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Posted: 4/4/2009 10:09:25 AM EST
[Last Edit: 4/4/2009 10:26:08 AM EST by arowneragain]
With all the new AR buyers here, it seems that the question frequently pops up as to whether a rifle with a 1-7" twist will shoot light (55 grain) ammo well.


I was bored today, so I decided to do a short, non-scientific test. I frankly wasn't in the mood to set up my chronograph and wasn't in the mood to shoot 10-shoot groups with current ammo prices. Yes, I'd rather use 10-shot groups.

I went to the local sporting goods place - the ONLY .223 load they had in stock (they used to have pallets of wolf) was hornady's 55-grain v-max load. This load has a reputation for decent accuracy, so I bought a box. I also had 10 rounds left out of a box of Prvi 75-grain match.

I took my Oly lower (it has an A2 stock and the best trigger of all my AR's) and my LT-104 scope mount with Swarovski 4-16x50, and grabbed two uppers:

First was my LMT 14.5" m4gery, with permanently attached Gemtech FH and a YHM free-float railed forend.

Second was my CMMG 16" lightweight midlength with a set of carbine handguards (non-FF) and a phantom 5C2 FH.

All shooting was at 100 yards.

With the LMT upper, 5 rounds of Prvi 75-grain match went into 2.375". That's really about what I expected from this rifle - its first 500 rounds were as a full-auto demo upper, and since then I've put about 1500 rounds through it, getting it quite hot a few times. The bore hasn't been cleaned beyond a patch with CLP since I've owned it - it is NOT a 'match' gun.

Then I shot 5 rounds of the hornady 55-grain v-max load. 5 rounds went into 1.5". That's GREAT accuracy from a worn 14.5" chrome-lined upper, and demonstrates that 1-7" twist service-grade barrels can shoot 55-grain ammo well enough.

As a side note, of those 5 rounds, I had TWO blown primers. Both resulted in stoppages, and both demonstrated why .223 varmint ammo loaded for use in bolt guns, even at .223 pressures, is NOT the best choice for defense ammo, bullet performance notwithstanding. Even if the v-max was a SD bullet, or even if you placed one perfectly onto a perfect-case target, it's useless if the primer blows and causes a stoppage in mid-fight. Crimped primers and case necks, for defensive ammo, ALWAYS.

Ok, moving on, I took the scope/mount and lower and put them on my CMMG upper.

Between the light barrel and non-FF handguards, I wasn't expecting much here.

5 rounds of PRVI went into 2.2". That's not bad - and the group was strung vertically, which suggests an inconsistent hold on my part. The group was only 7/8" wide - who knows what this rifle would do with a FF handguard or a more consistent hold on the sandbags?

I then shot 5 rounds of the hornady 55-grain v-max load. 5 shots went into 1.2". I was pleasantly surprised.

As a control, I took out my Tikka 595 in .223 and shot 5 rounds of the hornady 55-grain v-max load. This rifle is about 13 years old and over the years it's been a laser-beam, shooting several factory loads sub-moa, some well under sub-0.5 MOA, and one handload 'in the teens' - and all of this not just at 100 yards but also at 200 and 300.

So, anyway, I shot 5 rounds of the 55-grain hornady v-max load. They went right where they were supposed to (the rifle was sighted-in 2.5" high at 100 with another 55-grain load, but hasn't been shot in several years), 5 shots centered 2.5" high in a nice, round group of 0.81".

Disclaimer: 5-shot groups are statistically worth very little. However, this is enough to demonstrate that GOOD 55-grain ammo can group quite well in a barrel with 1-7" twist, even in chrome-lined 'service grade' barrels such as LMT or CMMG. These aren't match barrels; these are barrels I'd go into a fight with.

Further, I wouldn't look at any of these groups as being substandard - it's been over a year since I did any bench shooting, I'm out of practice, half my sandbags were still sitting in deer stands, so I wasn't in a comfortable shooting position (especially with the bolt gun) and it was a bit breezy today - light gusts from right to left.


Lessons learned:

55-grain ammo is NO PROBLEM for 1-7" twist barrels.
Varmint loads are NOT suitable for fighting carbines, no matter how cool they perform on varmints.
As O_P says, shooting stuff is fun.


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Link Posted: 4/4/2009 10:22:20 AM EST
nice!

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Link Posted: 4/4/2009 10:24:18 AM EST
[Last Edit: 4/4/2009 10:56:33 AM EST by bearfan620]
Nice work...thanks for taking your time to post and clear up some of the rumor mill. I shoot 55 grain Remington UMC in my 1:7 DD M4 and it's accurate enough for me! I'm not a match gunner, and for SHTF purposes, if I can empty my mag on man sized targets....errrr zombies..... at 100 and 200 yards then I'm OK, because that's why I bought this rifle. And realistically, I should hope I'm not engaging targets at even 100 yards for HD or else there are some bigger problems.

