Benji 392PA Accuracy issues

[beejwest]

Hey all, need some advice from the hive mind here.  I have a 392PA that I've had for several years.  When I purchased it new, I went through it, cleaned it, took thinner and solvent with a Qtip to the inside 2-3" of muzzle end of the barrel to remove any overspray (there wasn't any) and did the Qtip test (no burs etc.)  Crown looks unremarkable in every way.  I threw a Williams peep on it and a threaded end cap for a moderator.  I tested accuracy before and after the threaded slip-on adapter and it was no different.   

After all that I got OK groups shooting at 15-25 yards and assumed it was just me with open sights not being mega-accurate.  The moderator really changes the POI and I checked for clipping but found no evidence of it.  I even stepped up to a .25 moderator for extra clearance with no success with the POI shift.  The shift was mostly consistent so I didn't worry too much. I got into PCP's, had a couple spawn, and got busy with life.

A few dozen PCP's and several years later, and I'm re-interested in the 392.  I thought, "I'll buy a scope mount finally and wring all the accuracy out of this thing...." So I put a Baker mount on, and a Hawke 2-7 scope.  I've tried it with and without the moderators now in a controlled indoor environment in my basement shooting a measured 20 yards.  The best consistency I can get is about 2" groups (I say groups lightly) at that range.  Obviously, I have put approximately 15 different types/weights of pellets through it trying to find one, just one, that groups well.  Best seems to be JSB 18.1's, but I haven't found anything else. I've tried the H&N FTT in all three common head sizes to see if head sizing was an issue, no such luck. 

I need some ideas on this rifle for accuracy improvements!  Everything seems tight on it, the solder looks good, mount and all screws for rings are tight, no breech wobble, etc.  Velocities are consistent shot to shot at 635 for 14.3 gr pellets.  It just wants to be a shotgun, not a rifle!  I really like the wood and the idea of the pumper and would even consider 'roiding it if it were accurate.   

What's next?

[longhunter]

May sound crazy, but, try loading the pellets by pointing the gun down, and letting the pellet fall into the breach. Sometimes, the pellet will cock slightly, when the bolt is used to feed the pellet, shaves off some of the head in the transfer port.

[beejwest]

Thanks @Longhunter.  I'll give that a try.  Hopefully more ideas will flow as I want to like this rifle a lot!

[north country gal]

How's the trigger? Done any mods? These are light weight rifles, after all, so a good trigger is a plus. Definitely helped when I lightened the trigger on our 397Ps.

I assume that Bawke has an AO, right? Even at 20 yards, you can get some parallax.

Not to discourage you, but I have found it to be something of a mystery on why some our 397s shoot so well and some are just okay, even when doing the same mods and checking the same specs. I suspect it may just be luck of the draw on the barrels. By the way, whatever the reason, our 397Ps prefer Crosman Premier domed heavies. Seems to be a thing with Crosman/Benjamin guns we have.

[beejwest]

Trigger is lightened and polished.  About 3lbs, slight creep, but workable.  I have only tried CPHP in it as far as Crosman pellets are concerned.  I'll find some heavy domed.  Thanks for that tip off.  Definitely an AO on the hawke.  I had it on another pcp and it seemed to work fine there so no reason to suspect it, but i may swap just to be sure. 

How's the trigger? Done any mods? These are light weight rifles, after all, so a good trigger is a plus. Definitely helped when I lightened the trigger on our 397Ps.

I assume that Bawke has an AO, right? Even at 20 yards, you can get some parallax.

Not to discourage you, but I have found it to be something of a mystery on why some our 397s shoot so well and some are just okay, even when doing the same mods and checking the same specs. I suspect it may just be luck of the draw on the barrels. By the way, whatever the reason, our 397Ps prefer Crosman Premier domed heavies. Seems to be a thing with Crosman/Benjamin guns we have.

[north country gal]

Best of luck, BJ. Yeah, solving the accuracy mystery can be frustrating. Hang in there.

[35 shooter]

I have a 392p that has only shot 1 pellet well so far.... a gamo magnum pointed.
Also have a 397pa that only shoots 1 pellet well... a beeman 8.4 gr. Pointed.

On the other hand, my new to me 392pa shot 6 out of 7 of the first pellets I tried in it .
I got lucky with it in that it also shoots NOE cast 20 gr. Pellets into tiny ragged holes also.

