender shooting was 75-100 yards). Consistency, good components and fitting the load to the particular gun is where you find accuracy...

 

[rfwobbly]

Does seating at different depths have any relevant impact on accuracy with pistol cartridges? I'm just thinking in regards to the riffling engagement. [snip] However right now I'm just loading 45acp practice ammo. A question about seating depth in a different thread made me wonder if it has any real impact on accuracy in semi automatic rounds at distances of 30 yards or less.

IMHO, no not really. In order to move the bullet closer to the rifling in an auto pistol, you have to remove more of the bullet from the grip of the case mouth. Engagement of the bullet into the case mouth seems to be important for 2 reasons: 1) Structural integrity, so that when the cartridge slams into the feed ramp the bullet is not knocked off-axis. 2) Pressure build, so that a higher pressure is obtained before bullet launch. This second one has parallels to the way NASA holds a rocket on the launch pad using explosive bolts.

And too, most auto pistol games have a large permissible "hit zone" attacked with multiple shots, whereas most rifle competitions have the much smaller concentric scoring rings and a single shot.

 

[243winxb]

45 acp practice ammo

A cast bullet may be seated to just contact the rifling in some chambers, not all.
My Gold Cup will make contact when seated like in photo. OK for slow fire, but may not work for you in timed or rapid fire.

Only a match grade 1911 would notice, more so at 50 yards.

I learned this tip from an old NRA reprint on the 45 acp years ago.

 

[hdwhit]

460 Shooter asked:
Does seating at different depths have any relevant impact on accuracy with pistol cartridges? I'm just thinking in regards to the riffling engagement.

Whether impact is worth mentioning seems to me to depend in large measure on who precise you can shoot. I don't shoot pistols beyond 25 yards - and most often at around 15 yards - and all I'm looking to do is be able to hit a gallon size milk jug. Any difference a few thousandths difference in shooting depth would make is something I would probably never notice.

But, as already mentioned, different seating depths mean different pressure profiles and different distances that the bullet travels before engaging the rifling and for precision shooters, I suppose that could produce differences that would be noticeable.

 

[wrench459]

I load my boolits long so that I can cram more powder into the case.

 

[Slamfire]

I have talked to my Bullseye Pistol buddies about ammunition. Bench rest rifle reloading concepts mean nothing to the 1911. The ten ring is four inches at 25 yards, and also at 50 yards. Bullseye is shot one handed, the 50 yard target is way out there. I can shoot 4 MOA all day long with my rifles at 100 yards, shooting a pistol 4 MOA, is real hard.



This shooter, I was scoring his targets at a 25 yard reduced match, he was using factory 185 grain cartridges, the seating depth was set by the factory and it is the same for everyone.








Factory ammunition will hold the ten ring all the way out to 50 yards, I can't do that, few shooters can.My current goal is to hold the repair center at 50 yards, something I occasionally do with a 22 LR, never mind a centerfire. When I have gotten into ammunition discussions with the real good, real serious pistol shooters, who test stuff in ransom rests, you won't see accuracy improvements due to seating depth, weighed charges. And I remember being told you won't see any difference in group size between sorted and mixed brass. I am talking with people who fired hundreds of thousands of 38 Special rounds in target pistols and a similar amount in 1911's. I do expect that when you get into bolt action "pistols",you will start to see rifle reloading issues, but not in revolvers or autopistols.

I do not recommend loading an autopistol round bullet anywhere near the rifling. I have had issues with getting the slide to go into battery because the bullet was too far out and jammed in the rifling. I not only could not get the slide to go into battery, the bullet had jammed in the throat and it took finding blocks of wood to knock back the slide. The bullet jam was something I could not clear by racking the slide with my hands, it was jammed in there too tight. I always kept the bullet away from the throats in a revolver for a similar reason: I want to close the cylinder!

 

[HEAVY METAL 1]

I profess to not being an ace handgun shooter, but I see a noticeable improvement in my Ruger KP89 when I seat the bullets long.

