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Potential Benefits of Fire Lapping of Remington XRC II

07 Apr 2012
@ 07:13 pm (GMT)

Danny Strong

Hi All,
I noted in a previous email reply that a Rem SPS gained considerable benefit from fire lapping. I intended giving teh barrell a real clean using solvent and then JB paste. Would fire lapping be better.

I would say that after cleaning, I'll shoot this thing first before doing anything. It might be a shooter straight out of the box.

Thanks

Replies

10 Apr 2012
@ 10:08 am (GMT)

Quote this

Nathan Foster

Re: Potential Benefits of Fire Lapping of Remington XRC II

Hi Danny, yes, shoot it first and see.

One of the major issues with accuracy, lies within our own abilities to recognize what factors/variables are causing problems.

In an XCR 7mm Rem mag, poor accuracy factors can include:
Lack of any bedding
Poor bedding
Non optimal hand loads
Trigger to heavy at its lowest setting
Trigger creepy at its lowest setting
The bore
Shooting technique

I have not included optics on the above list but you will need to keep in mind that your Zeiss scope may be detrimental to accuracy due to minimal eye relief, increasing perceived recoil, destroying technique by forcing you to move your head back under recoil so as to avoid a cut eyebrow. I do not recomend this brand of scope for use on magnum recoil rifles or light weight rifles in standard calibers.

If you refer to my barrel break in article in the knowledge base, you will see how I inspect the muzzle, looking for chatter marks and or severe fouling. By inspecting the muzzle at the angle specified bopth before and after shooting, you can determine fairly quickly whether the bore will need fire lapping. Please follow the steps in that article as you move forwards.

I currently make my own fire lapping projectiles, I knurl the projectiles first before coating them in grit. I then run the projectiles at pretty high pressures. The result is two fold, firstly the burrs in the bore are either removed or smoothed out. Secondly, the bore tends to end up muzzle tight as opposed to muzzle loose which is a big problem these days across many brands, right up to Sako.

Considering a muzzle loose bore in layman's terms, imagine that the bullet is swaged right down at the chamber end of the rifle and then as the bore becomes loose at the muzzle end, the rifling has less control of the bullet. The result is a poor shooter. Also, even though the muzzle is loose, severe fouling (extreme cases) can be evident at the muzzle due to copper vaporising and becoming re-deposited further down the bore. Having a bore that swages the bullet down towards the muzzle has a huge effect on accuracy. It can turn a 4 MOA shooter into a tack driver.

I have written that fire lapping can be a good option. The truth is, in some instances, it is the only option short of re-barreling. Any increased wear at the throat during fire lapping is irrelevant if the rifle is in-accurate to begin with. Besides, throat wear is something which is quite misunderstood anyway.

People avoid using JB paste on the throat, worrying that it will wear the throat down. Try to understand that the opposite is true. If the steel is left to its own devices, it will become porous, just the same as a weld edge (heat effected area) resulting in serious wear down the track. the secret to good throat life is to keep the throat well polished, keep the pores of the steel closed- or from forming at all. Any steel worker / sheety / engineer will understand this. We do have control over the throat, some of the information floating around about throat wear is not very helpful in this regard.

Just think in opposites, the softer you treat the throat, the more it will wear, the harder and more vigilant you are towards polishing, the longer it will last. You won't read this anywhere else I am afraid, so if you want cross referencing for verification, you won't find it unless you explain this to a metal worker and ask for his perspective. Stainless workers have the best insight (regardless of the type of steel used- stainless or Chrome moly etc) as these workmen preserve steels via grade selection and appropriate polishing methods, not coating (paint).