Barrel consistency & chokes

[HectorMedina]

Hector, would you be kind enough to share your fire-lapping process?  Why use tin pellets, rather than lead?  How do you know when you are done?  Gloss level, and/or subsequent grouping ability?

If the pellet head and skirt circumference are all that is loaded with grit, and you shoot them through a breech choked barrel, does that mean that the barrel stays mostly un-lapped between breechblock and muzzle choke?  Would you consider shooting a grit compound covered cleaning pellet that is backed up by a regular pellet to help for that?

Peter;

If I told you, I would have to kill you . . . .

;-)

J.K.!

It is a process I got to after years of testing and trying different methods. Once explained it is very "logical", but even after the discussions we've had here (where all the bits of information needed are spread here and there) it seems it is not that obvious. So, let's tackle the issue:

When you have a HUGE internal pressure, you can be sure that any "squeezing" suffered by a bullet while it is travelling down the barrel, will get pushed back as the pressure re-forms the bullet to obturate the bore. Even in the lowly 0.22" RF, unless you have a barrel substantially longer than 16" the pressure never drops enough to not re-obturate the barrel.
Airguns are completely different, especially spring-piston airguns.
In these there is not enough pressure to re-obturate, so you NEED a pellet with a little "spring" to it.
Pure tin is ALMOST as soft as lead, but not quite, and that small difference has proved to be important in my tests and work.

If you have a really bad barrel, and you try to fire-lap it with lead pellets (or even worse, felt pellets), then the dimensions of the bore may be such that you are emphasizing the differences in bore and land diameters, as the abrasive pellets may strike the constrictions a bit cock-eyed.
If you try the same thing with Tin pellets, then the pellet "springs back" just enough to remove the high spots evenly all around and along the bore/lands.
It is also important to keep, as much as possible the SHAPE of the rifling, felt pellets and lead pellets tend to "round off" the rifling.

I control the process by pushing lead pellets through with a cleaning rod. Sometimes a flexible cleaning rod.

When I feel a smooth passage, it is done.

It rarely takes more than 15 valve-grinding compound loaded pellets (rolled between two steel plates that hold the abrasive), to do the job, usually, it is done by the 7th.

For ACCURACY:
It is not about the finish, it is about the dimensions.

Now, fire-lapping for LEADING, is a different story.

;-)

HTH, keep well and shoot straight!






HM

[subscriber]

Thanks, Hector

[GS2]

I know this is old. But for anyone who is looking into barrel consistency or lapping. I removed the “Breech choke” on my D34 by lapping it. The gun now has smaller groups. Extreme spreads were also reduced. When slugging the barrel now the pellet no longer falls through the loose section that NCED describes in his gun. What’s not to like.

[subscriber]

George,

Indeed, what is not to like?   I am curious to know if average velocities went up or down? 

[GS2]

Speed stayed pretty much the same, but ES, SD, and group size went down. I did loosen it up a little more, (more lapping) just waiting for better weather. Still a much shorter loose spot just before muzzle.

[HectorMedina]

I know this is old. But for anyone who is looking into barrel consistency or lapping. I removed the “Breech choke” on my D34 by lapping it. The gun now has smaller groups. Extreme spreads were also reduced. When slugging the barrel now the pellet no longer falls through the loose section that NCED describes in his gun. What’s not to like.

Thanks, George.

Steve Herr has done pretty much the same exercise in fixed barrel guns with the same results.

Food for thought.

THANKS again.



HM

[SpringerGuy]

Guys

Great to learn so much information on airguns for us beginners. I am going to swage a pellet thru my Sabaka Japanese BSA clone. 

It is a perfect air rifle for this test.  Recently I obtained a Sabaka Japanese BSA clone that shoots 4.4mm pellets or darts but a .177 pellet will bind.  Seller told me it needed seals when it just needed
the correct size pellet.

[GS2]

Thanks Hector, I looked up Steve and found the write up on Connecticut custom Airguns about his dive into the D 54. Excellent work on the gun and the write up. I found this the most interesting, “The two things that had the most impact on getting rid of the fliers were the breech lapping and the front sled modification, with the front sled modification having the most impact overall. My D 34 doesn’t have the Sled. Steve also mentioned that the Breech constriction is a common “ problem” with breakbarrels. I agree. But it can be fixed!

[GS2]

If manufacturers pressed the barrel into the Breech block before pulling the rifling button through, we wouldn’t have this problem, and  barrels would be better.

[nervoustrigger]

Possibly.  The amount of interference with the button is pretty important, so forcing it through a constriction may produce bad surface quality and/or shatter the button.

[GS2]

I thought it would be more of a cost factor. We are only talking a few thousands of an inch, But if depth of cut and / or hardness of barrel matter I understand.

[HectorMedina]

Guys

Great to learn so much information on airguns for us beginners. I am going to swage a pellet thru my Sabaka Japanese BSA clone. 

It is a perfect air rifle for this test.  Recently I obtained a Sabaka Japanese BSA clone that shoots 4.4mm pellets or darts but a .177 pellet will bind.  Seller told me it needed seals when it just needed
the correct size pellet.

Is it SABAKA or SAKABA?
Markings are supposed to be SKB
It seems they made some copies of other airguns.
Would you be so kind as to start another thread and post some pictures?

BTW, H&N makes 4.4 round shot for the German Kirkmesse rifles (DIANA NEO and DIANA Oktoberfest), so you may want to experiment with that. If it has a rifled barrel, you can also try the H&N Excite Do NOT use BB's or DustDevils. They may damage the rifling (if there is one).


THANKS!




HM

[SpringerGuy]

Forrest

Thank you for choke write up.  I took your advice and pushed a pellet thru my barrel.  The rifle was an old Japanese Diana clone   "Sabaka" and it appears choked at the first 4 inch of the breech end. Is this unusual?  I started with the air guns just a few years ago so not really experienced.  Different for the powder burners I started collecting them 45 years ago and worked as a gunsmith for the US Army. 
 Headed down to your world going to Naple FL, I think that is in Broward county?  If it close we could do some shooting if you are free.

Randy