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Impact of bullet seating depth


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Let's say you have a pistol that will run just about any length round you feed it, which my Beretta LTT 92 seems to do.

This means that for a given bullet and desired muzzle velocity, I can vary the seat depth to whatever I want and still achieve the that velocity as long as I adapt the powder volume appropriately.

In this scenario, what information do I use to select the bullet seat depth? Why would I pick one seat depth (and corresponding OAL) over another?

Here are my thoughts / questions / what I've read so far. I'd love to hear the experts confirm or deny these claims!
 

  • Larger powder measurements should have less variance (as a %) from the powder drop, resulting in more consistent velocities
  • Larger internal volume will reduce pressure, putting less wear on the gun (not sure this matters if you're loading minor power factor)
  • Smaller internal volume increases pressure which helps burn cleaner if you're running really light loads
  • I read that loading short and getting max peak pressure (but with the same velocity) makes the gun feel softer shooting. Is this true or urban legend?
  • I suppose at some point you need enough seat depth just to hold the bullet properly. But I'm thinking if you're within any reasonable range this is a non factor?


Am I missing anything? And does any of the above really make a significant difference? Or is it so insignificant that you just pick something in the middle and never think about it again?

Edited by matto6
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50 minutes ago, matto6 said:

Am I missing anything? And does any of the above really make a significant difference? Or is it so insignificant that you just pick something in the middle and never think about it again?

 

Yup.

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If you are reloading and want accuracy...

you can experiment with various details.

I can tell you to start in the middle and try adjustments

from there to see if you get any improvements.

 

I found bullet weight and powder  make a lot of difference.

 

I have read that loading as long as possible can help.

 

what I have not been able to see

is that after a certain point the skills you bring to your aim make a lot more difference.

 

so you can use the reloading to hunt what your pistol likes

and you will get better too.

 

my bullets are within my skill... they print close to where I aim.

the flyers on my targets are me.

 

to tell if you are using the most accurate loadings

you have to have the skills to see any improvements.

 

I trialed clays and 115 gn bullets...

 

three things,  the cases displayed flattened primers on about 10 percent.

the bullets printed where I aimed and where I did not aim.

this was clear to me. 

and the felt recoil was variable.

 

that was a lack of consistency from my reloading that I did not like.

I trialed hp-38 all the above problems went away.

 

148 was no more accurate for me than 115...

so I decided I'd go on 124 until I had a reason to pick anything else.

 

If your reloads have problems for you, you are likely to notice it.

 

I like the feel of heavier bullets in recoil. 

I can't say the powder driving them made much difference it my perception.

 

miranda

 

 

 

 

 

 

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only other thought I would bring to the table is your other guns of the same caliber.  Load short enough that it works in all of them. Unless you have some other specific reason for separate supplies.

Like you have a steel open 9mm major gun, that you load to 1.180 oal, and specifically dont want to shoot that stuff in your poly production gun 

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3 hours ago, Joe4d said:

only other thought I would bring to the table is your other guns of the same caliber.  Load short enough that it works in all of them.

Makes sense, kind of.  But part of the goal of loading for competition is to customize the ammo to your particular gun to optimize whatever it is you're trying to optimize.   I don't really need 25.0001  power factor rounds for my carry gun.

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16 hours ago, Miranda said:

If you are reloading and want accuracy...

I'm actually not chasing accuracy.  I'm starting out in steel challenge and USPSA.  I'm mostly focused on learning recoil control at this point.

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11 minutes ago, matto6 said:

Makes sense, kind of.  But part of the goal of loading for competition is to customize the ammo to your particular gun to optimize whatever it is you're trying to optimize.   I don't really need 25.0001  power factor rounds for my carry gun.

Woah, unless you have multiple reloading presses can you imagine adjusting your dies and powder dispenser each and every time you're reloading for a specific gun?  And then there's bringing the right ammo for the right gun when going to the range😁

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20 minutes ago, matto6 said:

Makes sense, kind of.  But part of the goal of loading for competition is to customize the ammo to your particular gun to optimize whatever it is you're trying to optimize.   I don't really need 25.0001  power factor rounds for my carry gun.

havent seen OAL make any difference other than wont feed or wont chamber.
If I can load all my ammo so it feeds and chambers in all my guns that is what I want.
No way a half inch here or there will matter in IDPA or USPSA...

