$20 each is not that bad of a price for immediate delivery of a small qty of a 5/16-18 unc x 2.0 inch grip MS tension bolt.  You're darn lucky you even found some in stock somewhere.  

The MS20074 is a 125ksi cad plated, alloy steel, drilled head, hex bolt.  Due to environmental issues, nobody really does cad plating any more.  You can check the MS spec here:

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=39785

If it's allowed, you may consider using a more readily available equivalent.

tbuelna:  Thanks for the response and the link.  A quick look at AN 5-24 bolts shows single item prices at about $0.84.  O.K. multipy it by 10 or even 20 and you are still less than the $20. price I got.  I don't see the reason for the high prices.  I have bought some 3/8 "Supertanium" bolts of even higer than 125ksi for less than $20 each.
In the meantime I have drilled the heads of some grade 8 bolts and have done the first flight test.  Since there are 4 bolts holding the rotor head on primarily in tension and the ship at full gross weighs 1500# even with a safety factor of 4, I have reserve strength.
BTW I recently purchased special 3/8-24 Lh and Rh studs with certs to grade 5 with rolled threads and paid much less than $20 each.  These were special order also.  With this kind of history, I was shocked to get a $20 ea. price.

We may be seeing you soon, on the TV news.

I'm ever hopeful that you were being hypothetical in your post??

I take it that your alternative bolt is an approved alternative and is also approved for use with the original nut. Also that the drilling of the head was in accordance with an approved spec.
And also that your modification/concession has sufficient justification, and is signed off.

Just replacing a bolt for a (maybe superior?) bolt does not automatically ensure you wont have a problem. You have just increased the joint stiffness, and as such it is possible that your fundamental frequencies have shifted, your load transfer dispersal may have altered, and many other reasons.
Things are normally as they are in the aero world for a reason.

40818:  Thanks for the meaningful response.  I did examine the bolted joint with your comments in mind.  As it turns out the stiffness of this joint is already determined by a keying action between two of the pieces joined by the bolts.  The bolts are primarily in tension only with little chance to encounter shear loads that are already dealt with thru the heavy key-like construction of the two pieces.  What you have said about varying fundamental frequencies has been observed by a slight change in a bolted joint design on the resonance of the helicopter tail boom.  
thanks

ZI did not mean to sound flippant, but have you examined the juncture of the head & shank of your "replacement" bolts? The MS20074 tension bolt has a very important radius designed into this juncture. There is a special chamfered washer, that in tension applications must be used with this bolt. I have seen many bolts in the field ( same spec, different d. ) with the heads popped off, due to someone installing the washer 180 out, & torquing to spec. Call any wheel shop, I bet their NDT guys can enlighten you.A hardware store bolt grade "whatever" has no inspection system in place, is not approved for aircraft use, even in the experimental catagory. Ask your DAR inspector about it. As for "supertanium", can you define what standards "supertanium" is inspected to?

You've lowered the fatigue strength. The MS bolt uses a J threadform and is class 3 whereas I believe your commercial bolt is not a J thread and is class 2.

JohnSchwaner:  Thank you very much for your informative post.  I will certainly look into this and will probably bite the bullet and get the MS bolts just to avoid the nagging feeling in the back of my head when I'm flying over nasty places and the "new vibrations and noises" start.