Barrel Wizardy .... Making a "Reverse" smooth twist type barrel

[Motorhead]

Measuring my barrel twist rate at 18", I assume it is actually 17.7" as per LW.

With a MV of 750 fps I get 30,508 RPM at the muzzle using the above formula.

After marking a pellet with a RED Sharpie, I got nice clear marks on the two targets and could accurately measure the rotation at one turn in 16.3". Assuming a velocity of 700 fps at the targets, I get 30,920 RPM at the targets. Which is well within experimental variation, as the two numbers should be the same. So this very simple method for measuring spin rate actually seems to work.

Great way to test spin without a doubt ..... Thinking about it however am incline to think the SMOOTH BORE is going to remove any such markings/ ink etc from the pellet that would or could leave a mark on a paper target as it passed threw ?

At this juncture will leave the deeper engineering on the side lines and take RESULTS be them positive or negative to this project. I have no more smooth bore barrels or a willingness to cut down good rifled barrels in changing the spin rate .... This project is going to stand alone on this ONE barrel cobbled together.

* hope to get on paper today, tho it is raining and rather breezy so that may get postponed ... but we're on it ASAP.



Scott

 

[Michigander]

The mark seems to come from the nose as it pushes through the paper, and that part shouldn't rub off in the barrel. But sure, whatever works. You can always explain why it works later!

 

[Motorhead]

The mark seems to come from the nose as it pushes through the paper, and that part shouldn't rub off in the barrel. But sure, whatever works. You can always explain why it works later!

Ah .. missed that, like a hand of a clock, just on the head of pellet. Excellent

 

[Motorhead]

Well the rains stopped and wind laid down this morning. Paper target stand set out at 100 yards, few sighters to tweak the scope back to a rough zero and we're off to the races !!
Using the JSB BEAST 16.2 grain pellet at @ 980 fps, shooting off bags on a table, this is 14 consecutive shots taken @ 5-8 seconds apart.


While NOT MOA accurate and sadly not as accurate as my other 19" LW conventional / choked barrel ( which does > 1 MOA ) it is not bad and seen a lot worse at this distance.
So it does work to a point but as noted on targets there are tell tail signs these pellets were DESTABILIZING showing signs of KEY HOLING with a few holes having lead smears in a slightly oblong created hole.

Next test was SLOWING THINGS DOWN while also trying some lighter pellets ( Ran the 16.2's down to @ 800 fps, 13.4's in @ 930's and 10.3's in @1040 ish ...... Things actually deteriorated and groups opened up dramatically

Not worth showing honestly.

SO WE'RE DONE ...... Have no parts and pieces I'm willing to chop up for variations of rifled to smooth ratios ..... This was fun, was bored and now off to do something else.

 

[Michigander]

Thanks for taking us along on your experiment. I enjoyed following.

 

[GeneT]

Thanks for taking us along on your experiment. I enjoyed following.

+1. It's hard to draw conclusions from a single barrel. I do think the results of the empirical rpm measurement would be interesting if you're willing to do them.

GsT

 

[John "spysir" Blount]

Good clean fun. Thanks for sharing.



John

 

[tor47]

Interesting experiment. Got me thinking a litle of how friction work. From my engineering background we learned that moving friction is less than static friction. As soon a the static friction is overcome (tires on your car on snow), and the same object start to slid, the friction becomes less (that is why you easy can loose control of you car). If we for example assemble our pcp`s, many have probably discoverd that if we twist objects sideways while pushing them forward (pushing an endcap with tight o-rings into the tube), the friction will be less than simply pushing it straight in. When the pellet are moving forward in smooth barrel, the forward movement should probably lessen sideways friction also compared to if the pellet had to start from zero velocity.