Colt Match H-Bar "twist"?
mar...@hotmail.com
How do you determine the barrel "twist"?
I don't see any barrel markings, I don't see anything
mentioned in mfgr. booklet and nothing mentioned
on box???
What is the "optimum" twist for .223?
How does this relate to proper ammo. selection?
Bterr
Check your serial number and call the factory. The newer Colts have a 1 turn
in 7" twist to stabilize the new, heavier military round with the steel
penetrator.
DMorisoli
#How do you determine the barrel "twist"?
#I don't see any barrel markings
If it is a Colt barrel, it should be marked on top of the barrel just ahead of
the front sight. It should say something like:
CMP NATO 1/7 HBAR
The 1/7 indicates the twist. Most Colt HBARs are 1/7. However, I have seen
some 1/9 also. (Most of the flattop models are 1/9).
If indeed your barrel does not have these markings, I would doubt that your
rifle has a genuine Colt factory barrel.
Good luck
Burt Mitchell
Try looking on the top of the barrel in between the front sight and the
muzzle. My Sporter Match HBAR is labeled there in big letters. What it
says is this: CMP 5.56 NATO 1/7 HBAR
so it's a 1 in 7 twist. It seems to me that the post ban models I was
looking at the other day had similar markings on the barrel. It might just
be memory playing tricks on me. If yours is a post ban model, the twist
rate should be 1 in 9. You can check it yourself by means of a barrel
cleaning brush and rod. Put a mark on the rod. Push the brush into the
barrel until the mark has made one revolution (turn). Measure how much of
the rod went into the barrel. If it went in 9 inches you have a 1 in 9
twist rate.
If you're not shooting competitively, you can shoot just about any 223 ammo
of 55 grains or heavier and get good performance. I've managed to shoot a
few 1" groups (at 100 yards) with 55 grain ammo. I've also managed to shoot
a really lousy group at 100 yards with the 69 grain ammo that the 1 in 7
twist rate is supposed to be best for. You should be just fine with 55 or
62 grain ammo.
Burt
--
| Burt Mitchell | Illegitimus non carborundum est |
mar...@hotmail.com wrote in message <6b2iip$b...@xring.cs.umd.edu>...
#How do you determine the barrel "twist"?
#I don't see any barrel markings, I don't see anything
#mentioned in mfgr. booklet and nothing mentioned
#on box???
#What is the "optimum" twist for .223?
#How does this relate to proper ammo. selection?
#
#
Chuck
mar...@hotmail.com wrote:
#
# How do you determine the barrel "twist"?
# I don't see any barrel markings, I don't see anything
# mentioned in mfgr. booklet and nothing mentioned
# on box???
# What is the "optimum" twist for .223?
# How does this relate to proper ammo. selection?
Insert cleaning rod with a tight fitting patch. Put a mark on the
rod where it meets the barrel's muzzle. Also make a mark on the rod
so that you can note its rotation as you push it into the bore.
When the makes one complete turn, again place a mark at the muzzle.
Remove the rod and measure the distance between your marks.
There you have it...one turn in X"
Heavy, long bullets need faster twist rates than shorter, lighter ones
to properly stabilize them, so they tell me.
I believe there is a good aritcle covering this subject in the current
issue of the "American Rifleman"
Hope this helps.
Chuck
DDeardorf
To Marie34,
All Colt Barrels will have the twist rate on the top in front of the
front sight. 1/7 is the new standard for the AR 15 A2 system. This rate was
choosen by the Army as the bets twist rate for the new M855 (SS109) round. This
round is a 62 gr. FMJ Boattail. The old AR 15 A1 had a twist rate of 1/12 and
was mated to the old M193 55 gr FMJ Boattail bullet.
Bushmaster and Amarlite have 1/9 and 1/8 twist rates, respectivly. Some
belive the 1/7 rate is too fast and will burn out the barrell early. I read
about many AR 15s and own both a colt and Bushmaster. I have see no differnce
in my accuracy with 55 gr practice ammo(Federal, Reminton) with either rifle.
Also, Shooting Times ran a torture test on a Colt Match Target (Post Ban name)
and put 10,000 rounds through it. Only in the last 1,000 rounds did accuracy
suffer. This was after shooting the barrel till it was litteraly smoking.
Groups averaged 1 1/2 to 2 inches with PMC 55 gr Ammo. i would not woory about
the twist rate too much.
Common theroy is light bullet, slower twist rate(1/12) and heavy bullets
need a faster rate(1/7, 1/8, 1/9).
Good luck, Dave
AuntGary
To determine the rate of twist in rifle or pistol just fit a tight patch on
your cleaning rod and mark a line or scribe around the circumferance of the
rod. Now pull the rod back out of the barrel and measure how far it travels to
make one revolution. In some it will be 7, or 9, or 10 and even 12 in the
original AR15's.
The 7in twist will stabilize a 70 grain bullet and the 12in will best stabilize
the 52 grain bullet.
Here's where the fun begins. If you want a nearly recoiless rifle, match the
velocity of the bullet to the twist. My Mini 14 in 7in twist will shoot a 63
grain bullet with a much reduced load of fast bulky powder with just enough
force to cycle the action. The clack, clack of the bolt will be much slower
and produce tight groups to 100yds.
Check your loading manual for optimum velocity vs twist.
Mike Morrow
Dave wrote:
#Common theory is light bullet, slower twist rate(1/12) and heavy
#bullets need a faster rate(1/7, 1/8, 1/9).
The bullet's length-to-diameter ratio is the most important factor in
determining the required rate-of-spin. Faster rates are needed for
larger ratios. Of course, for a given caliber, a heavy bullet will
generally be longer than a lighter bullet. The 1:7 twist of the M16A2
barrels is designed to stabilize the current tracer bullet (M856?),
since it is longer than the M855 62gr ball bullet, which is in turn
longer than the old M193 55gr bullet. Tests at FN showed that 1:9 would
stabilize the M855 equivalent bullet, but not the tracer round, even
though the weight of the tracer round is very close to that of the ball
round.
I think the physics that applies is the same that makes a short top have
a stable spin at lower rpm than it would take to stabilize a long top of
the same diameter.
"Hatcher's Notebook" (Stackpole Press) has a discussion of rifling twist
determination, and "The Black Rifle" (Collector Grade Publications)
presents FN's rate-of-twist experiments for 5.56x45mm.
Winchester Model 94 rifles in .44 mag use a rifle twist of about 1:28
inches (or there about) to stabilize a heavy, short bullet. The
length-to-diameter ratio is small enough for such a slow twist to do the
job, even though the bullet is rather heavy.
Mike M.