Bullets keyhole'ing...14.5 barrel

O

Oden

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GunNutz
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North end of Garafraxa Rd, Upper Canada
The facts in issue...
Got a chrome lined 14.5 barrel from a undisclosed company on the west coast.
Get it married up with the other bits and pieces and off to the range.
Send some 55 grain fmj's downrange and every shot keyholes.
(Keyhole'ing Websters' noun: spinning wildly out of @#%*'ing control)
Change ammo, different brand, still 55 grain, same thing.
Bump up to a 69 grain, same story.
Only thing I can think of is a bullet weight to rifling ratio problem.
Go home, stick cleaning rod down the pipe and measure a half twist of the rod in 8 inches... which if my math is right, would mean somewhere around a 1:16 twist rate :shock:
I personally have never heard of a twist rate this high in an AR barrel.
Sound right or should I go get an evaluation from my doctor on Tuesday?
 
Highest twist rate was on the SP1 rifles which was a 1:12 twist and stabilized 55 grain rounds nicely (but nothing higher very well). 1:16 sounds way off kilter, if it was a new barrel it should be 1:9 which seems to be standard for regular AR barrels. Sounds pretty weird, I would return the barrel and exchange it... something is not right with it.
 
Sounds like a .22lr twist rate........ :shock:
Pretty big ####up on the shops part..........more bad publicity to go with the locked thread......... :?

The only other thing to check is try and see if a bullet will drop into the muzzle end of the bore.......if the bore is too big for the bullet it will tumble as well.
 
Ditto to the above

IF it is a 1:16 55gr will keyhole - you could dropping a .22 kit and seeing how it goes - or a short 40-50gr Flat base bullet.

As well try slugging the bore.

Some AR15's will have 1:14 bores - it was dropped in favour of the 1:12 for the cold weather stability of M193
 
HeadDamage said:
Any chance the they are hitting the flash hidder for some reason or the muzzel is damaged?
Click to expand...

That's what I wondered as well, but the thought keeps coming to me. How easy is it to mistake a rimfire vs centerfire .22 barrel??? How are the blanks marked or packaged? Is it possible to make an honest mistake?
 
1/16 would indicate they used a .22 rimfire barrel blank. Most .22 barrel blanks are rifled with a 1/16 twist, which is too slow for anything in .223. I'd send the barrel back if I were you.
 
How do you go about verifying the twist rate of the barrel? I also bought a 14.5" barrel and havent shot it yet so I'm pretty worried I'm in the same boat.
 
mattfrombc said:
How do you go about verifying the twist rate of the barrel? I also bought a 14.5" barrel and havent shot it yet so I'm pretty worried I'm in the same boat.
Click to expand...

Take a cleaning rod with a tight fitting patch on it, shove it all the way through the bore from the muzzle to the chamber. Pull it back a bit so it clears the chamber and just enters the bore. Now mark a line on the cleaning rod right at the muzzle on the very top. Now pull it out slowly letting the rifling turn the cleaning rod. When your mark is at the very top again (one complete revolution of the rod), measure from the mark to the muzzle in inchs, that's your twist rate.
 
As it would be, I also purchased a 20" HB chromed lined at the same time and it too has the same rifling ratio. (I double checked my math with an actual 1:7 & 1:9 barrel)
I also thought about the bullet hitting the flash hider but it's overbored a fair bit and no visable marks of taking hits.
A .224 bullet doesn't fall into the barrel from the muzzle end, so I would say the bore isn't oversized.
A .22 cal barrel blank, ie 1:16, makes a lot of sence at the present time.
I'll just have to wait till Tuesday and see what happens when I make the call.
 
Any impingement by the flash suppressor on the line of the bore?

It's unlikely, but possible (it's a known flaw on M-14 type rifles).

Look for any shavings of copper in the area of the FS.

NS
 
Hey Hitzy! You looking for a dedicated .22 cal barrel?
Got two I can part with... :lol:

As far as the FS NavyShooter, all is good there, that was the first thing I had checked. The rounds are going downrange true to the bore line.
Still getting half decent groupings for the circumstances, about 5" grouping @ 50'.

If I was in the market for a <50' CQB weapon with a little more bite I'd have it made.
I would imagine getting hit with a keyhole'ing round might have a higher ouch factor then normal...
 
greentips said:
No pimping of your own sales in the discussion forum!
Click to expand...
Does this include people with for sale ads in their sig line and links to their for sale posts?
 
Whoa it was a joke...
...purchased two barrels, wrong twist rate, Hitzy says "make good .22lr upper", suddenly I have two barrels "for sale" ha ha...ha??

(the barrels aren't posted in the exchange forum for the record)

I will post results after contacting the company.
 
Couple things as pointed out... 1:16 twist won't stabilize a 55 gr bullet (1:14 barely stabilizes a 50gr

And usually a rimfire barrel bore is smaller than a centrefire bore. 22 LR bullets are spec'd at (I think) .221 instead of .224. The bore size difference usually matches that.
 
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