Thanks, guys - I appreciate your on-point comments and suggestions. Having spent most of my rifle days with bolt action guns, I had no idea that some of these companies made semi-autos.
One thing that struck me - it looks like all the rifles mentioned are DI rather than gas piston which I thought had pretty much become the norm in AR type rifles. What's the reason the PR semi-autos use the older DI system?
Also, I'm familiar with a number of smiths who are known to produce superb bolt-action guns. I assume there are similar names in the semi- auto world. Who would they be?
Rudy - thanks for comments on technique. I was curious about one thing - is the reciprocating mass the factor that makes semi-autos more difficult to shoot accurately?
I think that larger amounts of reciprocating mass makes them tricker than the small frame systems. Basicly all gas guns but even more so with the large frame, you have a recoil impulse broken into 3 components. The first, just like the bolt gun, appears when the cartridge is fired. The second component appears as the bolt of a gas gun is unlocked and slams to the rear extracting and ejecting the spent case. The final phase is the impulse of the bolt returning forward feeding, chambering and locking.
Now a lot of things can happen in that cycle of operations and the whole key to successes is to do all of that constantly. Any change the forces at play, whether shooter induced like poor body position or improper follow thought at one of those points can have significant impact on the constancy of which the next round is chambered. Looking at the mechanical side of things, even difference in spring tension of a loaded magazine vs. empty magazine against the bottom of the bolt carrier can cause accuracy issues.
Again, your adding more mass and more energy with the large frame system, getting it to work right to produce accuracy and reliability in an individual rifle can be time consuming (or sometimes you luck out) but the real challenge for an manufacturer is coming up with a recipe that can produce the same results across the board. Thats where companies like JP, Knights and LaRue standout, they each have their recipes for what works. Knights tend to sacrifice a bit of that top end accuracy for reliability in extreme environments. JP is hands down the most consitanly accurate gas gun but run it hard in the dirt and grim and you might choke it. And LaRue seem to run some where in between the two.
Back to gas gun mechanics though beyond reciprocating mass there are some key design differences between bolts and gas guns. Specifically, we are looking at lock time, the time between the break of the trigger and cartridge ignition. With bolt guns once cocked and locked, things get pretty simple. The typical trigger groups consist of the trigger (the part your pressing strait and to the rear), this moves an actuator lever, and in which turn engages the sear, which releases the firing pin in order to strike the cartridge primer. Not counting the springs and pins holding everything in place that’s less than a handful of moving parts to make things go bang.
Fewer parts and less movement means a quick lock time. Most bolt actions are clocking in right around 2-4 milliseconds. I know this doesn’t sound like much but given the whole trick to good shooting is to pull the trigger without disturbing the sights, this is critical. Hence, why trigger control is a fundamental of marksmanship, the reality is even a small, nearly unperceivable deviation of the sights during these few milliseconds will cause grouping errors at distance.
Conversely a typical trigger group of a gas gun consist of: the trigger, when pressed this releases the hammer, and in turn, the hammer flies free in long (comparatively speaking) swinging arch and slams the firing pin forward order to strike the cartridge primer. Sounds simple enough right? However, the big catch here is that lock time, because that hammer has to swing all the way around. Naturally covering that extra distance not found in bolt guns eats up a bit more time. In fact, good luck even finding a manufacture who will bother posting their triggers lock time, but on average a good gas gun trigger is going to be double the lock time of a bolt gun.
In a nut shell you can start to see that gas guns deal with the unfortunate reality of physics. For every action you’ll have an equal and oppose it reaction, this simply means gas guns harder to shoot then bolts when precision and accuracy are your goals.
