Fire bore lapping

[MnMike]

I did a quick pass through the FAQ and did not see this. Has anyone tried the abrasives loaded onto the bullets and fired, to smooth the bore? There are, I think, three grade of abrasive that are used.

mike

[quickdtoo]

One member used Tubb's, accuracy was worse afterwards. The rifling is so shallow, you don't want to do anything more than polish the bore, that's covered in the FAQs under barrel break in.

Tim

[DalesCarpentry]

Not to stir anything up here but I have to ask. Why is the rifling so shallow in H&R rifles? Does the shallow  rifling  cause premature barrel failure?

[MTGlass]

I haven't fire lapped a Handi, yet.  I'm still on the fence, working on seeing if my daughter's 7mm-08 will shoot well without it.

You might want to pose your question to Verl Smith of LBT (board sponsor) over in the Cast Bullets forum.  I've used his method and materials on three SA Rugers, an M-77 .308, a Model 7 in 7mm-08 and two Marlin .45 leverguns with microgroove rifling, all to good effect.  The instructions included with Verl's materials are good enough to do the job, but the Beartooth Bullets Technical Guide has a much more thorough treatise on the subject.  I used some of Beartooth's lapping bullets when LBT was out of operation for a few years.  Back in July 1993 Ross Seyfried had an article in Guns & Ammo about fire lapping.  I have that edition open on my desk now.  It's what got me interested and started in fire lapping.

Look in the left frame for "Book"  http://www.beartoothbullets.com/bulletselect/index.htm

Personally, I would never use jacketed bullets for fire lapping.  According to everything I've read, slightly oversize, 12-15 BHN cast bullets charged with the proper lapping compound will cut evenly on the top of the lands and down in the grooves.  Jacket bullets will mostly ride the lands and will spring back to original diameter after passing through a constriction.

Be aware, there are those who scoff loudly at the concept claiming accelerated throat erosion, etc.  I'm not a bench rest shooter an am quite happy with the results.

[Fred M]

DALESCARPENTRY.

Quote.
Why is the rifling so shallow in H&R rifles? Does the shallow  rifling  cause premature barrel failure? 

Shallow rifling is less expensive, it produces less stress. Specially in the production used by H&R barrels are not stress relieved.

When barrels are later contoured and more metal is removed at the front of the barrel than th e back the barrel looses some stress more at the front than at the back. This loosing of stress causes the barrel to expand, more up front than at the back.

Fire lapping a barrel bore that is bigger in front than at the chamber will only lap the tighter part of the bore not touching the the rest of the bore, I have measured the bores of several rifles and found the grooves to be 0.002"

I also fonund the bores to be 0.0015" bigger at the muzzle than at the chamber end.

You figure out what fire lapping will do in a Handi barrel. Besides Handi bores are very smooth the ones I looked at with a 22x bore scope. No need for fire lapping.

[DalesCarpentry]

Fred M.                    Allright so fire lapping will only lap the tight part of the barrel! will this cause a shorter barrel life? I don't know this is why I am asking this question. It would seem that if you fired enough bullets it would do the same thing as the fire lapping. I would not want to assume anything. You know what happens when you assume. ( you make an ASS out of U and ME ) Thanks Dale.

[Fred M]

Shooting lots of bullets through a barrel does noodle away the the edges of the lands, flame cutting the throat and the start opf the rifling. It very rarely increases the size or the depth of the grooves.

Grit impregnated bullets will remove metal if the bullet is the same size as the grooves. So shooting lots of bullets and fire lapping do not produce the same bore condition.

Before anybody undertakes a fire lapping prodedure a very thorough barrel inspection and slugging should be made. Just because a barrel does not shoot
well does not mean it needs fire lapping.

One thing I am quite certain of, a factory Handi barrel will  not benefit much from fire lapping, shooting moly plated bullets will.