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Link Posted: 4/4/2009 10:25:20 AM EST
Great info.

Thanks!


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Link Posted: 4/4/2009 11:09:27 AM EST
The nly strange thing is getting blown primers from .223 ammo. The only blown primers I've experienced have been using 5.56 ammo in a .223 chamber, and never teh other way around. You might want to let Hornady know about the problem and include the lot number, their a pretty good company, and would likely want to improve their QC and do some checks on that lot for safety/liability reasons.

You're right though, it wouldn't be a problem in a bolt action rifle, but some LEOs practice with this ammo.

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Link Posted: 4/4/2009 11:24:07 AM EST
With all the jaw flapping that goes on around here it is good when OP or someone else takes the time to actually try and shoot something and then report to us.
Thanks.

Yes I realise that to be a scientific and statistical test one needs to shoot boxes and boxes of ammo in precisely controlled conditions but thanks for your effort - we do get what you were going for.

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Link Posted: 4/4/2009 11:34:10 AM EST
Great report - cleared up a lot of stuff for me.
Many Thanks for your effort.

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Link Posted: 4/4/2009 11:40:45 AM EST
good post. Hopefully this stays at the top for a while so ppl can see it.
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Link Posted: 4/4/2009 11:44:47 AM EST
1:7 chromed lined COLT barrel. cut to 18" by randall at ar15barrels.com

hornady 55gr. VMAX
LC once fired.
surplus WC846(BLC-2) powder.
loaded on my DILLON XL650

100yrds. group.

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Link Posted: 4/5/2009 9:56:01 AM EST
Originally Posted By SSN_Doc:
The nly strange thing is getting blown primers from .223 ammo. The only blown primers I've experienced have been using 5.56 ammo in a .223 chamber, and never teh other way around. You might want to let Hornady know about the problem and include the lot number, their a pretty good company, and would likely want to improve their QC and do some checks on that lot for safety/liability reasons.

You're right though, it wouldn't be a problem in a bolt action rifle, but some LEOs practice with this ammo.



I may grab the lot # and send them a link to this thread. I, too, would never have expected excessive pressure signs from this ammo in that barrel. Cases fired in my .223 showed no signs of undure pressure (I realize that case observations aren't a perfect way to measure pressure, of course) but the cases from the LMT string all showed flattened primers and prominent ejector marks. The rifle's chamber was relatively clean - dirty, yes, but not obstructed or anything. Further, the hornady load was shot after the PRVI load, so any excess oil in the chamber would have been removed by then. This is the first time I've ever noticed anything like this out of any factory ammo in any chamber of known quality, and I frankly don't know what to make of it - I just know now that a bolt won't close with a spent primer in it's way.

Maybe it was just a matter of a handful of cases that were overly soft for some reason?


As a side note, I later went home and re-mounted my Eotech and BUIS to the LMT upper, and remounted my aimpoint to the CMMG upper. I re-zeroed at 50 yards, and the eotech returned to within 1/4" of zero. The BUIS needed 3 clicks (IIRC, that's about 2 moa) of windage to zero, and the aimpoint (in an old M68 mount) needed 3 moa of adjustment to return to zero. Both rifles shot 2-MOA 5-shot groups with PRVI M193 at 50 yards. That's honestly the very limit of my ability to shoot with no magnification. One day I may have to run another test with these rifles with some M193 and a good scope.
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Link Posted: 4/5/2009 10:26:19 AM EST
Nice report, thanks!
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Link Posted: 4/5/2009 10:38:02 AM EST
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Link Posted: 4/5/2009 11:16:21 AM EST
69 & 77 get VARGET.

....but at 100yrds., these 55gr. VMAX shoot really well in this barrel.
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Link Posted: 4/5/2009 3:04:43 PM EST
Were people really doubting this? I don't think I've ever seen someone claiming 55gr ammo wouldn't shoot from a 7-twist barrel. It's generally the other way around, people pointing out that heavy ammo won't be stable from slow-twist tubes.

My 26" upper has printed a 0.3" group with 45gr JHPs.

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Link Posted: 4/5/2009 3:35:23 PM EST
Yes, but at 100yds the bullet is still rising in relation to the line of sight. The real test is how it performs as it descends. Try several weights out of the same 1/7 twist at 200 and 300, and see what happens.

The reason this discussion persists is due to a thread once called the ammo oracle; don't know if it's still around. It showed how a light bullet with a high spin rate would keep its nose up as it descends, rather than tracking down. This leads to turbulence, which affects accuracy.

Not that your test is invalid; some folks seem to think the jacket will spin off, or you'll keyhole.

