Keyholing

Cerdan

Cerdan

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I recently acquired a FireDragon barrel chambered in .357Sig for my Sig P229. Took it out to the range and fed it some handloaded Hornady 147gr. RNBT. To my great surprise, I had next to no accuracy, so I brought the target in a bit closer. That's when I noticed the dreaded "keyholes" in my target.

Now, I've already tried this recipe in a factory .357Sig barrel in my P226 with great success, so I know it's not a load problem. Also, I fired some factory 124gr. BEB out of the FireDragon barrel and the bullets stabilized.

Upon visual inspection of the FireDragon barrel, I was immediately struck by the rifling, which doesn't look "cut" like in my other barrels. The rifling's smoother, subtler. It says on the document that came with it that the "barrels are bored and rifled using ECM (electro-chemical machining)", with a 1:16 right-hand twist.

So, anyone have any idea why 147gr. bullets couldn't stabilize in that barrel?
 
Check your crimp and loosen it off a bit if you can. A crimp that's too tight is a classic for keyholes.....
 
Hmmm, thanks for the input everyone. Unless there's a huge difference in bullet diameter between the 124gr. BEB and the 147gr. RNBT, I don't see how the problem could be due to an oversize bore, since the former shot well through that barrel.

I don't think it's a crimp problem either since those loads shot well enough in my P226. I'll look into it though. Actually, those 147gr. bullets aren't well suited to .357Sig. In order to stay under max OAL, I have to seat them a bit deeper than the ogive would normally permit it; I have to crimp a little higher on the bullet, at the base of the nose...

I'll do some more tests I guess.
 
Well there actually could be difference in diameter between your two bullet weights but you'll have to measure to find out.

As for the crimp, I hate to admit that I don't know why, but I do know that it is so. Too much crimp makes keyholes (and lousy accuracy)
 
Cerdan said:
Hmmm, thanks for the input everyone. Unless there's a huge difference in bullet diameter between the 124gr. BEB and the 147gr. RNBT, I don't see how the problem could be due to an oversize bore, since the former shot well through that barrel.

I don't think it's a crimp problem either since those loads shot well enough in my P226. I'll look into it though. Actually, those 147gr. bullets aren't well suited to .357Sig. In order to stay under max OAL, I have to seat them a bit deeper than the ogive would normally permit it; I have to crimp a little higher on the bullet, at the base of the nose...

I'll do some more tests I guess.
Click to expand...
Shorter bullets tend to be more affected by bore size, as they have shorter bore riding surface.They also sometimes require a different rate of twist to stabilize, although this usually isn't much of a concern at handgun velocities..
 
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Thanks a lot John, I'm definitely saving that article for future reference. I've only had the time to breeze through it, but it's already given me a few leads.
 
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