My Diana 54 .177 is giving extremely erratic velocity (up to 130fps ES). I have read a couple of people write about the "breech seal" but I am not exactly sure were too look and what to look for. I opened my gun this weekend and did not see anything that looked fishy so I closed her up again.
What can cause this? Will deviations in pellet size be the cause of this or the breech seal? I lately use unsorted H&N Baracudas (kodiaks) and found that some of the pellets went in easily and other with great difficulty and accuracy is not what it used to be.Previously I used sorted Baracuddas Match (4,50mm) and never had a problem with accuracy but they have become unavailable here in South Africa for the time being.
I want to test other pellets and see if the velocity remains erratic but I dont have a chrono and the gent who let me borrow is is overseas.Any ideas?
How is the tension on the rail system? Is the setscrew loose? Has the barrel been clean in the last 500 shots or so? I would have guessed the spring is broken for sure but since you have checked it and it is fine, I'm not to sure what it could be. You could pull the front sight off and put a little suction on the muzzle of the barrel to see if your breech seal is holding pressure.
When I opened her up the spring wasnt broken nor was there any visible damage to any parts,the spring was slightly bent but i dont know if it is shorter cause i have nothing to compare it with. Does someone have the length of a new sping? I was a bit dissapointed that the plastic guide had such a loose fit inside the spring,I can now SEE why a maccari or custom guide will make a big difference. I will try what you said,thanks.
I used to clean the barrel every 2000 or so pellets (when I felt like it) but before we chronied the gun we gave the barrel a decent cleaning and I was really shocked at the amount of gunk/lead that came out the barrel and this was with super shiny H&N Baracudas (Beeman Kodiaks).
When i chronied the gun with the gent we used "dry"pellets with a huge(130fps ES) and Napier power Lube pellet lube which increased velocity slightly as well as consistency, at this point the gun was shooting about 16fpe then we tried a thick lube called LP10, I think this lube detonated(even though there wasnt any evidence of that)because velocity steadily increased shot-to-shot from 830fps (16,30fpe) up to a max of 970fps (22,25fpe) with the heavy baracudas over a string of 15 pellets. Any explanation?
If accuracy is still good, I would say the chronograph you were using might have been giving bad readings. A 130 fps spread over shots would give you much bigger groups than normal. Could be caused by the lighting? Just a thought.
Regarding accuracy what happens is the following: there will be two or three shots that lands on each other and then for no apparent reason there would be a couple of fliers opening up the groups. At 20-30m this is not a problem but moving to 50m and FT this is a big problem. I am hoping to shoot some JSB & Air Arms over a chrony on Friday then I will know for sure if it is the pellets or the gun,I really hope it is not the gun!
I had the same experience.
Some time ago I bought different tins of RWS R10 heavy in different diameter.
In my HW97K, the 4.48mm were very erratic (as in your gun)
Changing to 4.5mm improved the results significantly and ES was now 7 f/s.
So it might be an idea to try some different pellets.
I do not have a Diana 54 but do have the Diana 46E .22. It is a very accurate rifle. Fact my most accurate. I have a Chrony so am able to take many readings. I have several rifles both .177 and .22, different makes and to restate the 46E is the most accurate and able to get a bullseye with almost any quality pellet, even mixing them up during a single shooting. OH,the hopeless one is the China Dome .22, all over the place. I record the standard deviation (SD) as the ES is usually very much higher. An example of one of the better sessions the SD was from 18.0 to 0.0. The 18.0 being the Copperhead Wadcutter and the 0.0 being the JSB Exact Dome. But better deviation does not give you a better score, that is bullseye for higher numbers. Overall with all my rifles it is the Gamo Hunter that shoots the best. That is overall now, as it does not seem to have any fliers. But as you have heard before, each rifle has it's favorites. Hope this helps. To tell you the truth, I don't worry about it, just look for the tightest group and let that be your choice.
F Nash
My erratic velocity mystery has been solved.
The solution?
I just brought other pellets!
I brought the Crosman premier 10.5gr's and they work beatifully,I might have just had a bad batch of H&N Baracuda's. Hope to confirm this as soon as the H&N Bracuda Match 4.50mm becomes available again.I am ecstatic that there is not a problem witht the gun! Hope to kick some butt at this weekends HFT.
Thanks for the advice guys
It is amazing what .5 (half-a-grain) in pellet weight can do.
When I was searching for the best pellet (.177 cal.) for my Diana Mod. 27, I tried everything from 7.9 grains (Crosman Copperheads) to H&N Silver Points (11.1 grains). The H&N Baracuda @ 10.1 grains (4.50mm) turned out to shoot best in all weather conditions. The Baracudas prevent the 27 from making a lot of noise, the time lag is just right and the rifle feels more pleasant to shoot with the correct weight up front the transfer port. The air compresses well and the pellet rsists the air rush just so. No more or less is desirable.
Not that the other pellets didn't hold their own, as the Diana 27 is not pellet fuzzy, but for long range (30-50 meters) accuracy, the Baracudas improved dramatically the rifle's performance, which can only mean one thing: the preferred pellet weight for my 1970-vintage D27 is 10.1 grains.
Crosman Premier 10.5 (Die #2) didn't shoot better that H&N Baracudas, no matter what I did. So, I went out and ordered 2K, which sit comfortably by my trusty (Maccari-tuned) D27.