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danielparrish
I had a chance to run down and shoot a couple of targets this evening. Knurled and un-knurled at 100 yards. I will say, that I am pushing the limits of this bullet with my barrel twist, which is 1-18. I think someone with a faster twist will have better results. The difference is not astounding but noticeable. I don’t normally shoot at 100 yards, especially with my .25 but thought it would be a great challenge for the 100 yard challenge on GTA. My final thoughts? I think if you are wanting to tighten the group for a particular bullet, its worth the try. The comment that bullets should be sized to the thousandth of an inch is spot on. But, this is a very cool way tighten the groups if it is not exactly spot on. I tried lite knurling, knurling only the back band and knurling the back band as well as the rear portion of the nose as the file rested on that part naturally. I got the best results on knurling both the nose and band with and aggressive knurling. Ymmv. So anyone trying this, please post your results. I’d love to see them. (there are two bullets in one hole on the top of the knurled target picture) That group is 1.1 inches.
danielparrish
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rsterne
I knurled these between two medium files. Light pressure, but making sure I got good definition. Laying a file on the table, I then laid one on top of the bullet and pushed the top file forward, effectively rolling the bullet between the files. I tried a light knurling but did not get the same results. As someone else has stated,(Michael aka knifemaker on gta) a checker file may do a better job at this. In casting, any imperfections or miscalculations is sizing, will throw off accuracy especially at longer distances. Also, not being able to slug my particular barrel from the breech I could not get an truly accurate measurement of my barrel lands and groves. I tested .251,.252,.253,.254 to see what gave me the best groups. I settled on .251 as the best over all grouping, but was still not satisfied with the consistency of the groups. I knurled 12 bullets and shot 3-6 shot groups at 100 yards all within an inch. It appears the knurling allows the bullet to fill the groves lightly and evenly, giving more consistent groups from shot to shot. Not having a perfect bullet sized to the correct thousandths, this was the best compromise. I would like to state that this is NOT my original idea, but rather, I saw an older post on GTA made by Mr. Bill G as to knurling swaged bullets. I could not remember where I saw it, and Mr. Sterne graciously reminded me where I had read this. Many thanks to Mr. Bill for the idea. Hopefully we will see him soon back in the air gun arena, swaging and knurling
.I think this idea may have merit for airguns, allowing bullets to work in the non-standardized barrels we have to deal with…. I’d love to see a knurling tool somewhat like the Corbin one, but with an adjustable stop so that you could set it and have every bullet come out to the same diameter / depth of knurling….
Bob
edmundgeer
So I gather your barrel still has the factory choke? I took mine (AF .25cal) this morning to the gunsmith where he will remove .75″ off the muzzle and re-crown. I am also having him lap, polish and slug the barrel for me. I slugged it myself with molten lead and found a pretty severe restriction about 3″ from the breech. Not sure if it is a tooling mark or what. Hopefully lapping the barrel will work it out. My best measurements are .253 lands and .255 Groove in front of the choke. The coke brought it down to .25 L and .253 G. The restriction is almost as bad as the choke as if you push a slug through the breech and then tap it through the restriction it is loose until it hits the choke. Should get it back by next week. I have some RS257’s 63gr slugs to test once I get the barrel back. it will be interesting if I get better groups than the 2.5″ 60 yard groups I was getting. If all goes well I plan on buying the 51gr mold.
rsterne
edmundgeer
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