Accuracy of 11.5" barrel?

[bchandler]

Ok, I was thinking of taking the SBR plunge and going with an 11.5" barrel. Can anyone explain to me about how much accuracy this length takes away from a standard 16" barrel?

Also, how many FPS will I lose?

[GixxerSixxer]

Accuracy and velocity are two different issues. If it's a good quality barrel that has a good crown put back onto it the accuracy won't be lost.

Velocity will be lost by cutting the barrel down. This just means you'll have to point the gun higher to make hits at long range.

To compensate for reduced velocity in defensive situations it's advised to go with a 1:7 twist and shoot heavier bullets.

[bchandler]

Thank you for your quick reply. I actually found this site through searching:

http://www.bushmaster.com/faqnew/content_by_cat.asp?contentid=205&catid=103

So, if I decided to use an 11.5 for home defense, I should order a 1/7 and use 70+ grain ammunition? Will this twist still stabilize 55gr plinking ammo at the range? Would a 1/9 and good quality ~62gr HP ammo be suitable for defense, so that I could shoot 55gr from the same barrel?

i never shoot over 100yds anyway... I know this is fairly close range, And I wouldn't really try to shoot over that with an 11.5 anyway... more likely I will keep it to 25-50 yards. But how much difference are we talking here? Supposing I use a 1/9 and 55gr plinking ammo?

I know some of these are noob questions... I just got my AR last week!

[GixxerSixxer]

1:7 will allow you to shoot a 55 grain bullet. Past 100 yards the accuracy tends to decrease because it's a fast twist on a light bullet.

Some people shooting very light .224 bullets have had issues with the bullet pretty much spinning apart from a 1:7 twist.

You could also get a 1:8 barrel and shoot 55 grain and 70 grain bullets easily.

What kind of accuracy are you after? Angle of man or 3/4 MOA groups? What's a long shot for you, 100 yards, 200 yards, 300 yards?

If you're looking to fit all the shots in a 6" zone at 100 yards the 1:7 will be fine. Most 1:7 twist barrels are chrome lined whereas it can be tedious trying to find a 1:8 chrome lined barrel you want. More 1:8' CL are available, Sabre Defense makes one but they are really backed at the moment.

[bchandler]

Well, I would like to keep it as accurate as possible, even though I know 6" at 100yds is plenty combat accurate.

What I am gleaning from this conversation is:

1/9 is more accurate for 55gr plinking ammo, but restricts my home defense rounds to light bullets (how light? Under 70gr?)

1/7 is more accurate for heavy bullets, but I lose accuracy at the range with 55gr ammunition.

Realistically, this rifle will still be primarily used for range work (It is my only AR for now!). So I suppose I would want more accuracy with the light 55gr rounds. For home defense, I'm not seeing a situation requiring more than 15-25yds tops... it's not like I'm going to try to gun a guy down when he's running away 200yds away. For these reasons I am kind of leaning towards a 1/9, if my above assumptions are correct.

So, IF I decide on a 1/9, what kind of groups can I expect at 100yds with 55gr? 25yds? And what kind of home defense ammunition would be ideal for my barrel?

Thanks so much for taking the time to help me! Maybe one day I can help someone else with the same questions :).

[c4igrant]

Fragmentation range with a a 10.5 or 11.5 tends to be around 50-70yds. So I would generally want to shoot either the 75gr TAP or the BH 77 MK's. While you can generally shoot this ammo out of a 1/9 twist, I would stick with a 1/7.

The best, most reliable barrel I have seen to date is the LMT 10.5 (AKA MK18).


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http://www.gandrtactical.com/images/archive/LMT%20105%20upper.jpg

[bchandler]

what is "fragmentation range?" Does that mean the bullet will break up at 50-70 yards in mid-air?

[c4igrant]

Originally posted by bchandler
what is "fragmentation range?" Does that mean the bullet will break up at 50-70 yards in mid-air?

No. It means that the bullet is going fast enough to fragment upon contact. This is of course a good thing when your trying to kill something.




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[RWBlue]

Originally posted by bchandler
what is "fragmentation range?" Does that mean the bullet will break up at 50-70 yards in mid-air?

frag range is only with mil. spec ammunition

if you are in frag range and someone shoots you, the bullet will tumble and fragment in the target.

[bchandler]

I see. So, that is desirable, right?

If I will be using premium HP ammunition this shouldn't be a concern, right?

Can someone give me advice on 1/9 vs 1/7 for range plinking (accuracy with 55gr) and what defense ammo to use out of that barrel?

[bchandler]

Well, I found the ammo oracle, looks like I have a lot of reading to do... I'm about half way through but already my options are expanding rapidly. Didn't know there was so much to consider when choosing an 11.5" setup.:shocked:

[RWBlue]

yes

yes

if I was getting a 11 inch barrel. I would get a 1/7 ang shoot 62-70gr bullets.

if you want to shoot 55-62gr and use the gun for anything serious, I would suggest getting a 14-16 inch 1/9.

[bchandler]

Well, after a lot of reading, it looks like with an 11.5" barrel, I should probably use a 1/7 twist with heavy bullets for defense, either TAP 75gr or Black Hills 77gr (though at apartment interior ranges anything would probably work). And for range use (still a bit confused on this one), any 55 or 62 should do fine? Which would be more accurate out to 50 yds?

And switching back to my 16" would be the way to go for any serious range shooting or longer range confrontations, with 55gr ammo, moving up to heavier ammo past 200yds or so.

Am I on the ball here?

Also, will the black hills 77gr or TAP 75gr still fragment inside a human target at very close range? Apartment range defense is what I'm interested in.

[GixxerSixxer]

For 11.5" I'd put a +1 on going with 1:7 barrel.

For general range use if you still want to keep the 11.5" Upper then shoot the M855 bullet it's a 62 grain bullet that won't be as "overspun" as a 55 grain. Look for SS109 ammo if you can find it. The 1:7 twist tends to be more of a problem with light weight varmint bullets, so shooting a 55 grain bullet like XM193 at the range won't be considered stupid.

If you want to do range stuff and play around you can also just buy a 16" or 20" Stag Upper and just swap that onto your Lower. With a 1:9 you can easily handle 55-69 grain bullets. Some guys are capable of shooting heavier bullets through their 1:9 barrels. Some guys are not. You don't know if you're lucky until you try out a box of heavy grain ammo.

The TAP ammo will work good for indoors. TAP also has low flash so night vision isn't destroyed or furniture isn't caught on fire. Keep in mind that a 11.5" barrel will put out a lot more flash and noise than longer barrel so a good flash suppressor and maybe electronic hearing protection would be wise for home defense.

[Rogueplayer]

Grant- what flash hider is that??
Thanks




http://www.gandrtactical.com/images/archive/LMT%20105%20upper.jpg

[c4igrant]

Originally posted by Rogueplayer
Grant- what flash hider is that??
Thanks




http://www.gandrtactical.com/images/archive/LMT%20105%20upper.jpg

Vortex.


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