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Link Posted: 4/5/2009 5:01:56 PM EST
[Last Edit: 4/5/2009 5:22:36 PM EST by Molon]
Originally Posted By Geohans:
Yes, but at 100yds the bullet is still rising in relation to the line of sight. The real test is how it performs as it descends. Try several weights out of the same 1/7 twist at 200 and 300, and see what happens.

The reason this discussion persists is due to a thread once called the ammo oracle; don't know if it's still around. It showed how a light bullet with a high spin rate would keep its nose up as it descends, rather than tracking down. This leads to turbulence, which affects accuracy.

Not that your test is invalid; some folks seem to think the jacket will spin off, or you'll keyhole.



Testing performed by C.E. Harris at Aberdeen Proving Ground and later at Sturm-Ruger has shown that the above statement is false. The testing showed that “overspinning” quality light-weight bullets from a fast twist barrel does not become an issue unless you have a gyroscopic stability factor greater than 5.0 (which would require something along the lines of a 1:6” twist barrel launching a 55 grain bullet at over 3500 fps) or unless firing at an angle greater than 85 degrees.

After the U.S. Military adopted the 1:7” twist for the M16A2, C.E. Harris did extensive testing comparing the accuracy of light-weight bullets fired from 1:10” twist barrels and 1:7” twist barrels using 52 grain Sierra MatchKings. The accuracy testing was done from 200 yards, well into the downward slope of the trajectory, and the accuracy results from the two different twist barrels were nearly identical.

Contrary to what has been posted on the Internet, quality 55 grain bullets can shoot superbly from fast twist barrels. The 10-shot group pictured below was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.

Also, I've launched Hornady 40 grain V-MAX bullets at over 3,600 fps from chrome lined, NATO chambered barrels with 1:7" twists with no ill effects.







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Link Posted: 4/5/2009 5:06:04 PM EST
[Last Edit: 4/5/2009 5:07:57 PM EST by chapperjoe]
the question i have ... does M193spec ammo produce 55gr vmax accuracy?

when most people think of running (or speak against running) 55gr through a 1/7, I don't think they mean vmax...

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Link Posted: 4/5/2009 5:10:54 PM EST
Somehow, I'm skeptical that this will stop:

A. the question about 1/7 twist for 55 grainers

And

B. All the supposed experts who say a 1/7 isn't good for 55 grainers. Heck, I even here some people that know a thing or two say it's not ideal. Or that you'll lose like 10% accuracy. Well, I don't agree because what you have just shown and because any 1/7 I've had has shot 52's very very well. Better than even some heavier loadings in that barrel. I have a 1/7 that absolutely hates the 69's. Go figure.


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Link Posted: 4/5/2009 5:12:20 PM EST
Originally Posted By chapperjoe:
the question i have ... does M193spec ammo produce 55gr vmax accuracy?

when most people think of running (or speak against running) 55gr through a 1/7, I don't think they mean vmax...



It doesn't matter. That has nothing to do with twist and everything to do with that ammo and barrel combo. You should know better than that. If you don't, you haven't shot enough. IMHO. Sorry, but this subject gets to me. Time for me to stop posting over here. I'll probably start saying things I regret.
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Link Posted: 4/5/2009 5:18:36 PM EST
This is a "ful of win" post, thanks for your efforts!

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Link Posted: 4/5/2009 5:23:27 PM EST
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Link Posted: 4/5/2009 5:29:05 PM EST
Originally Posted By SB_Matt:
Decent write up. I think a video is better. While I did not shoot at 100 yards. I show that well made, quality barrels will shoot light bullets accurately. There has always been a debate about this in some form or fashion. I shot 40 grain bullets at 300 yards with good accuracy.

CLICK HERE


That's IMPOSSIBLE THEY SUPPOSEDLY BLOW UP RIGHT AFTER THEY LEAVE THE MUZZLE. THIS CAN'T BE.

Maybe this thread will get tacked, because that is one thing "they" almost ALWAYS point to. The 40 grain bullets. Which I could see how sometimes maybe it is problematic, but it is on the extreme light side. And it is usually brought when people are asking specifically about the 55 grainers. Anyways, good post.
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Link Posted: 4/5/2009 5:36:11 PM EST
[Last Edit: 4/5/2009 5:36:40 PM EST by vicious_cb]
I really dont get the point of shooting really lightweight varmint bullets anyway. Whats the point in shooting 36gr or 40gr bullets? Just so you can watch the little ground hogs explode into a dozen pieces? A heavy grain bullet will kill varmints just as dead. I have no need for a 1:9 or even a 1:8 for that matter.

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Link Posted: 4/5/2009 5:49:16 PM EST
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Link Posted: 4/5/2009 6:01:05 PM EST
my 1/9 twist barrel stabalizes 75gr. bullets well, even out to 300 yards. every barrel is different, theres no way to make a blanket statment about this, too many variables.

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Link Posted: 4/5/2009 6:20:20 PM EST
Very interesting ,and good to hear .

