I’d not heard the term ‘gundrilling’ before I spoke to Tosh of Suzutomo Gun Tailoring (SGT), earlier in the week. However, I knew from my initial impressions of SGT’s 416 upper that there was something very special about the barrel. The outer/inner fit is sublime.
I like stuff which fits properly. Being of a mildly OCD persuasion, if stuff is slightly off, it niggles me. Even at Xmas. It’s one of the reasons I like SGT kit so much, because I can relax around it 😀
It’s also one of the reasons SGT’s forthcoming 416 lower was on my Xmas list.
Anyway, gundrilling is one of the ways in which SGT has added value and potential performance gains to its 416 upper. It’s also a highly effective process, in terms of OCD satisfaction:
The outer/inner fit of a PTW barrel assembly should not be loose. You don’t really want your inner moving about. Movement will affect accuracy, however marginal. Put a carbine inner inside a loose CQBR outer barrel and see what I mean. Regardless of proper shimming at the buffer tube cap to keep the hop itself square, the inner barrel flexes when the gun is fired. This is because the inner is not properly supported by the outer.
That’s why Systema does its very best to provide a well-fitting outer barrel. But SGT goes much, much further.
Tosh published some words about barrels on SGT’s Facebook page and an edited version is reproduced here.
“Obviously the outer/inner cannot be tight, but we try to make SGT’s barrels just right, to keep the inner barrel straight and snug. To make this happen, we use gundrilling to make a perfect outer barrel that will effectively keep groupings tighter by supporting the inner barrel properly and by keeping it straight.
Gundrilling is the same method used in RS barrel manufacturing. It is the best straight hole drilling technique and much more expensive than traditional twist drills. However, the most common technique used in airsoft barrel making is pipe lathed into barrel. This never achieves a straight hole. It’s also the cheapest method. Anything cheap, assume it has been made with the extruded pipe method.
Once our steel rod is gundrilled, we lathe to center the rod. Then we carry out the final cosmetic lathes. Since there are a number of processes to achieve an extremely precise milling, the cost of our barrels is extremely high. But, the expense of these processes turns into performance gains. Plus, you know you have one of the best engineered outer barrels in airsoft.
There are no bends in the reflection inside our gundrilled hole, so you know the barrel is straight without even using a caliper. With conventional twist drills, you will see milling marks. A pipe extrusion’s hole wall may be smoother than that of twist drilling, but the hole is not properly centred. Or, there will be bends in the reflections which tell you the hole is not straight. The process is not meant for barrel making, but for pipes which handle the flow of gas or liquids.”
“Gradation of light is uniform.”
“The wall is very smooth and minimal milling marks are visible. After parkerizing, these milling marks will be filled in.”
“The steel rod has been gundrilled, then centered and lathed to make sure the rod diameter is parallel to the hole. The rod is then lathed once again, to make it into an SGT barrel.”
“The gundrilling machine.”
Why choose steel for the outer barrel, though? Uptake of aluminium barrels only appears to be increasing.
“We choose steel over aluminum for various reasons.
The RS 416 uses steel (or stainless steel) barrels. And for airsoft applications, steel is also the best choice. Steel is stronger. It resists bending and is less affected by temperature. Our barrel will stay straight in all humanly habitable climatic conditions.
For example, the linear coefficient expansion rate of aluminum is 23.1 opposed to steel’s 11.8. Aluminium’s volumetric co-efficient is 69 as opposed to steel’s 34. In other words, our barrels are more dependable than aluminium barrels in every way.
Our outer barrel will keep your inner barrel straight and sound for a lifetime of use.”