open sighted Diana N-tec 350 hits low with heavy grain pellets

[David110]

Baracuda 21.14 grains and 5.50 head size, fits smoothly not loose but not tight at all.
H&N FTT 14.66 grains, 5.53, the head "clicks" in to fit then goes in smoothly not crazy tight but tight.

The shooting distance is 14 yards, handheld, sitting, 5 shots each.
I aimed only at the top target for both pellets, as you can see the barracudas shot about 4 to 5 inches low.

I don't have a chrono to check the digits but I made sure the seals are airtight with some caveman tests (half cocking, blocking the air chamber hole with my finger, waiting a few seconds and then feeling the negative/positive pressure cocking/decocking).
Also blowing in the barrel to do a breach seal test. everything is very airtight.

If I compensate those 5 inches my open sights get too loose.
What could be the problem? I was hoping that my magnum would love these heavy grain pellets.
Cheers.

[LAalex]

Going from ftt to cudas  is roughly a30% increase in weight.  I would give jsb 16 & 18 gr a chance.  21 gr is a lot to ask of a springer even a powerhouse like the 350.  Those ntec guns are nice I hope you will continue to update this post  as you shoot more

[David110]

A 5" drop from gravity in only 15 yards with a magnum? I don't think physics would allow this unless something is majorly wrong with the power plant of the rifle.
Unfortunately, JSB is non-existent where I live, I would have to look for inferior brands of pellets like Gamo or BSA to match what the gun can handle.
The gun feels amazing unscoped, I know a scope would allow me to go lower further with the proper droop mount. But I don't believe it had a droop, especially considering this is with iron sights.
Any other ideas?

[Yogi]

H&N FTT is what I shoot in my 340 N-tec.
You want the pellet to "click-in" and have a snug feel when loading....

-Y

[David110]

Yeah, I was describing the feel of pellet size 5.50 Baracuda vs 5.53 FTT in relation to my particular barrel in case it has something to do with the pellet throw? The barracudas weren't loose at all either.

[Yogi]

I think it is safe to safe that the 5.50 Barracuda is not the right pellet.

-Y

[subscriber]

David110,

Its not gravity causing the heavy pellets to drop so much more at such a short range.  It may be vibration harmonics, with the muzzle pointing down further when the heavy pellets emerge.  You can test that theory by attaching taping something with about the weight of a can of pellets tightly to the barrel just behind the front sight.  That may make the problem worse, which case you move the can back two inches and try again.

There are thread on this forum about muzzle weights.  Hector Median could probably give you much better advice than to "try something".  He has made muzzle weight that are screw adjustable for Diana Air rifles.

Before you do anything else, check to see if any of the stock screws are loose.  That is the most likely cause for point of impact problems.  How that might affect a heavy VS a light pellet I am not sure, except that it affects corrupted harmonics with extra motion of action in stock.

Is the pellet seating fully in the breech cone?  Load a few of the "low" type pellets, but open the breech again before shooting them.  Is there any evidence of the skirt making contact with the breech around the transfer port hole?  Addressing that is a separate matter.  It also raises a few more options n terms of possible ways to affect point of impact - including preventing the breech from fully closing, so the barrel points down.

[David110]

subscriber,
Exactly what I thought re. gravity. It's the spit pattern of the muzzle. I was going to test it tomorrow and hold the rifle gangster style on the side 😂 to see if the pellets still go down or if they go to the right.

When it was scoped I removed the front globe sight, the gun never amazed me with the scope, as soon as I put the open sight back I noticed it puts pellets inside the same hole more often and the group is tighter. I thought it was either the weight of the gun became easier to hold, or the weight of the front sight calmed down the nozzle.

I'll try the weight test you suggested.

And yes, pellets are seated all the way in and I make sure everything is tight after each shooting session, so that's not a problem.

[subscriber]

I was going to test it tomorrow and hold the rifle gangster style on the side 😂 to see if the pellets still go down or if they go to the right.

Brilliant.  Why didn't I think of that

[David110]

Confirmed. The side hold made the pellet fly to the right.
Next, I'll test the cudas with a different head size, I think the shop has the match in 5.52 or 3.
I hope that works because I really don't want to add anything to the gun like a muzzle weight.

[subscriber]

That simple test is telling, David.

Tuned muzzle mass harmonic devices are not that complicated.  I remember posts on this forum by Hector Medina specifically for Diana (RWS) models, and am still looking:  Meanwhile I found pertinent info on spring airgun harmonics:  https://www.ctcustomairguns.com/hectors-airgun-blog/truly-taming-the-harmonics-in-spring-piston-airguns

A lot more discussion at the links below.

Springer barrel vibration:




https://www.gatewaytoairguns.org/GTA/index.php?topic=134643.0





https://www.gatewaytoairguns.org/GTA/index.php?topic=111946.0

https://www.gatewaytoairguns.org/GTA/index.php?topic=12693.0

https://www.gatewaytoairguns.org/GTA/index.php?topic=12693.0

https://www.gatewaytoairguns.org/GTA/index.php?topic=121751.0

https://www.pyramydair.com/blog/2008/10/a-harmonic-tuning-muzzlebrake/


Scroll down:  https://airgunwarriors.com/community/postid/34428/

[David110]

What about sleeving the barrel with a carbon fiber tube, does this help? I'm trying to think of available/easy fixes first. The weights probably can't be shipped here without a firearms license.

[subscriber]

What about sleeving the barrel with a carbon fiber tube, does this help?

Absolutely.  Anything you do to alter the vibration can make it better.  However, it can also make it worse.  Generally, the stiffer the barrel the higher it resonant frequency, and the smaller the vibrational amplitude.

