Moderators and long for calibre bullets

[VarmLR]

Has anyone else experienced issues when shooting long for cal bullets and using a moderator?

I've been having issues with getting the 6.5 CM on target as bullets seem to be going everywhere.  I tried dismounting the scope, checking rings, re-mounting the scope, checking that the mod is firmly attached and even dismounted the action from the stock and re-seated to ensure everything was properly aligned, all to no avail.

After shooting two boxes of factory today just to rule out my home loads as being the issue, I discovered the culprit.  The 140gr ELD Match bullets had taken obvious lumps from the last but one internal moderator baffle, and chipped the end baffle.  This wasn't apparent previously when I checked at the range using home loads, but the issue must have had the same cause there.

I removed the mod then re-bore sighted and adjusted the scope and put three bullets more or less through the same hole at 50 yards.  At last it holds zero and was shooting factory into tiny groups.

The cause may be due to be one (or both!) of two issues:

• Either the threaded insert for the moderator is not precisely aligned or;
• the bullet is leaving the muzzle with an appreciable yaw angle and clipping the inside of the mod.

I did consider whether the 1/8 twist was sufficient for the 1.4 inch long projectiles but if it starts out unstable, it would still be unstable at 50 yards I'd have thought, so however improbable it seems, I'm wondering whether these long for cal bullets do exhibit some yaw on exit?

Anyone else experienced this?

The mod was brand new and is now going back to the shop to be checked and replaced.  I may be wise to use a 30 cal mod in the circumstances.

[chaz]

Hi Varm,

From memory, haven't you got the same mod as me the Aim Point Triton Predator ".260" or "6.7mm"? If so, I've not had any problems with mine at all. In fact it's the best moderator I've owned. Albeit the most expensive... I don't recall the groups with the 1 box of 140gr ELD Match ammo i bought, but they were within 1 moa. I feel for you, as i'm the one who usually gets the defective "Friday" items.... Not sure if you're supposed to post SN's of mods, but mine is 174550. Anywhere near yours?

[VarmLR]

Hi Chaz

it could be any number of things including an imprecisely machined thread adaptor which that mod design uses, as this is what could introduce the variable forcing the mod to be slightly off-axis.  I can't see any Tikka rifle having a factory cut barrel thread being anything but spot on but it's these things I now have to check.  I've heard tell of occasional issues with certain bullets exhibiting yaw on discharge as the guys at the shop are putting this forward as an explanation.  I can't see how it could be as that implies instability and without the mod, this thing prints bug-holes so my money's on a defective mod.  Yes, it is exactly the same as yours.  We'll find out tomorrow what the score is I guess when I return it as I have opportunity to try another out.

[onehole]

A good visual check for an indication of bad mod fitting is to remove bolt ,,,ensure empty,,,fit mod,,,,place white paper on floor ,,put butt on the paper so you can look squarely down the barrel and mod,,,,if the barrel bore when held concentric does not look concentric with the bore of the mod then there is a machining problem ,,,could be threading and facing of either barrel or mod or combo of both.The human eye can easily see a problem here it should all look absolutely concentric.,,,,,Saw a Sako 22lr the other day that had a badly formed facing of the barrel behind the threaded portion which forced the mod off centre!!........?O

[chaz]

My money is on the thread specific adapter.  Incidently what powder are you using? I.m having great results with viht N150. Both in accuracy and velocity with no pressure signs. Around 2800 fps with 140 Scenars. Hope you get sorted ok. Theyve always been great with me.

[VarmLR]

We looked at it this morning and the issue is with Tikka's design for their thread and shoulder.  They have a "mini" shoulder squared off several mm in front of the main barrel shoulder.  This does not allow the mod to screw up firmly to the main barrel shoulder and risks pulling the mod off axis if the thread within the threaded insert does not coincide with pulling the mod square onto the mini shoulder which looks to be an odd way of doing things.  Why they couldn't cut a conventional thread up to the main barrel shoulder I don't know but my guess is that Tikka may come back and stipulate that moderators which have an extended section beyond their internal threads allowing them to square up with the main barrel shoulder have to be used.  Obviously this does not affect muzzle brake use.  

I shot several groups using factory ELD Match 140 and group size was 0.3 moa so at least I know that rifle and optics are fine.

That's the rifle going back to Gunmark along with the mod so I now have to wait (insert time guess here) until I hear back to see what the outcome is.  Back to loading for the .308 meantime.

