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Posted: 3/2/2008 5:31:16 PM EDT
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I’m fixing up a couple of “space guns” for competition, mostly 200 yard offhand matches. I don’t want to chew up my brass, and the rifles will be kept clean & will be firing light loads. I figure there is no point in going with a really strong extractor spring, but it’s not like they come with clearly marked strengths. I ordered some springs to add to the several flavors I had on hand, and did some testing. Other than taking note of several physical characteristics, I also set up a deflection test to measure how much the springs compressed under 8 ounces of pressure. Here is a photo of my set up.  The spring is located under the hinge half way between the pivot & the tip. This gives a factor of 2 leverage, so I only used a 4 ounce weight. Test results: Colt (from Brownells, Colt #SP64026): Copper plated, ground ends, ~2.1 turns, 25.5 mil wire. Black buffer (for carbine, not rifle?) Deflection: 3.5 mils & 4 mils Colt (From Specialized Armaments, Colt #SP62770) Blue buffer, ~ 2 ¼ turns of 26 mil wire. Copper plated, ground ends Deflection: 7, 6.25, 7.2 and 3.5 mils. Not sure about the really stiff one, double checked results & got same answer. Maybe carbine spring by mistake? When installed, slightly softer than Bushmaster (but so close it’s hard to tell). Rock River: Black buffer, ground ends. ~ 3 turns of 26.5 mil wire. Deflection: 3, 3.5, 3.25 and 3 mils Bushmaster: Blue buffer, ground ends, 3 turns of 23 mil wire Deflection: 4 mils (Strong, but smooth, when installed) Bravo Company Extra Strength: Black buffer, 4 turns of 25 mil wire, not ground Deflection: 6.25, 9 and 10.5 mils (very stiff when installed, suspect wires were hitting) Wolff Extra Strength: No buffer, 4 turns of 24.5 mil wire, not ground Deflection: 5, 6.5, and 6.75 mils (not installed) 2nd Hand Colt Bolt (spring presumably Colt): 2.5 turns of 21.5 mil wire, blue buffer & ground ends. Deflection: 11 mils (softest when installed, but still plenty of snap) DPMS: Black buffer, ~ 3 1/4 turns of 26.5 mil wire, ground ends Deflection: 3, 3.7, 3.7 and 2.8 mils (not installed) (nearly identical to Rock River springs) There was quite a bit of variation, but in general thicker wire & more turns will tend to be stiffer. The deflection test isn’t very definitive. The Bushmaster springs measured quite stiff, but were not significantly stiffer when installed than the Colt rifle springs, which had almost twice the deflection. There isn’t a lot of room for the spring when it is compressed. I suspect the reason they are slightly tapered is to give the wire room to compress without just stacking up into a rigid mess. Because the ends aren’t ground and they have four turns of wire, I would think the Wolff & Bravo company springs would run the risk of jamming up if the wires run into each other. The two Bravo Company bolts I have were VERY stiff. I could barely get a cartridge to snap into the bolt head by hand. They presumably work OK, but personally, I wouldn't put them in a SHTF rifle. Most of the other springs would work fine. I’d really like to know where the thin Colt spring came from. It was in a Colt bolt I bought off the equipment exchange, and is of unknown vintage. It is noticeably easy to snap a cartridge into the bolt, but it seems to hang on just fine. The new Colt rifle springs (blue buffer) I bought are considerably stiffer. |
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