Is it unusual for a 223 with a 1-9 twist barrel to NOT stabilize Federal GMM 69gr BTHP?

I do not have pictures because the range would not let me remove targets and I left phone at home. I was hoping to shoot the 69gr Federal GMM or maybe the 60gr Nosler partition in my CZ Royal. The first shot looked HUGE, but I decided to shoot a few more and see what would happen. Sure enough when I went down range they were tumbling before hitting the paper. I'll try some lighter bullets next.

I thought the longer bullets like 69gr would stabilize in a 1-9. I will continue my search for the perfect load. Maybe 62gr or 60gr will work?

We just discussed this in another thread:

The M16-A1 had a 1:12" twist and was designed to shoot 55gr military ammunition. The M16-A2 came out with a 1:7" twist and was designed to shoot 62gr military ammunition. The 62gr (M855) military ammunition is long for its weight because it contains a steel core and less lead. It is about as long as a 69gr match bullet. The 1:7" twist is marginally okay with the 55gr military bullets but the 1:12" twist does poorly with 62gr military bullets. Again, this was based around military ammunition.

Civilian rifles started being offered in 1:9" twist so they could do a decent job with both 55gr and 62gr ammunition. Today, most match shooters are using heavier civilian ammunition with 69gr-77gr bullets that require a 1:7" twist. But match ammunition can be found in other weights, including some with 52gr bullets.

So, in general:
1:12" twist best for light bullets of 50gr to 55gr
1:9" twist best for bullets of 55gr to 62gr
1:8" twist best for bullets of 62gr to 69gr
1:7" twist best for bullets of 69gr to 77gr

Individual bullets and rifles vary. The HPBT bullets from Hornady in 68gr and Sierra in 69gr (in your Federal ammo) are long bullets for the weight. People have varying success with those in a 1:9" barrel, again depending on the individual rifle. Since your rifle doesn't appear to "like" the 69gr ammo, I suggest you try the lighter bullets you mentioned.

69gn bullets are the upper limit for a 1 in 9" barrel but they should stabilize. They may need a little more powder than Federal is offering in that load.

Like Grenadier said, it maybe that particular bullet.

Sounds like you are looking for a hunting load for your .223. The Nosler 60 grain Partition will work fine, but Nosler has recently introduced a 64 grain bonded bullet (it doesn't have the polymer tip so it is not labelled "Accubond"). I picked up some recently off of their website as "overruns" and they shot excellent groups in a 1-14" .22-250. They have a slightly blunted nose, so they are pretty short for a 64 grain .224" bullet and should stabilize in just about any barrel. I haven't seen any terminal results from them, but would assume that they act much like an Accubond at impact.

Thank you. Very informative. I deal mostly with much bigger calibers.

Yes, I am looking for a hunting load. That said I am a brain-pan shooter. I won't attempt heart/lung shots with this caliber unless its a pig or varmint.

Yep 69grain "should" stabilize in a 1-9 twist. I shoot a bunch of 69G SMKs in my rifles and they do well.....


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drew

I had great load in my Kevlar CZ 223 with 60gr Vmax and 23 gr of Benchmark. FS

drewhenrytnt--Certainly not trying to change your opinion. Many years ago, I would have thought the same. Heavy bullets, premium bullets and only a head shot and still a big maybe using a .224. Those were my thoughts before I saw it done, many times. I can assure you that a .223 with plain old cup and core 55 grainer through the boiler room is a bang flop deal.

In my experience yes it is unusual... My 1 in 9 Colt AR's have had no trouble with 77 grain Sierra's.

A 1-9 .223 should stabilize a 69 gr. bullet. If it is the Sierra 69 gr. bullet it only measures 0.900" long. My Ruger 77 Hawkeye with 1-9 twist stabilizes the Hornady 75 A-Max which is 1.105" long (though this includes the plastic tip).

I hope you won't be offended if I ask, are you sure your rifle has a 1-9 twist?

Positive it is 1-9.

I don't believe a 1:9 twist would have a problem stabilizing 69 grain bullets.

"Positive it is 1-9."

Well, then we have to look elsewhere. The best predictor of stability I've found is from JBM ballistics. Here's the link:

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Twist and bullet length are two of the factors, others in the formula are bullet weight, muzzle velocity, ambient temperature and air pressure. Recently they added length of plastic bullet tip (if present) to the formula.

Try plugging your numbers into the formula and see what it predicts. If you don't know your bullet length JBM also has a web page listing length of hundreds of bullets, or you could just measure a bullet if you have a caliper.

The resulting number from the formula displays in red (not stable), green (stable) or yellow ("on the bubble"). My 75 A-Max/1-9 twist is in the bubble zone but in my rifles it works, at least at an elevation of 1,700 ft. and temperatures of 55 - 60F. I suspect on a subzero day the bullets would not stabilize but haven't tried it yet.

I've found this formula to agree with my actual shooting results - but as your experience shows, bullet holes in paper are what matter.

If you say the bullets are tumbling before they reach the paper. I assume this is @ 100yds. I'd slug the bore. Tumbling usually point to another problem besides twist. Could it be an oversize bore, or undersize bullets? I'd look there, and then try some other brand of 69 grain bullets as a test. JMO

Jerry

My Savage is 1 in 9 twist and it will stabilize everything up to and including 75 grain Hornady HPs.

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Did you measure the twist or does the box say 1-9?

I ask because it has been known to happen that the twist is published one way, actually is different.

I shoot 75 hornady BTHPs from several 9 in AR s, some with 16 inch others with 20 inch bbls all with aplomb.

Measure it to be sure, sounds like it may be a 1-12or less if 69s are not stabilized, I assume it has at normal bbl length.

I measured it using the tight patch on a jag and three dot method on the cleaning rod.

Still waiting on a reply from CZ.

it's not the weight of the bullet, it's the length of the bullet. A lead filled 69 grain bullet is much shorter than a solid 69 grainer meaning the solid would require more twist to assist in stabilizing it.

There are many other factors involved such as powder, primer, seating depth, barrel, etc... but the point is the same.

I am late coming to the party but the table and other stuff in Grenadier's post is made up fantasy, not based whatsover on facts.

Many 1:12 will stabilize 69 gn Sierra Matchkings just fine. They will stabilize most if not all hunting bullets up to 65 gns. I have used them in Matches, shared my results with Sierra techs; they weren't surprized at all that a 1:12 would stabilize the 69gn SMK.

The military used 1:7 because the tracer version (M856??) would not stabilize well in all environments. They were going to go with 1:9 for the M885.

Over-stabilization is only measureable in thousandths of inches in highly accurate benchrest guns with a bullet with a normal thickness jacket, or with very lightly constructed lightweight for caliber bullets. For example, shooting a 40 grain Blitz in a 1:7 at high velocity will disentegrate enroute to the target. Shooting a 52gn Sierra Matchking with the 1:7 twist and high velocity may open the group a few thousandths of an inch over a 1:10 or 1:12 twist gun, and just as likely not.

Bullet length, weight, and construction determine twist rates. The old Greenhill formula is valid in only one type of bullet that they used for the test.

No reason that your rifle is key holing the bullets due to a verified 1:9 twist.

Check the crown for damage or if it's not concentric. The second thing I would look at is the condition of the rifling in the bore, especially in the last four inches toward the muzzle.

You have not mentioned if you have any type of muzzle devise or not. If you do, it may not be installed concentrically to the bore, causing this problem.

Last bug not least, you may just have a bad barrel that needs an inch or two cut off and it recrowned to fix a harmonics problem.