 

[Blue68f100]

It all depends on the gun and load. I've have a few guns that prefer a specific OAL. On my HBP I had to shorten the round (0.015") in order to eject a live round. As you know shortening the OAL raised the pressure. This surprisingly reduced my group size from 3.5 down to 2". So it can happen but is very rare. On one other gun it did the opposite, increased the group size. Sorting pistol brass can make a difference if your a level where you can see it. The one factor that is over looked a lot is most pistol brass these days are short. Barely meet min specs and get shorter after each reloading cycle. Since it head spaces off the necks you what as long as brass as you can get for optimum accuracy. You do not want the brass being driven forward 0.010" than slides back when fired. This is a constant changing variable. It best to have minimal movement. 0.002"-0.003" head space is all you want for consistency. Different mfg cases have different volume so sorting does help.

There was a current thread on what OAL played on handgun ammo. The conclusion is it does depending on load and gun.

 

[sbwaters]

My SA 1911 .45 ACP likes ’em long. My CZ75B 9MM likes ’em short.

Go figure.

 

[FROGO207]

I go with what feeds reliably and go from there.I cannot shoot the difference in accuracy so reliable feeding is the game winner for me. Then I will try it from max to min within the "it feeds" range. The revolvers I crimp in the groove. Usually all the same accuracy as far as I can see. YMMV

 

[LiveLife]

I do not recommend loading an autopistol round bullet anywhere near the rifling. I have had issues with getting the slide to go into battery because the bullet was too far out and jammed in the rifling. I not only could not get the slide to go into battery, the bullet had jammed in the throat and it took finding blocks of wood to knock back the slide. The bullet jam was something I could not clear by racking the slide with my hands, it was jammed in there too tight.

Very good point.

How many of us actually measure sample resized case lengths before we determine maximum/working OAL/COL? Not many. So if you did the "plunk test" with a longer case then loaded up using shorter cases, bullet nose may contact the rifling when chambered.

Because resized case length of mixed range brass vary, when I determined longer than SAAMI max length max/working OAL for 40S&W, I measured sample resized case lengths and factored case length variance and subtracted .004" (average range I measured from my mixed brass) from max OAL on this thread - https://www.thehighroad.org/index.p...-for-lead-plated-bullets.743416/#post-9362819

Although SAAMI max for 40S&W is 1.135", Glock/M&P/Lone Wolf barrels will accommodate various TCFP bullet lengths to 1.149" and reliably feed/chamber 1.145" from the magazine.

BTW, even though 1.149" was max OAL from the "plunk test" and 1.145" was "compensated" working OAL factoring case length variance, 1.142" OAL ended up producing smallest shot groups.

Does seating at different depths have any relevant impact on accuracy with pistol cartridges? I'm just thinking in regards to the riffling engagement.

... loading 45 acp practice ammo. A question about seating depth in a different thread made me wonder if it has any real impact on accuracy in semi automatic rounds at distances of 30 yards or less.

For years I have contemplated the benefits of decreased gas leakage from longer OAL/COL vs more consistent chamber pressures from greater neck tension/none or less bullet setback/more efficient powder burn from shorter OAL as ultimately, accuracy results from more consistent chamber pressures/muzzle velocities/lower SD numbers.

Since you are loading lighter practice load, using shorter OAL will likely produce higher more consistent chamber pressures from greater neck tension, less bullet setback and less bullet seating depth variance. Keep in mind, actual chamber pressures and resulting accuracy depend on "chambered OAL/bullet seating depth" and not "finished OAL/bullet seating depth".

As you know shortening the OAL raised the pressure. This surprisingly reduced my group size from 3.5 down to 2".

Some may argue for more or less gas leak affecting chamber pressures but I think that is overshadowed by faster sealing of case mouth with chamber from more efficient powder burn/faster chamber pressure build. 45ACP is large case volume cartridge and operates at lower pressures. At lower charges, inefficient powder burn may occur and benefit from shorter OAL/deeper bullet seating depth. Another factor to consider when using dense powders for 45ACP is powder position. As Walkalong often mentions, many reloaders don't factor this into their load development and large case volume 45ACP with dense powders will leave primers not covered with powder charge when round is slammed forward when chambered.

