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Discussion Starter #1
First of the year and time to get some of the stuff in my two file cabinets "culled". I came across a test I did several years ago after reading a post from someone who claimed that the Ruger Mark pistols, all of 'em, lose velocity due to the bolt being sent backward during the firing sequence. Seems the author of that felt that a fixed breech type pistol, like the Thompson/Center Contender in .22 Long Rifle caliber didn't shed velocity like the Ruger Mark pistol does because the bolt is open long enough for gasses produced by the cartridge to escape.

I set up my chronograph, along with a pile of three sandbags and then used my Ruger Mark II KMK10 pistol and a bunch of Federal .22 rimfire ammunition. I fired 5, 10 round vollies to get the averages involved with the printouts below.
First, 5, 10 round magazines full were fired with the bolt being allowed to blow back and then return, unimpeded. Then, another 5, vollies of 10 rounds each were fired with my thumb holding the bolt forward, arresting any rearward movement.
Here are the printout results:



So, what little velocity may be lost with a "free moving bolt", it doesn't seem to involve any great loss. And besides, when viewing slow-motion camera footage, long after this test was done, the video clearly shows that the bolt doesn't even start to move backward until the bullet has long left the muzzle.
 

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Well, I call 50 rounds per test a statistically significant number of data points. Good study.
 

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Discussion Starter #3 (Edited)
Well, I call 50 rounds per test a statistically significant number of data points. Good study.
Thanks. Yah, I suppose 100 rounds for each method would be more "statistically correct", but I wasn't planning on plotting a chart anyway.
 
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