Diana 27 - Part 4
by B.B. Pelletier
Today, we'll look at velocity after fixing the Diana 27 breech with a new leather seal. Vince is our resident spring rifle expert, and he voiced some concern about the new seal being cut flush with the breech face. I admit to the same misgivings, but when I looked at other vintage breakbarrels, I've noticed they all look the same--a flush seal. And they all work well. I think maybe the leather acts in a dynamic way when hit with the high-pressure airflow from the transfer port. It moves to seal the breech.
At any rate, I tested the same pellets that were used in the failed velocity test before, so we have a direct before and after comparison.
Before the seal replacement, Wasps averaged 444 f.p.s. before oiling the piston seal and 225 f.p.s. after.
The Eley Wasp is not readily available anymore in the U.S., but I still have a few tins set aside for tests like this. It's very oversized for the .177 Diana breech. As a result, a considerable portion of the bottom of the skirt remains outside the breech. The Diana breech is cut on an angle; so when the pellet is seated, the bottom goes in last. The Wasp doesn't go in all the way. When the breech is closed, the pellet is actually damaged at this point.
Eley Wasp is a domed pellet that's large in both .177 and .22 calibers. It's not a premium pellet in price but does shoot surprisingly well in many guns.
Wasps are large and don't go into the barrel as deep as they should. Because the breech face is angled, this lip sticks out and gets damaged when the breech closes.
When the breech closed, it bent the lip of the skirt up. That's hard to see in this photo, but you can see where it smashed the side of the lip against the breech face. It actually did this on both sides of the skirt, but the field of view is so narrow that the opposite side is out of focus.
Because of that (I think) the velocity with Wasps was very erratic. They recorded several in the 588-620 f.p.s. range, but others went 242-269 f.p.s. I wondered about that and decided to seat them deeply in the bore with a ballpoint pen. That put them about 1/8" into the bore, where no skirt damage was possible. But it also delivered only the lower velocity range, and there was usually a spray of oil from the top of the breech. When I seated them just by finger pressure, there was no spray. Wasps don't seem to be a good pellet for this rifle.
The RWS Basic is a wadcutter that weighs 7 grains. Before the breech seal was replaced, they recorded an average of 475 f.p.s. when the piston seal was dry and 212 f.p.s. after it was oiled.
After the seal was replaced, they averaged 658 f.p.s., with a tight spread of 650-666 f.p.s. They fit the breech very well and may turn out to be a great pellet for this rifle.
Crosman Premier 7.9-grain pellets
Before breech seal replacement, light Crosman Premiers recorded 580 f.p.s. before oiling the piston seal and 321 f.p.s. after. After seal replacement, they recorded an average of 588 f.p.s. with a spread from 577 to 595. They're a very good fit in the breech and will possibly be another accurate pellet in this rifle. Notice that they came the closest to the after velocity before seal replacement. I'm not sure what that means, but it's worth noting.
RWS Superdomes seemed to be the least affected by oiling the former bad breech seal. They recorded 412 f.p.s. before oiling the piston seal and 393 f.p.s. after oiling.
After breech seal replacement, Superdomes averaged 591 f.p.s., with a range from 582 to 601. They fit the bore well and look like yet another candidate for an accurate pellet for this gun.
This breech seal replacement seems to have worked well. The rifle has all the power we expect from a Diana 27, and I note that much of the spring twang is now gone. That must mean the internals are in good shape.
The rifle has gone from average to excellent with just a breech seal replacement and a trigger adjustment. The next step is to pull it all apart and dive into the internals.
I'm currently under the gun on several deadlines, so the next report isn't going to happen soon. But I want you to hold me to it, because this is one rifle you will all want to see revealed.