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Is this too much for a 1 in 9 twist? I have a box given to me and would like to try them but if it won't work there is no point of trying and wasting components and barrel life. The Berger number is 22421. 77 grain is supposedly too much but a number of people have used the Sierra 77 grain with a 1 in 9 twist.
I'd try them, but, you can check length to see if they are longer than the SMK's. Not the whole story but it might get you in the ballpark.
I find that there is a difference between the stated twist from the factory for a caliber and the actual twist that was reamed into the barrel on any particular day.
It can vary by maybe a 0.5 quicker than spec which is enough to allow a 77-grain high BC bullet to stabilize.
I have two .223s that shoot 77 SMKs and TMKs great; one shoots them better than any other caliber.
You really have to test performance in your particular barrel.
I have long since stopped assuming that each barrel will perform like someone else's.
Experience can be misleading, too.
The same rifle that shoots 77 better than any other caliber doesn't shoot some 75 gr bullets very well.
I think it may depend on the bullet shape as well as the bullet weight when you are near the limit of the twist.
That is good advice from both of you. I will load up maybe a half dozen and try them. I guess the money spent if it is wasted won't break me and the 223 barrels last quite a while too. If they do work, I think they are a premium dollar bullet and it would be a shame to waste them if they will work.
I think they will work. I just shot a group and it was 9/16". I have done better with other bullets but I have also done worse. A little wind too so that could have had an effect. I did use the maximum listed powder charge, heard speed helps stabilization some.
Actual stability can be affected by how the bullet is made, eg, how far forward or back the CG is located, length of ogive vs drive band, length and angle of boat tail, etc. When you get to marginal cases it all matters.
The two Berger bullets I have used both like being seated into the lands. A jump of even .005 would open the groups a bit.
Go to the Berger website and check the twist rate calculator.
IMO, all of the twist rate calculators I've tried are very conservative and they are based upon equations used at the turn of the 20th century for artillery calculations when the shells looked like a loaf of bread instead of the match bullets that we now shoot that look like needles by comparison.
The key to a particular barrel's stability is really determined by how close to spec the rifling was reamed.
I have had the good fortune to have two .223 barrels rifled when the lathe used to ream those barrels were set a bit faster than spec.
When I use the spec'd twist rate in the calculators, they always report that the bullets that shoot great in both of my .223s won't stabilize.
I agree with CFJ. The stability equations are an estimate and nothing more. There are several key assumptions used in those that make the results a guide rather than hard and fast data point. Bullet shape, CG location, CP location (aerodynamic center of pressure, key to stability) are all assumed to be symmetric. Not germain here but they are also designed for projectile velocities in the Mach 2.5 range (2800fps?).
Mfg have to assume a muzzle velocity when labeling their stability criteria. For the .223 Sierra probably uses the common AR barrel length to set their twist requirement. Adding 6 or more inches of barrel makes a big difference. They also have to assume worst case atmospheric data, such as down to 0deg F.
I have only really 'tested' marginally stable bullets with two rifles, my .50 muzzle loader and the Axis .223. The .223 did well with slightly heavier bullets than normally suggested by the mfg or by the stability equations. The muzzle loader followed the equations almost to the point, despite being way off from the normal velocity regime used for developing those equations (flat base, round nose bullet).
If not they would make great sub sonic plinking AR loads
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