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Old 02-11-2013, 11:34 AM   #1 (permalink)
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OEM bore finishing


Having read through some posts floating around on the topic, I'm curious as to whether or not anyone here knows (not guesses) how, and to what degree barrel bores are typically finished.

I've seen threads on flex honing, buffing/polishing, etc., and am curious as to whether these would produce a finer, or rougher finish. The one question no one seems to have asked is, "What was the original finish?" If we don't know that, then we cannot determine whether other methods are an improvement or a detriment, leaving aside the whole additional pile of questions on the benefits of an increasingly smooth bore.

Please note that the latter is not my question here. I don't care to debate the merits of a super shiny bore. I just want to learn/determine the general baseline finish.

And "Um, yeah, my barrel came super shiny from the factory, so, um, like, maybe 600 grit?" is not exactly the kind of answer I'm looking for.

In my case, I'm particularly interested in stainless barrels. Lapco, for instance, seems to have really high quality initial finishes on their bores. So do the DYEs, and so do some others.

But exactly how is it done, and to what degree?

If you have direct, correct knowledge of the process, whether for aluminum, brass, stainless, whatever, I'm all ears.

Thanks very much!
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Last edited by Menace; 02-13-2013 at 10:52 AM.
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Old 02-11-2013, 04:20 PM   #2 (permalink)
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It depends on the manufacturer. Some cheap-o barrel from overseas might be just drilled and reamed. More popular manufactres have a few other finishing options like honeing, burnishing or ballizing. However those processes involve a lot more capital investment.
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Old 02-11-2013, 05:05 PM   #3 (permalink)
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No barrel manufacturing, but a lot of grit on stainless experience.

On stainless, 600 grit still has a visible trail while appearing "shiny" at angles. 800 starts reflecting better. 1500 grit on an otherwise clean surface is a foggy mirror. After 1500, a buffing wheel will get a clean mirror shine.

I have seen a stainless freak insert that looked no better than a 600 grit finish on the inside. The marks were very even at two angles, like it was honed going in and out. I don't know if that is common. I have a couple of old stainless barrels (TASO, 32 degrees) that appear to be around 1500 to 2000 grit inside.

What is sad is a mirror bore with a dozen waves in it.

I have often wondered exactly how they got those shiny bores myself. I always assumed it was some sort of full length slurry cut and polish.
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Old 02-11-2013, 06:03 PM   #4 (permalink)
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I'm guessing/hoping, from my own experience in metalworking, that the bores are finished at the very least to the equivalent of ANSI/CAMI 2000. That would be a bare minimum, but I suspect at least with the Lapcos and DYEs that the finish is significantly higher than that. There is lots of talk about 'stiff arbor honing', but that tells me only something vague about the method used on the bore, and nothing about its refinement.

And yes, I'd considered a slurry, simply based on volume. But there might also have been final polishing phases with bobs and paste, or the equivalent, at least in the cases of the higher-quality bores.

The wavy finishes may well be indications of something like a short hone or polishing bob improperly controlled. Yuck. It's a nauseating thing to look at, and to think about. Someone did it, someone saw it, and someone signed off on it.

And then someone bought it.

But there surely have to be barrel makers here, or at least those who have been in on the process.
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Old 02-11-2013, 06:53 PM   #5 (permalink)
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Barrel manufacturing is a kind of "black art" we don't hear much about anymore.

Back in the day, an ad might have bragged that their barrels were "gun drilled" or "micro honed", but you don't see that much anymore- today's trend is to just tell you the bore size.

Now, to start with, virtually no manufacturer drills from solid bar stock these days. Most manufacturers buy special-order extruded tubing; special order to get a specific bore size- most off-the-shelf pipe or mechanical tubing isn't the right ID or OD for a paintball gun barrel.

That tubing is often only minimally finished- in the case of, say, Pro-Lite, Carbine and A5 barrels, the only "finishing" was a couple passes of a relatively rough hone (I'm guessing 400 grit) and threading. I'm not sure they were even turned externally.

From the look of older (early-mid 2000s) Autocockers, their barrels weren't even honed. Whatever size the extruder produced, was the finished bore size.

Now, while I don't know for sure, I suspect that most manufacturers do something like roller burnishing. For example, they get raw, extruded tubing in, say, .682" (just throwing numbers out) or so, cut it to length, and then pull or push a roller burnisher through it.

The burnisher essentially just rolls the surface smooth, like using a rolling pin on cookie dough. That "squashes" the metal, resulting in a .683" or .684" (or whatever) finished bore.

The rolled blanks are then fed into whatever CNC lathe does the threading and external profiling. (Though with the right setup, a bar-fed machine could burnish, profile and part off- we're just concerned with bore finishing at the moment.)

The burnisher is faster than honing (essentially one pass vs. multiple passes) doesn't wear nearly as fast as abrasives, and produces a much smoother finish.

Making a stainless barrel however, would be different- stainless, to my understanding, can't be roller burnished because it work-hardens. Those barrels would have to be bored and likely honed and polished.

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Old 02-11-2013, 07:00 PM   #6 (permalink)
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i was talking to my boss today at lunch...

he asked me why im not producing my own barrel!

i was like uhhhhh i didnt think we had the machines to do it in house at our shop

his idea was to buy tube close to size, bore, roller burnish, thread, done
he says we have the tooling for it..... i dont believe him
now i gotta talk him into buying some material to "prove me wrong"
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Old 02-11-2013, 07:15 PM   #7 (permalink)
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I have a roller burnisher for barrels... Very expensive tool.

But it's also the right tool for the job. A part that has been spade drilled and then burnished can end up with an incredibly fine finish. Far superior to honing.
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Old 02-11-2013, 07:16 PM   #8 (permalink)
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Old 02-11-2013, 09:12 PM   #9 (permalink)
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Doc and Alpha,

Thanks for the reminder on burnishing. And given the info on the Elliott burnisher you listed, Doc, that is pretty impressive, even to a jaded finisher.

.05-.2 microns? Zoiks!

ANSI/CAMI 2000 grit is ~15,000-ish mesh. That's about 1 micron.

This burnisher produces a finish comparable to a mesh of over 100,000.

You can get abrasives lower than that, but wow. That's mighty smooth.

But again, is this the method used for stainless?
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Old 02-11-2013, 09:23 PM   #10 (permalink)
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Well I have measured an eclipse barrel at 6 micro inches finish. when I bore a barrel I run a reamer and then a flex hone to get out the tooling marks. 600 grit for about 15 seconds I have measured that finish at around 18 micro inches (if memory serves). I recently decided to start on a project for dansoslow and make him a custom barrel. I tried reaming a tube that was already close and I was not able to get it quite right in the middle. I had to flip the barrel over to reach the whole length. So I am embarking on plan B I went ahead a bought 2 11/16" gun drills 22" long and plan to try making the barrel 100% from solid stock. I will let you know how it goes cause its going to be an adventure.
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