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Old August 12, 2012, 12:06 AM   #1
bamaranger
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.22 stock/action bolt torque settings?

I took the Savage MkII TR action out of its stock the other day to add an accessory. Darn thing was shooting fine! When I reassembled, I found I had not written down my stock bolt torque settings and had to make a guess, and put 25"/lbs on it.

REassembled, the rifle is not shooting as well as before. Could be bad ammo, could be alot of things, but......what torque setting would y'all recommend for a wood stocked, heavy barrel .22?
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Old August 12, 2012, 09:32 AM   #2
Kitts
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Sometimes there is a little play in the fit between the action and stock and you want it to relocate in exactly the same place every time. On an unbedded rifle, I prefer to assemble with the barrel pointing up. This forces the rear tang of the action against the stock the same way every time. Double check that the bolt does not rest against the stock (in its recess) when closed...it should be resting closed on a metal to metal contact not metal to wood.

You can also mark the action screw as to its position in relation to the trigger guard/stock once you (re)find the proper torque. Use a tiny dot of white out to index the screw head or a tiny scratch to do this. This is more accurate and repeatable than a torque setting for clamp load. torque setting alone is only accurate to within 25% of actual clamp load because much of it is due to friction on the screws. I use a torque screwdriver to get my initial settings and once found, I put an index mark on the screw head so I can repeat the clamp load better on assembly.

Most of my CZ's use a torque between 18-24 in/lbs on the screws. Anything over 35 in/lbs is likely to compress wood in the stock and permanantly deform it from my experience. Quite often the right amount of clamp load can be ammo dependant also...find the right setting using the same ammo you intend to normally use.
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Old August 13, 2012, 05:56 PM   #3
bamaranger
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load

Clamp load.

Kitt, that is a term I have never heard. I am betting that you are a bonafide engineer type of some kind. And I had never heard that torque settings could err as much a s25%.

But, it all makes sense. And marking the bolt seats makes sense too.

Normally I am very good about recording such things, but not this time. I will continue to shoot the Savage w/ assorted torque settings, 'till it straightens up. To best of my knowledge and belief, the scope and ammo are good .
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Old August 15, 2012, 12:14 AM   #4
Kitts
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"Clamp force" is quite appropriate for these applications since critical torque applications usually rely on "bolt stretch" to achieve a certain percentage of a a fasteners proof or yeild strength.

According to the Machinery's handbook, a tradesman tightening by feel is only +/-35% accurate, and using a torque wrench only improves the accuracy to about +/-25%. A method called "turn-of-nut" can get within +/-10%, but this relies heavily on a reliable starting point from which to start counting turns.

If you have good bedding/pillars then marking off the screw with an index mark basically follows the "turn of nut" procedure fairly close...thats why I like it.
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Old August 15, 2012, 07:48 PM   #5
Bart B.
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A repeatable clamping force between stock and receiver's dependent on the turning friction of the screw against the receiver and whatever the screw head's held in. So, these have to be kept clean and uniformly lubricated.

The torque tool's design helps, too. 'Twas mentioned that different types of tools get different tolerances in clamping force. The best torque wrenches ratchet or click free after the set torque value's reached; these typically produce the most repeatable clamping force.

I've made 60-inch pound "No Hub" soil pipe torque wrenches for Win. Model 70's set to 60 inch-pounds and tested them with torque gages; they've been acurate to less than 3 inch-pounds; 5%. And using them on 1/4x32 stock screws has produced clamping force spreads of 5%.

I think marked points on screws against a fixed reference for clamping values are worthless when the stock material around the screws changes dimensions from temperature and/or humidity. Mechanical engineers I've asked about this agree.
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Old August 16, 2012, 07:25 AM   #6
madcratebuilder
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Quote:
I think marked points on screws against a fixed reference for clamping values are worthless when the stock material around the screws changes dimensions from temperature and/or humidity. Mechanical engineers I've asked about this agree
Yes it is, but the poster noted that it was used with a pillar bedded rifle. With a pillar it works well. The clamping force is applied to the metal pillar, not the wood.

It's nice to see someone else that has a "Machinery's handbook".
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Old August 16, 2012, 09:29 AM   #7
Bart B.
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madcratebuilder, I agree. Wood stocks, even those with a bit of expoxy around stock screws as "synthetic" pillars, compress more that steel or aluminum pillars. I've known a few top competitors with aluminum pillar bedded receivers just tighten stock screws until they "feel snug" and win matches so set up.

But I've never used pillars; don't believe in nor have needed them for best accuracy. The most accurate centerfire rifles I know of with wood or synthetic stocks on conventional receivers are conventionally epoxy bedded.
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