personal experiance only i have heard many conflicting opions on this subject so please only if you have tried this yourself will 75gr hornady tap 5.56 or75gr 223 stabalize well enough in a1x9 twist to give 1to 1 1/2 in groups at 50 to 100 yds if you can already get3/4 to1moa with 55 ,60,62gr loads now at 100yds please state make and model of firearm.If you hav,nt tried the tap but another brand of75gr ammo please state brand of ammo and bullet type. THANK YOU
I have seen the 75 gr TAP key hole out of about 15 DPMS rifles with 1/9 in our old issued rifles. I’ve also seen 69 gr key hole in two BM. 1/9 is only truely reliable up to about 62 gr in ALL 1/9 barrels. Heavier than that and it is suspect barrel to barrel.
The reason that some barrels marked 1/9 will shoot decently with the heavier rounds is that they a cut closer to a 1/8 than a 1/9 but, as said before, this is different from barrel to barrel even within the same company.
It’s not really a matter of experience, but of empirical evidence. 1x9 cannot stabilize a 75gr. round. A barrel marked 1x9, but closer to 1x8 on a warm day can.
For you guys in the know…I tried some 77 gr Sierra HPBTs in my 16" 1/9 and they shot great…much to my surprise.
Any possible explanations why?
what type of gun do you have
Kinda on topic, but just an example.
Cousin has a Remington 700 20" with a 1:9 Twist Barrel.
As far as Black Hills Ammo. Shoots 69grain LIGHT OUT !!!, Small Bug Holes if shooter does their part. Tried BH 75grn. = No Go, Tried 77grn. = No Go. The 75grn. might work out of a handload, but with the way BH 69grn shoots he’s sticking with it. Handloads will probably be 69grn SMK as well. Rather be shooting then T&E loads. Range is 100 yard zero & ammo T&E, Max is 600 yards… so far. I’ll take a 1:7x/1:8 w/ 77grn for further or most likely a Larger Caliber, .260Rem/.308Win.
All depends on each rifle/barrel. Some will shoot it some wont. Just got to try to see what it likes.
IMHO: 1:9 w/ bulk ammo for training/practice should be fine, IF Anyone ALREADY has the rig. If your building NEW, no reason not to go 1:7 from a QUALITY Manuf./Source with all the fixings.
The 69gr keyholing is suprising. 62gr M855 projectiles are as long as your average 69gr bullet. If 1:9 is marginal for stabilizing M855 then they have no place on any rifle.
The February 2010 issue of Small Arms Review has a test of the Ruger SR556 (1:9 twist). They claim 1.5 MOA with Black Hills MK262 MOD1 77 grain ammo.
hmm - that is suspect. No way 75 or 77gr will not key hole on a 1/9 twist barrel. If anyone here is familar with the Century Tantal (5.45) that Century used a modified 5.56 1/9 twist barrel. Loads of key holing except when using the lighter 52gr Wolf Ammo. The heavier longer 70gr ammo would key hole.
I’ve seen BM rifles that were probably closer to 1/10 and would not stabilize anything over 55 gr. Like I said just depends on the barrel from one to the next. Just one more reason to stay away from companies that have shit QC.
The twist may actually be closer to 1/8 even though it’s marked 1/9. This is not uncommon.
1/8 is a very effective twist rate and some of the more accurate barrels out there use it.
I tried Hornady’s 75gr A-Max (reloads) out of my 16" 1/9 marked stag upper early last year and ended up using it as my groundhog load for the summer. As stated, 1/9 gets a little finicky when you get up there in weight (length) due to very slight differences in exact rate of twist or imperfections in the barrel. Not sure how the length of the projectile differs between the two, so that may play a part. Best thing to do is get a box and try it… might surprise you.
will a 20 in bbl stabilize better than a16in
Observations of marginally stabilized projectiles/twist rates are pointless without the atmospheric conditions present at the time.
Higher velocity will increase stability but not significantly.
Very good point. The rifles that I saw crap the bed were DPMS 16" carbines shooting our issued duty ammo 75 gr TAP several years ago. We were shooting on a fall day in the low 70’s with little wind and the usual north Texas humidity (dry during the fall). 15 of the 25 rifles would not perform with the issued ammo.
We now issue LMT 10.5 SBR’s
What is Keyholing?
I always read threads on this b/c I have one of those Monster Colt HBARS. 24 inch barrel in a 1/9 twist. Praire dog gun. I have not played with heavier ammo, but wondered if the heavier barrel and 24 inches would make it better for heavier ammo? I always thought its crazy to have that gun in 1/9. Kreiger super heavy barrel. The gun shoots 1/2 inch with quality Hornady 55grain hunting ammo.
When the bullet has destabilized during it’s trajectory (spinning/flipping) and creates a “keyhole” shaped hole in the target.
thanks
I have a hard time believing that a true 9" twist barrel will cause 77gr rounds to keyhole. I have a Colt 9" twist 16" barrel and shot 77gr SMK Fed GMM and got about 2MOA at 100yards, but no key holes. My 7" twist LW50 barrel puts the same rounds into about 0.5MOA at the same range.
Most 9" twist barrels like weights up to 68-69gr ammo. Like SWATCop1911 said it can be hard to tell which twist rate handles which weights (lengths) because some manufacturers don’t mark or measure their twist rates correctly. It is pretty easy to measure you own rifle’s twist rate.
I was recently ate the range and shot a couple of sub MOA groups at 100 yards with a 7" twist rifle using 50gr Federal rounds, that actually surprised me.
Cameron
Here’s what happens when the Hornady 75 grain A-MAX is fired from a 16" Colt 6721 barrel with a 1:9" twist.
