I have posted about this same barrel in the past and haven't shot it much at all. It is a 15" MGM barrel with a 6 hole MGM base and 3 weigand rings. I have done this load development with same powder charges but I did it once at the manuals over all length, and got horrible groups so this time I decided to do it with the bullet seated a little longer at .020" off the lands. Still not good results. I have a leupold VX3 handgun scope on it also. I was shooting the gun resting the forearm on a sandbag and a sandbag under the grip. Let me know what yall think the issue may be. I have done tons of research on the 460 accuracy and load data and I have found that there are several other people that have had the same issues. I know for a fact that it is not shooter error as I take the same frame and put a different barrel on and shoot 1/2 - 3/4 " groups and I am not recoil shy. Another thing I will say is I have a S&W 460 revolver and can shoot 2-3" groups at 100 yards just resting my forearms on the hood of my vehicle. I didn't know if there could be a problem with the barrel or what? Also this load development was done at 70 yards so these groups are horrible and in no way will I accept it. I know there are a couple others on here that have a 460 encore barrel so please share. I am not trying to sound like I know it all I'm just confident in my shooting ability and can call a pulled shot if it happens. I trim all my brass to trim length and I have played with the crimp and nothing seems to make a difference. This test was done using H-110 and 240 gr xtp mags. Also I have the base and rings all tightened down to 30"lbs. So here is the group please let me know what yall think. Sorry for the long write up I really just want this gun to work and I would like to get it shooting 1.5" groups or so at 100 yards.

BTW the smallest group is 47.0 gr of powder and it is 4" center to center and the largest group is about 8"

To get the most out of your gun, you got to be STEADY, put a sock filled with old media under the but of the grip,rest the forearm as you usually would, a trigger job would help tighten things up also, good luck.

Do you have access to a chronograph? Can you check the spread of your speeds? Is the 460 particularly sensitive to powder load variations?

How about different bullets or powders?

These suggestions would tighten up decent groups, but your photo points to something else with 4-8 inch groups like that at 70 yards.
Do you have something you can slug the barrel with to check dimensions? Any reason the bullets would lose stability at weight and velocity you are shooting?

Beyond the simple thing above, I would make sure the optics are rock solid. Sounds like you have a solid scope base and rings, how about the instillation? Is the base locked in place with something when you screw it down? (double stick tape, little dots of epoxy....? Any burs anywhere on the bottom to mess up contact? Any friction enhancer between the scope and rings? Were they lapped or was the scope bedded? How was alignment between the three rings?

Racksmasher- I did a trigger job and it is at 1.5 lbs and Karl I will post up all my speeds shortly to see if that would help

46.0gr 2290-2290-2290-2310 ES 20
46.5gr 2343-2322-2322-2306 ES 37
47.0gr 2343-2385-2347-2433 ES 90
47.5gr 2393-2372-2510-2364 ES 146
48.0gr 2530-2424-2446-2450 ES 106

Btw I shot all of these shots in a round robin I shot one of each charge and let the barrel cool. I also noticed when doing it that the higher the powder charge the more the spread in velocity was. Also, I weighed every powder charge.

I haven't taken the base off I just checked the screws for tightness from MGM and they were good so I guess it wouldn't hurt to take it off and check. Alignment looks good between all 3 rings.

I had a similar problem with a revolver that a gunsmith had drilled for a scope. He had not used anything on the threads to hold the screws tight. I could not tell that they were loose until I took the scope out of the rings.

I do know that 1 of the screws are stripped but it was that way when I got it. I'll take the base off and put just a tad of blue loc tite on the screws and check the base

That's odd. I used to use that exact same powder/bullet combination, and I got the exact opposite results. Increasing the powder charge decreased the velocity variation and tended to increase accuracy.

Lone wolf I was shocked at how close and consistent the lowest powder charge was. Still kinda odd the the spread gets bigger with more charge

Yeah, that's the exact opposite of what I expect with H110.

That said, I don't really think any of the data explains the groups you got. If I was you, I'd take the most consistent group in terms of velocity, load up about ten more rounds with that load, and try again at around 100 yards.

Oh, I just thought of something else that could be a factor in the inaccuracy. Have you ensured your bullets are aligned properly when you seat them? I've noticed that if I don't flare the case mouth enough, the bullets are sometimes either canted slightly (more of an issue with the FTX) or the case is bulged only on one side as if the bullet is slightly off center. Unfortunately, I never shot my old 460 at far enough ranges to see if either issue would affect accuracy, and I haven't shot my newer PC 460 enough to know what makes it shoot well or not, so I don't have any real data to support this theory.

Yea I had that issue when I first started reloading for my 460s. They are good now. Actually I called rcbs with the issue and they sent me a seater plug that works way better! I also don't seat my bullets with one press stroke I seat a bit and rotate the case in the shell holder and I usually seat a bullet in 3 strokes

OK, go back and re mount the base and rings, start from the beginning,I know you are a accomplished shooter, seen you around the Web, just rule out the easy variables, again , good luck man!

Well I took the base off and there were metal lips at the top of the holes from being drilled and tapped. Also 3 out of 6 screws stripped. So probably my problem. I took some sand paper and knocked the lips off to flush with the barrel. My buddy is a machinist so do y'all think I should have him re drill and tap so I can use heavier duty bolts? And if so what size do y'all think?

Were the screws stripped, or the holes? If it was just the screws, I'd get some new ones and remount the base and scope before attempting to drill out the holes.

