Rocky (and others), after receiving the the first two responses I cut and posted them in a note and added comments that turned out to be nearly identical to yours. Being unfamiliar with firearms workings I think his mental assumption about recoil (identified by my last comments to him)is likened to a recoil operated rather than gas cycling action. My take is that if talking about a recoil operated action then the best answer might be that it takes very little energy for the bullet to break the bond of a crimped case that holds it - though I might never believed that after hammering away on one of those blasted enertia bullet pullers. Here are my responses if interested. Let me know how to improve on them - or if I am in error. Thanks folks.
Pete,
thought I would ask your question about speed loss due to cycling a semi automatic action to see if anyone came up with something different. Here are the first two responses:
IMHO the gas used to cycle the action will decrease the speed as compared to a bolt gun. I may be wrong, but I have never chrono'ed a semo auto that was as fast as the same ammo was in a bolt gun with the same barrel lenght..The difference IME was between 100 and 200 fps difference..
I call this a "possible indication" more than scientifically measured. The reason might be that this particular barrel is slower than others. Two identical loads fired from two different barrels, even if the barrels are on identical rifle models, will yield at least slightly different speeds. Other factors in barrel speed include manufacturing techniques- ie button rifled or hammer forged as well as how fresh the cutting tools were when they made a particular barrel. If I bought a box of 270 ammo and put one round in my CZ and one in a Savage there would be a difference in speed. Just the nature of absolutes. Certain makes do 'tend' to be faster than others and twist rate of the rifling is assumed to be the same here- BUT in certain calibers you can find different twist rates because some are geared towards shooting lighter or heavier bullets in that caliber. 223 is a good example of this. So, overall is there a difference? A small one possibly is the answer- just as suspected.
Here is the second response:
In theory, yes. In practice, no.
First the gas "lost" isn't really lost completely. So even though there's a small pressure drop, it is very VERY small, percentage-wise.
Second, most gas actions tap the gas fairly near the muzzle, so there's little time left before the bullet clears the muzzle - and nearly all the bullet speed already attained.
Third, you'd have a hard time deciding, because the individual variation from shot to shot is almost always larger than the loss of speed due to gas bleedoff.
All these can be clearly demonstrated by simply blocking or turning off the gas system (in guns like the Garand where you can do so.) Measure bullet speed with the gas system on and off and compare
Note here Pete is that I believe you were looking at recoil in the way it is used in an inertia system firearm. Like a Benelli rifle or shotgun or a lot of semi pistols. The recoil on these are noticeably sharper in my experience- but the cycle times are faster. You can shoot a Benelli recoil\enertia operated semiauto shotgun - maybe some Beretta's too - Martin's new one might be recoil operated, -anyway you can pop three rounds off with amazing speed. Very fun but you don't want to keep doing it. For a practical application of your question as it pertains to rifles we should consider it as it pertains to gas operated devices and that is what the post above is speaking to.
