Tuning Barrel Droop

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M

Moe M.

Member
Oct 14, 2020
173
132
Massachusetts, United States
I've never experienced it personally, so I don't have a clue about how to remedy the situation, but I am open to suggestions.

So, my shooting buddy traded a couple of air soft guns he is no longer using for a Benjamin Trail NP in .22 cal., the gun is in good shape and shows very little use and no abuse, it cocks, loads, and fires as it should, it came through with a cheap bundle scope, I think it's a Center Point scope.

The problem is that the gun is shooting about 18" low from POA at 25 yds., the windage is fine, and when an aiming point is marked on the target the gun shoots a fairly tight group, it's just 18" low, the problem is not with the scope, I think it suffers from barrel droop, it's the only thing that makes sense to me.

I looked for a scope mount that adjusts for that condition and found several but they are all made to fit an 11mm scope rail, the Benjamin Trail has a factory welded on Picatinni rail, the gun was purchased on the secondary market and has no warrantee, my friend doesn't want to return the gun, he'd rather try to fix the problem.

Any ideas on how to resolve this problem will be greatly appreciated.

HM 
 
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O i have no count on how many times i have clicked the wrong way on my scope,,,,,, every GD time it is a huge embarrassment, and still i keep doing that now and then.

As i have extensive experience in straitening things to within a few 1/100 mm, just like for instance FX do with their straw barrels, i would have no qualms checking and maybe straitening that barrel on the gun.

Granted the hardened gear axles i straitened did take a bit more force than FX use in their otherwise very similar rig, for straitening their barrels, they use a little lever,,,, i used a lead hammer.

The 20 moa rail adapter is probably the more easy way to go for you guys, though it might not be enough for longer ranges.

Maybe a set of adjustable scope rings would be a option too, to line up the zeroed scope as much as possible to the POI before using any turret adjustments. ?
 
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Homer,

The Benjamin Trail NP XL .22 is a much maligned air gun. You find more than a few members who state it was the only gun they could never shoot well and were glad to be rid of. My experience started in 2020 when I approached my neighbor, a fellow Florida shooter, with a concern that my .177 Crosman F4 didn't have the power to deal with invasive armadillos. He handed me a Trail NP XL, he'd purchased over a year prior for $250, and said to keep it. Told me he hated it, hard to cock, very inaccurate and too heavy. He also gave me a large amount of .22 ammo, he'd tried without success. I tried it and found all criticisms to be well founded. I gave barrel a good cleaning, performed Crosman trigger modification, as seen on YouTube video, learned "artillery hold," and began search for best ammo. Finally settling on the H&N Sniper Magnum (17.90 grain) and a scope mount, as shown, that provided better eye relief, I ended up with a powerful, accurate shooter. I was so impressed with the Centerpoint 3-9x40 scope, I found a used one on eBay for my Crosman F4. Centerpoint Scope has more than a few supporters on this forum, as a good, budget priced product. Hope this helps, WM
IMG_20220106_212238.1649516184.jpg
 
 
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That rifle was known to have a rather slim diameter barrel if you consider the effort it takes to cock. Many have been bent by strong arming the rifle while cocking it. It has been recomended often to only use enough effort to cock the gun and not overdo it as the barrel can be easily bent. As recomended just carefully bend it back into position then use patience when cocking in the future. 
 
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Interesting.

I had a similar problem with my HW90. I found I could measure the amount and location of droop with an inexpensive, magnetic, electronic angle gauge. That can help you decide if it's better to bend the barrel or maybe use a tapered compensator mount or shim your mounts.

I first zeroed the gauge on the barrel block. The muzzle tip showed a 0.2 degrees upward bend. The barrel block to receiver was about -0.4 degrees, and the back of the receiver, right over the trigger block, was -0.9 degrees. Surprising.

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Bending the barrel to match the back of the receiver would require adding 0.7 degrees to the the muzzle. I decided to use a UTG compensator mount instead. (https://www.pyramydair.com/product/utg-drooper-scope-rail-11mm-to-weaver-adapter-compensates-for-droop?a=4191).