Since this big run on ammo started ,I've been using mostly 55 grain in my Colt 6920 . (That's a 1/7 twist carbine as well )

I honestly would like to see a series of tests that include 50 yards,100 yards ,150 yards,and 200 yards with
55 grain,62,and 77 in a 16 inch barrel with a 1/7 twist .
Especially using a dot sight sighted in for 50 yards like so many of us have .

Preferably from an average Joe just wanting to see for themselves instead of some gun mag writer trying
to prove their point of view .

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Link Posted: 4/5/2009 6:22:28 PM EST
Great info...

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Link Posted: 4/5/2009 6:51:28 PM EST
Originally Posted By mercdank:
my 1/9 twist barrel stabalizes 75gr. bullets well, even out to 300 yards. every barrel is different, theres no way to make a blanket statment about this, too many variables.


Thats not really true. If your 1:9 stabilizes 75grs well then its either not a true 1:9 more like a 1:8.8 or something or you have a really long barrel to give the bullet enough velocity to stabilize with the slow twist,

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Link Posted: 4/5/2009 6:52:30 PM EST
Originally Posted By cobrasks:
Very interesting ,and good to hear .

Since this big run on ammo started ,I've been using mostly 55 grain in my Colt 6920 . (That's a 1/7 twist carbine as well )

I honestly would like to see a series of tests that include 50 yards,100 yards ,150 yards,and 200 yards with
55 grain,62,and 77 in a 16 inch barrel with a 1/7 twist .
Especially using a dot sight sighted in for 50 yards like so many of us have .

Preferably from an average Joe just wanting to see for themselves instead of some gun mag writer trying
to prove their point of view .


So cough up several hundred dollars for the ammunition, take a couple days off of work and do it. Be sure to post your results.

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Link Posted: 4/5/2009 6:59:04 PM EST
Originally Posted By Molon:
Originally Posted By cobrasks:
Very interesting ,and good to hear .

Since this big run on ammo started ,I've been using mostly 55 grain in my Colt 6920 . (That's a 1/7 twist carbine as well )

I honestly would like to see a series of tests that include 50 yards,100 yards ,150 yards,and 200 yards with
55 grain,62,and 77 in a 16 inch barrel with a 1/7 twist .
Especially using a dot sight sighted in for 50 yards like so many of us have .

Preferably from an average Joe just wanting to see for themselves instead of some gun mag writer trying
to prove their point of view .


So cough up several hundred dollars for the ammunition, take a couple days off of work and do it. Be sure to post your results.



PLUS ONE.

Then you can get all the guys that tell you how they can shoot 1 hole groups at 200 yards using XM193 and a 4 MOA red dot. Your turn!
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Link Posted: 4/5/2009 7:15:55 PM EST
Originally Posted By Geohans:
Yes, but at 100yds the bullet is still rising in relation to the line of sight. The real test is how it performs as it descends. Try several weights out of the same 1/7 twist at 200 and 300, and see what happens.

The reason this discussion persists is due to a thread once called the ammo oracle; don't know if it's still around. It showed how a light bullet with a high spin rate would keep its nose up as it descends, rather than tracking down. This leads to turbulence, which affects accuracy.

Not that your test is invalid; some folks seem to think the jacket will spin off, or you'll keyhole.


Are you saying that a bullet "noses over" in flight?
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Link Posted: 4/5/2009 7:20:15 PM EST
Originally Posted By SB_Matt:
Decent write up. I think a video is better. While I did not shoot at 100 yards. I show that well made, quality barrels will shoot light bullets accurately. There has always been a debate about this in some form or fashion. I shot 40 grain bullets at 300 yards with good accuracy.

CLICK HERE


Interesting video.

This is a good thread
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Link Posted: 4/5/2009 8:16:53 PM EST
Originally Posted By Molon:
Originally Posted By Geohans:
Yes, but at 100yds the bullet is still rising in relation to the line of sight. The real test is how it performs as it descends. Try several weights out of the same 1/7 twist at 200 and 300, and see what happens.

The reason this discussion persists is due to a thread once called the ammo oracle; don't know if it's still around. It showed how a light bullet with a high spin rate would keep its nose up as it descends, rather than tracking down. This leads to turbulence, which affects accuracy.

Not that your test is invalid; some folks seem to think the jacket will spin off, or you'll keyhole.



Testing performed by C.E. Harris at Aberdeen Proving Ground and later at Sturm-Ruger has shown that the above statement is false. The testing showed that “overspinning” quality light-weight bullets from a fast twist barrel does not become an issue unless you have a gyroscopic stability factor greater than 5.0 (which would require something along the lines of a 1:6” twist barrel launching a 55 grain bullet at over 3500 fps) or unless firing at an angle greater than 85 degrees.

