Home Forums Hunting & Shooting Gunsmithing Barrel blank lapping question?

I bought a Shilen .270 barrel blank a few years ago and finally got around to threading and contouring. It's for an Enfield and I've already got the cone cut, and everything looks good so far. This is a chrome-moly barrel, and hasn't been chambered or crowned yet. I'm wondering if I should lap it before I go any further. Shilen does lap some of their barrels but it hasn't been done to this one. I know it has to be done before it's chambered and crowned if I'm going to do it. I don't want to change dimensions or round off any corners; just polish it a little. I thought I'd just give it a few passes with 600 grit lapping compound. I've never done this before but I think I know how it's done. I think I would cast a lead slug in the breech end of the barrel by plugging the barrel an inch and a half or so in with a wood plug wrapped in a cleaning patch, and then preheat a little before pouring in the lead. Then I'd push it out the muzzle till I could remove the plug and the lead slug came out a half inch or so. Then I would score it lightly with my knife and apply the compound. I'd push it back and forth till it just protruded out the ends never letting it come all the way out. After a dozen or so trips I'd call it finished and clean up the mess.

So my questions are: Is it worth the effort or should I just chamber it like it is? Do I have the right idea as far as technique goes? What should I change about my plan? I'd appreciate any help I can get.

I would chamber it as it is. I prefer to lap after chambering but before crowning. I cast the lap at the muzzle end and.push it right out. I charge the lap then run it up and down about ten strokes, index one groove, then repeat until I have gone right around. If there is a spot that seems tight, I'll work at that area until it feels uniform.
If all you want to do is polish, you may do as well to simply use extra-fine steel wool with some J-B compound.
The reason I prefer to lap after chambering is that the throater may leave a bit of a "feather" on the trailing edge of the lands. The lap will remove this. Of course, so will the first couple of shots!GD

Were it mine, I wouldn't bother lapping it just yet. I would wait to see if it needed it. You can always lap the bore later if needed, but from my experience with Shilen barrels, the standard non lapped variety, they don't need it.

I have read on this forum that the lap will cut much more in the area where it changes directions. Also they say you should never lap a finished barrel. Probably for the same reason. Isn't JB softer than barrel steel? Last Shilen barrel I fooled with was a 25/06 and it copper fouled very quickly. That's the reason I was thinking about lapping it to begin with. Maybe I'd be better off to leave it alone. Thanks.

A lap cuts much more where it changes direction? Perhaps, but I've not seen a great deal of evidence to support this contention. However, this is why I do lap prior to cutting and crowning. Just in case.
"They" say not to lap a finished barrel. I've lapped a lot of finished barrels over the last 35 years or so and have always seen an improvement. By the way, I do not lap every barrel I install but do lap those which appear they could use it or if I am asked to do so.
J-B is alledged to be softer than barrel steel yet it still polishes and appears to cut. GD

Not a pro at all but 600 grit doesn't sound worthwhile.

Hart barrels had some information on their lapping process and they said stop at 220 grit if my feeble memory is correct. They thought that overly smooth barrels fowl more and had greater friction/pressure. To me lapping is to remove tool marks perpendicular to the bore and secondarily to improve uniformity slightly.

Done improperly it can ruin a good barrel, like using a flexible rod or inadequate bore guide.

Also keep in mind some manufactures start with the barrel .0001 or so undersized and then lap to final dimensions.