Here are a few tips for getting the most, the easiest, from high-velocity semi-auto .224s. READ IT ALL
Here’s the conclusion of my “trilogy” on the movement of .224-caliber rounds into the left lane of rifle cartridge choices. The focus last time was on the 22 Nosler and .224 Valkyrie, and here are some ideas on making the most from either, or another similar.
First: Getting high (higher) velocity is really not rocket surgery: make the bullet smaller and the case bigger. Rounds like .243 Win. showed that clearly. However!
Speed, greed, need, (and heed)
Higher and higher velocities bring about a “debate.”
After messing with all this for decades, there are two things I know for sure about bullet velocity: more velocity shoots better; more velocity shoots worse. But! It’s not velocity itself. It’s a common belief, and totally plain wrong (and wrong-headed), that lower-velocity shoots better groups. It’s also wrong that higher velocity shoots better groups. Working with one cartridge and one bullet, for example, I’ve had plenty of times when the faster the bullet went the better it shot, and the slower the bullet went the better it shot. That’s all to do with the “combination” of the propellant and bullet and barrel and son on and on and on. Point is: it’s way on better to find a combination that shoots better and better the faster the bullet goes. That didn’t have a lot to do with the point of this, but it is important to keep in mind — velocity is not evil.
I know I don’t have to go into benefits of higher velocity. Hard to argue with those. What I do want to go into is a look at how much more and at what cost. Virtually every downrange improvement has some sort of cost. The cost of higher velocity is barrel life, mostly.
As said, higher velocity comes from more propellant. More propellant produces more flame and more gas. There’s a term, “overbore,” that gets around in discussions of, usually, large cartridges, like magnums. It actually is a mathematical device that compares the barrel bore area to the cartridge case volume. It is “V” (case volume) over (divided by) “A” (barrel bore area) and the answer, “O,” is therefore a ratio. The bigger O gets the more overbore the combination is. Applying that, something like .243 Win. is overbore. That’s also why a barrel chambered in that round lasts no more than 1200 rounds at true peak accuracy. That round is not considered overly powerful by anyone I know, yet, has the same sort of (bad) effect on barrels as does something like a .300 Win. Mag.
As said last article: clearly, barrel life in Nos. or Valkyrie is going to substantially shorter compared to .223 Rem.
Higher and higher velocities also come from varying propellant choice. Specifically, slower-burning propellants literally fit better into higher-capacity cases. Recollecting back on something I’ve mentioned umpteen times in these pages: propellant burning rate has a whopping lot to do with semi-auto manners. Slower-burning propellants elevate gas port pressure, which brings on the “over-function” symptoms, none of which are good. There’s a comparison of 22 Nosler with .22-250. They’re similar in structure. General consensus is that a favored propellant in the .22-250 is H-380 (if you don’t like that one, and I don’t, it’s going to be another in that burning-rate range). So. Point: 22 Nos. and Valkyrie do not get the most they can get from a “safe” .223 Rem. propellant (I break that off at nothing slower than H-4895). For good instance, I run Varget in my Nos. and that’s the same propellant I run in my PPC. It’s a little too slow, my opinion, for a stock gas system in an AR15.
Most running a 22 Nosler or .224 Valkyrie are looking to exploit speed, so will, therefore, be shopping or specifying 24-inch barrels (that’s a “standard” available length). That, combined with a standard 12-inch “rifle” gas port location, will, not can, escalate pressure within the gas system. That combination also puts a .223 Rem. over-pressure. (Reason is that the post-port length add increases “dwell-time,” which is the duration that the gas system is containing maximum pressure.) The best solution to excessive port pressure is to move the gas port! “We” (competitive High Power Rifle shooters) have been doing that for better than 20 years.
Yardstick: Plus-1-inch for .223 Rem. and plus-2-inches for Nos or Valkyrie. That makes a huge difference! Of course, this mod is only possible if you’re going with a custom barreling op done by a competent and savvy builder.
Without that, there are two options that, I say, should be used in tandem: a valved gas block and increase buffer/spring mass and resistance. The adjustable block reduces the amount gas that gets into and is contained within the system and the other offsets the effects of the harder hit the bolt carrier group will be subject to.
I am a bigger fan of the “architectural” solution rather than the adjustable gas block. They won’t last forever…
Another important spec I want to hit on: barrel twist rate. As said last time, the .224 Valkyrie was, so they say, designed to handle the biggest of the high-bc .224 bullets and, specifically, the Sierra 90 MatchKing (and similar). That’s why, as also said last time, commonly offered twist rate with that chambering is 1-7. Folks, 1-7 isn’t enough, in my experience, for 90+ .224 bullets. I (“we”) use 1-6.5 twist for 90s and the others in 20-inch barreled Service Rifles (.223 Rem.). That’s quick. Those shoot 77gr “magazine” bullets really well also. With Sierra now offering a 95gr .224, go with a 6.5. The extra velocity from Valkyrie and 22 Nos does indeed boost rotation, but I strongly suggest not relying on that promise for stability. It’s edgy.
1-6, by the way, tends to blow up bullets.