PDA

View Full Version : Firelapping


midnightrider
August 9, 2010, 11:36 PM
I was going to firelap the barrel on my 243 rem. 700. with the Wheeler engineering kit I have

what velocity shot I be shooting when firelapping? I know it should be slow velocity, but how slow?

on the Tubb rifle lapping kits they say to use starting loads, I have heard of guys using 5 grains of Red Dot. I dont hav any Red Dot. I have plenty of Unique. Or should I go with reduced min. rifle loads?

any help with this would be great!
- A.J.

hooligan1
August 10, 2010, 06:28 AM
What's the need,midnightrider? why does anybody want to prematurely wear their barrels? Ido know what it is, but I don't know why it's done.:o

Unclenick
August 10, 2010, 11:01 AM
Usually it's to remove constrictions, which is essential to cast bullet accuracy. A bonus is much easier cleaning. Done properly, it does not remove more than a ten thousandth at the muzzle and maybe three at the breech, and it moves the throat forward only about one thousandth.

My first Garand's original military barrel fouled so badly that its accuracy deteriorated before I could complete a match with it. Firelapping reduced cleaning effort by a factor of 6 (based on patch count), and so reduced fouling by a similar amount. The accuracy remained good through a match after that and clean up became a short job rather than all evening with patch after patch of copper solvent.

The Wheeler kit is a low grade knock-off of the Neco kit. Wheeler openly violated Neco's patent. The Wheeler owner, being an attorney, threatened to keep Neco tied up in court until it wasn't cost effective to keep fighting to protect the patent, so Neco gave up.

Where the Neco kit uses lab grade abrasives to speed cutting and limit particle diameter distribution, the Wheeler kit uses standard grade abrasive. The Wheeler instructions illustrate a barrel with toolmarks left at the inside corners of the lands and claim that is a correctly lapped bore. It is not. As a result, I have little faith that they understand the process.

The bullets normally used in firelapping, whether it's the Neco-type multi-grade process or a single grade process like LBT or Beartooth sell, are usually cast bullets. The principle is to pass a bullet lap through constrictions that will act harder on the constrictions than on wider places. If the bullet is too hard it tends to spring out and rub wide and narrow places equally. If the bullet is too soft, the firing pressure bumps it up after passing through constrictions with the same result.

Over a lot of experimentation, it is generally agreed by all the fire lapping proponents that a bullet cast to about BHN 11 is the best hardness compromise. That is wheel weights plus 2% tin or else 16:1 lead:tin alloy. Neco sold correctly cast firelapping bullets, though I only see their pre-embedded kits up on their site now. Their page used to have both, but the embedded type is repeated, so you'd have to call and ask if that's a web site error and if the bullets are still available?

The correct charges for the cast bullets are low. For the .243, about 5 grains of Bullseye should be good.

The Tubb Final Finish system is not a firelapping system. It is a polishing system. It runs long jacketed bullets at full starting loads. The bullets are intentionally bumped up to bear against all parts of the bore evenly, as it is not intended to be a constriction remover. Tubb uses it on his custom lapped barrels (which have no constrictions) to extend the throat life by cleaning up heat stress cracks. It will make a barrel easier to clean, like firelapping, but will not straighten it or remove constrictions.

hooligan1
August 10, 2010, 11:55 AM
Thanks unclenick:) Two more questions, If a rifle is getting 1/2 moa at 100 yds, and is capable probably of doing better, could there still be a need to fire-lap? Why isn't this done as a final step at the factory?:o

midnightrider
August 11, 2010, 03:25 AM
thanks uncle

hooligan, if a barrel shoots .5 groups at a hundred with factory ammo I woulndt do much to the bore. maybe if you can see rough edges in the muzzle just a few shots with some fine compound smooth them over to make cleaning easy.

Iread a interesting arcticle on firelapping rifle barrels. the author said that he only fired 12 shots and it was overdone in the throat area. so firing a few shots and checking the throat dimentions with a borescope is critical. what he basically said was one only needs to fire lap enough to give the barrel a slight taper from beginning to end.

10-96
August 11, 2010, 04:26 AM
Just wondering...
How many rounds are through the rifle so far? Do you reload? Well, there's a lot of questions that play into the accuracy of a rifle. Fire lapping is permanent and irreversable if done wrong. Have you made sure the action screws are equally tight, bbl floated, action bedded, different recipes tried on the loading bench?
A half-inch group aint bad. A lot of what is done is done as an answer to a problem, not a problem looking for a question.

midnightrider
August 11, 2010, 05:37 PM
its a rem 700 in .243 win. and yes I reload I am pretty new to reloading the 243. Its got maybe 60 rnds through the barrel. I have reloaded for 30-06 a couple years and have crafted some good accurate loads through load development without lapping the bore. but then again that rifle has over a thousand rnds through the barrel. Over time just shooting a rifle will smooth over some rough edges.

I have bedded all of the critical areas in the stock. After reading that article I would be very careful on how many shots with more coarse grits down the tube. without a borescope (which I dont have) I am going into dangerous territory in terms of ruining the barrel. So i figure just a few of each grits wouldnt hurt anything. I may be wrong though.

-A.J.

Unclenick
August 11, 2010, 10:13 PM
Hooligan,

Firelapping usually either improves accuracy or leaves it alone. It always reduces fouling and makes cleaning easier if the bore was not previously hand-lapped. Hand lapping is what the custom barrel makers do at their factory, but then you are buying a barrel that costs several hundred dollars without installation to get that extra attention. Volume commercial makers can't afford the extra cost. Firelapping carefully takes me a half a day to finish, and I'm guessing they won't want to add that kind of labor, either.

Every once in a while you hear of accuracy being reduced by firelapping, probably due to excessive lapping. The problem is, I never almost never know what the shooter did exactly that might have messed it up? How hard were the lapping bullets? Did he clean and slug the bore with a pure lead slug every 5 rounds to check progress? Did he watch the muzzle to see when the lapping had cleaned it up that far down the tube? Did he use a coarse abrasive, like 220 grit, on a .22 barrel (.22's have shallower rifling and 320 grit is about as coarse as anything going down them should be; Neco recommends 400 grit). How warm a load did he use?

I don't think a borescope can really tell you when the throat has had enough. You need a throat wear gauge. It's too easy for reflections off that smoothed surface to disguise changes of a few thousandths. I can't spot that by eye alone without something to compare to.

The bore taper seems to help with lead bullets and doesn't hurt with jacketed bullets. I can't say that it will necessarily shoot any better than a straight bore with jacketed bullets, as many benchrest rifles are straight, so it's obviously not a requirement. It sure doesn't hurt, though. I have one of the BlackStar barrels on my AR with 7.5" twist. Those were made with a half thousandth taper to the muzzle through electro-polishing. Mine shoots like a house on fire. Sorry their not doing business now.

hooligan1
August 12, 2010, 07:22 AM
Thank you unclenick!!:) I appreciate the answers.:)