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The UTG mount corrects for 10 inches drop @ 30 yards. But how much ANGLE does that equal? The basic equation is height = distance x sin(angle). Since we're looking for the angle we take the inverse sin (or arcsin) and the equation becomes angle = arcsin (height / distance). The UTG angle is = arcsin (10 inches / (30 yards x 36 inches/yard)) = 0.53 degrees. Make sure your calculator is set to degrees, not radians. To convert degrees to MOA multiply by 60. One MOA is a minute of angle or 1/60th of a degree. So 0.5 degrees x 60 minutes/degree = 30 MOA. 

Your Benjamin Trail NP shoots 18 inches low @ 25 yards. That equals arcsin (18 / (25 x 36)) = 1.1 degrees.

Also check for sideways barrel bend. Barrels can point right or left. This particular HW90 barrel pointed to the right about 0.2 degrees, I straightened it. This barrel is not typical of Weihrauch. I bought it second hand. I checked my other Weihrauch barrels, they're almost perfectly straight.

I think companies add droop to the barrel-receiver joint to compensate for wear. Droop is mainly a cosmetic issue. 
 
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I've never experienced it personally, so I don't have a clue about how to remedy the situation, but I am open to suggestions.

So, my shooting buddy traded a couple of air soft guns he is no longer using for a Benjamin Trail NP in .22 cal., the gun is in good shape and shows very little use and no abuse, it cocks, loads, and fires as it should, it came through with a cheap bundle scope, I think it's a Center Point scope.

The problem is that the gun is shooting about 18" low from POA at 25 yds., the windage is fine, and when an aiming point is marked on the target the gun shoots a fairly tight group, it's just 18" low, the problem is not with the scope, I think it suffers from barrel droop, it's the only thing that makes sense to me.

I looked for a scope mount that adjusts for that condition and found several but they are all made to fit an 11mm scope rail, the Benjamin Trail has a factory welded on Picatinni rail, the gun was purchased on the secondary market and has no warrantee, my friend doesn't want to return the gun, he'd rather try to fix the problem.

Any ideas on how to resolve this problem will be greatly appreciated.

HM
Click to expand...

AOA sells a fully adjustable set of Picatinni rings, however they should come gold plated for the price they sell for. Personally when I run into that problem I use the thin plastic from a coffee can lid. Cut yourself a nice neat strip from the lid and fit it so it is just a tiny bit smaller than the lower rear ring . Use one small drop of super glue to hold and control the plastic strip until you get the scope remounted.

I do not mess around trying to bend any barrels, I like the KISS system. So a simple strip of thin plastic works great. A piece of old 35 mm film works well also, however I have not seen that for years, hence the raid on the coffee can lid. I did that the other day and tole my wife it must have been those new plastic eating termites.

Cheers

Kit
 
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Simple solution step by step:

1. Remove the shroud. End cap should come off with an Allen key in the “muzzle” and the rest should be self explanatory.

2. Remove stock screws and take the action out of the stock.

3. Lay the barreled action, closed, across your thigh. Cocking slot facing up, pivot centered across the thigh, so that if you apply pressure it will not open.

4. Grasp the barrel on one hand, tube in the other, apply sharp pressure like you are trying to break a stick across your thigh. I’d wear gloves, if the cocking slot has a bur it will cut your hand wide open.

5. Reassemble gun and test fire with optically centered scope. Repeat as necessary until droop is gone.



It will take a few tries but you’ll get the droop out and it’s free.




 
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Barrel bending is a time honored solution. But afterwards, check the side-to-side bend too. The very first barrel I straightened had both vertical and horizontal wowies. I had to straighten it in both axes.

i would also get a laser bore sight. That shows you where the barrel is actually pointing. Zero your scope in in at short range, using a white garage door. Then move back and see if your zero moves sideways wrt the laser.

They're dirt cheap on Amazon.

https://www.amazon.com/s?k=laser+bore+sighter+for+all+guns&ref=nb_sb_noss




 
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