Lapping and Polishing barrels

When we talk about working on barrels, we hear terms like lap and polish. What does that mean? Lapping in the traditional sense involves pouring lead into a barrel to produce a big slug that is the reflection of the bore of that particular barrel. That slug is usually molded to a jag or rod to create a "lap". The lap is then coated with abrasive grit and worked by hand through the barrel. This is done to smooth out a bore, removing tight spots to give a more consistant barrel. Lapping can also be used to loosen up an overall tight bore, or an attempt to increase accuracy. In regards to choked airgun barrels, lapping isn't as easy because of the choke. Regardless most quality barrels are lapped by the barrel maker and thus leaving no need for you to lap your barrel. Because lapping actually removes metal rather aggressively, you can ruin a barrel before you even realize it. Lapping is a skill that is done by feel and experience and usually something done by gunsmiths when fitting a blank to a gun or trying to improve a bore for accuracy sake.

Polishing is similar to lapping as you are still messaging the bore, but working with very fine polishing compounds instead of the grits used to lap. Also, polishing is typically done with cotton patches or caliber specific bore mops instead of a lead lap. Polishing is a final attempt to remove micro fine imperfections and polish down edges to reduce fouling and possibly increase accuracy. I prefer using a caliber specific cotton bore mop usually coated in JB bore compound and soaked with Kroil. Some people use Flitz metal polish or other "polishing" compounds.

It is important to note that if at anytime you are going to change grit or compounds for lapping or polishing, you have to completely clean the bore before going to a different compound. Otherwise, you will still be pushing the heavier grit mixed with the finer grit which can be BAD!! This means that I also use a completely different mop for polishing with heavier grit vs finer grit. While lapping is all about feel and has to be done by hand, polishing is kinda like waxing a car. You can wax your car by hand or get the same results much quicker by using power tools. I used to polish barrels by hand and for whatever reason, decided to try a cordless drill to "speed up" the process. It worked great and I have been using a drill and dremel ever since.

Since lapping shouldn't be attempted by most and it is especially hard with a chocked barrel, I will give you this link with some good videos on lapping by Mr Perro.

Now, polishing can be straight forward and easy for any airgunner regardless of experience level. I do recommend that polishing be done with the barrel removed so that no compound or oils get into the the air passageways and cause trouble.

I start by removing the barrel from the gun and the breech o-ring if applicable. Next, I thoroughly clean the bore until patches come out completely clean. I will push a number of pellets thru the bore to identify any tight spots or just an overall feel of the bore and that is how I decide the amount of polishing for that barrel. (In some cases if the bore needs more than a basic polish, I will start with a heavier grit compound than JB and follow the same steps layed out below. If heavier grit is needed, I will competely clean the bore before the final polish with JB.) I then apply a healthy dose of JB to a cotton bore mop and soak on some Kroil. Attach the mop to a rod that I then chuck in a cordless drill. I vary speed and don't really have a set pattern in my use of the drill versus a cleaning rod by hand. I like to spend some time polishing the barrel port (if applicable) and the leade first. I don't really have a set amount of time I spent on each area or step, I just polish till I feel it is good. After the leade I will spend some time working through the choke. In the case of an FX ST barrel, polishing the small rifled section is done the same as I do for a traditional choked barrel. Polishing to smooth the pellets transfer as it passes from the bore to the choke or rifled section of an ST. After I feel the leade and choke are done, I will then polish the full length of the bore from end to end. When I have completed the bore, I use a dremel with a felt polishing cone that is coated in the same JB/Kroil mix and put a mirror finish on the crown. I end the same way I start by thoroughly cleaning the barrel before reinstalling it to the gun.

Unless I have an issue with a barrel leading up really bad, I only polish a barrel once. As I have refined my barrel prep methods, I now have a good system that seems to produce barrels that need less cleaning and more consistancy. I can't say that polishing alone has much effect on accuracy? I do alot of other things to address accuracy and feel polishing is just one little step towards the overall accuracy goal. Like many other things, lapping and polishing are skills that take time to learn and there are many different approaches to get the same results.

Hopefully some find this info useful and of some help. If I missed something or someone needs more clarification, please ask. I have done so many barrels both firearms and airguns that prepping a barrel has become almost second nature and I find trying to put it all to text is rather difficult for me.