Tapered throater?

[Engineering101]

When I recently picked up my 264 WSM from my gunsmith, I noted that no matter how far I stuck the 143 ELD-X out of the case I could not make contact with the rifling. I had given my smith a dummy round that I had asked him to use when long troating the rifle so I figured that he screwed it up. I called him up and he explained that he uses a tapered throater which he says is how "European" and "bench rest" shooters do it. I have since got it shooting 0.5 MOA so it seems to work but I had never heard of a tapered throater before. Can any of you gunsmith types out there explain a little more of what this is about? Thanks.

 

[Engineering101]

By the way, after getting a good shooting load with the 143 ELD-X using RL-33 I gave RL-26 a spin with the same bullet today. Got it moving 3,186 fps with top load of 65.0 grains. Primers were pretty flat but no sticky bolt. I didn't like the ES so I have now stuffed 78 grains of US869 behind the same bullet. You can have all kinds of fun when you can seat the bullet out as far as you want. Got room for more powder if needed. Sure would like to know if the tapered reamer is BS or for real though.

 

[shortgrass]

All throats in rifle barrels that I'm familiar with have a taper,,,,,,, kinda' like a funnel to guide the bullet into the rifing. Go look at some drawings at www.saami.org

 

[Engineering101]

Shortgrass

I am aware of normal throat designs and am aware of SAAMIs web site and drawings. In this case the rather long 143 ELD-X bullet can not be made to touch the rifling no matter how far out it is seated. It is the ONLY rifle I have like that and is supposed to be due to the special "tapered" throater my smith used which made a very long tapered throat. On the other hand maybe he screwed up the rifle and came up with this story. I'm just trying to see if other gunsmiths are aware of such a thing.

 

[rickiesrevenge]

Sounds fishy to me. All my throating reamers have taper in them.....

 

[lazylabs]

I would ask for the print for the tooling he used on your gun. How about doing a chamber cast?

 

[Canadian Bushman]

I would ask for the print for the tooling he used on your gun. How about doing a chamber cast?

Id also like to see the print.

If you push a bullet in with a cleaning rod, how far does it go?

 

[Engineering101]

This just got more weird. Based on your comments I decided to form a new piece of 264 WSM brass (from a piece of 270 WSM brass) which I did to the point it was ready to load but no primer/powder. Neck tension was set to 0.001". I wanted to see if I could get the action to seat the bullet so this time I dropped a bullet into the barrel until is stopped and then put the brass in behind it and tried to close the bolt and the bolt would not close so... there is some rifling in their after all. But this is where it got weird.

I then seated the bullet with my press to a COAL of 3.267", put the dummy round in the rifle and closed the bolt - but it almost got stuck. I was able to pull on the bolt and get the round out of the chamber. I then shortened the COAL to 3.249" and tried again. Same result. Also at a COAL of 3.238", 3.231", 3.224", 3,204". When I got to 3.190" the bolt was much easier to close and it was barely stuck. Same at 3.182" all the way to 3.115" at which point it didn't stick at all! Interestingly most of the exposed bearing surface of the bullet was scuffed up from being stuck so many times. I then pulled that bullet and seated a new bullet to a COAL of 3.120" and it didn't stick and had a very slight scuff/carbon mark from the dirty barrel. The dummy round I gave my smith to use to set the length to the rifling had a COAL of 3.104" so it looks like he did use it to set something but not the start of the rifling. I have not shot any ammo longer than 3.104". Looks like I could go to 3.120" with no issues but past that it would tend to stick in the rifle though I could get it out with a good pull on the bolt. Never seen anything like this before. If the gun didn't shoot as good as it does I'd be ****ed but at this point I suppose I'll just make a note that some throats can be tapered.

 

[Edd]

You will need ammo that is straight or a generous sized freebore if you expect to park .300+" of the bearing surface inside the freebore without some resistance.

 

[Engineering101]

Edd

My ammo is straight within +/- 0.001" but I think you are correct that there would be issues if it weren't.

 

[Edd]

The method you used to make your dummy round, the one described above, doesn't sound like it would produce a precision cartridge.

How do you gauge straightness on a + or - scale? Do you mean your bullet runout is within .001" of being perfectly aligned? And if so, aligned with what? What if your freebore is .0003" larger than the bullet diameter?

I don't understand how someone could have a custom chamber cut without knowing the specs on it. I would expect a Gunsmith to tell me the freebore diameter and the throat angle of the reamer he was planning on using before he ever stuck it in the barrel. After he was finished, I would expect him to tell me the freebore length.

 

[Engineering101]

Edd

I agree with your comments on what a gunsmith should do. My gunsmith is a little different however. His shop was featured on the TV show American Precision Shooting a month or so ago so he has some notoriety however he is well past retirement age and it shows. More than one guy has told me he has made mistakes on their firearms. I was having him do this rifle (264 WSM) because he screwed up the first attempt at making it a 26 Nosler and I thought the odds were in my favor that he could pull of the rechambering. The rifle does shoot pretty good so it looks like I was right about that. I won't be having him do anymore projects so it is a dead issue - almost literally.

As to concentricity of ammo. I use a Hornady checker/fixer to ensure ammo is straight. Works great. Can even straighten factory ammo.