Would .001" really make a difference?
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Would .001" really make a difference?


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Old 10-11-2013, 09:05 PM   #1
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Default Would .001" really make a difference?

I went shooting last night with a new batch of 147gr FP S&S Casting bullets for my FNX. I was shooting 4"-5" low. I had reloaded a bunch of these with 3.4gr of Bullseye. I had noticed that the box said 9mm .357 but didn't think anything of it until I was shooting low.

Went out this afternoon with the same weight bullet but ones that were from a 9mm .356 box. I also took some 115gr RN and 125gr RN. All three of these loads shot right to POA.

Would .001" with the same powder load make that big of a difference?
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Old 10-11-2013, 09:15 PM   #2
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Originally Posted by aandabooks View Post
I went shooting last night with a new batch of 147gr FP S&S Casting bullets for my FNX. I was shooting 4"-5" low. I had reloaded a bunch of these with 3.4gr of Bullseye. I had noticed that the box said 9mm .357 but didn't think anything of it until I was shooting low.

Went out this afternoon with the same weight bullet but ones that were from a 9mm .356 box. I also took some 115gr RN and 125gr RN. All three of these loads shot right to POA.

Would .001" with the same powder load make that big of a difference?
it can. that difference in how it engages the rifling of the barrel, or the difference in pressure when fired.
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Old 10-11-2013, 10:11 PM   #3
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Big difference in the grain of bullet here too. This affects how much of the bullet engages the rifleing, which will affect the poi
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Old 10-12-2013, 02:41 AM   #4
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Cast bullets always run .001" larger in diameter than jacketed bullets. Look at 45acp jacketed they are .451" cast is .452".

Not a big deal. It helps then engage the rifling better. Jacketed bullets are harder and copper is stronger than lead so it grips on to the rifling faster and better than lead.

In my Lyman 48th edition here are the loads.

147gr Lead 3.4gr bullseye will get you 942fps and is .1gr off max.
147gr FMJ 3.4gr Bullseye will get you 871fps and is the lowest recommended load.
That's a difference of 71fps that is a HUGE difference in speed and will most definitely change your POI.

What was the load for the jacketed bullets? Reloads, factory?

If they were a factory load You are ranging from 975fps to 1000fps. 30fps can make a big difference in POI.

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Old 10-12-2013, 03:01 AM   #5
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If I am reloading for just pop cans, I dont sort my bullets or brass.

If I am testing a load or testing accuracy of a gun.
I weigh and measure each bullet , I also weigh and measure the brass, sort it into groups and keep up with each group.

All bullets that weigh and measure the same, are grouped together, for accuracy consistency.

Just me.


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Old 10-12-2013, 03:36 AM   #6
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Originally Posted by phideaux View Post
If I am reloading for just pop cans, I dont sort my bullets or brass.

If I am testing a load or testing accuracy of a gun.
I weigh and measure each bullet , I also weigh and measure the brass, sort it into groups and keep up with each group.

All bullets that weigh and measure the same, are grouped together, for accuracy consistency.

Just me.


Jim
one thing my father taught me about reloading was, consistency equals greater potential accuracy.
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Old 10-12-2013, 03:45 AM   #7
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heavier bullets have more bearing surface and will have different poi than lighter ones. Its not as big a factor in fat slow rounds like a 45 but its really drastic in faster lighter ones like 9mm.

The barrel twist and ballistic Coefficient play a much larger role in poi shift in such rounds than difference in diameter.

Since 115grn is the standard 9mm load factory sights are set to that bullet type. The .001 isn't the issue.

In my carry 9mm I use ammo that shoots to poa.
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Old 10-12-2013, 03:50 AM   #8
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heavier bullets have more bearing surface and will have different poi than lighter ones. Its not as big a factor in fat slow rounds like a 45 but its really drastic in faster lighter ones like 9mm.

The barrel twist and ballistic Coefficient play a much larger role in poi shift in such rounds than difference in diameter.

Since 115grn is the standard 9mm load factory sights are set to that bullet type. The .001 isn't the issue.

In my carry 9mm I use ammo that shoots to poa.
wouldn't the type of bullet, cast lead vs. a JHP for instance make a difference as well if the bullets weighed the same?
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Old 10-12-2013, 04:00 AM   #9
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wouldn't the type of bullet, cast lead vs. a JHP for instance make a difference as well if the bullets weighed the same?
In a handgun only real diff cast vs jacketed same charge weight same bullet design as in hp or round nose so bearing surface is the same, prolly not enough to notice .

An hp will have more bearing surface than a non hp simply because the mass that filled the hp cavity has to go somewhere and its usually a longer body. This means there is more bullet surface for the rifling to act on . This effect isn't near as great as found in rifle rounds so its likely to be negligable as well.
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Last edited by JonM; 10-12-2013 at 04:05 AM.
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Old 10-12-2013, 04:03 AM   #10
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Quote:
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In a handgun only real diff cast vs jacketed same charge weight same bullet design as in hp or round nose so bearing surface is the same, prolly not enough to notice .
so bullet weight is the biggest factor in POI then?

i may not be really noticing it in the calibers i shoot and reload for, (44spl., 44Mag., and 45 auto) as i tend to keep within a pretty narrow window on my bullet weights that i use for reloading and stick to FMJ or JHP bullets.
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