The SAGA of a DIANA 56 T/H

[HectorMedina]

https://www.ctcustomairguns.com/hectors-airgun-blog/the-saga-of-a-56-th

A four part, in-depth, study of the two current "philosophies" in powerplant design.

Guest blog by our own Steve Herr.

Hope you enjoy!







HM

[Motorhead]

Yup ... factory Crowning is seldom ideal and attention to such details can make or break an otherwise excellent tuning effort.

[prosportfan]

Hector how much does something like that cost to do?

[HectorMedina]

Hector how much does something like that cost to do?

Jay;

If you mean the re-crowning, it usually is part of all the "barrel work" in a tune and costs about $75

Most of the times we are not faced with the need to remove almost 1/8" off the muzzle
This was a very particular case that needed a LOT of work.
IF you have such a lop-sided crown you may need to pay up to $150, it's simply the time it takes to get everything setup and squared properly.

Hope this answers your question.

Keep well and shoot straight!




HM

[wahoowad]

Mine in .22 shoots pretty darn good but still going to inspect that crown. Where are my glasses?

[prosportfan]

Hector how much does something like that cost to do?

Jay;

If you mean the re-crowning, it usually is part of all the "barrel work" in a tune and costs about $75

Most of the times we are not faced with the need to remove almost 1/8" off the muzzle
This was a very particular case that needed a LOT of work.
IF you have such a lop-sided crown you may need to pay up to $150, it's simply the time it takes to get everything setup and squared properly.

Hope this answers your question.

Keep well and shoot straight!




HM

That's still a good price Hector. I never seen a price list nor what is all involved in it.

[Nitrocrushr]

Mine in .22 shoots pretty darn good but still going to inspect that crown. Where are my glasses?

Or if you’re like me.....glasses AND magnifying glass😁

[fwbsport]

I had been visiting Fowler's Gun Room in Orange, CA where I started my parish ministry back then.  I saw an High Standard .22 Match pistol brand new for sale and examined the muzzle which clearly showed more barrel on the right than the left like an extension problem there.  To me I had thought the handgun wouldn't shoot inaccurately since the same exit (damaged crown or misdrilled crown) touched the bullet the same way out the barrel.  I didn't get that Match gun because something in my head was telling me an imperfect crown is NOT a good thing even though I didn't know why technically.

So now I see this detailed example on a crown needing repair and thank Hector for showing it.   

[Mossonarock]

Wonderful! I've been waiting for this update. I'm eager to learn what y'all learned and did. Although no one seemed interested in responding to my post about removing the cocking bracket from my D56, doing so really helped tighten up the groups on my rifle. However, I haven't given the crown much attention. Removing the cocking bracket smoothed out the recoil so much that now, through the scope, I can watch the pellet fly all the way to impact. Really cool! I really wish there was something that can be done about the lateral rocking from the slide rails but I don't think those brackets that hold the rails are removable from the rifle's action. On the rear rail bracket, one of the holes for the rail is too big. The holes in the slides are fine. I've rotated the rails around to be sure that the rails themselves aren't different sizes. Its the bracket, not the slide or the rail.

Could a regular PB gunsmith recrown an airgun? I'd rather bring my rifle to a local gunsmith than to mail it off but what ever is best. I can lap a crown but I can't cut one square if needed.

Can't wait to read about the rest of the story!

[HectorMedina]

Wonderful! I've been waiting for this update. I'm eager to learn what y'all learned and did. Although no one seemed interested in responding to my post about removing the cocking bracket from my D56, doing so really helped tighten up the groups on my rifle. However, I haven't given the crown much attention. Removing the cocking bracket smoothed out the recoil so much that now, through the scope, I can watch the pellet fly all the way to impact. Really cool! I really wish there was something that can be done about the lateral rocking from the slide rails but I don't think those brackets that hold the rails are removable from the rifle's action. On the rear rail bracket, one of the holes for the rail is too big. The holes in the slides are fine. I've rotated the rails around to be sure that the rails themselves aren't different sizes. Its the bracket, not the slide or the rail.

Could a regular PB gunsmith recrown an airgun? I'd rather bring my rifle to a local gunsmith than to mail it off but what ever is best. I can lap a crown but I can't cut one square if needed.

Can't wait to read about the rest of the story!

It's quite normal to be able to see the pellet fly to the target in a 54 or a 56 as long as the lighting conditions are good. It would seem to me that your "fin" was creating some problem with the action as it slid.

You CAN ream and replace the pins/rails by the next following size, you just need to be extra careful not to disalign anything.
I've also seen guns where the proper metric size pins were substituted and the SAE "equivalents" proved to be similar, but not the same. The bronze sleds are fairly easy to ream out to the next size.
It is important to note that there is NO CONTACT between the slides and the bracket's bottoms, except for the balls that the slides have. So, while polishing these surfaces can look good, the balls themselves will polish with use the channels that need polishing. Just a question of shooting enough your gun.

