Lapping locking lugs questions

[264magnum]

Hello

I just picked up an older Sako that is not bearing evenly on the locking lugs and they are pretty rough. Anyone have any ideas on lapping the lugs a little without removing the barrel. I would think that should be ok as long as the headspace is checked after. Is it feasible to use the bolt(shroud/firing pin removed) and lap the lugs a little using a compound that is easy to clean out?? I think without removing the barrel regular lapping compound might be too hard to clean out. I would like to do all this without having to turn the barrel in or remove it. Any experience would be greatly appreciated. Thanks for any help/ideas.

 

[guntech]

I think in cases like this lapping is about the worst thing to do.

I would suggest having the barrel removed, the locking lug recesses machined true and the bolt lugs machined true. The barrel then reinstalled and headspaced.

Lapping lugs that are this bad simply laps tapers into everything. It is not the way to fix it.

 

[mrd49]

OK: I'm going to chime in here, but I may be in over my head. I work on USGI M1 Garands, receivers and barrels-either USGI or aftermarket. If I'm out of spec, someone else correct me, but the concept is the same. Lapping the lugs to the receiver IS beneficial because you can get even mating of the locking lugs and receiver surfaces. (no brainer here... if when you chamber the cartridge and pull the trigger, there is little or no movement within the chamber, then all other things being equal, your velocity is more uniform, your brass stretches less, etc, etc.) IE: less things that are different from shot to shot.
THE PROBLEM: is that when you lap a bolt/receiver, you are increasing head space. Also, if you lap too much, you can wear through the case hardned outer surface of the bolt and sometimes the receiver, and expose 'softer' steel which will wear more quickly.
So what is the answer?????
1st: Get your self a complete set of headspace gauges, Go, No Go and Field for your particular caliber. Some say to forget the Field, but you will need it sooner than later. It is also valuable in determing chamber spec when used in conjunction with a No Go.
2nd: Using the gauges, determine how tight you are in the headspace realm. You will know what I mean if you read up on this. If your are really tight, barely closing on the GO, then you can probally lap a couple of thousands or two from the bolt and receiver mating lugs and still be OK. Use your headspace gauges to check frequently. You can cut more, but it is damn hard to glue those little chips back.
On a M1, if the stock bolt/receiver mating is 50 % or more, I leave it alone. If it is less, AND I have "room", headspace wise, I will lap.
Like I said, I'm a M1 mechanic/shooter and things may be a little different for you, but the concept is still the same. Should you decide to lap, I have a couple of 'Garand' ideas that may help you without breaking your budget. Hope this helps.

 

[45ACPKING]

OK: I'm going to chime in here, but I may be in over my head. I work on USGI M1 Garands, receivers and barrels-either USGI or aftermarket. If I'm out of spec, someone else correct me, but the concept is the same. Lapping the lugs to the receiver IS beneficial because you can get even mating of the locking lugs and receiver surfaces. (no brainer here... if when you chamber the cartridge and pull the trigger, there is little or no movement within the chamber, then all other things being equal, your velocity is more uniform, your brass stretches less, etc, etc.) IE: less things that are different from shot to shot.
THE PROBLEM: is that when you lap a bolt/receiver, you are increasing head space. Also, if you lap too much, you can wear through the case hardned outer surface of the bolt and sometimes the receiver, and expose 'softer' steel which will wear more quickly.
So what is the answer?????
1st: Get your self a complete set of headspace gauges, Go, No Go and Field for your particular caliber. Some say to forget the Field, but you will need it sooner than later. It is also valuable in determing chamber spec when used in conjunction with a No Go.
2nd: Using the gauges, determine how tight you are in the headspace realm. You will know what I mean if you read up on this. If your are really tight, barely closing on the GO, then you can probally lap a couple of thousands or two from the bolt and receiver mating lugs and still be OK. Use your headspace gauges to check frequently. You can cut more, but it is damn hard to glue those little chips back.
On a M1, if the stock bolt/receiver mating is 50 % or more, I leave it alone. If it is less, AND I have "room", headspace wise, I will lap.
Like I said, I'm a M1 mechanic/shooter and things may be a little different for you, but the concept is still the same. Should you decide to lap, I have a couple of 'Garand' ideas that may help you without breaking your budget. Hope this helps.

I agree 100% when it comes to garands and m14 rifles....... if you do try this method, use an very fine, soft base lapping compound...... the name is on the tip ofmy tongue but i'm gapping here....... and the label is too worn on the container .... DOH......
i would tend to stick with guntech's advice on a bolt gun though...... there's a very quiet rumour going around that he knows his szhit

maybe p.m. mystic player and alberta tactical rifle.... they all have have vast bolt gun experience and have always given me good solid reliable info in the past.

 

[Leeper]

Chances are your Sako is showing evidence that it is bearing primarily on the bottom (right hand) lug. This evidence is deceptive. The Sako trigger puts considerable upward pressure on the cocking piece when the action is cocked and especially, when the chamber is empty. As a consequence of this and the generous clearance between tthe bolt and receiver bridge, the bolt is misaligned in the receiver. Sinced most bolts are worked at least as often empty as loaded ( even loaded, the bolt will still be misaligned unless the ammunition is very tight in trhe chamber) the wear pattern will show greater contact on the bottom lug.
If the lugs are quite rough, this is evidence of galling from a lack of lubrication. The repair for this is, as Guntech pointed out, not lapping. Regards, Bill.