Air Gun Home :: View topic - 18" and 24" .22 bbl comparison (13-XX)

Doc Sharptail · Member

My new 18" barrel came in from scopesandammo.com
I mounted it on one of my steel breeched 22-89's. It replaced a 14" bbl. The gain over that bbl was roughly 60 fps. My more pressing concern was how it stacks up against a 24" bbl on the same platform.

Here's some numbers- unaveraged. Both guns are set up for pump and dump with flat top pistons, lightened valve springs, and discovery hammer springs over compression spacers of my own make. Kudos to Bob (R Sterne) for the hammer spring suggestion.... Since time was limited for me, just one shot at each number of pumps. (That's still a lot of pumping)

18"@ 10 pumps- 538 fps >>> 24"@ 10 pumps- 546 fps

18"@ 15 pumps- 610 fps >>> 24"@ 15 pumps- 607 fps

18"@ 20 pumps- 639 fps >>> 24"@ 20 pumps-660 fps

18"@ 25 pumps- 617 fps >>> 24"@ 25 pumps- 667 fps

18"@ 30 pumps- 643 fps >>> 24"@ 30 pumps- 691 fps

18"@ 35 pumps- 662 fps >>> 24"@ 35 pumps- 698 fps

18"@ 40 pumps- 668 fps >>> 24"@ 40 pumps- 716 fps

18"@ 48 pumps-656 fps >>> 24"@ 48 pumps- 708 fps

All shot with Die #1 Crosman Field/Target domes, 14.3 gr.

Both guns start retaining air at 52 pumps. I arbitrarily made 48 pumps the cut-off because that's where velocity drop-off starts with both guns. I was getting a little too winded to include data for 45 pumps. Previous experience says the spread is only 5 or 6 fps, so I let it go at that.

I've read on various forums how an 18" bbl is the optimal length for a .22 cal. air rifle. It may be true, for those who can muster more power than I am able to. For the way things are set up for me, it looks like optimal may be around the 20" length- heck it might even be 19" Wink

At any rate, that 18" bbl does come close to the 24" in terms of performance. It all depends on how serious I want to get over 40-50 fps.

I have yet to test the new bbl for accuracy. I'll have more on that in a later post...

A pair of double deuces. 18" bbl at top, 24" bbl at bottom. That's the 14" bbl I took off below the guns..

Regards,

Doc Sharptail

Brutuz · Senior Member

Great results Doc.

My 2289g with 18" barrel does 633 fps @ 21 pumps, pump it more and it doesn't dump all air.

rsterne · Moderator

HI Doc....

I would analyze your results slightly differently.... Without more shots at each velocity it's difficult to be certain, but I think there is a clear trend for the 24" barrel to get better relative to the 18" as the velocity increases.... At 10 pumps the difference was less than 10 fps (and minus 3 at 15 pumps, probably an anomaly).... I would discard the 18" - 25 pump number, as it doesn't fit the velocity trend with increased pumps for that barrel (should be about 640ish).... At 30 pumps, the difference is 48 fps, at 35, it's 36 fps, back to 48 fps at 40 pumps, and up to 52 fps at 48 pumps....

Logically, this should be so.... If the 18" barrel can develop all the velocity that the air charge is capable of (say at 500 fps) then the 24" shouldn't be able to improve on it.... Once you are pumping three to four times that much, the extra air you are cramming into the valve is still expanding at a significant rate when the pellet reaches the end of the 18" barrel, while it's still accelerating the pellet in the 24"....

I personally think the idea of an "optimum barrel length" is flawed.... unless you are specifying other conditions (ie on CO2, or in a gun that shoots about 500 fps).... The more air you pack in the valve (or the more air you get that valve to dump), the longer the barrel you need to take advantage of that increase in expanding air....

Bob

Doc Sharptail · Member

Bob-

I'm in full agreement with you over the un-averaged results. A proper test session will probably take me the better part of a full day- which I don't have right now, between work, and small game season. I'm well aware of how skewed results can be, like I've posted are. That incomplete comparison took me 2 1/2 hrs to run. I'm pretty sure most of the discrepancies are due to the pellets. I've had some nasty fliers with them out of the 14" bbl, which to date has been my most accurate bbl. After the snow socks us in, Ill retest with 10 shot averages- sometime when I can give it the time it deserves.

There's supposed to be a reachable point with the 24" bbl where pellet drag will stop velocity increases- and the 18" bbl surpasses it in terms of velocity. My best guess is this occurs well above 1250 fps- which I won't reach with my limited valve volume and pressure. I'd need a different platform for that....

Interestingly enough, I found the front breech screw stripped on the 24" bbl gun. It still runs up enough to give the t.p. a proper seal- but I think this is where I'm getting a lot of my low temperature p.o.i. shifts. It will have to be drilled out and re-tapped for a larger screw- a time consuming job, if it's going to be done right. Now to chase down screws and find my taps...

Regards,

Doc Sharptail

rsterne · Moderator

I haven't taken the time to test every combination.... but my experience has shown that longer barrels (up to 24", the longest I tested) provide more velocity at the top end.... let's say when you are over 700 fps.... In the 500 fps range, the 24" is better than the 14", but I would doubt if it has much advantage over the 18" (talking 13XX or 22XX in .22 cal here).... Rolling Eyes

I think a lot of the "18 in. barrel is the optimum" chatter has come from 22XX's on CO2 where I can certainly see it.... Cool

Nice catch on the breech screw.... could easily be your POI shift problems....

Bob

Slavia · Moderator

rsterne · Moderator

I think you mean a 3mm metric screw, not 4mm.... the 0.5mm pitch is right, though....

Bob

Doc Sharptail · Member

I replaced it by drilling and tapping the hole to #6 x 40 TPI- The Weaver base screw I used is actually shorter than that tiny 4 X 48 TPI original. Turning the head down on the base screw was pretty time and labour intensive. This is the 2nd 13-XX of mine to get this treatment....

I wonder why Crosman went with such a p.o.s. set up for the front breech screw Crazy/Loopy

Regards,

Doc Sharptail