Barrel extension...

[Jim Holmgren]

I got this stupid idea that I thought I would share.

After reading the thread about Barrel lenght vs. fps suppressed, where a small fps increase could be seen with a suppressor, I wondered if one replaced the ldc for a smoothbore tube with same ID as the Groove diameter.

I know some muzzleloades have a short length of smoothbore at the muzzle for easier loading.

But what if we would take a smooth bore barrel and thread it after the "real" barrel for a fps increase?

So lets say we have a 18" .25 cal barrel and take a 1/4 id seamless pipe of 10" length and thread it to it?

So what would happen with the accuracy in this case and would barrel rigidity matter for the smoothbore part as that part are not rifled so it would not have the same harmonics?

[rsterne]

Alignment would be critical, of course, to avoid any step that could shave the bullet.... I think you might be creating a node at the joint and end up with different harmonics.... and you would have to sight to whatever the direction the extension was pointing....

It would cease to be an LDC, but would be slightly quieter because the residual muzzle pressure would be less, just from the extra length for the expansion of the air.... I guess my question would be why?.... It could not be any better than just using a longer barrel of the same total length.... and could certainly introduce more variables.... ie problems....

Bob

[K.O.]

well how about we take a smooth bore barrel and add some rifling to strip thru at the end... like smooth twist.. but polygonal maybe..?

 

To much chance of uneven drag happening with the smooth after the rifling... I think the best you can do is an air stripper on the end of the barrel...

now if you can get it right you can also do a squeeze bore... with a round that was designed for it might get some accuracy...

https://en.wikipedia.org/wiki/Squeeze_bore


http://castboolits.gunloads.com/showthread.php?274296-Arthur-Langsford-22-17-squeeze-bore-chamber

[rsterne]

Let me take a guess here.... I don't think that the pressures we run have a hope of swaging a bullet down from .22 cal to .17 cal.... or even a fraction of that far.... Here is what happens to a 40 gr. .22LR bullet to swage it down to .172 cal.... and it ends up needing a 6" twist....



Smooth twist barrels end up with a fraction of the spin rate in the bullet that is machined (pressed) into the barrel.... I measured the angle of the mandrel from an FX video showing the process and calculated the twist rate at about 16".... but measurement of the rotation rate showed spin rates of about 1 turns in 13 FEET....

Bob

[HunterWhite]

Could it be that an extension SLIGHTLY larger than the bore could force the projectile  to be centered by the air compressing between the projectile and the extension?

[rsterne]

I don't think it works that way.... Once the bullet moves off center, the air would tend to rush into the gap, if anything pushing it along the other side of the smoothbore portion (as well as leaking past it)….

Bob

[K.O.]

Bob he did not mention Boolits and nor did I... but

What I was thinking was something like the 24.7g RWS Power Bolt and maybe even  could be done with the right Boolit along the lines of the power bolt...and maybe a taper bore rather than a sudden squeeze bore/choke...

and maybe .25 to .22 it is a .03 squeeze rather than a .048" squeeze...

Have a feeling lube and a polished barrel would be very important...

I think the biggest advantage is the ease it would allow .25 porting to be done...and you end when it comes to exterior ballistics with something with the B.C. of a Heavy .22... Boosting both fpe and sd/ff mix a touch...

[K.O.]

https://rws-munition.de/fileadmin/datasheets/rws-power-bolt-1-60-g.sports.en.pdf

[Jaycee]

I have a feeling this would be inviting problems, why not just install a longer barrel?

[rsterne]

You mentioned the.... Arthur Langsford 22-17 squeeze bore chamber.... which was designed to reform a 40 gr. .22LR bullet to .17 cal.... It would have to extrude the bullet roughly as per my drawing.... That is why I posted it, to show what is involved, how much the shape of the lead changes.... and offer my opinion that it is not possible with airgun pressures....

Bob

[K.O.]

Sorry Bob I thought I had the two more sentances type and they did not make it somehow... they said that Scott(Motorhead) had proved we can swage a .22 to .20 and still get accuracy... and that it to me seems it would be easier to swage a pellet or bullet like pellet than a 40g .22 Bullet...

Maybe it was a glitch cause I was using my old XP unit that day and it is having some probs here and there... need retired and need to use my windows 10 system... or maybe I had a glitch and just thought I typed what I was thinking..

I took me a while to get back cause I was trying to locate the article on the extruder barrels... I saved it as a couple JPGs

[K.O.]

I have a feeling this would be inviting problems, why not just install a longer barrel?

Well when you look at the Benchrest barrels they are short and have harmonic tuners for a reason..