After the U.S. Military adopted the 1:7” twist for the M16A2, C.E. Harris did extensive testing comparing the accuracy of light-weight bullets fired from 1:10” twist barrels and 1:7” twist barrels using 52 grain Sierra MatchKings. The accuracy testing was done from 200 yards, well into the downward slope of the trajectory, and the accuracy results from the two different twist barrels were nearly identical.

Contrary to what has been posted on the Internet, quality 55 grain bullets can shoot superbly from fast twist barrels. The 10-shot group pictured below was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.

Also, I've launched Hornady 40 grain V-MAX bullets at over 3,600 fps from chrome lined, NATO chambered barrels with 1:7" twists with no ill effects.



http://www.box.net/shared/static/gos6vq3szi.jpg





I defer to Mr. Harris; maybe I misremember the Oracle, or maybe it was just old info.

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Link Posted: 4/6/2009 4:40:46 AM EST
[Last Edit: 4/6/2009 5:13:03 AM EST by Molon]
Originally Posted By Geohans:
Originally Posted By Molon:
Originally Posted By Geohans:
Yes, but at 100yds the bullet is still rising in relation to the line of sight. The real test is how it performs as it descends. Try several weights out of the same 1/7 twist at 200 and 300, and see what happens.

The reason this discussion persists is due to a thread once called the ammo oracle; don't know if it's still around. It showed how a light bullet with a high spin rate would keep its nose up as it descends, rather than tracking down. This leads to turbulence, which affects accuracy.

Not that your test is invalid; some folks seem to think the jacket will spin off, or you'll keyhole.



Testing performed by C.E. Harris at Aberdeen Proving Ground and later at Sturm-Ruger has shown that the above statement is false. The testing showed that “overspinning” quality light-weight bullets from a fast twist barrel does not become an issue unless you have a gyroscopic stability factor greater than 5.0 (which would require something along the lines of a 1:6” twist barrel launching a 55 grain bullet at over 3500 fps) or unless firing at an angle greater than 85 degrees.

After the U.S. Military adopted the 1:7” twist for the M16A2, C.E. Harris did extensive testing comparing the accuracy of light-weight bullets fired from 1:10” twist barrels and 1:7” twist barrels using 52 grain Sierra MatchKings. The accuracy testing was done from 200 yards, well into the downward slope of the trajectory, and the accuracy results from the two different twist barrels were nearly identical.

Contrary to what has been posted on the Internet, quality 55 grain bullets can shoot superbly from fast twist barrels. The 10-shot group pictured below was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.

Also, I've launched Hornady 40 grain V-MAX bullets at over 3,600 fps from chrome lined, NATO chambered barrels with 1:7" twists with no ill effects.



http://www.box.net/shared/static/gos6vq3szi.jpg





I defer to Mr. Harris; maybe I misremember the Oracle, or maybe it was just old info.


You remember correctly. Lot's of "theories" get posted on the Internet with no real data to support them and it's often started with people who misinterpret the original concepts to suit their own misbeliefs. "A little knowledge is a dangerous thing."



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Link Posted: 4/6/2009 5:39:40 AM EST
[Last Edit: 4/6/2009 5:51:37 AM EST by arowneragain]
Glad to see this post is generating some discussion. I'm really surprised by how often this subject comes up. I'm also glad to see other folks posting groups - the proof is in the pudding, so to speak.

As to whether an expensive varmint load is equal to M193, obviously, it's not, REGARDLESS of barrel twist.

Having said that, I've shot 8" 5-shot groups with M193 at 260 yards out of the LMT - that's less than 3 MOA - and that's also with an Eotech and no magnification, from a guy with poor eyesight who benfits greatly from magnified optics. Saturday's 50-yard groups out of this upper were 2 MOA with PRVI M193, which, by the way, happens to be more accurate IN MY UPPERS than Q3131 or XM193. Next time I feel like removing optics that have to be re-zeroed ( Note to self: get more LaRue mounts) , I'll test the PRVI at 260 yards out of the LMT.


Getting back to the pressure signs from the hornady load in the LMT upper, the lot # was 3090666, and here's a picture of the fired cases:



If you'll notice carefully, you can see not only ejector marks, but also EXTRACTOR marks on these cases. The photo doesn't do them justice, but you can see them in a couple of the cases.

(edit: look for a perpendicular line across from the ejector mark - that's from the extractor)


I'm going to send a link to this thread to the hornady folks.

This same upper has fired Q3131, XM193, WWB, REM-UMC, and black hills ammo, in addition to the PRVI M193 and PRVI 75-grain match, with no signs of excessive pressure; the only difference being that normally I'm using a carbine stock with h-buffer, and these laods were fired from an A2 stock with rifle buffer. Still, that shouldn't cause such pressure signs - those marks have already been made by the time the action begins to cycle, if I understand the AR gas sytem correctly.