In my limited experience with 39x guns says they can be extremely pellet picky to shooting almost anything you put in them.

But, if you’ve tried 14 or 15 different pellets through it, i don’t know what it could be other than the crown.

[RBQChicken]

I think Longhunter is on to something.  I've had to polish the leade on my 392p's.  Kind of a lip there that needs to be taken off so you have a smooth ramp up into the barrel.

[Hack21]

Have you loaded a pellet and then backed it out with a dowel to examine the rifling marks? Both my 2014 392 and 2004 AS392 had poor leades that damaged the pellets and loaded them crocked.

It seemed like there was very little transition from the free bore to the rifling. To make matters worse, a portion of the transfer port was into the rifled area. So pellet skirts would protrude into the transfer port as they were being sized and the port would shear some of the skirt. The rifling would engrave very unevenly as well.

On both of them I used a 3/16 wood dowel with 600 grit sandpaper. I shaped the end of the dowel to a slight taper and cut a slot into it to receive the sandpaper. I cut the sandpaper into strips that were maybe 5/8" x 3/8". I would fold the paper lengthwise and slip it into the slot. The tag ends get folded back.  Cutting the paper to a longer or shorter length changes how tight the fit is.

This worked best with the valve removed so that I could view the rod and sandpaper through the transfer port. The goal was to get the sandpaper right to the transition of the free bore to the rifling and rotate the rod by hand. Avoid spending any more time than necessary in the portion of the free bore that receives the bolt o-ring to avoid enlarging it. Once I found the proper depth, I would put a mark on the rod where it would line up with the butt stock end of the action.  After a few revolutions, the paper would be loaded with brass. I would remove it and wipe the brass with my fingers and then fold the paper so that I could rotate it in the opposite direction on the next insertion.

A bright light shown into the chamber will show the freshly sanded lands and the grooves will contrast as they will be dull. I stopped often to test fit pellets and inspect their skirts to see the improvement. I took note of the force to chamber as it changed also. Meisterkugelns pellets seemed to work best for this as their skirts are large and thick.

I used felt pellets to keep abrasive out of the barrel. I shot them from the muzzle backwards with compressed air as well. As a last step I polished the free bore, leade, and first inch or so of rifling with JB bore paste.

Both rifles load pellets like butter now. The second one shot well before and very well afterwards and seems to like almost any pellet. The first one only likes H&N Sniper Lights and to some degree Meisterkugelns and Ruger Pointed pellets. That rifle improved slightly and is still picky. Using a TR Robb pellet sizer to size the skirts to the groove diameter helps as well.

So my experience was that the leade is poor and some work will improve accuracy to a degree. However, the rifle that started picky stayed picky. It shoots roughly 1.8+/-0.5 MOA at most distances up to 50 yards or more with the sniper lights. It also prefers a clean barrel and 2 dry patches on a patchworm on a periodic basis help it as well.

Good luck.

[shibumei]

Sounds like Eric knows a thing or two about a 392..  Hey, It rhymes. I've got a PA397 so paying attention...

[beejwest]

Wow Eric! Thank you!!! Looks like I have my work cut out on a rainy day! Great post!

[Hack21]

BJ,

You also can touch up the crown with a brass screw. I did this on one and didn't get much of an improvement. But I was confident at least that the crown was good.

Good luck.

[beejwest]

I've done that with a few Mosin's, so I'm familiar.  Screw size for the 392?

BJ,

You also can touch up the crown with a brass screw. I did this on one and didn't get much of an improvement. But I was confident at least that the crown was good.

Good luck.

[Hack21]

I've done that with a few Mosin's, so I'm familiar.  Screw size for the 392?

BJ,

You also can touch up the crown with a brass screw. I did this on one and didn't get much of an improvement. But I was confident at least that the crown was good.

Good luck.

BJ,

Nervoustrigger (Jason) usually chimes in and has some great tutorials here on "accurizing" barrels. He recommends a #6 screw for .177 and a #8 for .22 and this is what I have done as well. This is worth a read or reread before diving in. With the barrel and screw both being brass I would plan to use 2 or 3 screws for this job as they will probably wear faster than they would on a steel barrel.

https://www.gatewaytoairguns.org/GTA/index.php?topic=130555.0

Also, here is a picture of my AS392 leade from the factory.

Thanks.