Slug tuning help

[vmaxpro]

This is drivin me nuts. I can get 4 or 5 in the same hole at 100 and then a few flyers like 2” away any direction then back to the same hole for a couple. Am I very close to a tune? I dont know. I shot nsa 26.8gr that were hammering one day then all over the map the next?

 

[Pacoson71]

Barrel fouled?

Regulator seeping pressure? 

Air pressure off regulator? 

 

[vmaxpro]

Im thinking I got sent a pellet liner instead of a slug. I mic a slug at .2501. The bore should be .250 when I push one through I can see atleast .002 of daylight.

 

[nielsenammo]

The slug liner is still choked so push it down to the other end and see if you see light

 

[vmaxpro]

Nick do you happen to know what the land and groove diameters are in the fx liners?

 

[vmaxpro]

Barrel fouled?

Regulator seeping pressure? 

Air pressure off regulator?

I wondered about the reg creeping. I think im so close on a harmonic tune that 5 bar throws it off. Id love to find a window of +-10 bar

 

[Bob_O]

You can tell the slug liner by the twist rate.....easy to measure from the outside of the liner. Should be around 1:16.

Also, it's possible to get inconsistency in slugs.

VK slugs in .217 always worked well for me. NSA slugs worked well for me also.

 

[stoti]

How fast are you shooting the 26.8gr?

Stoti

 

[vmaxpro]

This is a .25. Stoti, about 1050 for the light nsa, 950 for the vk’s

 

[vmaxpro]

Also, 34gr jsb still driving tacks so I ruled out anything loose or scope. And I mean driving tacks, one hole at 70 yards. Im not giving up on slugs lol im so close! Yesterday I was grouping the nsa’s under 3/4” at 150 yards no prob. 

 

[bubblerboy64]

This seems to be a common thing with slugs. I often got two groups . Two or three touching and another group off to the right or left an inch or so. If you figure it out pass it along.

 

[stoti]

That's the nature of many .25 cal. slugs, unfortunately. Lol Bubblerboy and I have been talking about this exact thing for a long time. Any little change, and I mean any.... grip on the gun, pressure on the gun, any torque on the gun, variations in air pressure, etc... can often cause a slight shift, which at 100yds can mean inches. When I was testing slugs in my 600mm Crown, I had this happen all the time, 8-9 shots that were perfect and then a flier. I don't know if your shooting out of a magazine but that can be a cause for it too. A single shot tray is always better for this type of testing. Eliminate all the variables you can! Maybe try them a little slower? I always preach shooting slugs pretty fast but all of the Nielsen slugs I've tested usually shoot best between 900-1000fps and more specifically about 920-960fps. Maybe back it off to something like 970fps with the valve up front wide open and then slowly lower the velocity with the valve until you find the sweet spot. Shoot 5 shot groups until you see the groups shrink and then test that velocity more thoroughly. All guns are obviously different but I can tell you that with my Impact MKII, every single slug I've tested for Nick, like 30 different slugs, I got to shoot very well! Sometimes it takes a long time, a lot of tuning and can get frustrating but they all seem to shoot great. The dish base slugs shoot very well but in the Impact, the flat base, large hollow point slugs are generally easier to tune and shoot better. I hope you get it figured out, please let us know when you do! 

Stoti

 

[stoti]

Oh, that's funny Bubbler..., look at my previous post!

Stoti

 

[Bob_O]

940fps max is what I shoot for. Eliminates shockwaves caused by air going too fast past the sides of the slug.

 

[StarlingChaser]

Stoti you bring up a topic I have been thinking about. Actually I thought abut posting the question. I have the same thing happen with slugs as vmaxpro. I tune on the bench with bipod and bags. When I shoot starlings I shoot all sorts of ways and sometimes, more than I can justify I miss easy shots. I might have the bottle leaned against a post, have the bipod closed and laying on a fence, etc. Sometimes I take the bipod off and rest the bottle in a tripod. All this seems to throw of shots. Can different pressures from different angles on the bottle really make that much difference. I have an aftermarket rail extender for the bipod that has a rigid foam liner between the bottle and rail. I often wonder if that is really a good idea but that is how it was made so that is how I used it. Sorry if a liitle off track but this issue with vmaxpro is very common. Obviously the different pressures on the bottle does not flex the block but could chance vibration? The pic kinda shows it. I also have the 700mm barrel on it now.

 

[stoti]

I was shooting one day and moved from one target to the next, instead of repositioning my gun, I just rotated the rear of the gun so my scope was on the other target. I shot a few and it was off. I picked up my gun, repositioned it and bingo right back on target. I always reposition my gun now and it's never happened again. However, cheek weld, firmness of your hold, all that stuff matters. That's why it's so important to do everything exactly the same every time. Eliminate all the variables. It may not matter at 50yds but the farther you shoot the more important all the little things become.

I don't think it's necessarily the bottle but torque on the gun in general.

Stoti

 

[bubblerboy64]

940fps max is what I shoot for. Eliminates shockwaves caused by air going too fast past the sides of the slug.

That is interesting. Bob. I have noticed that the gun shoots a little louder with slugs or at least I think so. I’ve wondered about slug diameter. We’ve talked about weight and shape. I ‘m curious about diameter . Maybe a half thou one way or the other ??? 

 

[Bob_O]

Sorry, I meant in flight.

 

[vmaxpro]

What I dont get is why is it only slugs? When shooting pellets, doesnt seem to matter for me. I can shoot it free recoil, tight, loose, bipod, etc no change. One thing I tried, but could of been a fluke. I used a tool to jam the slug with full engagement into the rifling and it seemed consistent but I ran out of time. Monday Im machining the one liner to have 1.5 degree lead and chopping off all the freebore. Its only going to work for the vk’s tho I cant seem to push the nsa’s by hand.

 

[L.Leon]

While I may try slugs at some future date, when many of the above stated variables are worked out. One of the big pluses of shooting PCPs is the lack of recoil, or hold sensitivity, compared to Springers. Seems like shooting slugs introduces this hold sensitivity to PCPs? Bless all you guys who have the time to figure it out.