6BRA Reamer Spec vs. fired brass

[dlwheel]

Finally received my JGS 6BRA reamer based on Alex Wheeler’s print, but with a .272 neck. Anyway I cut three barrels and fired one of them 3X and sent brass to Harrels for a die. But before I sent them off I measured at the neck and at the base to compare to the reamer spec. At the neck the FF brass measured identical to the print at .4600.
But at the .200 datum, the print shows .4713, but all my brass measures .4690.
Is this to be expected?

I fireformed the rounds with 30.0g H4895 with 105JLK’s running 2815fps.
Thanks.

-David

 

[Northridge]

This is not abnormal as your loads are light enough your not seeing the growth in the body yet, you have to be carful to not go to tight as you will have adverse results and premature clickers if the sizing die is to tight or not sizing enough. I would be really surprised if your reamer is undersized. I would recommend fireforming with a load like you did then two additional firings at a stiffer load to get a more accurate chamber diameter.

Shawn Williams

 

[dlwheel]

This is not abnormal as your loads are light enough your not seeing the growth in the body yet, you have to be carful to not go to tight as you will have adverse results and premature clickers if the sizing die is to tight or not sizing enough. I would be really surprised if your reamer is undersized. I would recommend fireforming with a load like you did then two additional firings at a stiffer load to get a more accurate chamber diameter.

Shawn Williams

That makes me feel a bit better. I’ll be FF the rest of my brass weather permitting this week. However even though the load is light, the primer looks ‘pressurey’. I went up to 30.4 at 2860fps and could definitely feel the edges with my thumbnail. As I FF the rest, I’ll keep shooting a few formed brass and keep an eye on the size.
Thanks.

 

[expiper]

if your reamer is made according to the print it is perfect,,,,your brass will open up a little when you get the vel. up to where you want it,,,when getting a new reamer I would not cut more than one bbl. before actual use just to make shure it is what I want,,,if you are getting a little "splash" on the primer at these low vel./pressure your fireing pin may need bushed or change the weak spring,,,you didnt say what action was used,if it is a Rem this is common,,,Roger

 

[dlwheel]

if your reamer is made according to the print it is perfect,,,,your brass will open up a little when you get the vel. up to where you want it,,,when getting a new reamer I would not cut more than one bbl. before actual use just to make shure it is what I want,,,if you are getting a little "splash" on the primer at these low vel./pressure your fireing pin may need bushed or change the weak spring,,,you didnt say what action was used,if it is a Rem this is common,,,Roger

The action is an Impact
https://impactprecisionshooting.com/collections/actions

 

[Eric Leonard]

On the brass I sent Harrells I hit it once with 29 H4885 and a 105 jammed and then twice more with 30.5 .

 

[dlwheel]

I had seen a post from SheldonN concerning his dies and he talked about the body of the die needing to be in a range of +.0004 to .0008 to prevent clickers. (I hope I’m representing what he said correctly)... at any rate when I saw that my fired brass was nearly .030” under the reamer spec, I was concerned.

 

[timeout]

I had seen a post from SheldonN concerning his dies and he talked about the body of the die needing to be in a range of +.0004 to .0008 to prevent clickers. (I hope I’m representing what he said correctly)... at any rate when I saw that my fired brass was nearly .030” under the reamer spec, I was concerned.

I'm thinking that you mean nearly .003" under.

 

[KenOath]

.0023” to be precise..Give them a couple more hits and measure you should be closer than you are.

 

[The Pumpkin]

I had seen a post from SheldonN concerning his dies and he talked about the body of the die needing to be in a range of +.0004 to .0008 to prevent clickers. (I hope I’m representing what he said correctly)... at any rate when I saw that my fired brass was nearly .030” under the reamer spec, I was concerned.

Your BRA may be a cup size small. D

 

[Clancy]

Did you use a standard BR gauge? My print says that is what I’m supposed to use.

 

[dlwheel]

Did you use a standard BR gauge? My print says that is what I’m supposed to use.

The go is .004” less than std BR go.

 

[Clancy]

The go is .004” less than std BR go.

Thanks. I guess I have a different print. I called JGS yesterday and they confirmed that this print headspaces off the neck shoulder junction and to use a standard gauge.

There are several versions for sure.

 

[gunsandgunsmithing]

Thanks. I guess I have a different print. I called JGS yesterday and they confirmed that this print headspaces off the neck shoulder junction and to use a standard gauge.

There are several versions for sure.

It wouldn't hurt a thing to give it the .004" crush unless your dies won't push the shoulder back there. I would prefer my brass be formed that way, FWIW.

 

[Clancy]

It wouldn't hurt a thing to give it the .004" crush unless your dies won't push the shoulder back there. I would prefer my brass be formed that way, FWIW.

I don’t know where I’d get one this late in the game?

 

[dlwheel]

I’m not sure the .004 crush requires a unique print. The crush merely allows firing virgin brass w/o jamming.
For me That means I can FF during s match. They are that consistent. .