Some of the thread links above include carbon fiber sleeving, although a search specifically for that will show tensioned sleeve barrels - the holy grail.  Will find some and post links to that...

[subscriber]

A barrel weight is easier to apply and easier to remove;

but here is plenty of carbon fiber barrel sleeve info and discussion:

https://www.gatewaytoairguns.org/GTA/index.php?topic=80600.0

https://www.gatewaytoairguns.org/GTA/index.php?topic=71756.msg683790#msg683790

https://www.gatewaytoairguns.org/GTA/index.php?topic=83403.0

https://www.gatewaytoairguns.org/GTA/index.php?topic=154337.0

https://www.gatewaytoairguns.org/GTA/index.php?topic=174653.0

https://www.gatewaytoairguns.org/GTA/index.php?topic=68666.0


https://www.google.com/search?q=site%3Awww.gatewaytoairguns.org+carbon+fiber+sleeving&tbm=isch&ved=2ahUKEwi_xJv83qHrAhWrAzQIHZy8DkYQ2-cCegQIABAA&oq=site%3Awww.gatewaytoairguns.org+carbon+fiber+sleeving&gs_lcp=CgNpbWcQA1CRYVivkAFg2ZUBaABwAHgBgAG6AYgB6QySAQQyMC4xmAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=SDU6X7-AFKuH0PEPnPm6sAQ&bih=533&biw=1117&rlz=1C1NDCM_enUS793US793

[David110]

Thanks, subscriber, this is a wealth of info and a lot to play with. I'll update as I figure it out.

[HectorMedina]

Baracuda 21.14 grains and 5.50 head size, fits smoothly not loose but not tight at all.
H&N FTT 14.66 grains, 5.53, the head "clicks" in to fit then goes in smoothly not crazy tight but tight.

The shooting distance is 14 yards, handheld, sitting, 5 shots each.
I aimed only at the top target for both pellets, as you can see the barracudas shot about 4 to 5 inches low.

I don't have a chrono to check the digits but I made sure the seals are airtight with some caveman tests (half cocking, blocking the air chamber hole with my finger, waiting a few seconds and then feeling the negative/positive pressure cocking/decocking).
Also blowing in the barrel to do a breach seal test. everything is very airtight.

If I compensate those 5 inches my open sights get too loose.
What could be the problem? I was hoping that my magnum would love these heavy grain pellets.
Cheers.

Kia Ora!

David, DIANA barrels are usually on the large end for 0.177" but "tight" on the 0.22".
I would try a number of pellets, while JSB's are reilable, some guns do prefer Crosman, RWS's, and SOME H&N, in a "Night hunter" I am preparing (complete with night-vision optics), I am not having ANY luck with Baracudas, but the JSB's in lead and tin are one-holers, and the Crow Magnum's out to about 30 yards are good enough for hunting raccoon sized critters (about the size of your Possum).

¿Have you tried loading a Baracuda, then closing the barrel and then opening the breech again? That shot pattern seems to indicate skirt deformation upon closing the breech, as well as a breech that does not fully closes.

Besides, it really all depends WHAT you want to do with the gun, the task defines the projectile.

The 350 NTec has enough energy to make the real expanding pellets expand (Predators, CrowMags, Super H Points). Crosman HP's are not truly expanding pellets, but because of HOW they are made, they are usually more accurate than the domed heads. And, after all, a 0.22" hole is still an 0.22" hole.

Since the muzzle weight is, essentially, a hollow tube (in the case of the 350, it needs a bit of a design change), I don't see why it should be stopped at Customs. BUT a well made HT does need a completely cylindrical barrel and I am not sure yours is.
AFAIK piston airguns are not regulated in NZ, so accessories shouldn't be either. But the law may have changed since I was there in 2014.

Do the closing without firing test and let us know what happens.







HM

[dtdtdtdt]

A suggestion before you start making barrel weights, sleeves, harmonic stabilizers etc.

Wrap a length of solder around the end of the barrel to see what the impact on group size and position is. Tape it in place with painter's tape.  Shoot a couple groups, move it back a couple mm or so retake and try again.  Shoot a couple groups.  continue until you see something or not.

That way you won't get much invested until you know what's really going on. 

I have seen a picture of a national champion rifle shooter in the mid 1930s whose barrel was wrapped end to end with solder.  He couldn't get a heavy barrel rifle so worked out his own !!! He was a long-deceased member of my gun club.

I did some pellet tests a few years ago at 17yds in .177 and was surprised how much the groups moved around on the target depending on weight.  As you noted gravity shouldn't have that much impact at such a short range.  I found that the very heaviest pellets weren't tolerated by my rifle and gave much lower velocities that I anticipated.  As others have said, 21gr is pretty heavy for a springer - even a magnum like the 350. 

[David110]

Thanks for all that great info and suggestions guys.

Hector, what I want to achieve is long-range shots which is why I'm excited about the heavy grains. I'd prefer to tweak the gun to be more pellet friendly if I can rather than have to order specific pellets online. I live in the rural deep south.

What do you think about sleeving the barrel with a 2mm thick carbon fiber tube?     20mm OD X 16mm ID.

The pellet goes in deep enough, I don't think it touches the chamber end at all when closed.
I try to push them as far as I can to avoid deformation
Here is the after picture.

Can you send me the link to the muzzle weight you recommend?

[David110]

Here is the before pic just for reference.

[David110]

For comparison, this is the H&N FTT in 5.53, again the barracuda is 5.50. I think this shows the mark from the breech closing and this one shoots exactly where I put it. The 5.50 fits like butter (doesn't fall in but also not tight AT ALL) and the 5.53 FTT clicks in at first then goes in smoothly.