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How do I know if MY gun needs fire lapping

3K views 5 replies 5 participants last post by  MikeG 
#1 ·
I've been reading and searching a bit about fire lapping a handgun. How do I know if my gun could benefit from fire lapping?

My gun shoots vary accurately and has not had problems with severe leading. When I slugged the bore, there was a tight spot right by where it screws into the frame...however, the darn 5 groove rifling makes it a bit hard to accurately slug.

Also, I poured some soft 358156 bullets that didn't lead, but did develop some pressure signs, in spite of only moderate velocity (was hoping to drive these gas checked bullets a little harder). One person on "cast boolits" suggested that maybe a barrel constriction was swagging down the bullet to being undersized by the time it moves to the muzzle, thereby allowing pressure and powder to blow by...his words, not mine.

Here's a before and after of one of the bullets.




Any suggestions or opinions on whether or not fire lapping may be needed in the situation I just described?
 
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#2 ·
Welcome to the forum pps. Rules are simple, be nice and join in.

Best I can say is get one of Marshall's Beartooth Bullets Technical Guides. The wealth of information there can really help you determine what you need. It's available by clicking on the Beartooth bullet tab at the top of the page. There are also some good articles available there in our tech section.

I've done several handguns now with Marshall's fire lapping kits and every one increased in accuracy and ease of cleaning not to mention a velocity increase with the same loads I was shooting before.
 
#3 · (Edited)
Completely agree with Bob's suggestion, the manual is great. I've fire lapped a number of revolvers (8) and two rifles and all but the .22 improved accuracy. The balance were .44 and .45 caliber.

To me, it's kinda "you've got nothing to lose", it's cheap and the labor invovled is interesting work.

I purchased a Springfield XD .45 ACP last year and sent back to the factory for upgrading. Action job and the barrel upgrade options were two different custom barrels replacements or they would make the existing facotry barrel work like a custom barrel (cheapest option). I had already fire lapped it but figiured for $100, I'd let the experts upgrade it. When I got the pistol back, I was not charged for the barrel work and called them to ask why, and was told the fire lapped barrel was as good as they would have reworked it. They may have just had a busy or off day, but I was pleased, never-the-less.

Dan
 
#4 ·
PPS, if you don't mind some imput from someone who has not posted in a while (years), I do have some observations based on your pictures and a little advise. However, it might be a bit long winded.

For starters, your mould appears to be on the cold side. This is evidenced by the rounded corners on the driving bands. If the leading edges are not even, there is the possibility of more friction on one side than the other causing the bullet to be forced out of alignment. Another evident point is the dimples in the surface of the bullet. (Good photography by the way).

I also noticed that the gas check is still attached and covered with lead smears (I shoot my cast bullets into piled snow banks during the winter and retrieve them in the spring. I have never been able to retrieve a slug with the gas check still attached). One of the gas checks added benefits is that its leading rim/edge expands while traveling down the bore due to the pressure exerted on its base and actualy forms the "last line of defense" against smearing lead. Seeing the smears in your photo might suggest that you do indeed have a tight spot in the first inch or two of your barrel. Lapping will cure this. When the bullet passes through the tight spot, it is sized down (ventury effect) and does not have enough friction to obturate once it passes the restriction and re-seal.

Another observation is that your sizing die is not properly sizing the lead slug. This is evidenced by the longitudinal stryations on only part of the circumference of the driving bands. You might need a smaller sizing die. this is only a guess, but I surmise that you are using a Lee push through sizing die. These are great dies and I will not aim fault at them. However, they need to be purchased a size smaller and honed out to the proper size of projectile needed. I use Lee sizing dies to size my slugs and then use a LubraSizer with a larger die to lube the bullets. The Lee die seems to keep the bullet more concentric during sizing than shoving it down into a die then shoving it back out.

The size of the bullet is of utmost importance if accuracy is wanted in cast bullets. I could go on forever about this, but I think I have overstayed my welcom on this post. There is a plethora of expert casters on this site that can expand on what I have said and can also point out things I have not. I hope you gain the knowledge you seek here.

Good luck and Happy Casting!
Allen
 
#5 ·
Thanks so much for the input. Allen, indeed the mold was a bit cold. The bullets that came out a bit frosted had some beefy, sharply defined edges. I'm pretty sure that there is a stricture in the barrel where it screws it to the frame.

I will get Marshall's kit, which I understand includes the technical manual. The only reason I've been hesitant to fire lap is that this has been a very accurate gun, in spite of the fact it chronographs about 100fps slower than my 4" Ruger. The BC gap on the Ruger is .004", while the gap on the Smith is only .002".

Any hints on getting an accurate slugging of 5 groove rifling? I'm fairly sure that I'll pretty much go by feel when slugging the bore after fire lapping, simply to feel for the stricture, or absence thereof.

Once I get the fire lapping done, then I'll test fire some more of the soft lead gas checked bullets into the rubber mulch bullet trap to evaluate whether or not I get lead smeared on the check. I'll also try tweaking a lee sizing die to .359" to see if I get better results (in terms of leading, velocity, and accuracy) with the .358 vs .359 As it stands, the .358 sized bullets have to be given a slight amount of force to go through the chambers on my Smith...the Ruger however lets the .358 drop through...so the Ruger will probably do better with .359 I'm guessing.

All this casting, sizing and handloading is a relatively new (and fun) hobby for me. Though I've shot for years, I'm finding this learning process to be almost as much fun as the shooting itself.
 
#6 ·
Just go by feel. If there's a constriction, you'll know, and that is the main thing you want to check for.

No constriction, you don't need to lap unless you want to reduce fouling. It may help.

Also, just size the bullets for the cylinder throats. You are correct you may need different sizing for the different guns.
 
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