I have tested this on different occasions and found 100% case fill loads perform better than longer OAL loads that will throw powder charge forward leaving the primer exposed when chambered. One such example is with 9mm 115 gr FMJ and 4.8 gr W231/HP-38 which is my 9mm reference load. Although 4.8 gr is max lead load, 1.130" OAL produced lower muzzle velocity variation than 1.160" and smaller shot groups and now I currently use 1.110". I am sure there are other factors at play like greater neck tension but IMO, lighter target loads benefit from shorter OAL - https://www.thehighroad.org/index.p...n-9mm-40s-w-45acp.799231/page-2#post-10228100

 

[Zaydok Allen]

Thanks for the replies all. I have some things to think about, but the feel I'm getting here is that for the type of ammo I'm making, it is not likely to be an issue I need to be too concerned with.

Since you are loading lighter practice load, using shorter OAL will likely produce higher more consistent chamber pressures from greater neck tension, less bullet setback and less bullet seating depth variance. Keep in mind, actual chamber pressures and resulting accuracy depend on "chambered OAL/bullet seating depth" and not "finished OAL/bullet seating depth".

That's a good point. My practice ammo gets chambered once and then shot, so I doubt bullet setback will be an issue for me, but none the less, I hear what you are saying.

I bell my casings as little as possible, so I'm not just beating my brass up. When I set my crimp die, it seemed pretty near perfect with minor tweaking. The end result is cartridges that look the same as factory ammo. However, what I will do when I get a chance to shoot some of these is measure the OAL, which is consistent at the max of 1.275", chamber one round as if I was going to fire, eject it, and then re-measure it. If there is any significant setback, I'll adjust my crimp as much as I can without screwing up my head spacing.

As a new reloader, I didn't realize the wide margins and differences in data that can exist from one loading manual to another. Awhile ago I noted a difference in velocities of max loads of Unique in the Hornady and Lyman manuals. One had higher volume being listed as a max than the other, and the velocities were quite different. As I studied the data closer, I realized the seating depths were entirely different and the pressure difference between the two had to be the reason why.

It seems like if I decide to shorten my cartridges a tad, to ensure there is no premature riffling contact or lockups, that as long as I keep it in-between published max loads and only modify the seating depth slightly, I should be fine, correct? Obviously I need to chrony my loads to make sure I don't have an over pressure situation, but it seems logical.

 

[ATLDave]

It seems like if I decide to shorten my cartridges a tad, to ensure there is no premature riffling contact or lockups, that as long as I keep it in-between published max loads

Do you mean to say that you would be aiming for a load that is above one source's max but below another? That's... aggressive. I wouldn't do that, at least not without a lot of other work and testing.

Obviously I need to chrony my loads to make sure I don't have an over pressure situation, but it seems logical.

Chronographs don't measure pressure. They measure velocity. Now, one of the main determinants of velocity is the total area under the pressure curve that the bullet enjoyed while it was in the barrel, so you're getting a very indirect measure of that. But total pressure/area under the curve is not generally what blows up guns. Peak pressure is more frequently what blows up guns, and chronographs cannot tell you that. Different powders correlate very different peak pressures to given velocities, and different bullet types can have a similar non-relationship.

 

[Zaydok Allen]

Do you mean to say that you would be aiming for a load that is above one source's max but below another? That's... aggressive. I wouldn't do that, at least not without a lot of other work and testing.



Chronographs don't measure pressure. They measure velocity. Now, one of the main determinants of velocity is the total area under the pressure curve that the bullet enjoyed while it was in the barrel, so you're getting a very indirect measure of that. But total pressure/area under the curve is not generally what blows up guns. Peak pressure is more frequently what blows up guns, and chronographs cannot tell you that. Different powders correlate very different peak pressures to given velocities, and different bullet types can have a similar non-relationship.