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Link Posted: 4/6/2009 5:40:43 AM EST
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Link Posted: 4/6/2009 9:18:40 AM EST
Originally Posted By JJREA:
Originally Posted By Molon:
Originally Posted By cobrasks:
Very interesting ,and good to hear .

Since this big run on ammo started ,I've been using mostly 55 grain in my Colt 6920 . (That's a 1/7 twist carbine as well )

I honestly would like to see a series of tests that include 50 yards,100 yards ,150 yards,and 200 yards with
55 grain,62,and 77 in a 16 inch barrel with a 1/7 twist .
Especially using a dot sight sighted in for 50 yards like so many of us have .

Preferably from an average Joe just wanting to see for themselves instead of some gun mag writer trying
to prove their point of view .


So cough up several hundred dollars for the ammunition, take a couple days off of work and do it. Be sure to post your results.



PLUS ONE.

Then you can get all the guys that tell you how they can shoot 1 hole groups at 200 yards using XM193 and a 4 MOA red dot. Your turn!


I'd like somebody that can actually shoot half decent to do a real test .

I pretty much just blast stuff ,but I'd like to see the results .
Sure I've seen some charts but I'm amazed that somebody here hasn't done
a real write up to show their results .That'd make a good sticky thread .

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( or a couple hundred bucks laying around or time off work anytime soon)

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Link Posted: 4/6/2009 6:47:21 PM EST
[Last Edit: 4/6/2009 6:51:56 PM EST by chris65]
Originally Posted By arowneragain:
...
I took my Oly lower (it has an A2 stock and the best trigger of all my AR's) and my LT-104 scope mount with Swarovski 4-16x50, and grabbed two uppers:

First was my LMT 14.5" m4gery, with permanently attached Gemtech FH and a YHM free-float railed forend.

Second was my CMMG 16" lightweight midlength with a set of carbine handguards (non-FF) and a phantom 5C2 FH.
...


Just wondering about both barreled uppers, and whether they have relieved M4 Upper feed ramps and M4 barrel extensions. It would also be worth testing the vmax loads for bullet set-back into the cases after feeding: measure oal before loading, load, slowly extract, measure oal again. Try on 5-10 loaded rounds.

Edit: also, pull a vmax load and weigh the powder charge to give us and Hornady more info...

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Link Posted: 4/6/2009 8:03:13 PM EST
Originally Posted By arowneragain:
Glad to see this post is generating some discussion. I'm really surprised by how often this subject comes up. I'm also glad to see other folks posting groups - the proof is in the pudding, so to speak.

As to whether an expensive varmint load is equal to M193, obviously, it's not, REGARDLESS of barrel twist.

Having said that, I've shot 8" 5-shot groups with M193 at 260 yards out of the LMT - that's less than 3 MOA - and that's also with an Eotech and no magnification, from a guy with poor eyesight who benfits greatly from magnified optics. Saturday's 50-yard groups out of this upper were 2 MOA with PRVI M193, which, by the way, happens to be more accurate IN MY UPPERS than Q3131 or XM193. Next time I feel like removing optics that have to be re-zeroed ( Note to self: get more LaRue mounts) , I'll test the PRVI at 260 yards out of the LMT.


Getting back to the pressure signs from the hornady load in the LMT upper, the lot # was 3090666, and here's a picture of the fired cases:

http://i78.photobucket.com/albums/j85/clatch/DSCN4293.jpg

If you'll notice carefully, you can see not only ejector marks, but also EXTRACTOR marks on these cases. The photo doesn't do them justice, but you can see them in a couple of the cases.

(edit: look for a perpendicular line across from the ejector mark - that's from the extractor)


I'm going to send a link to this thread to the hornady folks.

This same upper has fired Q3131, XM193, WWB, REM-UMC, and black hills ammo, in addition to the PRVI M193 and PRVI 75-grain match, with no signs of excessive pressure; the only difference being that normally I'm using a carbine stock with h-buffer, and these laods were fired from an A2 stock with rifle buffer. Still, that shouldn't cause such pressure signs - those marks have already been made by the time the action begins to cycle, if I understand the AR gas sytem correctly.



Hornady had a problem a little while back with some lots of their 5.56 TAP blowing primers. (I never experienced this, but several reliable sources reported it.) The rounds weren't overpressure and Hornady reported that the problem was traced to some out of spec lots of brass in which the caseheads were too soft. Looks like that might be the same issue with your ammunition. I would definitely give Hornady a call about this.
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Link Posted: 4/6/2009 8:41:03 PM EST
Originally Posted By vicious_cb:
I really dont get the point of shooting really lightweight varmint bullets anyway. Whats the point in shooting 36gr or 40gr bullets? Just so you can watch the little ground hogs explode into a dozen pieces? A heavy grain bullet will kill varmints just as dead. I have no need for a 1:9 or even a 1:8 for that matter.


