Monday, June 23, 2014

Ported Barrel Observations

Recently, following a nice stock class game, a rather unorthodox idea crossed my mind: A sniper rifle for that class of games.

No, not a loser rifle, you dummy. Grow up and have fun with the game already.

Also, not technically "stock class"... Not quite.

I was inspired by the blog of a paintball sniper. The concept was simple. A single-shot breechloading pneumatic. Accuracy-oriented. A rigidly mounted barrel, muzzle blast reduction strategies, consistent velocities, provision for sights, you know the drill. We know darts have the potential to be quite accurate, I just wanted to push toward that direction with some deliberate effort.

And, I still will, in the future... With stefans, of course. Where the "stock class" part of this concept came in was that it was going to be a .62 caliber and shoot slightly modified Nerf sonic micros. The mod was a wrap of 33 tape on the tip, to cut friction on the bore and improve the gas seal. Wasn't going to fill domes with anything. At that point, it ain't no freakin stock class. May as well just shoot a stefan at the guy. As if my planned 250-350fps was going to fly, but the idea was deliberate low ROF used only from range and with restraint. After all, assault rifles would wreck me bad up close.


So, as a first step of proving the projectile itself capable of accuracy, I pulled out an old UMB (No OPV, before someone comments), cleaned and lubed it, got the chrono, made a starting test set of barrels from a nice stick of Charlotte Pipe 1/2" PVC, crowned and cleaned all of them, 33 taped me a set of micros to a perfect fit, and started slinging them at various velocities over the house at Site B and into a tree to observe stability. These should be about 1.4, 1.5g by the way. Keep that in mind for the chrono data later, this rig had some energy.

I was having problems with my solid test barrels shooting wild at as low as 240fps that I suspected were muzzle blast. The logical next step was to add some blast mitigation and see where that got me... So this happened.


This is an 18" barrel. I patterned my porting after the Smart Parts patent. Eyeballed dimensions: porting starting 1/4" from the muzzle, about 4" ported length. Double helix pattern, 5/32" hole diameter, 17 holes x 2 rows.

And a shot down the bore.


I then proceeded to chrono this before I shot it for comparison. In addition to proving the projectile, and this time giving it a de-blasted test, I was testing out ported barrels. Lots of myth has surrounded them in nerf. Some would call them strictly a velocity nerfing device used to make OP guns not OP, and run hoppers in CQB events, and the like. But is this the case? Would porting a barrel used to fire a dart, rather than a paintball, cause a huge unheard-of efficiency problem?


The results regarding the 33-taped sonic micro projectile: Still fails, at least after a few shots and recoveries worth of wear it is not going to hit the side of a school bus at 250fps and 70 feet plus. Stock Class First Strike it ain't. It acts like a damn elite. Well, too bad. I wanted that to succeed. I guess there is a limit to micro stability.

But the ported barrel?

Now, the solid length (i.e. the active bore, before the porting releases the pressure behind the projectile) of this barrel is about 1/2" longer than my 14" solid barrel (which is actually a little under 14") that was in here, so note the italic figures. Chrono session, zero attention to statistical integrity due to sheer number of configurations and impatience but it gets the message across, units of feet per second:

18" Solid - 5 pumps:
246.2
250.1
251.7
255.7
246.5
248.0
245.3
244.6
247.0
237.7

18" Solid - 7 pumps:
288.0
278.7
252.4
277.9
280.3

18" Solid - 9 pumps:
320.9
300.1
311.0
296.8
314.7

24" Solid - 5 pumps:
243.6
241.0
225.6
231.6

24" Solid - 7 pumps:
298.3
289.3
284.8
274.9
293.6

24" Solid - 9 pumps:
308.4
325.0
323.0
320.5
332.2

14" Solid - 7 pumps:
229.7
231.6
234.9
239.2
219.4

14" Solid - 9 pumps:
250.9
261.4
243.5

18" Ported - 7 pumps:
249.4
233.2
232.2
233.7

18" Ported - 9 pumps:
257.5
247.3
266.8
270.3


Well isn't that somethin'. With only 1/2" more accelerative length and almost 4" of what should have been nothing but velocity-killing drag tacked on the end according to the typical ideas of barrel porting in nerf, the 18" ported still hung right with, or maybe beat, the 14" solid efficiency.

This is yet to be tested with projectiles having a PE foam barrel-sealing component like a stefan does, but my micros mostly had a rather tight fit in the barrel, and the results I suspect would be similar. Exception may be super tight underbores, which means, spring guns with cylindricals (...should be stepped up and then ported...) but overall, I suggest you try a ported barrel if you are doing the high-velocity thing. It has promise. I will note that the porting definitely reduced blast and I would say, visibly reduced oscillation of the projectile near the muzzle, but then again I have no highspeed of that for ya. Less blast is better, that's not really disputable.

My project is still alive and back-burnered but it will probably not be of mainstream game use.

[Edit 04-24-14 In the paragraph describing the porting, "4 rows" was incorrect, this is "2 rows"]

1 comment:

  1. What is the point of those holes?

    ReplyDelete