Nelson conversion group movement info

I'm not familiar with the .22 conversion as most of those here. My son was testing a barrel I sent him. Shot about 80 rounds of various brands of ammo at 50 yards using sand bags to support his hands. There were different group sizes but all in the X ring except the first shot fired from each mag of 5 rounds. The first round was always a flyer though in the 10 ring! He e-mailed me photos of the targets, I suggested loading each round by hand to eliminate any possibility of the bullet being shaved. About 1/2 hour later he did so. Oddly the group center changed to about the 3 o'clock junction of the 9 and 10 ring. group size increased so impact was in 10, 9 and 8 rings using ammo that shot the best in the above test. He then tried the same ammo using the magazine to load, group didn't change and shat the same as the hand loaded. Not sure what happened between the tests! He checked everything and all was tight, used a new MatchDot with Weaver brand rings (not copies) and being a 2650+ experienced shooter error was not him!
 Anyone have any idea as to what caused the problem? Maybe MatchDot? I suggested removing a red dot from one of his other .22s that worked great and try it on the conversion.

Try varying the tension on the Nelson’s guide rod. There is a point of diminishing returns if the rod is over tightened. I do my two Nelson units by feel, but should probably use an inch-pound torque wrench for repeatable setting up of the unit. Probably why I clean mine with a small brass brush, aerosol cleaner and high pressure air. Keeps from having to dismantle the unit and taking a risk of over tightening.
I use a DeltaPointPro on mine with excellent grouping ability when using SV ammo, SK+ and Midas especially. Neither unit likes the same ammo, about typical of .22 barrels, but both hold x-ring at 50 easily. Doesn’t matter much which receiver I use, assuming it has a decent trigger. Call Mr. Nelson up, he may have a hint or three. He answers the phone every time I call. Always good to hear from the maker of this fine equipment. Of course, being the victim of a cold-barrel may not help.

Cold Barrel?

Make sure that the guide rod didn't loosen up!
Doesn't take much movement to open the groups up.

Froneck wrote:Cold Barrel?

I couldn’t help myself

Frank,
I’ve probably shot 30+ .22 conversions over the years. I have never noticed a group shift or flyer as you’ve explained. I haven’t found that guide rod tension makes much difference either; but loose just doesn’t work lol.
I have typically always shot more X’s at 25 yds with a Marvel than a Nelson. I believe it’s because Marvel indicates off the bore rather than just chucking up the barrel in CNC lathe.
My 2 cents.
Jon

Adam said locking screw was tight. Was odd the group moved for no reason plus group size increased quite a bit! Seemed to work OK for 80 rounds then group moved. Possibly because the Accuracy X frame is SS? I'm thinking that maybe he set up everything at home and being in Hot Florida AC was keeping room cool, since he works at a range the gun was kept cool in the car, then cool in his office. Maybe had a chance t warm-up and the difference in expansion between SS and Steel something moved. Thought first round flyer every time was odd then group moved for no reason.

Frank,

By design the barrel is fixed in the receiver. The slide is loose on the receiver rails. The sights/optic rail is attached to the fixed barrel. Any amount of expansion/contraction of the receiver related to temperature could only possibly affect the slide stop pin attachment force by the guide rod, but I believe only minimally. The angular attachment of the barrel block would still keep the barrel firmly/rigidly in place. 
Since the barrel and sights/optic rail are acting as one unit, the amount of expansion/contraction of the receiver would not affect the grouping of the pistol. A temperature change from 50 to 90 degrees roughly expands the receiver 0.0006". My thermal dynamics are super rusty, but the temperature change is less than minimal.

There is most likely another problem going on..............
Jon

I agree! The odd first round flyer though only out from the X ring into the 10 was odd. Also flyer was not in the same direction, up, down, left and right! Then for some reason 1/2hr later group moved plus group size increased quite a bit! Not sure how he fed the rounds by hand to prevent any possibility of shaving but in handling the gun something moved then when using the magazine again what ever it was remained.The Accuracy X .45acp shoots great X ring group, trigger is great too. But lock-up in 45acp is not the same as fixed barrel in .22 conversion with scope attached to the barrel.
 Those that use a torque wrench, what is the torque use on the barrel locking screw? Maybe it has to be tighter or possibly too tight!

Perhaps the slide stop pin broke where the guide rod contacts it?

That would be pretty odd, but so is the issue!

I often find 1st round from loading with open slide deviates from loading with slide closed. Maybe?

Problem with Nelson conversion is closing slow. The long gap from when the round leaves the magazine lips and the chamber face (about 1/4") allows the round to fall out before being chambered. So pulling the slide back all the way seems to prevent that when released. But the thought to chamber each round by hand to prevent any issues seemed to have started the problem that didn't change when magazine chambering was resumed.
 Adam is moving about a hour north so he is busy with that project, testing might take a back seat. I'll be doing another barrel as well as completing my conversion that shortened the 1/4" gap to less than zero (bullet is slightly in the chamber before brass leaves the magazine lips).
 I guess a broken slides stop pin would case a problem but the conversion is new and the pin size is strong enough for the .45acp. But anything is possible.
 My guess is the scope, could be the first round issue might have been created by pulling the slide all the way back before release. Then as blow-back pushed the slide back it wasn't as far. Something in the scope was loose and finally is free to move at will. Maybe a lens ring was tight because lens was at slight angle, vibration allowed it to straighten and is now loose. But that too is reaching but possible. As I mentioned I suggested another scope that works great be removed from another gun and tried.
 Barrel unscrewing from the block??? It was loctited but threads are LH, I think they should be RH! The scope rib should prevent that issue. Maybe it's just enough, if barrel twisted slightly right the group would move left. Florida heat loosen Loctite??

Froneck wrote:Florida heat loosen Loctite??

It's been pretty hot, but not quite that hot!

Yeah I know it takes about 250° F to weaken standard Loctite and more for the high temp. stuff!
 Threads were cleaned with acetone, Loctite applied, barrel screwed in and out a few times to insure Loctite coated everywhere. Then allowed to sit for a few days so Loctite cured.