A round that dont work will matter big time

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8 minutes ago, Silver_Surfer said:

Woah, unless you have multiple reloading presses can you imagine adjusting your dies and powder dispenser each and every time you're reloading for a specific gun?  And then there's bringing the right ammo for the right gun when going to the range😁

I do it all the time. Micrometer seater and powder bar. Open gun loads are IFP or JHP. PCC loads are plated RN, screwing around minor loads are coated. 

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At some point you start to think about how securely the bullet is held by the brass, bottom feeders seem a lot less problematic in this regard than wheel guns, but it is something to check before loading a whole lot of rounds. 

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I did some tests on 9mm seating depth in my custom barreled (Kart) 9mm 1911. Accuracy and velocity didn't seem to vary noticeably over my test range (.010"). It was a PITA to make absolutely sure the rounds were exactly the correct length, shooting the gun off bags, etc. What I learned is that truly low BC projectiles with blunt ogives aren't picky on seating depth.

 

YMMV, but my philosophy now is to load for function and not to sweat the exact seating depth. I set my dies for my most picky gun or bullet profile and just seat everything to that OAL. The variation in projectiles and brass matters way more than my OAL variation ever could. I'm cheap and use mixed brass (though I will use new brass for something truly special) and coated bullets. Maybe people with more expensive tastes can tell the difference in seating depth on a non-bullseye pistol but I sure can't. Better bullets and new brass made a way bigger difference in group size and ballistic results than varying seating depth.

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11 hours ago, matto6 said:

I'm actually not chasing accuracy.  I'm starting out in steel challenge and USPSA.  I'm mostly focused on learning recoil control at this point.

 

yeah, why did I bother to write at all?

 

I decided you didn't think past feeling an obligation to say anything...

so I'll give you a little more of an answer...

 

if you are in competition, you are chasing accuracy.

give some thought to: who do you think you are fooling?

the absolute hardest thing you will be doing is being completely honest with yourself.

don't worry about me... I am as good at self delusion as anyone

 

I shoot and aim and hit and miss.

when I _know_ where I aimed and called the shot and the bullet went elsewhere

I blame ammo or pistol...

when I do not know the call, I blame me.

guess which miss is more common?

 

back to you...

recoil control is not yet a tuning item for me.

what I was told is that in a semi auto pistol

you can try different rate springs to match the load of your ammo

with the idea that the return force of the spring comes back 'just right'

to have your pistol back on point.

try some springs see if you notice improvement

 

in general, build ammo that runs reliably in your gun.

when you know it is the ammo is the problem, go fix it.

 

miranda

 

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What follows is my personal opinion; I don't claim to have any scientific evidence or any evidence at all beyond my gut reaction... YMMV.

 

For a given gun the primary component of recoil is going to be the power factor of your ammo.

 

Everything else is secondary and rather subtle as well.

 

For example: Let's say you have two different loads. One is loaded to a PF of 125 and the other is loaded to a PF of 130.

There is nothing you can do for the PF 130 load as far as changing bullet weights, powders, primers, load length that will result in it recoiling like the PF 125 load.

 

Can you make subtle changes in how you perceive the recoil of the PF 130 load as a result of changing one or more of those variables?

 

Absolutely; and many do exactly that including myself (eg. heavy bullets, fast powder vs. light bullets, slow powder), but realize that you are chasing something that is probably an order of magnitude less impactful than the actual PF of your load.

 

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2 hours ago, ddc said:

What follows is my personal opinion; I don't claim to have any scientific evidence or any evidence at all beyond my gut reaction... YMMV.

 

For a given gun the primary component of recoil is going to be the power factor of your ammo.

 

Everything else is secondary and rather subtle as well.

 

For example: Let's say you have two different loads. One is loaded to a PF of 125 and the other is loaded to a PF of 130.

There is nothing you can do for the PF 130 load as far as changing bullet weights, powders, primers, load length that will result in it recoiling like the PF 125 load.

 

Can you make subtle changes in how you perceive the recoil of the PF 130 load as a result of changing one or more of those variables?

 

Absolutely; and many do exactly that including myself (eg. heavy bullets, fast powder vs. light bullets, slow powder), but realize that you are chasing something that is probably an order of magnitude less impactful than the actual PF of your load.

 

 

Actually you are 100% correct and simple physics is the reason why.

 

Power factor is nothing but momentum (mass x velocity).  Momentum = recoil.  That's physics and not debatable.

 

You also hit on a point many misunderstand: the difference between physical recoil and how we perceive it.  Faster vs slower powders, lighter vs smaller bullets, none of that matters if the product of mass and velocity is still the same.  Recoil is unchanged, but how we perceive it might change, mostly because of the time over which recoil is generated.

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