[onehole]

8 hours ago, VarmLR said:

We looked at it this morning and the issue is with Tikka's design for their thread and shoulder.  They have a "mini" shoulder squared off several mm in front of the main barrel shoulder.  This does not allow the mod to screw up firmly to the main barrel shoulder and risks pulling the mod off axis if the thread within the threaded insert does not coincide with pulling the mod square onto the mini shoulder which looks to be an odd way of doing things.  Why they couldn't cut a conventional thread up to the main barrel shoulder I don't know but my guess is that Tikka may come back and stipulate that moderators which have an extended section beyond their internal threads allowing them to square up with the main barrel shoulder have to be used.  Obviously this does not affect muzzle brake use. 

I shot several groups using factory ELD Match 140 and group size was 0.3 moa so at least I know that rifle and optics are fine.

That's the rifle going back to Gunmark along with the mod so I now have to wait (insert time guess here) until I hear back to see what the outcome is.  Back to loading for the .308 meantime.

That's exactly the problem that was on that Sako 22RF barrel,,,,it went back and I understand my friend had a full refund,,,,,O

[chaz]

3 hours ago, VarmLR said:

We looked at it this morning and the issue is with Tikka's design for their thread and shoulder.  They have a "mini" shoulder squared off several mm in front of the main barrel shoulder.  This does not allow the mod to screw up firmly to the main barrel shoulder and risks pulling the mod off axis if the thread within the threaded insert does not coincide with pulling the mod square onto the mini shoulder which looks to be an odd way of doing things.  Why they couldn't cut a conventional thread up to the main barrel shoulder I don't know but my guess is that Tikka may come back and stipulate that moderators which have an extended section beyond their internal threads allowing them to square up with the main barrel shoulder have to be used.  Obviously this does not affect muzzle brake use.  

I shot several groups using factory ELD Match 140 and group size was 0.3 moa so at least I know that rifle and optics are fine.

That's the rifle going back to Gunmark along with the mod so I now have to wait (insert time guess here) until I hear back to see what the outcome is.  Back to loading for the .308 meantime.

I'm shocked at that. How do i get on with my identical set-up then??        I haven't had any problems, but like yours my moderator can't butt up tight against the barrel. I had it come very slightly loose once, but that was within the first few shots after buying the set-up. I tightened it up and it hasn't come loose since. I also check it now and again, especially if out target shooting. Please excuse my stupidity, but what is the  "mini" shoulder squared off several mm in front of the main barrel shoulder? The gap where the barrel moderator threads stop, and the flat face where the "un-cut" part of the barrel starts? I'm worried about my set-up now. Should i contact Clinton at Dauntsey?

Cheers

Chaz

[VarmLR]

6 minutes ago, chaz said:

I'm shocked at that Paul. How do i get on with my identical set-up then??                                     I haven't had any problems, but like yours my moderator can't butt up tight against the barrel. I had it come very slightly loose once, but that was within the first few shots after buying the set-up. I tightened it up and it hasn't come loose since. I also check it now and again, especially if out target shooting. Please excuse my stupidity, but what is the  "mini" shoulder squared off several mm in front of the main barrel shoulder? The gap where the barrel moderator threads stop, and the flat face where the "un-cut" part of the barrel starts? I'm worried about my set-up now. Should i contact Clinton at Dauntsey?

Cheers

Chaz

Yes, just that part Chaz, where the thread stops and there is a gap to the main shoulder.  Look closely and where the thread stops, the short section of barrel behind it to the main shoulder is squared off at the end of the thread.

 No, you don't have to be concerned as yours is fine and obviously hasn't the same issues.  I could elect just to change the thread adaptor and may not suffer the same issue with another but as there is an issue, the systematic checks are that both rifle and mod are independently checked and the importers will need the rifle back for this.

[chaz]

2 hours ago, VarmLR said:

Yes, just that part Chaz, where the thread stops and there is a gap to the main shoulder.  Look closely and where the thread stops, the short section of barrel behind it to the main shoulder is squared off at the end of the thread.

 No, you don't have to be concerned as yours is fine and obviously hasn't the same issues.  I could elect just to change the thread adaptor and may not suffer the same issue with another but as there is an issue, the systematic checks are that both rifle and mod are independently checked and the importers will need the rifle back for this.

Cheers Varm, i'll leave it at that then for now anyhow...

Chaz.