Gunsmithing Lost accuracy past 100 yds / New Chassis?

[Yankee88]

Tried searching, couldn't find anyone else with the predicament I am in.

Just switched my rifle over to an MPA chassis from a McMillan A5. Torqued to specs, rear contact of recoil lug, etc. (not bedded just dropped in).

Fairly certain barrel is fine, dont have anymore than 1000 rounds through and I shoot 140s at moderated 2790. Plus it was fine in the McMillan stock.

At 100 yrds I am shooting .5 MOA, but at 200 they are all over the place (probably 12-14", high or low, and left off target). Went back to 100 and ran some 1" dot drills to make sure it wasn't me, it wasn't (I mean thats a big spread regardless, but just wanted to rule it out). Checked the chassis bolts again and everything was still torqued, checked barrel for contact and nothing. I didnt get chance to go past 200yds due to the range I was at, but something is definitely wrong. I was hoping just dropping it in would be fine as others have said it would be, but do I just need to get it bedded or what did I mess up or missing?

Thanks

 

[spife7980]

I dont see how a chassis could influence what happens to the bullets down range. This would point me to saying that it has to be your positional differences, 200 yards being way higher than 100 so youre not building your position correctly or something like that. I dont see your bullets could suddenly have that much turbulence. Especially since they worked before you switched.

 

[LRI]

Have your salt shaker in hand...

Most round actions are patterned in some way off the M700. Assuming yours is the same. Most chassis type stocks use a V block configuration of some kind. Seems pretty cut and dry on how it'll register in it once its all screwed together.

The tang fuggers this up. The action effectively narrows as you move to the tang feature. The problem is the stock doesn't. At some point the tangent line of contact ends, but the action keeps going for a bit.

We can easily demonstrate how this isn't ideal. Remove the front guard screw from the action and tighten the rear till it stops. On most of these chassis setups the action will be doing a wheelie up by the recoil lug. Around a 1/4" or so.

What this does:

If you snug down both screws to an identical value that is capable of distorting the action (and 50 inch lbs will do this all day long) you are bending your receiver. "Hunching its back" the way a cat does when petted.

Back everything off and snug the front down to 50inch lbs. Then snug the back down so that it's tight, but not to an absurd level. Play with this and shoot the rifle. A sweet spot is likely to be found. You can run it that way or have the tang portion bedded so that the problem is solved for good.

Good luck.

C.


-Last:

Make sure the safety linkage on the trigger isn't bound up. If you see ANY sort of impression, burnish, nick, etc... down in the trigger well then it is. That must be resolved first. Ensure the safety functions with everything assembled. If it doesn't, you have an issue. This will cause the same sort of thing as goofy guard screw torque problems.

Jewel and Timney are famous for doing this... Most chassis DO NOT have sufficient clearance.

 

[Yankee88]

Have your salt shaker in hand...

Most round actions are patterned in some way off the M700. Assuming yours is the same. Most chassis type stocks use a V block configuration of some kind. Seems pretty cut and dry on how it'll register in it once its all screwed together.

The tang fuggers this up. The action effectively narrows as you move to the tang feature. The problem is the stock doesn't. At some point the tangent line of contact ends, but the action keeps going for a bit.

We can easily demonstrate how this isn't ideal. Remove the front guard screw from the action and tighten the rear till it stops. On most of these chassis setups the action will be doing a wheelie up by the recoil lug. Around a 1/4" or so.

What this does:

If you snug down both screws to an identical value that is capable of distorting the action (and 50 inch lbs will do this all day long) you are bending your receiver. "Hunching its back" the way a cat does when petted.

Back everything off and snug the front down to 50inch lbs. Then snug the back down so that it's tight, but not to an absurd level. Play with this and shoot the rifle. A sweet spot is likely to be found. You can run it that way or have the tang portion bedded so that the problem is solved for good.

Good luck.

C.


-Last:

Make sure the safety linkage on the trigger isn't bound up. If you see ANY sort of impression, burnish, nick, etc... down in the trigger well then it is. That must be resolved first. Ensure the safety functions with everything assembled. If it doesn't, you have an issue. This will cause the same sort of thing as goofy guard screw torque problems.

Jewel and Timney are famous for doing this... Most chassis DO NOT have sufficient clearance.

Awesome. Thank you. This seems like the most logical reason as what you explained is occurring. If I just set the action in the chassis, it will teeter up and down a bit from the front of the action.

Mine as well just bed it and be done with it rather than fiddling what order I torque the screws and how much. seems like a pain in the ass.

 

[Primus]

Great Info!

 

[Eric32]

i know all the chassis makers swear up and down not to bed the chassis.

what your saying makes a alot of sense, when bedding the tang portion of the rifle do you snug the front screw to spec lets call it 65 in-lbs and let the bedding ooze out of the rear tang area?

or do you do a 1/4 of a turn on both screws front and rear to make sure everything is lined up and let the action rest on its own.

or bed the action fully and just torque the front screw to 50 in-lbs and the rear float with the screw in for alignment purposes.

 

[EXTREMEPREJUDICE]

This seems like the most logical reason as what you explained is occurring.

Sorry, can't buy it.............. I would never disagree with Chad on any gunsmithing, nada, no way he's forgotten more than I'll ever know. But if your rifle is indeed shooting .5 MOA at 100 yds and then opening up downrange....................I'm with Spife on this one, it has nothing to do with the rifle.

 

[spife7980]

i know all the chassis makers swear up and down not to bed the chassis.
what your saying makes a alot of sense, when bedding the tang portion of the rifle do you snug the front screw to spec lets call it 65 in-lbs and let the bedding ooze out of the rear tang area?
or do you do a 1/4 of a turn on both screws front and rear to make sure everything is lined up and let the action rest on its own.
or bed the action fully and just torque the front screw to 50 in-lbs and the rear float with the screw in for alignment purposes.

You dont want to screw it in in any way, the point is stress free bedding. Tightening on the fasteners is putting stress on it. What youll do is press it down into the mud and then use surgical tubing or electrical tape or something to keep it held down. An external force that wont bend the action. http://www.6mmbr.com/pillarbedding.html

 

[Eric32]

how you keep the action aligned with the action holes.

 

[colchester]

how you keep the action aligned with the action holes.

Quickest easiest way , take a 1/4 28 screw about 1.5" long cut off the head. Wrap the screw with blue masking tape until it is a snug slip fit in the hole in the chassis. Screw the screws into the action and bed it up

 

[Eric32]

primo idea thanks

 

[Iamero]

Have you seen the movie Wanted? I think you're curving bullets like Angelina Jolie!

Im curious what proper torquing does for your accuracy past 100 and whether a bent back action can turn your bullet into a floppy banana down range.

Every burnt out barrel I've had wouldn't even group well at 100, but if it didn't I haven't seen accuracy drop off that bad at 200. Are any of the shots at 200 key holing? I imagine that would be a really good indicator if your bullets weren't stabalizing (by either a shot out throat or overtorqued action).