Steroid 392 Accuracy Factors

[danbrando]

I'm new to this forum but have been shooting my Steroid 392 for several years.  From my experience, I believe there are four main factors that establish accuracy in a 392:

1. The barrel.  As has been noted many times over- you have to clean the paint out of the barrel or you won't hit anything.  Other than that, hopefully you can find one with a good barrel.

2. Pellets.  My gun likes JSB, AA, and some H&N pellets.   18-21 grains seem to hold the most consistent accuracy.  Lighter pellets or other brands have not provided any kind of consistent groupings.

3. Air pressure.  My gun seems to shoot consistently under 10 pumps.  Over ten pumps, I start to get alot of upward barrel deflection.  I have not found a good way to manage this barrel deflection, so if I want to be accurate, I shoot with no more than 10 pumps.  Does anyone know what I'm talking about here?

4. Grip.  The movement of the hammer seems to really affect my consistency in aiming.  I've found that when I have a real firm grip on the gun, my groups shrink.  To the point that I can shoot to one-hole groups at 14 yards pretty consistently.  If I just set the gun on a sand bag and shoot with no grip, my group opens up dramatically.  I attribute this to the movement caused by the hammer in the gun.  I think it moves it while the pellet is still in the barrel.

Does any of this make sense to you guys who shoot a 392 frequently?

[35 shooter]

My 392 is stock, but as you say, has a heavy hammer fall.
Mine won’t shoot from a sand bag rest on the forearm, but a folded towel on top of a cabelas catalogue, and it’s pellet on pellet at 20 to.25 yds. And 1” or less at 50 yds.

I can set the forearm on a sandbag and cock and pull the trigger with no air in it and watch it jump off target  through the scope at least 2 out of 5 times just from the hammer fall.
From the folded towel( soft rest) it won’t move at all.

My sand bags are packed pretty tight and I have no doubt if I took some of the sand out, it would shoot just fine from the bags, but they’re set “just right” for my powder burners.
I just set the but stock in the v of my off hand for a rear rest.

My stock 392 loves gamo magnum pointed pellets and jsb 16 and 18 gr. domes.

[Psipumper]

I think those points make sense. I haven’t done any testing of the upwards barrel deflection. Firing with the pump handle open vs shut should show that. A lighter hammer  with a balanced type poppet valve could improve accuracy in some situations? Hmm. Another selling point for a balanced valve conversion in a 392.

[longhunter]

No way around the barrel deflection issue. And, the older guns have more. Upwards of 1/8 of an inch.

[danbrando]

With that much barrel deflection, how can we ever be accurate varying pumps?  The only way I see it is to carry around a card that shows deflection at different pumps and you make sight adjustments in the field.  Seems very complicated.

I’m not that sophisticated.  I’ve come to the conclusion that my gun is most mechanically efficient at 10 pumps.  I’ve sighted it to zero at 14 yards at 10 pumps with 18 grainers.  That produces a pretty flat curve between 10 and 33 yards.

I shoot everything with 10 pumps.  Mainly because I’m an accuracy freak.  Plus I like the workout.

My gun produces one hole accuracy at 14 yards.

If I vary pumps, I don’t know if I could hit the broad side of a barn.

By the way- my comments are not a knock on the steroid 392.  I love the gun- but it has limitations and quirks.

[BerkshireHunter]

Well, I just ordered one with the Pyramid sale. Wanted a 392 for along time so I hope it’s a good one.

[Psipumper]

No way around the barrel deflection issue. And, the older guns have more. Upwards of 1/8 of an inch.

Only way around it would be Crosman to redo some engineering. Seems moving the   pump pivot pin position to tube centerline would be a start.
Additional pressures from the steroid treatment would make for more deflection I guess.
Would the pistol scope out towards the end of the barrel help this?

[35 shooter]

Well, I just ordered one with the Pyramid sale. Wanted a 392 for along time so I hope it’s a good one.

Odds are you’ll love it. Just check inside the muzzle for paint overspray.
I got it out with que tips and finger nail polish remover.