In answer to your first question, no. I worded that poorly. I meant that as long as I am staying below the max loads in both source's load data, and stay between their listed OAL, I should be well within safety margins. I'm not loading any max loads right now either. I'm just trying to get the basics of reloading down at this point, and I know you need to work up loads, not start high. Lyman lists 1.275" for OAL on a 230 gr FMJ Unique Load. Hornady 9th lists 1.210" as the OAL. The Hornady has higher velocities as a result with the same charge. It does seem like one could save a little bit of powder in the long run by seating deeper, within limits of course so you don't increase the pressure to unsafe limits.

In response to your second comment, thank you. Yes I understand what chronographs measure, and that it would be a very indirect and imprecise measure of pressure. However, your point about the pressure curve and peak pressure not being clearly indicated by velocity is a good one, and points out that I wouldn't really be able to tell diddly squat from the velocity alone. Thank you for straightening me out on that. I guess signs of stress on the spent cases and primers is all that would really indicate over pressure, correct?

 

[ATLDave]

I guess signs of stress on the spent cases and primers is all that would really indicate over pressure, correct?

Even that is a pretty limited. Remember, one uses the same exact primers in 45 ACP and 10mm (and in a lot of .41 and .44 magnum loads). 45 and 10mm have, what, a 16,000 PSI SAAMI peak pressure difference? I don't think a CCI Large Pistol Primer knows what kind of case it's going in... it doesn't flatten at 25k PSI in a 45 and stay rounded for a 10 at 36k!

The good news is that it sounds like you're not trying to push max, and you're working on a cartridge that is generally pretty forgiving.

 

[Zaydok Allen]

That's exactly why I decided to start with 45 acp. 10mm is my next cartridge to start loading. I have dies and a conversion. I just nteed a tool head.

Going to work on 45 for a while first though.

 

[ATLDave]

10mm was the first cartridge I learned to load! It's also pretty easy. My main suggestion would be, if you're loading full-power rounds, to pick a nice slow, bulky powder for it. You will find some WIDELY varying data for some of the mid-range powders. IIRC, my Speer(?) manual had a load for 180 grain 10mm with a starting charge of Unique that was well above max in a couple of other sources!

 

[Zaydok Allen]

Really? That's a little disturbing. I'd like to see 180 grain loads moving around 1200 to 1250 ft/sec at the muzzle for practice ammo out of my 5" gun. I also want to get into loading some hot 200 grain loads at some point. I'm glad to hear it's easy to load for. I wasn't that impressed by the velocities I saw in the two manuals I have. I need to get a few more.

Is it just that the other sources were overly conservative?

 

[ATLDave]

IDK. I ended up concluding that Unique is just not a great powder for that round. I switched to AA #9 for full power loads and have not looked back. I've never tried Longshot or 800x; I think those and AA#9 are usually the powders identified as being the best suited to top performance in 10mm. Western's online data says #9 will get you into your desired range under a 180 grain pill, and well into the 1100's with a 200 grain projectile.

 

[Zaydok Allen]

Thanks for the head's up. I've been looking at Longshot, as I already have some I'm going to try with 45, but AA#9 is the other one I was curious about as this is the 3rd or 4th time I've heard it's a good powder for 10mm.

Thanks!

 

[ATLDave]

It really is. Meters wonderfully (although I'd still weigh every charge for working near or at max), gives almost perfect case fill (basically comes up to the bottom of the bullet), burns clean at full pressure, not known to have spiky or weird traits, and not quite as flashy/gassy as Longshot (often sarcastically called "Loudshot").

 

[FROGO207]

The big thing to me is to always work up your loads and stop if things get dicey. Starting at the middle or higher is not sound practice IMHO especially if you have not reloaded for a long time already. Those that have might possibly get away with it to an extent as they have some experience about what to expect. I still work up my loads if nothing more than one round at each step. Want to keep all my bits and pieces from getting hurt.