Is it possible NOT to get accuracy from A-max 162?

[westcliffe01]

No. The neck OD is determined by the chamber. The throat is the first part of the barrel after the chamber where the rifling is tapered. If the throat is slightly too large (50um too big would already be a problem) the first part of the barrel after the chamber would almost certainly have no visible rifling at all.

Thank you for the tip with a heavy flat base bullet to test if throat diameter is too large. I'm thinking would it be possible to measure this diameter by measuring the throat diameter on a fired case?

I have not talked to my gun smith about the issue yet. We only have a few of those here in Denmark and the guy who made my barrel is supposed to be the best of them. He is also a old angry man who don't believe the customer is always right and he is not know to handle criticism well So I would like to be absolutely certain something is wrong before approaching him.

 

[freshdk]

No. The neck OD is determined by the chamber. The throat is the first part of the barrel after the chamber where the rifling is tapered. If the throat is slightly too large (50um too big would already be a problem) the first part of the barrel after the chamber would almost certainly have no visible rifling at all.

Ah, now I understand I will try with a flat base bullet if I cannot get these Amax shooting..

Otherwise I would appreciate some more opinions on if a barrel simply cant work with a specific bullet for no obvious reason or something must be off somewhere?

 

[westcliffe01]

With any sufficiently long bullet, you should be able to regulate the distance from the chambered position to the engagement with the rifling lands. I do not hear that is your problem. With a boat tail bullet, if the throat diameter is too large, the back of the bullet may not be guided adequately when it leaves the mouth of the cartridge. The guide length (cylindrical length)of a flat base bullet is longer than the guide length for a similar weight boat tail bullet and sometimes the pressure acting on the base of a flat base bullet might even expand it a little, leading to a better guide.

This issue with the throat diameter is usually the reason why you have problems with any form of boat tail bullet, yet flat base bullets will shoot fine. Of course there are many additional things that can go wrong when chambering a barrel. The chamber may not be aligned with the bore. Sometimes there is no throat and the rifling ends with a square edge. These things can be measured with a dial indicator and observed with a borescope system. But it is quite tricky setting up a barrel so that the bore actually runs true on both ends, especially when there are 3-5 rifling lands to mess around with the dial indicator.

1000 rounds is not a huge amount through a 7mm-08 but there will still be some wear in the throat, so that is going to make the job of diagnostics difficult at this point.

So again, the easiest way you will pin point a well known issue like the throat diameter will be to shoot a box of 20 flat base rounds and see how much better they do than your reloads.

If this confirms the issue, you will either have to adapt to shooting flat base rounds, or, have the chamber set back - with specific instructions regarding the type of bullet you are planning to shoot, or, buy a replacement barrel and specify exactly what bullet you plan on shooting and you might want to review some reamer specifications to that you can specify the diameter throat that you need with a tolerance.

If a barrel is rifled and then lapped, it is normal that the last few inches of the blank at both ends would be oversized from the lap reaching the end of its stroke and not being properly guided. I don't know if your barrel maker laps the blank or not or if he did, perhaps did not remove enough material to get back to a "good" bore diameter. These are some of the mistakes that can be made when making match barrels, but the supplier should know these risks very well and be taking care of what is important to you. So far I have bought several Shilen barrels and not had a problem with an oversized throat on any of them. In fact, the only problem so far is that one throat was undersized. Opposite problem...

 

[freshdk]

Thank you very much for explaining in details! I will try to get my hands on some flatbase bullets to see how they react

 

[ladebenken]

Of course it`s possible not getting the A-max to shoot. Its a fact that every rifle doesnt like all bullets.

My first tip when someone doesn`t get a bullet to shoot is simply to try another bullet or powder, or some factory ammunition that is known for accuracy. Norma or Lapua. In that way we will reckognize the problem, is there something wrong with the rifle? Ammunition? Or does the rifle simply don`t like that one bullet? There is many other good bullets for longrange shooting & hunting in 7mm.

Hilsen fra andre siden av Skagerak. (Norge)