Airmax MKll Barrel Turning

[mrjohns@artelco.com]

I heard some of you have drilled and tapped a hole so you could add a grub screw to stop the barrel from turning on the Mrodair Airmax pistol.  Where on the pistol are you drilling the hole to put in a screw? I thought about removing rear sight and putting one in, under the sight. Can you tell me where you added the screw?  When I remove my moderator and screw it back on the barrel moves and it always changes my point of impact.  Somebody will say don't remove it, but I also use on my air rifle. Poor folks have poor ways.  Thanks in advance for any advice.

[Ribbonstone]

How loose do you have that front end cap/LDC adaptor screwed in?

If screwed in tight, it tensions the barrel...and unless you screw the LDC on with more force than the tension force, the barrel shouldn't rotate.


Guess I'd start by being sure the barrel is actually rotating.  A quick witness line (pencil/grease pencil/ scratch/ whatever) would show any barrel rotation.   

If yours does rotate, then a set screw would be in order.  If it doesn't rotate, then it is more likely to be an alignment issue than a rotation issue (although I will say that adding the weight/length of the LDC  can change the vibration of the barrel at the shot).

As for alignment, it's one of those designs where you can look straight down the barrel from the rear...so can get a pretty good idea if the LDC is going to be a clipping problem from a careful look-see.

[mrjohns@artelco.com]

Yes sirI did mark the breech end of the barrel and it is rotating. I think it is common knowledge among owners of this pistol that these barrels rotate. I just would like to find out where they are putting the grub screw.

[SilentMatt]

I have one on each side of the receiver, they land in the flats on the breech nut.

[Ribbonstone]

All I can say is that while a whole lot of folks have had the barrel rotation problem, I haven't...but that's a test sample of "ONE"  and an older MK I.

Still have the graphite pencil witness mark (it won't rub off, breech block doesn't scrape the metal, just the top of the o-ring) and it's had the  LDC off and on several times (both as a pistol and as a carbine).

YEah...wife was a kindergarten teacher for 35 years....I'm butt-deep in big fat blunt pencils.



 So I can say, with justification, that this barrel don't rotatate.  The tension force is greater than the rotational foces of screwing on the LDC...so the barrel doesn't rotate.

Been working with it for quite awhile..well before there was a MkII....hasn't shown any tendency to rotate if the end cap/LDC adpator is tight enough to resisnt rotational force of screwing on the LDC.

AHs been an open sight pistol (added the sights).

VArious red-dot pistol.

Scoped pistol.

But with the added length of the LDC, it's become a carbine.



Was close to the end of a fill, so I tried two 5 shot groups at 20 yards on the ragged end of a used target.



Yeah...there might be a little difference.  But it's not rotation.  Likely just that adding the length/weight of the LDC slightly cahnged the barrel vibration.

Think you made up your mind that set screws are the way to go.

It's not that I'm against adding set screws...would certainly keep the barrel stable so long as they had a decent sized barrel dimple to snug down into AND you are sure the barrel is pointed the best way when you do set it in place (the skinny barrels don't seem to be dead stright).


EDIT:

Just going to mention...if the barrels really were dead straight, it wouldn't make any difference if they rotated or not.

[anti-squirrel]

I've had mine almost as long as yours, Ribbs, and mine has not rotated one bit.  Same model with a Rocker1 LDC, and I keep the LDC off when stored as I sometimes change which LDC I'll be using.  Mine has maintained the same accuracy all along- if anything it has become less picky.

Maybe the newer models have this issue?

[Wayne52]

I've had mine almost as long as yours, Ribbs, and mine has not rotated one bit.  Same model with a Rocker1 LDC, and I keep the LDC off when stored as I sometimes change which LDC I'll be using.  Mine has maintained the same accuracy all along- if anything it has become less picky.

Maybe the newer models have this issue?

Same here Pete, if I twist the LDC on too hard it will spin the barrel  and throw the POI off. Mine isn't pellet picky at all and I must say I have to agree with you it's even less pellet picky since being broke in good.  When it was new the sniper magnums didn't group that well but after 1000 rounds through it, they group just as good as the JSB 18.13 domed now.

[Ribbonstone]

Enough evidence that they rotation can be a problem, and I'm not opposed to the set screw solution.  If you find you need the set screws, I'd much prefer to tension the barrel before tightening the set screws.

[SilentMatt]

If you find you need the set screws, I'd much prefer to tension the barrel before tightening the set screws.

The set screws just capture the barrel nut(part# 5) flats to keep it stationary, allowing you to tension the barrel.

[Ribbonstone]

Would still rather have any slack pulled out the system (at least some tension) before I set screwed the set screws down. I'd also rather have the barrel (which isn't totally straight or we'd not give a ding-dam about it rotating) pointing in the "best" direction when it was fixed in place.

[SilentMatt]

I get what you're saying now. I used used non marring set screws, so I think the nut would be able to slide forward into the seat with any tension on the barrel. I get a  very noticable POI shift with every dissasembly, and muchh less when I really reef on the barrel. My LDC is sandwiched between the muzzle nut and shroud, so the 1.75" diameter LDC allows me to get a good grip as I twist it on. I think Bob posted something about the tension needed to increase accuracy of a barrel, and it was surprisingly high. Not sure if I'm getting near the needed torque, but it does seem to help.

True, the set screws don't allow you to clock the barrel, but they should hold it in the same position if the barrel is fully seated in the nut.

[Rallyshark]

I have one on each side of the receiver, they land in the flats on the breech nut.

I did the same thing to mine, and have never had an issue since  

[BSJ]

You can keep the set screws loose enough that they will prevent the nut from spinning, and still allow tensioning the barrel. Then tighten them all the way afterwards.

I used metric screws on mine as well. Keeps the number of needed wrenches to a minimum when working on the gun...

[Wayne52]

I find with mine if by mistake I happen to spin the barrel it doesn't take much to tweak it back to where I want it.  I keep mine in a tactical case for transport and never have to remove the LDC. Every now and then I check the LDC to make sure it's snug. Only on a couple of occasions I've found it loosened up and that's been a while ago.

[anti-squirrel]

Okay- curious question- how many of you use an O-ring in the thread-on mount for the LDC?  I've found this ensures my LDCs never loosen this way, and I use a small mark for indexing when I take it off.  This way I'm ensured the same fit every time.

[Ribbonstone]

As for me and the MKI, Rocker 1 LDC, use no o-ring and three fingers tight (two fingers and a thumb)... it's not loosened.


Other PCP's, other LDC's, other abutments, I seem to need the o-ring to stay consistent.