The longer you make a barrel the heavier it needs to be to keep harmonics in check... also may be the efficincy gain could be worth it...

People are putting Aluminum tanks on Mrods to save weight... why not just use a smaller tank..  

Point is I am wondering if the gains would be worth the effort... and at what point...from .22 to 18 or .25 to .20 we could go from 270 to ..25 or .22 etc. ...

of course we would have to do it a different way than the Myra barrels we do not have the chamber pressure... but by the end of the barrel 100 fpe is 100 fpe... one starts with a hi temp hi pressure charge that cools quickly (powder) and the other(air) a cooler lower pressure charge that cools much less and falls in psi slower...

So muzzle pressure of 100 fpe air and 100 fpe  powder is going to be very close in a 19"-24" barrel...

I have read in many places it is around 750 psi with 40g standard velocity .22lr...  way down towards the bottom in this link is the heading PRESSURE CURVES... it has a chart illustrating such... 

http://www.varmintal.com/a22lr.htm

So yeah in the end just trying to wrap my head around just what we could do and how far it could be pushed... and at what point it would be worth the effort.. muzzle velocity,retained energy and drop gains were significant in the Myra barrels...

He found the cost in energy to swage .22 to .20 was 2.5% of the charge... 

  ? 

the L.W. .22 (and My clearance AT 44 long) are already swagging from about .22 to .215... CZ says their .22 lr are choked to .212

the question is could we design  a system (round and barrel) and retain accuracy..?   tall flat top pyramid bands..? tall skinny ranch doggy bands..   nose bore rides only at muzzle..?  or just something like a H&N Snipermag/JSB Monster .22 with .25 size head and skirt...

So a near 20% gain in velocity and 50% gain in energy  is what he got... and then the gains in drift and drop...


seem to me I need to figure out what we would gain just by

doing what Scott did but doing it some what abruptly at the end of the barrel... so in the barrel it has the lower sd of a 18g jsb and externally the sd of a .20 18g JSB just to get a rough estimate of the gains..?

or maybe  25.4g .25 to .22... and oops need to add form factor to external... just want to see as if it is possible...

[subscriber]

Jim,

 As soon as the pellet exits the rifled portion of the barrel, the typical pellet nose diameter would no longer be supported.  As the skirt diameter should still be supported in the groove diameter smooth tube, the typical pellet would cant over until the head OD met the smooth bore tube ID.  That would probably hurt accuracy a lot...

Now, if you can  find pellets with groove diameter heads, then the next question would be if any friction in the smooth bore section of the barrel would slow down pellet spin.  Slowing the spin may not matter much, if the long smoothbore section resulted in much lower muzzle pressure.  Lower muzzle pressure means less tendency for muzzle blast to flip  the pellet (or bump it off course).   The fact that FX Smooth Twist barrels work so well, shows how little (diabolo) pellet spin is actually required; when used in conjunction with an effective air stripper.

Of course, the smooth tube could sport a multitude of sub-caliber cross-holes near the forward section, that would act as an air stripper.  This air stripper could exist inside a shroud, if db reduction was a secondary goal.

Adding a smooth tube at groove diameter should be considered in conjunction with the question; is the rifled barrel chocked?  That may change the optimal inside diameter of the smooth tube.

If you can splice two tubes end to end; such there is no step, and with minimal angular mismatch; then how about splicing two rifled barrels?  If you do it right, your 20" rifled barrel just became a 40" barrel.  If you can't quite match the rifling lands at the barrel junction; perhaps deliberately indexing them land-to-groove would cause less disruption to the pellet.

All that said, the velocity gains from doubling air rifle barrel length is likely to disappoint you.  That is, unless you release twice as much air.  Even then, the aspect ratio of the combined barrel turns it into a rather poor flowing pipe, containing a mass of air in front (and behind) of the pellet (added inertia), that could weigh as much as the pellet.  In other words; great ideas may add some performance, providing you don't get too greedy in the implementation:  Long barrels whip a lot and are less accurate than shorter barrels of the same outside diameter.

As .22 LR ballistics were already brought up in this thread, this link shows the effect of barrel length on .22 rimfire velocity:  http://www.ballisticsbytheinch.com/22.html Scroll down.  It would appear than doubling a .22 LR barrel length would actually reduce the velocity...

[rsterne]

That is correct, long barrels add the most in performance only with longer dwell, and hence more air released by the valve.... If you have very short dwell, and hence only a small amount of air released, at some point adding barrel length will slow the pellet.... just like what happens in a .22LR....

Bob