RAW barrel machining spec . port size & port location for .30

[Jaxjax]

Does anyone know the specs for port locating via a simple L to R pull from breech layout & size of port for .30 ? I'll have the index flats just done full length in action area instead of 3 spot. My .30 barrel has the nipple protrusion in breech area which I assume is for a magazine which I don't use on bm500x action. I could measure for port location but getting the perfect center location is difficult. Same with port ID unless I order a go no go precision slug although that measurement I assume isn't hyper critical.
Joe

 

[SpiralGroove]

First off - You should consult Martin or Motorhead before doing anything.

1.) Do you own a lathe? - You may want to cut off the nipple protrusion in the breach if you're not going to use a magazine.
2.) Port size s/b around .70/.75%+ of the .30 caliber ammo. Oval porting is best - you don't want obstruct/damage pellet upon loading.
3.) Align breach port opposite where barrel muzzle is at 12 O'clock high .... when rotating (indexing).
4.) Breach port s/b within 1/4" or so of back of Receiver bottom - see where valve port goes through. S/B easy to determine....

5.) I'm not an expert, but this is what I did when machining my LW barrel blanks.

 

[Motorhead]

Some simple math will get the spec your after ..... once knowing a few things.

1) Does the barrel protrude into the magazine slot area ... * How much & write it down.
2) Measure the back edge of receiver at Mag slot ( Area barrel slides into ) to the edge of the rearmost set screw hole .... * write it down
3) Measure diameter of set screw hole, What is 1/2 of that diameter ? ... * write it down


* Just random numbers to teach you how to find what you seek. NOT THE SPEC YOU NEED !!!!!!!

So lets say protrusion #1 lets say is .080"
Distance from receiver edge to hole #2 is lets say .300"
Hole diameter and 1/2 that #3 is lets say .135"
Added together we have the center line of transfer hole to breech end of barrel.

That would have the transfer hole back from the end of barrel at breech be at .520"

UNDERSTAND that the rear set screw hole is drilled all the way down into the valve seat area.

 

[John "spysir" Blount]

I am certainly not current but was thinking the BM 500 used a thimble?


John

 

[Jaxjax]

I am certainly not current but was thinking the BM 500 used a thimble?


John

500x
No thimble in the one I have. I'm running a LW .30 & a soon .25 which will be non thimble also
Joe

 

[SpiralGroove]

Hey Jax,
You should probably send the barrel to Martin ..... and be done with it .

 

[Jaxjax]

Hey Jax,
You should probably send the barrel to Martin ..... and be done with it .

He is doing 2 for me....
1 Lilja .177 & 1 LW SS .25 no choke
I can get barrel crazy so nice to have options on having them done up.
Joe

 

[BillG]

All very good advice. I might add a focus on concentricity and axial alignment. I've built my own version of a true bore chuck that allows for these adjustments during setup. I find this alignment to be very important with regard to throat and lead. The possible deviation at the muzzle is extremely small but I do the setup anyway. For those of you who want to try this at home, a makeshift true bore can be made with a substantial walled piece of tubing chucked in a independent 4 jaw chuck. 2 sets of 4 set screws 90 deg apart. One set is out at the end and the other close to the chuck approx 2" apart seems to work well. find patience.

 

[nomojo65]

If you truly have a BM action it uses a thimble, the original TM actions didn’t. It’s easy to tell and from what you’re describing it’s not a thimble, and I would talk to Martin or Motörhead about putting a .30 barrel in a TM action? There’s other things to consider.

 

[Jaxjax]

If you truly have a BM action it uses a thimble, the original TM actions didn’t. It’s easy to tell and from what you’re describing it’s not a thimble, and I would talk to Martin or Motörhead about putting a .30 barrel in a TM action? There’s other things to consider.

I have talked with both. Martin is doing a .25 & .177 for me. But that won't be my last barrels I have done up. It's easier if I send lets say,...Hart the specs then having to send my barrel in to copy. I do notice the RAW HM1000x action seem to have differant probe systems then mine. Mine is already set by martin for .30 & its lights out but the Lilja .177 I'm having done up might be intresting as its not same spec as LW offerings. The .25 is standard unchoked SS .71 version. I am also keeping it at .71 & the Lilja at .75 per Martin. It's nice to have a working list of smiths to do barrels as many have long waiting time & just nice to have options on getting the work done.
Joe

 

[nomojo65]

I’m not familiar with the 500x action that’s something I haven’t seen before? It may be based off the 1000x action, Does it have the same footprint as the 1000x? First two set screws for barrel, third for thimble on my BM- 500. Mine is just .177 or .22 for short range 25m or 50yd. My newest TM uses a thimble as well.