[Muddydogz]

My steroid 392 has taken a boat load of vermin, mostly squirrel out to 30-35 yards. I rarely pump over 8 pumps and I see no accuracy difference when I use 6 pumps.
  I don't own a chrono but I think at some point those extra pumps are just making noise. I've had a few steroids and this one is far and above the others accuracy wise. Why? I don't know but I'm not complaining. I can't remember the name of the gentleman but a few years ago I bought a milled aluminum rail set up that ran the length of the barrel on the Benji's and he stated it would help with barrel flex. I just wanted it for scope mounting and ended up cutting a few pieces off it to make smaller scout mounts. I'll have to look that piece up.

[WECSOG]

Pump for range. Zero the sights at perhaps 10 yards with 4 strokes, then check the range it hits POA at 6, 8, 10, 12 strokes. More strokes for longer range; fewer for less.

At least that's one theory.

[danbrando]

After reading the replies and searching this forum for additional info, I decided to do some additional testing.  I was really interested in trying to figure out how to manage this barrel flex issue.  I also wanted to test the accuracy of heavier pellets, based on some things Timmy Mac has said.  Here's what I found:

With the proper hold, JSB 25.4 grain pellets were the most accurate ammo.  I was putting every shot into the same hole at 14 yards, however, after several shots, the barrel warmed up and my POI would drift a little bit.  At 10 pumps, they were exiting the barrel at 608 fps on average(just shy of 21 fpe).  18 grainers were very good, but would not produce 5 shot accuracy like the 25.4's.

I sighted this ammo in, to zero at 14 yards, on 10 pumps.  This gave me a nice flat trajectory between 10 and 25 yards. At 30 yards it was shooting around 1 inch low.  At 40 yards it was shooting 2.5 inches low.

What I found is that with the eleventh pump, it would cause barrel flex and I would shoot to the point of aim at 30 yards.  Very little gain in velocity with my gun though.  Air left over.

With 13 pumps, the barrel flex would shoot to the point of aim at 40 yards.  With little velocity gain.  Lot's of air left over.

So- with ammo that gives me 20+ fpe at the barrel, I have a gun that should be able to hit a bullseye from 10 to 40 yards without altering my POA, only pumps.

I thought that was a pretty cool find.  Now I just need to be able to estimate when that squirrel is at 30 yards not 40.

Also something weird is that I didn't see much difference in barrel flex from 11 to 12 pumps, or 13 to 14 pumps.  In other words, going 10 to 11 was a big deal, and so was 12 to 13, but the barrel didn't flex much different at 11 than it did at 12.

[35 shooter]

Okay, I did a search on bbl. flex and found it mentioned several times, but no explanation of exactly what causes it?

Are we talking straight up and down flex or side to side or both?

I have a stock 392 and 397, and yes, as I add pumps, the point of impact moves upward, but I thought that was due to more air in the valve, thus more speed?

I haven’t noticed any side to side change in impact, only the upward impact from more pumps.

Is the flex being talked about here only an upward movement, and what exactly causes the flex??

[danbrando]

From what I can tell, the barrel flexes upward based on higher air pressure.  More pumps equals more flex.

It seems to be pretty close to vertical on my gun.

I haven’t done much testing from 1-10 pumps to understand what happens there.  I’ve only tested 10 plus pumps.

[35 shooter]

From what I can tell, the barrel flexes upward based on higher air pressure.  More pumps equals more flex.

It seems to be pretty close to vertical on my gun.

I haven’t done much testing from 1-10 pumps to understand what happens there.  I’ve only tested 10 plus pumps.

Ok, thanks. So upward flex. Then since the bbl. is welded to the pump and air tube all the way, does the whole thing flex?
Lol, trying to get my head wrapped around this concept.

I just came back to airgunning about 3 years ago, so lots of things i’m Probably not aware of.
All my airguns are pumpers at this point... 392, 397, 1377, and a couple of 880’s... so do all pumpers have bbl. flex, or just the 39x guns with the welded bbl.?

[Psipumper]

There is more barrel deflection than I thought there was. At 30 yards, I was 10 inches lower when the pump handle was left open versus closed. I didn’t spend too much time but seems to group better with handle open. More testing needed .

[johnnyfoos]

After reading this : -

     "Barrel Flex"

 I'm going to go with :

    "add pumps, the point of impact moves upward,  due to more air in the valve, thus more speed"

With more speed the pellet will have less time for gravity to pull it down.

   Just my   $0.02