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Link Posted: 4/7/2009 8:04:16 AM EST
Got a response from Hornady:

thanks for letting us know. We feel that the combination of the
5.56 chamber and the short barrel contributed to the problem with the
lighter bullets. We have found in the past that unless the primers are
crimped in they can back out due to port pressure not exiting fast
enough. This seems to be a problem only with lighter bullets. Thanks


I can see how a fast-burning powder could produce a situation where gas pressure was still high in the barrel (and case) at the same time that gas was beginning to push the bolt forward so it could begin to unlock - resulting in a situation where a case head was being pressured from 2 directions.

I'm not well-enough versed in the intricasies of the AR gas sytem to offer any really intelligent comment here - but, anyway, that's hornady's response - good enough for me.


To reiterate:

Crimped primers for defensive ammo, always.

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Link Posted: 5/10/2009 8:31:35 AM EST
So how would these tests work on shorter barrels? IE a 14.5 incher...

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Link Posted: 5/10/2009 8:44:47 AM EST
Good report.

I don't think anyone's saying a 1 in 7" is bad for lightweight bullets, just that a slower 1 in 9" would be comparatively better. But the 1 in 7" is (dare I say) "good enough".

Actually, there's a lot more than just twist which contributes to or detracts from accuracy. The quality of the chambering job (concentricity with bore), the dimensional consistency of the bore and the consistency of the crown come immediately to mind.

I'd bet that if all things were equal other than twist, the 1 in 9" would outshoot the 1 in 7", but the delta probably isn't enough to worry about. And, an perfect 1 in 7" would outshoot a 1 in 9" that had some issues with the above mentioned areas.

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Link Posted: 5/10/2009 9:09:18 AM EST
I have a 28" kriger bull barrel (.930 at muzzel) with a 1:6.5 twist on my AR Match rifle. It shoots sub. MOA at 200 with 55gr.nosler BT bullets. It also shoots sieras from 69 to 80 grain well. I love the fast twist barrels and would not buy anything slower than 7.0 twist.

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Link Posted: 5/10/2009 9:15:51 AM EST
Originally Posted By hugegutpile:
I have a 28" krieger bull barrel (.930 at muzzel) with a 1:6.5 twist on my AR Match rifle. It shoots sub. MOA at 200 with 55gr.nosler BT bullets. It also shoots sieras from 69 to 80 grain well. I love the fast twist barrels and would not buy anything slower than 7.0 twist.



What load are you shooting?

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Link Posted: 5/10/2009 10:40:33 AM EST
I have found 0 grain bullets to be as accurate at 25 yards out to 1000.

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Link Posted: 5/10/2009 11:15:11 AM EST
I shoot a ton of the 55 gr. hornady vmax stuff @18.99 a box at academy. I think it is wonderful ammo, very accurate, shiny brass and always goes bang.

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Link Posted: 5/10/2009 11:51:51 AM EST
Originally Posted By Molon:
Originally Posted By Geohans:
Yes, but at 100yds the bullet is still rising in relation to the line of sight. The real test is how it performs as it descends. Try several weights out of the same 1/7 twist at 200 and 300, and see what happens.

The reason this discussion persists is due to a thread once called the ammo oracle; don't know if it's still around. It showed how a light bullet with a high spin rate would keep its nose up as it descends, rather than tracking down. This leads to turbulence, which affects accuracy.

Not that your test is invalid; some folks seem to think the jacket will spin off, or you'll keyhole.



Testing performed by C.E. Harris at Aberdeen Proving Ground and later at Sturm-Ruger has shown that the above statement is false. The testing showed that “overspinning” quality light-weight bullets from a fast twist barrel does not become an issue unless you have a gyroscopic stability factor greater than 5.0 (which would require something along the lines of a 1:6” twist barrel launching a 55 grain bullet at over 3500 fps) or unless firing at an angle greater than 85 degrees.

After the U.S. Military adopted the 1:7” twist for the M16A2, C.E. Harris did extensive testing comparing the accuracy of light-weight bullets fired from 1:10” twist barrels and 1:7” twist barrels using 52 grain Sierra MatchKings. The accuracy testing was done from 200 yards, well into the downward slope of the trajectory, and the accuracy results from the two different twist barrels were nearly identical.

Contrary to what has been posted on the Internet, quality 55 grain bullets can shoot superbly from fast twist barrels. The 10-shot group pictured below was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.

