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A few problems

26 May 2024
@ 10:47 am (GMT)

Josh Jackson

Gidday Nathan & forum members. Just wanted to write about some problems I’ve been having with a particular rifle lately and your thoughts on working out what is going on here. Side note: Nathan I have all your books so wouldn’t want you to rehash things here. If you would like to point out where in the books I could go to start figuring this problem out it would be great.
For the last 5 I’ve owned a Tikka 7mm08 suppressed that I have only shot factory ammo through, it’s been my bush gun. Recently I’ve started doing load development for the gun per Nathan’s books. The first round of powder charges went well. All loads except the last one were under book max. The last one was 0.4g above book max and I had light ejector marks on all 3 cases. Ok cool, max pressure found. Back off a grain and retest the loads. All initial loads shot under 0.6moa at 100 yards with good cloverleaf “patterning” I guess you could call it. Loaded up loads the exact same way I had previously using the same CBTO and powder charge weights as before. Fast forward to this mornings range trip. All I can say is it was disappointing. Every group shot minimum 1 MOA as well as having very light ejector marks on all cases. Please note, no ejector marks were heavy and only on one case was the bolt a little bit stiff to open. Funnily enough that was the lowest charge weight! I also wanted to point out that every case of every charge weight had heavy soot from the neck, down to almost the shoulder body junction. I clean my barrel thoroughly between every shooting session and regularly polish the bore every 100 rounds or so. The barrel is allowed to go stone cold between groups and I know it’s not my shooting. I have set up numerous other heavy recoiling rigs since buying Nathan’s books and have never had any issue like this. Components being used are Hornady new brass, ADI 2208 (varget), WRE primers and the 162ELDM. Range conditions on both days were as perfect as you could hope for and there is nothing obvious to me that has gone wrong, but obviously something has!
My initial thoughts are all related to fouling. I may have a carbon ring in the front of the chamber before the freebore. Or I may have carbon in my chamber somewhere that I’m missing during cleaning with a bore guide. I also notice that after firing and removing the brass cases I get a huge amount of gases exiting from the chamber end instead of the muzzle.
Anyway I haven’t inspected the gun yet after getting back from the range. I will do that tonight. If you have any thoughts let me know.
Nathan I was happy to see your email and am glad Riley is home with you and Steph and on the mend, I hope she recovers well


26 May 2024
@ 11:00 am (GMT)

Joshua Jackson

Re: A few problems
Also I have just checked and I can drop a projectile through the fired case neck into the case body, so it appears brass neck thickness is not an issue.
26 May 2024
@ 04:34 pm (GMT)


Re: A few problems
Hi Joshua

First reaction is this could be suppressor related, have you disassembled and cleaned your suppressor between range sessions, there is a video somewhere on Utube of Nathan at an NZDA meeting discussing "Pipe Bombs" !


27 May 2024
@ 07:29 am (GMT)

Nathan Foster

Re: A few problems
Hi Josh, sounds like you are doing your best to cover all bases. Should be a nice rig once its set up.

I can really only guess as to issues without having the rifle in hand. Will put some notes below and leave you to work through them.

Check scale calibration. Weigh a 162gr bullet, scales should be within a half grain of 162gr.

There will always be a difference between unformed and fully formed brass regarding accuracy and velocities. Pressure tends to be lower during forming due to energy expended on case expansion. A chronograph can be quite useful to determine changes etc.

If neck sizing, it could simply be tightness of brass with scuff marks not a major issue. This combined with changes from unformed to fully formed might be confusing you. Hard to say though. The Tikka does not have the same leverage at the bolt handle as other 90 degree lift designs so this can also confuse matters when neck sizing - makes a normal neck sized load seem hot. This jives with your comment regarding lowest load produced heaviest lift - the case may have been the stoutest load from your previous tests.

Normally good accuracy / sweet spot is found in the Tikka at around 41 and 41.5gr 2208 without pressure (about 2600 to 2650s @ 20"). Rifles max out at around 43 to 44gr. Unusual to hear about ejector marks and stiff bolt as a result of max pressures at the loads you quoted. One might assume minimal head space or polished chamber body (poor case grip). But other factors contradict this.

Yes, could be carbon in the freebore section. Try a tight fit bronze brush and carbon remover such as KG1 or CLR (calcium lime rust) from Mitre 10. Soak, scrub repeat etc.

Sooting of the case neck and shoulder normally occurs at low pressures, indicating the need to increase charges. However a suppressor can confuse issues. This is why I suggest removing the suppressor when testing, then adding it as a separate variable later.

Usual stuff regarding the suppressor when testing, make sure it is snugged up tight, make sure its bore is relatively clean. Baffles can be left as is.

Yes, the suppressor will cause smoke to exit the action while at the same time sooting the chamber. This issue is compounded if the barrel is short and when using medium to slow burn rate powders. Its a problem that is seldom discussed here in NZ. Realistically, best not to go shorter than 20" in 7mm-08.

Might pay to strip the bolt and clean the firing pin and inner body, just to make sure everything is fine in that area.

Thats about it for now. I have made a few contradicting comments so work at it slowly. All the best.


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