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Factory HK93, clean, late 80's manufacture (have to check date code), no burr on muzzle. 55 gr. South African M193 punches a nice neat circle in the target regardless of range. However, the pricey 69 gr. Federal BTHP appears to go through sideways leaving a profile of round at 50 yds (and I can't even hit paper at 100 yds with them). The simple answer, of course, is to stay with the 55 gr. projectile but I am curious as to the reason why this may be occurring. Is this an issue of barrel twist/projectile weight?

I note that my Steyr USR (blasphemy) pitches both of these rounds regardless of range with no problem at all.
 

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your getting 2790 to 2880fps with the type of slug.(69grn)
and a 17" bbl on the 93... thats why ya need a 1 in 7 twist to keep it in 1 hole.

stick with the 55grn slugs.17"bbl=(2980fps) 1 in 10" i think

this is just off the top of my head... iv been working way to many Hrs!
 

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I would say you need to check the barrel and it is a 1/9 or slower barrel twist. Also, you need different locking pieces depending on the grain weight of the 223 round you are using. I stick to 55 gr on all my X3 rifles because I know all my locking piece work 100 percent with them. My 53 rifles have newer barrels that are 1/7 twist, as marked on the barrels.
 

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The twist rate and bullet weight for 5.56 are usually corelated: 62g or less with 1/9; above 62 for 1/7. Recently it was pointed out to me by Boomfab that the twist is different for different LENGHTS of bullets. This makes sense as the heavier .223 bullet is usually longer. If you think about it, if the spacing between the rifleing is too great for the length of the bullet, it will make it wobble.
 

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The twist rate and bullet weight for 5.56 are usually corelated: 62g or less with 1/9; above 62 for 1/7. Recently it was pointed out to me by Boomfab that the twist is different for different LENGHTS of bullets. This makes sense as the heavier .223 bullet is usually longer. If you think about it, if the spacing between the rifleing is too great for the length of the bullet, it will make it wobble.
This is correct. It is based on length, not weight, although obviously the weight will increase with the length. I'm thinking everyone started referring to the different bullet weights because they are printed on the ammo box, the length of bullets are not. The Greenhill formula is:


C = 150 (use 180 for muzzle velocities higher than 2,800 f/s)
D = bullet's diameter in inches
L = bullet's length in inches
SG = bullet's specific gravity (10.9 for lead-core bullets, which cancels out the second half of the equation)

The original value of C was 150, which yields a twist rate in inches per turn, when given the diameter D and the length L of the bullet in inches. This works to velocities of about 2800 f/s; above those velocities, a C of 180 should be used. For instance, with a velocity of 2000 f/s, a diameter of 0.5 inches and a length of 1.5 inches, the Greenhill formula would give a value of 30, which means 1 turn in 30 inches.

Here's a link to a calculator:

http://kwk.us/twist.html


What I wonder is if the 1 in 7 twist in the 93's I have will cause similar problems if I shoot the cheapie light weight 55gr bullets. Time will tell, I still haven't had my 93 with the 1 in 7 twist to the range yet, only the 1 in 12 ones.
 

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The 55 grain XM193 ammo appears to shoot ok in the 1 in 7 twist black guns (93's, 53's and the assorted evil M-16 ;-). Accuracy appears to be fine for plinking and full auto fire .... for shooting groups or nail heads, tend to use the GMM and most often bolt guns.
 

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62 grainers for the 1 in 9 AR

Sounds like I should run the 62 grainers down the AR.

Is there any downside to running them thru a V93 ( besides lack of accuracy).
can they damage the weapon if I don't get a different locking piece ?

bear in mind most the time I'm shooting 120 yards max.
and i can load 55 gr'ers for the 93 ( already done 700 or so in the last month )

BTW, i thought i saw a couple tracers come apart when fired thru the AR, these a 55 grainers but they're as long as a 65 grain ball projectile...
 

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and your locking piece is fine. dont swap a thing.
your Hk93 was made for 55gn ammo
 

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Key-Holing

I had the same problem with a 1/12 twist barrel, I was able to score some Federal 50 grain ammo and had no problems hitting the 400 yard target with it. The lighter the grain the better in a 1/12 twist
 

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and your locking piece is fine. dont swap a thing.
your Hk93 was made for 55gn ammo
Is this taking into consideration a 1/7 twist? or the 1/12?

What happens if you would try and run 82gn through a 1/7 twist in a 53 with a suppressor? Will key-holeing and then baffle strikes likely occur?
 

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Is this taking into consideration a 1/7 twist? or the 1/12?

What happens if you would try and run 82gn through a 1/7 twist in a 53 with a suppressor? Will key-holeing and then baffle strikes likely occur?
I seriously doubt it. It wouldn't be THAT far off before it leaves the suppressor.
 

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GUYS your Hk93 was made even before 62gn ammo was made for the miltry.
and your locking piece is fine even for 70gn or hvyr 5.56
not that you would use that ammo any way......lol.

just forget even thinking about the locking piece... forget it was even talked about..ok.. stick with talking about the twist in the bore..ok..

after all your not going to push a 68gr 5.56 slug out of your Hk93
at any thing over 3120fps with a powder load that would need a diff locking piece..ok...nexed
 

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Why would you not want to use 70gr or higher?
I suppose there are at least two reasons: 1) they won't properly stabilize in a slow twist, and 2) they launch with less velocity.

I've shot Sierra 80's to 1000 yards before shooting highpower, and they shoot pretty good. The 69 Sierras were excellent 300 yard bullets. Anything under 300 yards or so the 55 grain weight class bullets seem to offer great performance in terms of accuracy and velocities.
 

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But if you have a tight 1/7 twist, wouldn't that be a good bet on it stablizing?

How would they launch with less velocity with a higher grain bullet?
 
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