Barrel change caused point of aim to shift; Normal?


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CaneCorso85
March 30, 2012, 10:50 PM
Hey guys,

I recently purchased a sig p229 BTFO (the one with the fiber optic front) in .40. In its original configuration it fires dead on. I purchased the Bar-sto 357 sig barrel and it was firing tight groups but consistently low 1.5" @ 15 yards. (1" @ 10 yards). I consider myself an experienced shooter and I had several other shooters give it a whirl as well. Consistent results. The gentleman I purchased the (already) used barrel from was gracious enough to take it back since it didn't appear to be working out for me. This was the only variable that had changed so I was sure it was the barrel. I then purchased the OEM sig 357 barrel expecting to be back on center. The results were the exact same. I put my .40 barrel back in: spot on. I used factory winchester and remmington ammunition as well as hand loaded ammunition, all with the same results.

Has anyone else experienced a shift in point of aim after swapping out different caliber barrels?

I intend for this pistol to be primarily used for 357 sig and it is a defensive carry pistol but I'd like to be able to run .40 through it as well with the same sight configuration. My main concern is that I've got over a decade of military/LE training (I don't say this to sound cocky) and I have ALWAYS trained to cut the target in half with the front sight tip. The last thing I need now is to have to remember to shift my point of aim if I'm employing my weapon. Thoughts?

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pikid89
March 30, 2012, 10:55 PM
my guess is that the factory sights are regulated for heavier .40 caliber ammo. .357SIG shoots a lighter weight bullet that produces less of a recoil impulse, causing the bullet's point of impact to be lower as the bullet does not move the gun as much in the time that it is inside the barrel.

This is why in .38 Special revolvers with fixed sights, 158 grn ammo usually shoots to point of aim while 130 grain ammo groups a bit lower

TurtlePhish
March 31, 2012, 12:23 AM
Changing a barrel will definitely change POI, just because it's impossible to make two barrels exactly the same. They'll have different "true" centerlines, although the difference may be in tenths of thousandths of an inch. But yeah, they'll hit in different places because of that little deviation.

Gtimothy
March 31, 2012, 11:22 AM
it was firing tight groups but consistently low 1.5" @ 15 yards. (1" @ 10 yards).



For defensive purposes, 1.5" low at 15 yards isn't going to make a bit of difference to the guy you are engaging! :cool:

CaneCorso85
March 31, 2012, 01:30 PM
For defensive purposes, 1.5" low at 15 yards isn't going to make a bit of difference to the guy you are engaging! :cool:
1.5" could be the difference between a vital organ or complete perforation. It could also be the difference between a hit and a miss. Assuming that you're only going to use your pistol at less than ten yards is a potentially fatal mistake.

CaneCorso85
March 31, 2012, 01:36 PM
my guess is that the factory sights are regulated for heavier .40 caliber ammo. .357SIG shoots a lighter weight bullet that produces less of a recoil impulse, causing the bullet's point of impact to be lower as the bullet does not move the gun as much in the time that it is inside the barrel.

This is why in .38 Special revolvers with fixed sights, 158 grn ammo usually shoots to point of aim while 130 grain ammo groups a bit lower
I hadn't considered it from that perspective. The perceived recoil between the two calibers is just about the same when both cartridges are loaded to their ideal velocities and powders with similar burn rates.

I had heard that sig may put different rear sights on their .40's and .357sigs despite them being the exact same pistol, save the barrel. Can anyone else confirm this?

(Sorry guys, I hadn't realized I posted this in the Social Situations section)

DPris
March 31, 2012, 02:05 PM
You didn't just "change the barrel", you changed calibers.
Why would you expect POI to remain the same?
I have a SIG 229 with a .40 & a .357 barrel, yes there's a difference in POI.
I would be quite surprised if there wasn't. :)
I had a SAK version of the same pistol, did exactly the same thing.
POI wasn't hugely off, but there was a difference.

I would expect the pistol to carry sights set up for the original caliber, and I'd expect switching to a different caliber to bring about the result you found.
Denis

9mmepiphany
March 31, 2012, 03:23 PM
A change in POI when converting from .40 to 357SIG is completely normal...I'd be very surprised, if not concerned, if the POI didn't change.

Even if you didn't change caliber, just the change in velocity would cause the faster bullet to strike lower on the target.

I don't own a 229, but the 226 uses different height sights for the models that are chambered in the 357SIG and the .40...I think .40 uses a 6 front and a 8 rear

CaneCorso85
March 31, 2012, 04:12 PM
Wouldn't the 357 shoot higher, if anything, being that it generally has a flatter trajectory than the bigger heavier .40? Does the velocity have to do with the position the pistol is in as the bullet exits the barrel mid-recoil?

It's a little more difficult for me to compare original sight configuration because it came with the tru-glo TFO front sight (which one, I have no idea) and the Siglite #8 rear. I'd like to keep my front TFO so I guess I'll need to get the #9 or #10 rear to fix the issue.

GLOOB
March 31, 2012, 04:53 PM
There's no appreciable bullet drop at 15 yards. What you're seeing is the effect of muzzle rise before the bullet leaves the barrel. The heavier bullets of the 40 are slower, so they're in the barrel a fraction of a second longer. During that fraction of a second, the muzzle rises an additional fraction of a degree.

In your case, it appears this fraction of a second equals 10 minutes. :)

9mmepiphany
March 31, 2012, 04:54 PM
You're trying to apply rifle trajectory principles to a handgun...the rifle's bore, when their sights are level, point upward, the handgun's bore point downward. Bullets that transverse the length of the barrel sooner leave the muzzle at a lower point in it's upward arc during recoil.

The rear sight blades differ in .01" increments for each number change and will change the POI by 2" at 25 yards. (the front sight blades change the POI by 1")

CaneCorso85
April 1, 2012, 01:48 AM
Thanks for explaining. I think I'll try the #9 rear and if that doesn't work than the #10. Hopefully my needs are in intervals of 2" because I really like my TFO front and truglo doesn't appear to make a shorter front sight.

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