Tight neck

[Elwood]

What is the safety tolerance for a tight neck?

 

Although my chamber isn't a tight neck by the time I have necked down 7x57 cases to 6mm by all account's I will have to turn the necks (no bad thing) My neck diameter is 2735 so I was planning on a loaded round measuring 270-271 giving me 1 1/4 - 1 3/4 thou clearance each side?

 

This is for a target rifle, so other than sand at Bisley and sheep Shiite at Diggle I will not be dragging it through crap and crud.

[1967spud]

Ian i would turn them down to .271 giving 11/4 thou each size then when it scome to re sizing resize to again .271 you may even get away without resizing if your tolerances are good

 

 

each case neck wall thickness should end up 13 1/2 thou

[The Gun Pimp]

Sheep that which promotes growth and vigour at Diggle???????????

 

For a 'field' rifle (i.e. non-benchrest) I like to work on three thou. - so I'd be looking for a loaded round neck diameter of 270 ish. Because benchrest is shot under cover with ample time for cleaning, we can run much closer tolerances but, if you shoot F Class, maybe 60 rounds in day without cleaning, the crud will build up in the chamber neck and those 'thous' can quickly dissappear.

 

Incidentally, it's not easy to measure your chamber neck diameter - how did you do it?

 

Cheers

Vince

[onehole]

I will go with Gun Pimp on this one.I have my 6.5/47 running too tight really and after 15/20 rounds I have to clean.Cases are on my to do list and will be looking to take two thou off total or do another batch of cases as they have gone round 7/8 times now.Just for your interest my loaded rounds with 123g Amax is 288.4/5 for a 290 neck plainly too tight for this rifle and an extended session.I use RL15 in this rifle and may be contributing to a bit of extra smut?

[Elwood]

Sheep that which promotes growth and vigour at Diggle???????????

 

For a 'field' rifle (i.e. non-benchrest) I like to work on three thou. - so I'd be looking for a loaded round neck diameter of 270 ish. Because benchrest is shot under cover with ample time for cleaning, we can run much closer tolerances but, if you shoot F Class, maybe 60 rounds in day without cleaning, the crud will build up in the chamber neck and those 'thous' can quickly dissappear.

 

Incidentally, it's not easy to measure your chamber neck diameter - how did you do it?

 

Cheers

Vince

 

Thanks Vince, that is good advice.

 

We measured the reamer and it came out 272, I then emailed the chap that had the reamer made up and he said that although the reamer may measure 272 the neck would actually be 2735, does that sound right?

[The Gun Pimp]

Reamers can't cut smaller, only bigger but, I'd be wary of assuming anything without actually measuring it - we are dealing with very small numbers here and even bullets can vary. The reamer could even be slightly undersize.

 

The best bet is to make up a round, neck-turned to exactly what you think the chamber neck is and see if it chambers. Put some felt marker pen on the neck and see if it rubs off. Of course, you will have to seat a bullet and maybe do two or three cases - but best to be safe than sorry.

 

If you seat the bullet back to front it will not engage with the rifling which could give a misleading result.

 

Obviously, I'm assuming you don't have a tube measuring mic.

 

Cheers

Vince

[Guest dasherman]

I'll measure it for you tomorrow Ian, my smallest 3 point bore mic goes down to 6mm.

[Elwood]

Reamers can't cut smaller, only bigger but, I'd be wary of assuming anything without actually measuring it - we are dealing with very small numbers here and even bullets can vary.

 

Cheers

Vince

 

That's how he explained it to me Vince, he being George Gardner from GA Precision.

 

Cheers Neil, no big rush as I haven't got the 7x57 brass yet, I'm just thinking ahead.

[1967spud]

I'll measure it for you tomorrow Ian, my smallest 3 point bore mic goes down to 6mm.

 

while your there neil can you measure the other one as well please ?

[Guest dasherman]

Measured your neck diameter before leaving work today, .2728" according to the bore mic, checked it 3 times and the same each time.