Why the concave milling under the rear of the bolt?

[OD#3]

Ever wonder why the '92 has a concave depression under the bolt near the rear?  I have.  This depression makes the action "hitchy", as the bolt moves forward during closing.  I don't know what purpose it serves.

Also, other than making the levering smoother and lighter, does the spring lightening involved in an action job on a '92 just make it smoother?  Or does it reduce wear on the moving parts significantly like spring lightening does for the toggle links?

[Coffinmaker]

YES!!

I was real tempted to just leave it at "yes" (as it applied to all) but then re-thought my evil, nasty, crusty exterior and .........

The concave area on the bottom of the bolt is to smooth the Bolt's movement over a fully cocked hammer.  The bottom of the Bolt and the contact area of the hammer need polished.  The hitchieness of which you speak is caused by a number of things, not just that concave area.

Reducing the springs in a '92 accomplishes "all of the above."  The lever latch spring is about 20 times as stiff as it needs to be.  Reduce the spring and polish the latch pin and you'll be amazed at the improvement.  Reduce the Ejector spring.  Way too heavy.  Depending on Mfgr, CAREFULLY reduce the Extractor.  Way too heavy.  Reduce the Main Spring.  Way Way to heavy.  Rub-N-Buff the areas that show contact wear.  Don't remove metal, just polish.

The simple way to do all the above is simply to purchase a Reduced Spring KIT.  That way, the only thing you'll need to grind on will be the extractor.  Exercise EXTREMA care with the extractor.  By reducing the above mentioned springs, you will have reduced undue wear to the moving parts of the rifle and ........ it will suddenly run extremely fast with just ONE finger.  The last item up for bids is to carefully shim the right side cartridge guide until it just "kisses" the rising cartridge.  This will eliminate popping out live cartridges (when you go fast) and prevent stove pipes.

Coffinmaker

PS:  Or as I was want to say originally >>>>>>   YES!! 

[greyhawk]

YES!!

I was real tempted to just leave it at "yes" (as it applied to all) but then re-thought my evil, nasty, crusty exterior and .........

The concave area on the bottom of the bolt is to smooth the Bolt's movement over a fully cocked hammer.  The bottom of the Bolt and the contact area of the hammer need polished.  The hitchieness of which you speak is caused by a number of things, not just that concave area.

Reducing the springs in a '92 accomplishes "all of the above."  The lever latch spring is about 20 times as stiff as it needs to be.  Reduce the spring and polish the latch pin and you'll be amazed at the improvement.  Reduce the Ejector spring.  Way too heavy.  Depending on Mfgr, CAREFULLY reduce the Extractor.  Way too heavy.  Reduce the Main Spring.  Way Way to heavy.  Rub-N-Buff the areas that show contact wear.  Don't remove metal, just polish.

The simple way to do all the above is simply to purchase a Reduced Spring KIT.  That way, the only thing you'll need to grind on will be the extractor.  Exercise EXTREMA care with the extractor.  By reducing the above mentioned springs, you will have reduced undue wear to the moving parts of the rifle and ........ it will suddenly run extremely fast with just ONE finger.  The last item up for bids is to carefully shim the right side cartridge guide until it just "kisses" the rising cartridge.  This will eliminate popping out live cartridges (when you go fast) and prevent stove pipes.

Coffinmaker

PS:  Or as I was want to say originally >>>>>>   YES!! 

Coffinmaker - yes!!
Late to the party here but .....had a 71 browning where they forgot to mill that concave into the bottom of the bolt - damn that action was stiff !! causes the mainspring to push the hammer nose up under the bolt for the whole length of the lever stroke - binds the bolt rails in the action groove where they run - the lack of that concave relief just screws everything up - I ran 500 rounds through that 348 thinking "ahh it will loosen up soon" - only figured it out one day I had my 71 and a 92 on the bench at the same time and noticed the difference in the underside of the bolts - then started playin - then went on internet and got pics of a 1886 bolt -- ahhh ! that explains that! ---- sooo - I call the US lookin for a spare bolt body  (in case my cold chisel /hammer /oxytorch approach goes kaput) - yeah we got it - 160 bucks - but no sale to Aussie land - sorry ----- will ya sell to me mate in Nebrasky if I pay - yep - he will send it on - dont wanna know he says - but we can do that. So lets fix this - for a commercial shop with the right tool this is a cinch - me without the right tools - some with the mill - lotsa dremel tool with grinding discs - took a couple hours - but really - took aboot as long to dismantle and re assemble the gun first time n all - (thought it was like a 92 ddint ya! - ha! ha!)

ps ---92 cartridge guides - if they went together right in the first place it is impossible for a round to poke its nose out the top of the action (that what ya call stovepipe?) - I got three in the rack right now - complete originals - one very early number 44/40, a 32/20, a 25/20 - tried this the other day to settle an argument with a friend that works on these guns (has rebuilt maybe a dozen using scrounged up parts) - with the round fully back on the carrier/lifter - no way nohow can that thing flip up to the sky - by time the case rim has come forward enough to start clearing the groove in the guides the boolit nose is already going into the chamber - yeah shimming it will fix it - but somebody proly already polished that metal off of there to break it first - small case actions a bit different - two little titty shaped lumps, very tempting for a novice to remove them to smooth it up - one on each guide just behind the grooves for the rim and two corresponding little clearance grooves in the lump on bottom of the bolt that houses the ejector - gotta remember the 92 designed around the larger case - 32/20 etc was an afterthought (lots of em sold in Aus though) so a small case 92 is essentially a conversion on a 44/40 - new bolt with smaller bolt recess - different cartridge guides - change the lifter - bore a smaller hole for magazine - etc . These things are complicated, and the tolerances between what works good and what dont work at all are pretty fine .