I have a Mauser actioned rifle in 9.3X64 which I have yet to fire. The action is nondescript, but resembles a commercial FN 98 action superficially. The barrel is D&T for a rear sight and a front ramp, but other than the caliber marking (underneath) it is unmarked.

The problem is that the bolt resists closing slowly. Operated quickly, there is no problem, but operated slowly it starts to resist the closing motion about 1/4" before the lugs start to engage. Evidently part of the cocking action is being carried out by closing the bolt.

I suspect that either the commercial trigger or the cocking piece is at fault, but I don't know a good way of determining which is the culprit.

I suppose I could replace the commercial trigger with a traditional two stage military style trigger, of which I have a good supply, to see if the problem is cured, but I don't know where to go from there. Unfortunately there is not a gunsmith I trust in the immediate vicinity. Suggestions, please?

I think the Mauser 93, 94, 95, and 96 actions are cock on closing. Is that what you have?

No, Rod, it's a 98 of some description, solid left wall like a commercial FN, but no markings other than a four digit serial number. I should have been more specific.

If I'm not mistaken, all 98's have a fraction of the cocking action activated on closing, but I believe this is supposed take place after the locking lugs are engaged and the bolt is being cammed forward as the bolt is closed. I believe it is this last part of the cocking procedure which allows the safety to be engaged.

Evidently something is out of alignment, causing this final part of the cocking procedure to begin before the locking lugs are engaged.

None of the cocking should take place on any 98 whilst closing the bolt; turning it down, yes.
Only way to trouble shoot it is to see it.
I have recently seen this; a guy ground a big notch in the bolt to hold the cocking cam nose, which made it partially "cock on closing". The fix is to shorten that nose.

I went down to the shop and did some further investigation. First of all, the trigger is a Timney. Secondly the measurements I took off the bolt in question were as follows:
Distance from rear of striker to bolt sleeve with bolt open: 9.3mm
Distance from rear of striker to bolt sleeve with bolt closed: 15.7mm
Difference 6.4mm

Using a commercial Mauser with its much longer striker, I took the same measurements, and the results were: 17.8mm/23.2mm with a difference of 5.4mm.

The commercial Mauser bolt had no resistance to closing and all of the 5.4mm retraction took place as the bolt was being turned into the locking lug recesses.

Question, if I shorten the cocking cam nose, will the safety still engage? Presumably the striker will be retracted 1mm less after the shortening operation.

No because the safety only knows where the cocking piece is in relation to the trigger. Not the sear nose. NOW, if you shorten the cocking piece nose too much, realize that it may no longer reset the sear fully on opening and might require some bolt retraction. All these things need to be in sync which is why I recommend you go slowly and know what each piece is doing before you do anything. I adjust them like the pinball wizard.
It probably worked with the original trigger. Maybe.

I just noticed that Timney makes a number of different triggers for Mausers and it might be possible that the trigger installed in my rifle was one meant for a cock on closing system. I'll have to try to see if I can determine exactly which trigger I have tomorrow.

The action described maybe a spanish Santa Barbara or Yugo Zastava. Both closely resembled the commercial FN.

The problem closing the bolt slowly may occur when the striker nut overrides the sear and the trigger/trigger sear engagement prevents the depressing of the sear.
That will freeze the further movement of the bolt.
(The reason for that failure is most often an oversized mounting pin hole in the aluminium house of the trigger or otherwise loose trigger/receiver contact).

If the trigger is perfectly fitted and the safety works easy when the bolt was rapidly cycled and closed as you described you may have a closer look to the bolt sleeve lock plunger.

That part sometimes causes the same problem you described.

Simply remove it and test the cycling of the bolt. If it works under this condition a slight modification of the plunger is necessary.

Hope that helps . Good luck.

Look for this, if the rear tang has been modified, does the cocking piece ride up over the tang before engaging the slot in the tang?

Following heavenknows' suggestion, I looked at the bolt sleeve lock and determined that the plunger had to be depressed to get the bolt to the point that the locking lugs would engage. With my other Mausers, the plunger touched the receiver at the same time that the root of the bolt handle touched the camming surface of the receiver.

I have a spare FN bolt, so I removed the bolt sleeve/firing pin/striker assembly from the original bolt and fitted it to the FN bolt. When I cycled the bolt in the receiver, everything worked perfectly. The bolt lock plunger touched the rear of the receiver simultaneously with the root of the bolt handle touching the camming surface and the engagement of trigger to the cocking piece first took place at the same point, so the last portion of the cocking procedure took place while the bolt handle is being lowered, and there is no resistance to closing the bolt up to that point.

Although the original bolt is numbered to the action on the bottom of the handle, I suspect that is was somehow mismatched. The problem is not entirely solved, since the substitute bolt has a .30-'06 bolt face, which will have to be opened up to match the 9.3X64 case head.

Yeah, if the cocking piece is running up the tang it will lock it solid. If the bolt sleeve lock and spring are all gunked up it can create a hard closing situation too. You can remove them and try it.

I would give the "original" bolt a try. The timing /fitting problem of the plunger certainly can be solved.One possible solution ,simply try to change the striker unit/bolt shroud.
Using an other bolt and only opening up the face may cause another problem. Because headspace may be affected.

http://www.gswagner.com/98bolt.../boltsleevelock.html
That may enlighten you

Glad I came to class today. Thanks for that link heavenknows.