It is the screws. I'm just worried about it stripping these little Mickey Mouse screws again.

I would get some more screws and try try a torque wrench if the barrel threads are still in good shape.
I have also taken to bedding the scope mount to the barrel with small dabs of JB weld (keep it away from the screw holes!) I find it pops loose with a little torque on the mount, but makes it rock solid until you really want it off. I have also taken to applying a little to the scope rings to eliminate any shifting there.

I had a local gunsmith drill and tap two holes for some 6 hole mounts on a couple contender barrels. On one of them, he hosed up the alignment and ended up up-sizing both new screws so I know it can be done, but replacing with factory screws would be easier and should work very well with a 6 hole base.

Yes ok thanks Karl. Some of y'all may frown on this but I used a drop of gorilla glue in a few places... Away from the screw holes. I'm going to pick up some more screws tomorrow and give it a test run. I do have a wheeler fat wrench with torque settings, but just curious what do y'all torque the base and rings to on big boomers?

Call me the odd one, but I've never measured the amount of torque I use when tightening the screws holding down bases. I always make sure the screws are quite snug in their holes, but not so tightly that I risk breaking something. To my credit, I've never had a base or rings give me an issue.

On heavy kickers, I put a small drop of Loctite in each of the holes before I put the screw in. That may or may not be what you're supposed to do, but like I said, all my scopes stay in place.

Cool thanks Chance

25 inch pounds

I too am curious as to what is causing your errant groups. I have a MGM barrel in .460 S&W as well and it seems to do very well with 250gr Hornady XTP bullets.

There is some risk associated with putting Loctite in the screw holes. The Loctite can fill the hole and prevent the screw from fully seating. Its best to apply a small amount (I use a toothpick) to the side of the screw. Additionally, cleaning the screws and the holes is very important. Flushing with alcohol or gun scrubber prior to the Loctite removes oil residue etc.

Yep, is better to apply to the fastener than the hole and not too much. One fellow used loctite on the base screws of his 22/45 pistol and subsequently locked up the action. Not sure why he felt the need for threadlocker on a 22LR pistol....

There are at least two of us ;-)

Eastex, have you tried any other bullets/loads out of it?

I have shot the 300 gr xtp mags with the same results

The only thing I can think of is that the stripped screws are the problem. The base wasn't loose at all, but the 3 screws that were stripped were all in a row starting from the breech end. I haven't confirmed yet but I'm going to see if the local hardware store has the right screws

Zee- that's a sweet looking set up. Is that one of Tony's grip and forend?

Ok, three screws being stripped is pretty significant.

I bought the grip/forend set used and am not sure the maker.

Ok I just went and bought some more screws and confirmed that the holes in the barrel are stripped too. I'm going to have to have them drilled and tapped

Calling MGM?

Yes I'm going to give them a call on Monday. This barrel has only around 100 shots so hopefully they will be able to help.

Well, that's not good. Hopefully MGM will get everything straightened out.

I have nearly the identical barrel, 15" Encore, full bull MGM with their break. I'm shooting a Red Dot with the cross hair reticle.
I have three rings on my red dot and it is staying put so far.
I had some issues with the 240grn XTP's so I went to the Barnes XPB 200grn at the suggestion of someone, can't remember who it was.
Getting a lot better groups. I'm using 45grn H110, OAL 2.330 which is real close to the rifling. I had to wait on more bullets and now I'm going to get some velocities soon. I'm getting about 1.5" at 50 yds with the red dot. This is going to be my close range, under 100yd gun for pigs and deer. I might put a regular scope on it and try after taking some game like this.
The photos show only two rings but I have now installed a third ring. Also the first ten rounds trashed the cheap Bushnell rings. I went to a Gun shop and got four 30mm Hvy Duty rings using torque screws. The red dot sets a little lower now with the new rings.

Nice setup Hawkeye, I looked into the barnes bullets but for about a dollar per bullet I'm out.

I have a similar set up, and have experienced similar issues. I'm working a theory on it and could use your help. What brand of brass are you using? I started out with Hornady and have experienced several failures due to case head seperations. I have also noticed a significant difference in the amount of effort required to resize, flare, and crimp the cases. I typically don't track the number of times a piece of brass is reloaded, but I do know that the variance in case hardness can cause accuracy issues. I have since purchased some Starline brass but have not had the time to try out loads.

Crimp. Why would I have case head seperations on a straight wall case, whose headspace is determined by the rim? I am thinking that at the pressures this cartridge is operating at, my "heavy" crimp is actually holding the bullet so well that as the pressure rises it stretches the case prior to releasing the bullet. H110/296 is a slow pistol powder, but using 40 plus grains is now a super fast rifle powder. The more times you reload the brass the harder it gets. The harder it gets, the tighter the crimp. The tighter the crimp the higher the pressure. The higher the pressure, the more case stretch, until if fails.

To see if this has any basis at all, I am going to use new Starline brass, and apply little if any crimp to the bullet.

If this doesn't make any sense, it's from too much coffee, or not enough booze.

You could be onto something when you mentioned too much crimp. I started shooting mine with no crimp just to see what they would do. Not consistent. I have gone to a medium crimp and the groups got smaller. I have never seen a straight wall separate except some old 45-70 brass that had a indention in the brass from the factory about 1" up from the rim. It was old, hard brass.
All of the brass I have is new Hornady.
Good luck trying the Starline brass. I might have to get some of it if you think it is good brass for the 460.
Mike