Also, I've launched Hornady 40 grain V-MAX bullets at over 3,600 fps from chrome lined, NATO chambered barrels with 1:7" twists with no ill effects.



http://www.box.net/shared/static/gos6vq3szi.jpg






I was going to say, didn't this get worked out in the 80's when the military switched to the A2? None of the manuals say anything about reduced accuracy, just reduced range (just to the original effective range of 250m), and that the point of impact would be different than the point of aim if the rifle were zeroed with the M855 ammo.
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Link Posted: 7/9/2009 10:48:09 PM EST
Originally Posted By Unicorn:
Originally Posted By Molon:
Originally Posted By Geohans:
Yes, but at 100yds the bullet is still rising in relation to the line of sight. The real test is how it performs as it descends. Try several weights out of the same 1/7 twist at 200 and 300, and see what happens.

The reason this discussion persists is due to a thread once called the ammo oracle; don't know if it's still around. It showed how a light bullet with a high spin rate would keep its nose up as it descends, rather than tracking down. This leads to turbulence, which affects accuracy.

Not that your test is invalid; some folks seem to think the jacket will spin off, or you'll keyhole.



Testing performed by C.E. Harris at Aberdeen Proving Ground and later at Sturm-Ruger has shown that the above statement is false. The testing showed that “overspinning” quality light-weight bullets from a fast twist barrel does not become an issue unless you have a gyroscopic stability factor greater than 5.0 (which would require something along the lines of a 1:6” twist barrel launching a 55 grain bullet at over 3500 fps) or unless firing at an angle greater than 85 degrees.

After the U.S. Military adopted the 1:7” twist for the M16A2, C.E. Harris did extensive testing comparing the accuracy of light-weight bullets fired from 1:10” twist barrels and 1:7” twist barrels using 52 grain Sierra MatchKings. The accuracy testing was done from 200 yards, well into the downward slope of the trajectory, and the accuracy results from the two different twist barrels were nearly identical.

Contrary to what has been posted on the Internet, quality 55 grain bullets can shoot superbly from fast twist barrels. The 10-shot group pictured below was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.

Also, I've launched Hornady 40 grain V-MAX bullets at over 3,600 fps from chrome lined, NATO chambered barrels with 1:7" twists with no ill effects.



http://www.box.net/shared/static/gos6vq3szi.jpg






I was going to say, didn't this get worked out in the 80's when the military switched to the A2? None of the manuals say anything about reduced accuracy, just reduced range (just to the original effective range of 250m), and that the point of impact would be different than the point of aim if the rifle were zeroed with the M855 ammo.


I dont know AR670-1,I do know fm 23-9, as far as m193 and m855 it has a test demonstrating there is no noticable accuracy difference at 300m in a 1/7 A2 when zero'd for the particular ammo. Effective range is greater than 250m for the A1, even though it was before my time, IIRC it was 75-100m less than an A2 @ 550m. Perhaps you are refering to the range at which the A1 was zero'd, 250 meters, (NOTE: A1 was way before my time, the only real deal I ever saw was in the Philippines, or the CHP, but that is prob. neutered version ?). I should note the FM says when possible use m855 in an A2,m193 in an A1 whenever possible. M855 should only be used in an A1 in a "combat emergency" as it was only effective at less than 90 meters. Going of memory so somebody correct me if Im wrong.


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Link Posted: 7/10/2009 3:00:42 AM EST

Originally Posted By vicious_cb:
I really dont get the point of shooting really lightweight varmint bullets anyway. Whats the point in shooting 36gr or 40gr bullets? Just so you can watch the little ground hogs explode into a dozen pieces? A heavy grain bullet will kill varmints just as dead. I have no need for a 1:9 or even a 1:8 for that matter.

Wouldn't a smaller lighter projectile at a higher velocity have a better chance of disintegrating on impact in the event of a miss?

I prefer that in the event of a miss, that round I just shot will have a better chance of destruction upon impact of the ground.
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Link Posted: 7/10/2009 3:41:35 AM EST
I have a friend that handloads the 55grVMAX
His M4 is a DDM4 BTW Very nice weapon
Accuracy is good for a Rack Grade M4 barrel
His DDM4 shoot the 55grVMAX Better than BLACK HILLS BLUE BOX 75gr


I use 2
LMT M4`s 14.5 1/7 twist aimpoint ML2 / 551 Iffytech

Ive shot better groups with WIN USA 45gr than some 55gr FMJ loads

Some types of M193 shoot better than some M855/SS109 vise/versa
But thats from my 2 M4`s

I get better groups with Wolf M193 2005 lot
Than the CAN LC M855 that I have

So far I havent found any M855 that was as accurate as the 1993 SANTA BARBRA SS109 & 2000 S&B ZV SS109 & my small stash of 1999 IMI M855
but again thats my weapons

I still like the BHB 77gr SMK the best
and on a good day at 50Y I can get clovers groups / all 5rds. touching (Aimpoint ML2/LMT M4 & 551 eotech/LMT M4 / range bag)

I cant shoot 10shot groups at 50Y and keep every round under 1inch

But hey its a M4
Not a match rifle

give me my 222rem BA and its another story
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