Firearms gunsmiths CAN recrown airgun barrels if they are extra careful and follow your instructions. Make sure you find out how they re-crown barrels because you cannot take the barrel out of the action, as in a lot of PB's. So they will need a lathe with at least 1.5 " hole through spindle, or they will need to build a special jig. If lathe turned, ask for a dished Match Crown, look carefully at this crown:



If they use handtools, then make sure they will turn a brass (not bronze and not steel) pilot to the specific internal diameter of your lands at the choke, and that they will cut an 11 degree crown with a flat dish at least 1/3 of the surface to protect it.

Airguns need special crowns because of the shape of the most common projectile and the slow velocity of the pellet in relation to the propelling pressure wave.

HTH






HM

[wahoowad]

I'm curious the thinking that the muzzle weight is too heavy. It is substantial, no doubt about that, but seems to add to the balance of what is a heavy gun.

[HectorMedina]

I'm curious the thinking that the muzzle weight is too heavy. It is substantial, no doubt about that, but seems to add to the balance of what is a heavy gun.

You are right in the sense that the T/H stock has more wood at the rear. So, yes, in a way, it "balances".

BUT it is a bit too heavy for the attachment system chosen, AND it is not adjustable.

Unless you are like Steve, that tunes the MV to the pellet without any power constraints, you really need something else.

BUT, that is another chapter  ;-)








HM

[Yogi]

[
Airguns need special crowns because of the shape of the most common projectile and the slow velocity of the pellet in relation to the propelling pressure wave.

HTH

HM

Hector,

If the pellet leaves the barrel at 800 fps, what is the approximate speed of the "propelling pressure wave"?

Thanks,

Yogi

[dan_house]

awaiting the rest of the installments.......

[HectorMedina]

awaiting the rest of the installments.......

Patience, my young grasshopper.

Allow Steve some time for fun!

;-)



HM

[Nitrocrushr]

awaiting the rest of the installments.......

I’ll try to finish the write-ups this weekend

Steve

[HectorMedina]

Hector,

If the pellet leaves the barrel at 800 fps, what is the approximate speed of the "propelling pressure wave"?

Thanks,

Yogi

Yogi

Point speeds have been measured, using Schlieren photography, to exceed the 1,100 fps.

Of course, as soon as the air escapes out of the barrel, the inertia of the atmospheric air is enough to create a "mushroom" that mushroom goes in front of the pellet as a highly turbulent flow.
Pellet has to travel through this "soup" unless some mechanical means are used to take the mushroom away from the pellet path.
That is the use of air strippers and well designed moderators.

When you use a FLAT crown (like the dished Match I showed), you are introducing a normal, initial angle to the mushroom, and so the spread is maximized, and the length is minimized. However, it is not reliable to cut flat crowns with hand tools, so the 11 degree crown is the maximum rake you should use in airguns. All our limited run guns had a Flat Dished Match crown put in the barrel by L-W.

Factories IN GENERAL, use a 30 to 45 degrees cutter with a flat face cut for the barrel, cheap, fast and easy. That is good for plinking, but not for high performance guns.

Hope this clarifies the idea.

Keep well and shoot straight!







HM

[Yogi]

Thank you , it does!

I knew that the "mushroom blast" got to the sides of the pellet, I did not know that it got in front of the pellet too.

Would a ported barrel help?

-Y

[fwbsport]

Thank you , it does!

I knew that the "mushroom blast" got to the sides of the pellet, I did not know that it got in front of the pellet too.

Would a ported barrel help?

-Y

I think this is why my HW80K .22 is supremely accurate compared to my other HW80s.

[HectorMedina]

Yogi and John;

Yes and yes.

Problem with airguns when trying to port a barrel is that the pellet''s skirt is STILL under a bit of pressure when it reaches the muzzle. Lead shaving is a very real possibility unless the porting is done with EDM and a VERY slight FORWARD rake. This reduces the pressure behind the skirt before the skirt hits the next leading edge.
Sophisticated airguns have two or three ports with varying degrees of rake, from zero on the first to about 5 degrees on the 3rd.
Of course we are talking of $2-3k airguns.

The "can", if properly designed, will reduce the turbulence in front of the pellet and also act as a harmonics tuner. Especially the English Non-Reflex typical design that uses two or more springs. It is "supremely accurate" within offhand shooting parameters, but it cannot compete under supported shooting competition. Not that that matters to you, I am just laying out my findings for everyone here.

Keep well and shoot straight!





HM