GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: Methuselah on January 21, 2025, 07:00:14 PM
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Top two pics in this thread
https://www.gatewaytoairguns.org/GTA/index.php?topic=217262.msg156576531#msg156576531 (https://www.gatewaytoairguns.org/GTA/index.php?topic=217262.msg156576531#msg156576531)
The bolt on my newly acquired Benjamin 397PA has to be "coaxed" to load, and rodding to inspect verifies they are being damaged.
Does it look repairable, or does it look like someone tried and that's the problem?
If you've done leade work, please post a few pics! I've never tried to do this kind of work.
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Top two pics in this thread
https://www.gatewaytoairguns.org/GTA/index.php?topic=217262.msg156576531#msg156576531 (https://www.gatewaytoairguns.org/GTA/index.php?topic=217262.msg156576531#msg156576531)
The bolt on my newly acquired Benjamin 397PA has to be "coaxed" to load, and rodding to inspect verifies they are being damaged.
Does it look repairable, or does it look like someone tried and that's the problem?
If you've done leade work, please post a few pics! I've never tried to do this kind of work.
Wish I were more familiar with that model so my comments may not be valid. Port diameter into bore looks TOO LARGE to me. Like someone tried to drill/increase port size to increase muzzle energy. Some pellets may go through fine while others start to drop into the large port and get "shaved"? If over-drilled I don't know how to repair that.
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I've never seen anything like that. Wow.
There are ways to fill it in, though. An epoxy or JB weld filler, then gently machine/dremel/drill/sand it out back to specs. That's a tough one, though. Good luck!
Cheers,
J~
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Could you make a bushing for it, and use green loctite to secure it, to put it back to spec? The transfer port could be drilled to size after.
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Could you make a bushing for it, and use green loctite to secure it, to put it back to spec? The transfer port could be drilled to size after.
I'd like to know how to make a repair like this since the barrel and breech are soldered to the pump tube.
Pellet damage, as described here, is something I've struggled with for a long time. The way I address it is to point the muzzle straight down, drop the pellet into the chamber, then hold the gun upside down and close the bolt.
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Could you make a bushing for it, and use green loctite to secure it, to put it back to spec? The transfer port could be drilled to size after.
I'd like to know how to make a repair like this since the barrel and breech are soldered to the pump tube.
Pellet damage, as described here, is something I've struggled with for a long time. The way I address it is to point the muzzle straight down, drop the pellet into the chamber, then hold the gun upside down and close the bolt.
I tried that, really doesn't work very often. They hang at least in one spot more often than not.
Where I got it wasn't auction, so I'm considering contacting the company.
It could easily be beyond my skill level.
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It sounds like the pellet is hanging up on a burr, and removing it from a blind hole like the exhaust port is going to take special tools and skills.
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“I'd like to know how to make a repair like this since the barrel and breech are soldered to the pump tube.”
Piloted reamer or counterbore using the existing bore for guide bushing.
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“I'd like to know how to make a repair like this since the barrel and breech are soldered to the pump tube.”
Piloted reamer or counterbore using the existing bore for guide bushing.
A piloted reamer is a good idea but it would cost some $ to have one ground up. Since the breech is brass and softer that steel, I think I would start with a piece of 1/4" mild steel round stock and turn it down on a lathe so that it was a sliding fit in the chamber then very gently tap the rod and sheer the burr off.
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I can't picture what you two, John/Kieth, are describing but I suspect what you are describing as a burr issue is the rifling land? If that turns out to be the case could it be the transfer port is a bit oversized and there is no leade?
Also I was noticing I don't see Benjamin or any other name on it, strange.
Perhaps I need to take it apart and get a pic from where the bolt is (right now I don't know how it comes apart and have my Norica broken down on what I'm using for a working table).
I was hoping the pictures were enough for you experts to figure things out, there's two or three stops or transitions between inserting pellets and final closed bolt resting position.
I can probably insert 5 - 10, rodding each, and get some pics but bottom line is gun isn't accurate and I'm betting it's at least possibly connected to what I'm seeing in the pics of the transfer port and leade?
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Piloted counterbore available in different inch and metric diameters. Pilot is removable and can be made of a softer material than the bore so as not to cause wear during use. You would need access to a metal lathe to fabricate a new pilot. I bought a lot of mine on Ebay and 2nd hand stores.
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This from the other side, if it helps...
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I've never seen anything like that. Wow.
There are ways to fill it in, though. An epoxy or JB weld filler, then gently machine/dremel/drill/sand it out back to specs. That's a tough one, though. Good luck!
Cheers,
J~
Looks pretty ugly.
This looks to be your best / easiest option.
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Look at TimmyMacs comments in reply#4 in this thread https://www.gatewaytoairguns.org/GTA/index.php?topic=31208.0
With brass barrels it's even easier. I used a wooden dowel I bought at Walmart. Easier to shape and groove than metal rods. Pull the bolt out and go through the back of the receiver. Shape the wooden rod so it's like a sharpened pencil end. Cut a slot to hold the sandpaper. Insert the rod through the bolt hole (back end of receiver). Get it up where you need to smooth things out, and turn it by hand. Brass sands very easily.
The nice thing about leade work is it's not as critical as crown work. With the crown, that's the last place your pellet has contact with the barrel. With the leade, you just want a smooth transition so you don't gouge up your pellets. Once they're past the leade, the rifling will do it's thing to make them fly true.
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Thank you Randy, great link. I'm somewhat skittish but may try the dowel. There was lengthy discussion on size and grit, what would you suggested for start and end grit?
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I used the split dowel / sandpaper method as well. I don't recall the grit that I used, but my guess is it could have been 400grit (smoother vs coarser would simply take longer and leave a nicer finish). I'm sure I did some of the work with CW rotation and some as CCW. I did polish with jb bore paste afterwards and used it to remove the paint from the loading ramp on the breech opening also. Use care not to enlarge the transition from the breech into the leade as the o-ring on the bolt probe needs to have the proper squeeze in order to seal properly.
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I think I used 220, then 320. I went both clockwise and counter. It does NOT take much. You do NOT need to use a drill or dremel. When you're spinning the dowel by hand you only get about a half turn with each spin before you have to re-grip the dowel. I bet I only gave it 10 or 15 half-spins before going the other way (counter clockwise). You have to pull the dowel out and wrap the sandpaper in the opposite direction to go CCW.
Just do enough to smooth out those grooves by the transfer port, and taper that vertical ledge going up to the lands.
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They only problem with this fix, being as the transfer port, judging by the pictures, is oversized to the point where it is almost the bore size.
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They only problem with this fix, being as the transfer port, judging by the pictures, is oversized to the point where it is almost the bore size.
I was concerned about that but being this is my first Benjamin pumper (Benjamin anything!) I have nothing to compare against.
I'd love to see some pics like the ones I posted of these 392/397 transfer port areas but all my searches turned up very little.
Going from mine and the one in this thread posted by Eric, the mating hole drilled up into the barrel doesn't get chamfered into the barrel on either, but mine's drilled higher into the barrel so the pellet gets less of a "guide past" the transfer port on the sides. This and of course mine appears rough and unfinished.
Great information from Eric & Randy!
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I cannot say for sure if they all looked like yours and mine. However, my 2004 AS392 and my 2014 392 both had this appearance (10 year span). Neither had any type of chamfer / taper in the leade, both were filled with paint that caused pellets to load poorly, and both had transfer ports that intersected the rifling. Both are accurate after some rework.