How does the 1/9 compare to the 1/7 twist rate in stabalizing the 75 and 77grn loads?

The 1/9 will not.

The 1/7 will.

1/9 twist will generally stablize loads up to 69gr.
However, some have had luck with 1/9 and heavier loads. Your milage may vary.

In warm (thin) air, with a long enough brl the 1:9 will generally stabilize the 75Gn Hornady OTM.

Havent tried the 77Gn OTM yet.

Tried the 75gr through my Bushy 16" 1/9 HBAR. During the summer, I'll print some nice groups with the odd unexplainable flyer about every five rounds or so.

As the range gets longer or the weather gets colder, the 75s start to open up to 4-5" at 100yds and worse at 200 for me (difficulty keeping them on an IDPA target using a scope).

Velocity seems to be an important key as people who are having good luck with the 75gr in 1/9 seem to usually have longer barrels. The other factor seems to be the barrel. Some people have barrels who like it and some don't. Forest had a good post discussing how he improved results with his barrel by giving it a good scrub with copper solvent.

So, 1/9 maybe, 1/7 definitely.

[url]ammo-oracle.com[/url]

Considering I've reported results in the Ammo Forum using 75gr Hornady, 77gr SMK, and 77gr Nosler using Bushmaster 1:9 twist barrels in lengths of 14.5" , 16" and 20" I can safely say your statement is incorrect.

You will not get the accuracy you would with the 1:7 twist - but its 'good enough for Govt work'.  I'd prefer 1:7 twist - but 1:9 will do.

BTW the 75gr & 77gr Black Hills ammo has stickers on them indicating the ammo is for 1:9 twist or better.

Has anyone tried the 75s and 77s in a 1/8 twist?

I shoot the 77grn. SMKs outta my 24" 1/9 Elite barreled CR6724, exclusively....., (ya need to push 'em fast, tho, in order to get max accuracy, they'll go 1/2 MOA in good air, if I do my part out to 800 yards)

While they (77 SMKs) will shoot outta the 16" 1/9 M4, the accuracy is not that great (good enough for close range work, but not for distance, IMO), they work MUCH better outta the DPMS 1/7 M4 upper CMMG sells.....

They also shot excellent, outta a RRA DCM/CMP Service rifle upper, w/ Wilson barrel and 1/8 twist.

Mike

I thought someone said 77gr is actually shorter than 75gr, and therefore 77gr will stabilize better than 75gr in 1/9.

Is this true?

I have said that before.  It is true.  If nobody believes me, I'll go get my calipers and compare the 75 Hornady to the 77 Nosler and the 77 SMK.

That twist will shoot them, no doubt about it. With the 1 in 9" some will, some won't.

http://www.bushmaster.com/faqnew/content_by_cat.asp?contentid=175&catid=100

heres what bushmaster has to say about it

Works for me [:D]

There are bolt guns that use 9 twist with longer barrels than most AR's, and this may be why B.H. label notes '9 and better'.

Hmmm...Ok. if i replace my 1/9 barreled upper with a 1/7 twist upper. How well well the 1/7 twist handle the M193 load?

I'm in no way disqualifying you, nor I'm in any position to say that. I was simply mentioning from my memory [:D]

It will be good for my 20" 1/9 if 77gr worked!

M193 will work just fine in a 1/7 twist.  I shoot it in mine all the time.  

You MAY get lucky with a 1/9 twist and the heavier loads, but your accuracy will suffer.

The 1/7 twist seems to me to be more of a universal twist.  Some don't agree.  But if a 1/7 will stabilize FOR SURE M193 all the way to the 77 gr, it seems pretty universal to me.  

I personally do not know where to get a 1/8, but 1/7's are "all over".

This might help, as stated above (for the most part, as all barrels and uppers are different) the 1/7 will handle the M193 just fine.

[url]http://www.ar15.com/forums/topic.html?b=3&f=118&t=162330&w=searchPop[/url]

Mike

The 1/8 twist is found on some of the CMP-legal Match AR's...

I wish 1/7 guns were "all over". You're very limited to barrel length and profile when you go with the faster twist. I would LOVE to buy a midlength rifle, but no one will produce a 1/7 chrome lined barrel, so... There goes that idea. Same goes gor 16" lightweight. There are none out there. 14.5" HB? Nope. 20" HB? Negatory. If you want 1/7" you're stuck with the abysmal M4 contoured 14.5" and 16", Gov't profiled 20", and... If you want to pay a premium... Colt 16" 1/7 HB, 20" HB, and 14.5" LW.

If only BushHamster or Armalite would get the picture and produce 1/7 barrels, all would be great.

-Cap'n

It's all about speed.  A given bullet, depending on it length, needs a certain RPM to stabilize properly in air (colder air requires higher RPM's).  If the barrel length and load you are using provide enough velocity for the bullet in question everything it fine.  The fact that "some barrels will, and some barrels won't" is due to the fact that different barrels produce different velocities with the same ammo, depending on the chamber and bore dimensions.  Longer barrels are better since it is easier to get the required velocities.  Instead of talking about required twist rates, we should talk about required RPM's for a given buller.  Then it is easy for anyone to figure what velocity they have to get to, out of their barrel, to stabilize a certain bullet.  If I handload 75 gr. bullets at a mild 2600 fps out of a 9" twist, I may be in trouble.  If a push them to 2800 fps I will probably be fine.  I have personally used the Hornady 75 gr. OTM loads in my 9" twist 20" barrel with very good results.  They chrono at about 2750 fps.  Given the option I would go for a 8" or 7" twist, but I wanted a chrome bore.

Why the obsession with HEAVIER and HEAVIER Bullets for the .223? Every caliber has it's working limits no matter what twist is involved (the .223 should probably stop around 70 grains or so)!

Because the heavier bullets offer better terminal performance.  Why should the .223 stop at 70gr?  Because you said so?  I think you pulled that number out of thin air.

I think you need to check the posts tacked at the top of the ammo forum.  Then try to tell me that the .223 should stop at 70gr.  [rolleyes]